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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#1
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Vernier caliper accuracy
Hi folks,
Can anyone tell me what the typical accuracy of a decent pair of vernier calipers is (when used carefully and correctly)? I just bought a dial bore gauge and am wondering if I can reasonably set the zero point with vernier calipers instead of having to buy a 3" to 4" micrometer. The calipers are Etalon brand, heavy and made in Switzerland. The bore gauge dial is graduated down to 0.0005". I'm not reboring an engine, I just want an idea of the wear, so I don't need the highest accuracy. From using these calipers, my own guess is that they're probably good to 0.002", but some of that might be my errors in reading them. I'd be interested to hear what other people think. Best wishes, Chris |
#2
Posted to rec.crafts.metalworking
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Vernier caliper accuracy
"Christopher Tidy" wrote in message ... Hi folks, Can anyone tell me what the typical accuracy of a decent pair of vernier calipers is (when used carefully and correctly)? I just bought a dial bore gauge and am wondering if I can reasonably set the zero point with vernier calipers instead of having to buy a 3" to 4" micrometer. The calipers are Etalon brand, heavy and made in Switzerland. The bore gauge dial is graduated down to 0.0005". I'm not reboring an engine, I just want an idea of the wear, so I don't need the highest accuracy. From using these calipers, my own guess is that they're probably good to 0.002", but some of that might be my errors in reading them. I'd be interested to hear what other people think. Best wishes, Chris Keep them within a few degrees of some standard (68 deg. F being the most common one); keep your hands off of them and wear gloves; develop a good feel, and you should be able to measure to +/- 0.001" with them. Your Etalon probably is like my TESA Swiss vernier caliper, which is my best one. You can easily check it with a few gage blocks. If you're going to do precision work, you need at least a few of them. A set is great but for checking mikes, calipers, height gages and so on, you only need a few in different sizes. Then you won't be chasing your tail. You'll know with good assurance how accurate your gages are. And they'll help you develop a feel for how much force to use when you're measuring. A couple of gage pins, like 1/4" and 5/8", or something like that, are also useful for that purpose. I have some precision toolmaker's buttons that serve that purpose. -- Ed Huntress |
#3
Posted to rec.crafts.metalworking
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Vernier caliper accuracy
Christopher Tidy writes:
I don't have any gauge blocks. Do you think they'd be a better investment than a 3" to 4" micrometer? The import 1-2-3 blocks are $10 at Enco. Then you have standards for whole inches 1 through 6 to better than 0.001". Add a granite slab and you have the beginnings of some serious metrology for all of $35. Just buy $15 more worth of anything and they'll ship it free, including the 61 lb stone! http://www.use-enco.com/CGI/INSRIT?PMAKA=630-4010 http://www.use-enco.com/CGI/INSRIT?PMAKA=640-0120 This spacer set is only $30 and does 0.050" to 4 or 5 inches in most 0.001" increments: http://www.use-enco.com/CGI/INSRIT?PMAKA=630-4050 |
#4
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Vernier caliper accuracy
Richard J Kinch wrote:
Christopher Tidy writes: I don't have any gauge blocks. Do you think they'd be a better investment than a 3" to 4" micrometer? The import 1-2-3 blocks are $10 at Enco. Then you have standards for whole inches 1 through 6 to better than 0.001". And you just answered the question I was about to ask . Thanks ! -- Snag Still learnin' after all these years . |
#5
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Vernier caliper accuracy
On Feb 19, 10:27*pm, Christopher Tidy
wrote: Can anyone tell me what the typical accuracy of a decent pair of vernier calipers is (when used carefully and correctly)? I just bought a dial bore gauge and am wondering if I can reasonably set the zero point with vernier calipers instead of having to buy a 3" to 4" micrometer. ... Chris I have good 0.0001" micrometers with a 1" setting standard for 0-1 and 1-2", cheaper second-hand ones for the larger ranges. At home I almost never need to measure larger sizes with absolute accuracy. I have both the inside and outside pieces and only need to cut them to fit together. I use an unzeroed bore gauge to check for taper while I'm boring the cylinder, and compare that to the bore gauge's reading of the micrometer set to the piston's OD. I've had Starrett and Phase 2 dial calipers checked for accuracy. The Starrett was considerably better than 0.001" over its range, nearly as good as I could read by interpolation. The Phase 2 barely held 0.001". When I checked the cal standards myself I noticed that the Phase 2 reading was sensitive to how I held it. So I bought an incomplete set of gage blocks cheap at an auction and practiced on them. After a while I could get the 0.0001" mikes to read to one division but don't believe my dial and vernier calipers to better than 0.001", if that. This Enco 1-2-3 block here shows 2.0002" at both ends, at 14C (my normal room temperature). That's good enough to set a 2-3" micrometer that reads to 0.001". jsw |
#6
Posted to rec.crafts.metalworking
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Vernier caliper accuracy
"Christopher Tidy" wrote in message ... Hi folks, Can anyone tell me what the typical accuracy of a decent pair of vernier calipers is (when used carefully and correctly)? I just bought a dial bore gauge and am wondering if I can reasonably set the zero point with vernier calipers instead of having to buy a 3" to 4" micrometer. The calipers are Etalon brand, heavy and made in Switzerland. The bore gauge dial is graduated down to 0.0005". I'm not reboring an engine, I just want an idea of the wear, so I don't need the highest accuracy. From using these calipers, my own guess is that they're probably good to 0.002", but some of that might be my errors in reading them. I'd be interested to hear what other people think. Best wishes, Chris I would suggest that you calibrate it against a new bearing bore. The accuracy that those are ground to is amazing. |
#7
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Vernier caliper accuracy
Richard J Kinch wrote:
Christopher Tidy writes: I don't have any gauge blocks. Do you think they'd be a better investment than a 3" to 4" micrometer? The import 1-2-3 blocks are $10 at Enco. Then you have standards for whole inches 1 through 6 to better than 0.001". Add a granite slab and you have the beginnings of some serious metrology for all of $35. Just buy $15 more worth of anything and they'll ship it free, including the 61 lb stone! http://www.use-enco.com/CGI/INSRIT?PMAKA=630-4010 http://www.use-enco.com/CGI/INSRIT?PMAKA=640-0120 This spacer set is only $30 and does 0.050" to 4 or 5 inches in most 0.001" increments: http://www.use-enco.com/CGI/INSRIT?PMAKA=630-4050 I belive Christopher is a bit far away for free shipping. Wes |
#8
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Vernier caliper accuracy
Grumpy wrote:
"Christopher wrote in message ... Hi folks, Can anyone tell me what the typical accuracy of a decent pair of vernier calipers is (when used carefully and correctly)? I just bought a dial bore gauge and am wondering if I can reasonably set the zero point with vernier calipers instead of having to buy a 3" to 4" micrometer. The calipers are Etalon brand, heavy and made in Switzerland. The bore gauge dial is graduated down to 0.0005". I'm not reboring an engine, I just want an idea of the wear, so I don't need the highest accuracy. From using these calipers, my own guess is that they're probably good to 0.002", but some of that might be my errors in reading them. I'd be interested to hear what other people think. Best wishes, Chris I would suggest that you calibrate it against a new bearing bore. The accuracy that those are ground to is amazing. Yup, I use bearings as standards after checking them, usually for setting dial snap gauges and bore gauges. An ABEC 1 bearing can be smaller than the nominal size but if you can check it against known standards they are an inexpensive was to have a working standard for checking and setting measuring instruments. John |
#9
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Vernier caliper accuracy
On 2010-02-20, Christopher Tidy wrote:
Hi folks, Can anyone tell me what the typical accuracy of a decent pair of vernier calipers is (when used carefully and correctly)? How new are the calipers? I would expect 0.001" accuracy, if zeroed properly, if the gibs are set right so the head does not rotate, and if you have sufficient light and magnification to read the vernier properly. I'm assuming that you are not calling dial calipers "vernier". Just to be sure, I'll cover them too. Digital calipers typically have a resolution of 0.0005", but check the actual accuracy against gauge blocks -- in particular at the size you want to set. Dial calipers can have cyclic errors a function of the gear pinion which engages the rack. I just bought a dial bore gauge and am wondering if I can reasonably set the zero point with vernier calipers instead of having to buy a 3" to 4" micrometer. The calipers are Etalon brand, heavy and made in Switzerland. The bore gauge dial is graduated down to 0.0005". Ideally, it should be set to a ring gauge, not a micrometer. These will typically be accurate to 0.000050". You really want the standard to be more accurate than what is being set. If you use a 4-5" micrometer, you will need a 4" standard to zero it before you use it. (And I'm assuming that the micrometer has a tenths vernier around the barrel so you can set it to 0.0001". Also -- you really don't want to hold the micrometer's C-frame, as it can expand with heat from the hand. Put it in a micrometer bench clamp so you can set it and not worry about it drifting as it cools off. I'm not reboring an engine, I just want an idea of the wear, so I don't need the highest accuracy. From using these calipers, my own guess is that they're probably good to 0.002", but some of that might be my errors in reading them. I'd be interested to hear what other people think. A lot of the variation in calipers comes from a loose fit of the head to the bar, allowing it to tilt when pressure is put on the jaw tips. If you have it pretty snug, you can keep this from being a problem. And the closer to the bar you do the measurement, the less the problem from a tilting head and jaws. Enjoy, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
#10
Posted to rec.crafts.metalworking
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Vernier caliper accuracy
Wes writes:
I belive Christopher is a bit far away for free shipping. Oh, right. |
#11
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Vernier caliper accuracy
Don Foreman wrote:
Hi Don, Sorry to everyone for the slight delay in replying. No. Calipers are not as accurate as micrometers because they spring more and provide less "feel". Their value is wide range and quick operation for ballpark measurements to within a coupla thou. That's often quite sufficient, certainly in roughing or intermediate operations. That was about the accuracy I was guessing. As calipers go, these are about as stiff as you can get. Probably weigh between 1 and 2 lbs. But obviously there's no mechanism to ensure a constant closing force, like a micrometer thimble. I figure that as I'm not reboring an engine (I just want to know how severe the wear on each part is, so I can decide what to replace), a measurement to a couple of thousandths is good enough for me. After all, the smallest oversize piston I've seen is +0.010". But if anyone thinks this is a bad plan, do let me know. I've found the Asian import micrometers to be very good value, and some come with a reference with which to check them. Don't know about sources in the UK but an Asian 3-4" mike can be bought here for about $35. I have some good mikes (Etalon, Starrett, Fowler) and some Asian imports. They agree to well under .001", usually to better than half a thou. The better mikes do have better ratchets or friction thimbles. I prefer a friction thimble, not found on cheap mikes. I've never seen a micrometer without a thimble. My 0.0001" Tesa micrometer (Swiss I think) has a friction thimble and my cheap Draper metric micrometer still has a ratchet thimble. What do people think of micrometers with interchangeable anvils, to give several measurement ranges? So for example you have four anvils which fit a 4" micrometer frame to give measuring ranges of 0" to 1", 1" to 2", 2" to 3" and 3" to 4"? My gut reaction is that they won't be as consistent as a single range micrometer, but for brand new ones, Mitutoyo's website claims this isn't the case. If calipers are good to a couple of thousandths, my inclination is to use them for the moment. Best wishes, Chris |
#12
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Vernier caliper accuracy
Ed Huntress wrote:
Hi Ed, The reason is thermal expansion of the caliper. If you're pushing for the best accuracy, and particularly if the room is cold, holding it in your hand for a few minutes can make a difference. If you warm a three-inch-long piece of steel by 30 deg. F, from your 40 deg. shop to 70 deg., it will expand by almost 0.001". If the piece you're measuring is the same temperature as the caliper, and if they're both steel, the actual temperature matters little, but a difference in their temperatures, if it's more than a few degrees, can result in inaccurate measurement. Right. I rarely wear gloves except for particularly dirty jobs. I prefer barrier cream. But it's time to back up. I suppose you realize that a slide caliper is not a high-accuracy gage. It's usually used for moderate-accuracy work. You were asking what accuracy you can achieve with it, and the answer is, using a good caliper, cotton gloves, and calibration with gage blocks, you probably can achieve +/- 0.001". But not everyone does. Some people have the touch and some don't. Thanks. That's the figure I wanted. These are good calipers and I think my touch is fair, but I'm not being careful about temperature and the scale on the calipers cannot be moved to calibrate them. Sounds like my guess of +/- 0.002" is probably fair. But it depends on whether you're measuring *relative* dimensions or *absolute* dimensions. If it's the former, you don't need a well-calibrated gage. If it's the latter, you'll never know for sure how accurately your gages measure unless you check them from time to time against a gage block (or a stack) that's somewhere in the middle of the gage's range, and another one near its largest opening. For a 3" - 4" mike, I'd want at least a 3" block (or a stack to make that dimension) and a 4" block or stack. I'd like to have a 1/2" block, too, to wring with the 3" block to test the midrange. What's a stack? If any of this is unclear, ask, and I or someone else will explain. FWIW, most home-shop work doesn't require accurate measurement of absolute dimensions. Usually we're trying to make two things fit together, and what you need to know for that is their *relative* dimensions. If that's the case, forget the gage blocks for now. In this case, I think it's the absolute dimensions. The engine's piston wobbles noticeably in the bore. It's an aluminium piston in a cast iron bore, so I suspect there could be much more wear on the piston than the bore (the bore looks good, without a ridge at the top). So I want to know how well a brand new piston will fit in the existing bore, before I buy one. Best wishes, Chris |
#13
Posted to rec.crafts.metalworking
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Vernier caliper accuracy
"Christopher Tidy" wrote in message ... Don Foreman wrote: Hi Don, Sorry to everyone for the slight delay in replying. No. Calipers are not as accurate as micrometers because they spring more and provide less "feel". Their value is wide range and quick operation for ballpark measurements to within a coupla thou. That's often quite sufficient, certainly in roughing or intermediate operations. That was about the accuracy I was guessing. As calipers go, these are about as stiff as you can get. Probably weigh between 1 and 2 lbs. But obviously there's no mechanism to ensure a constant closing force, like a micrometer thimble. I figure that as I'm not reboring an engine (I just want to know how severe the wear on each part is, so I can decide what to replace), a measurement to a couple of thousandths is good enough for me. After all, the smallest oversize piston I've seen is +0.010". But if anyone thinks this is a bad plan, do let me know. I've found the Asian import micrometers to be very good value, and some come with a reference with which to check them. Don't know about sources in the UK but an Asian 3-4" mike can be bought here for about $35. I have some good mikes (Etalon, Starrett, Fowler) and some Asian imports. They agree to well under .001", usually to better than half a thou. The better mikes do have better ratchets or friction thimbles. I prefer a friction thimble, not found on cheap mikes. I've never seen a micrometer without a thimble. My 0.0001" Tesa micrometer (Swiss I think) has a friction thimble and my cheap Draper metric micrometer still has a ratchet thimble. What do people think of micrometers with interchangeable anvils, to give several measurement ranges? So for example you have four anvils which fit a 4" micrometer frame to give measuring ranges of 0" to 1", 1" to 2", 2" to 3" and 3" to 4"? My gut reaction is that they won't be as consistent as a single range micrometer, but for brand new ones, Mitutoyo's website claims this isn't the case. Interchangeable anvils are fine if you keep them very clean, and if you check them against gage blocks. If calipers are good to a couple of thousandths, my inclination is to use them for the moment. Best wishes, Chris |
#14
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Vernier caliper accuracy
Ed Huntress wrote:
Interchangeable anvils are fine if you keep them very clean, and if you check them against gage blocks. Sounds like I should avoid them unless I buy the gauge blocks then. Chris |
#15
Posted to rec.crafts.metalworking
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Vernier caliper accuracy
"Christopher Tidy" wrote in message ... Ed Huntress wrote: Hi Ed, The reason is thermal expansion of the caliper. If you're pushing for the best accuracy, and particularly if the room is cold, holding it in your hand for a few minutes can make a difference. If you warm a three-inch-long piece of steel by 30 deg. F, from your 40 deg. shop to 70 deg., it will expand by almost 0.001". If the piece you're measuring is the same temperature as the caliper, and if they're both steel, the actual temperature matters little, but a difference in their temperatures, if it's more than a few degrees, can result in inaccurate measurement. Right. I rarely wear gloves except for particularly dirty jobs. I prefer barrier cream. But it's time to back up. I suppose you realize that a slide caliper is not a high-accuracy gage. It's usually used for moderate-accuracy work. You were asking what accuracy you can achieve with it, and the answer is, using a good caliper, cotton gloves, and calibration with gage blocks, you probably can achieve +/- 0.001". But not everyone does. Some people have the touch and some don't. Thanks. That's the figure I wanted. These are good calipers and I think my touch is fair, but I'm not being careful about temperature and the scale on the calipers cannot be moved to calibrate them. Sounds like my guess of +/- 0.002" is probably fair. But it depends on whether you're measuring *relative* dimensions or *absolute* dimensions. If it's the former, you don't need a well-calibrated gage. If it's the latter, you'll never know for sure how accurately your gages measure unless you check them from time to time against a gage block (or a stack) that's somewhere in the middle of the gage's range, and another one near its largest opening. For a 3" - 4" mike, I'd want at least a 3" block (or a stack to make that dimension) and a 4" block or stack. I'd like to have a 1/2" block, too, to wring with the 3" block to test the midrange. What's a stack? Multiple gage blocks "wrung" together, which add up to their combined dimension. If you wring three 1" gage blocks together, they'll equal a single, 3" block. The wringing technique excludes air between them, and adds less than 2 millionths of an inch to the stack height. This only works with good-quality gage blocks. Some of the other setting tools that have been recommended in this thread can't be stacked up with that kind of accuracy. The ideal accuracy of dimensional standards, such as gage blocks, is ten times or more the accuracy of what you're trying to measure. In other words, if you're trying to determine the accuracy of your micrometer to +/- 0.0001 in., you ideally should have gage blocks that are accurate to +/- 0.000,01 in. That's a workshop-quality gage block, grade A or a good quality grade B, which today is called a "grade 3" (or AS-1) in new blocks. If you're going metric, the picture is a little different. Having said all that, a cheap workshop-grade gage block will be more accurate than you need for most shop work. But the troubles with cheap sets are twofold: they have parallelism problems, as well as looseness in absolute dimensions; and they often won't wring. Back to Earth: For what you want, almost anything will do. g Any decent gage standard is a whole lot better than nothing. But you have at least one mike, and you might want to use it for more demanding work at some time. For that, get a few gage blocks. If any of this is unclear, ask, and I or someone else will explain. FWIW, most home-shop work doesn't require accurate measurement of absolute dimensions. Usually we're trying to make two things fit together, and what you need to know for that is their *relative* dimensions. If that's the case, forget the gage blocks for now. In this case, I think it's the absolute dimensions. The engine's piston wobbles noticeably in the bore. It's an aluminium piston in a cast iron bore, so I suspect there could be much more wear on the piston than the bore (the bore looks good, without a ridge at the top). So I want to know how well a brand new piston will fit in the existing bore, before I buy one. Best wishes, Chris It would really help to have a good engine man chime in here. There are several around; try a new thread with a title like "Measuring engine bores" or something like that. You may drag one up. Many of us can help you with handling gages but engine cylinders have other issues, like taper and ovality, etc. If it's an old engine, the pistons may be cylindrical. If it's a newer one, they're probably elliptical ("oval"). And they're tapered along their lengths, too. In engine work, you have to know not only how to measure, but what it is you're really measuring. It's not difficult but you do have to know what you're doing. You want to ask someone who really knows his stuff. Good luck! -- Ed Huntress |
#16
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Vernier caliper accuracy
"Christopher Tidy" wrote in message ... Ed Huntress wrote: Interchangeable anvils are fine if you keep them very clean, and if you check them against gage blocks. Sounds like I should avoid them unless I buy the gauge blocks then. Chris I'd avoid them unless you really need them. Full disclosure -- Mitutoyo was my client for many years, and I wrote all of their articles during those years and some of their instructional materials. They're quite honest about what they claim. Just be aware that things like interchangeable-anvil micrometers sacrifice some assurance for the sake of convenience. They can be as accurate as any mike; you just have to be a bit more careful. -- Ed Huntress |
#17
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Vernier caliper accuracy
"Pete Snell" wrote in message ... One thing to be very careful of with all calipers, is the comparative accuracy of the inner and outer jaws. On one set cheapie Chinese digital calipers I have, the difference between an inside and outside measurement (of identical dimension) was about 0.003" Pete Save that one for woodwork. g -- Ed Huntress |
#18
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Vernier caliper accuracy
On Mon, 22 Feb 2010 03:58:39 +0000, the infamous Christopher Tidy
scrawled the following: Ed Huntress wrote: Hi Ed, The reason is thermal expansion of the caliper. If you're pushing for the best accuracy, and particularly if the room is cold, holding it in your hand for a few minutes can make a difference. If you warm a three-inch-long piece of steel by 30 deg. F, from your 40 deg. shop to 70 deg., it will expand by almost 0.001". If the piece you're measuring is the same temperature as the caliper, and if they're both steel, the actual temperature matters little, but a difference in their temperatures, if it's more than a few degrees, can result in inaccurate measurement. Right. I rarely wear gloves except for particularly dirty jobs. I prefer barrier cream. Now that I'm no longer doing greasy mechanical work, I tend to wear gloves more often, to keep my finnernails clean. Barrier cream is great, except for that. But it's time to back up. I suppose you realize that a slide caliper is not a high-accuracy gage. It's usually used for moderate-accuracy work. You were asking what accuracy you can achieve with it, and the answer is, using a good caliper, cotton gloves, and calibration with gage blocks, you probably can achieve +/- 0.001". But not everyone does. Some people have the touch and some don't. Thanks. That's the figure I wanted. These are good calipers and I think my touch is fair, but I'm not being careful about temperature and the scale on the calipers cannot be moved to calibrate them. Sounds like my guess of +/- 0.002" is probably fair. Fair to high. 2 thou to start, 1 thou after you get used to it, 5 tenths once you're good and comfortable with your dial calipers. But for critical measurements, micrometers are the way to go. But it depends on whether you're measuring *relative* dimensions or *absolute* dimensions. If it's the former, you don't need a well-calibrated gage. If it's the latter, you'll never know for sure how accurately your gages measure unless you check them from time to time against a gage block (or a stack) that's somewhere in the middle of the gage's range, and another one near its largest opening. For a 3" - 4" mike, I'd want at least a 3" block (or a stack to make that dimension) and a 4" block or stack. I'd like to have a 1/2" block, too, to wring with the 3" block to test the midrange. What's a stack? When a gage block isn't thick enough, you stack another on top of it. If any of this is unclear, ask, and I or someone else will explain. FWIW, most home-shop work doesn't require accurate measurement of absolute dimensions. Usually we're trying to make two things fit together, and what you need to know for that is their *relative* dimensions. If that's the case, forget the gage blocks for now. In this case, I think it's the absolute dimensions. The engine's piston wobbles noticeably in the bore. It's an aluminium piston in a cast iron bore, so I suspect there could be much more wear on the piston than the bore (the bore looks good, without a ridge at the top). So I want to know how well a brand new piston will fit in the existing bore, before I buy one. Remember that the COE is different for steel and aluminum, with steel expanding less by half. Aluminum pistons are wobblier by nature. Don't go by the piston, go by the bore. It sounds like your engine is in fairly good shape, but check for elongation perpendicular to the crankshaft. Bores become oval from wear, where the connecting rod pushes 'em up and drags 'em down the opposite sides. If you bore it out, you'll need all new pistons by default. -- "Just think of the tragedy of teaching children not to doubt." -- Clarence Darrow |
#19
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Vernier caliper accuracy
On Mon, 22 Feb 2010 04:09:32 +0000, the infamous Christopher Tidy
scrawled the following: DoN. Nichols wrote: Hi Don, How new are the calipers? I would expect 0.001" accuracy, if zeroed properly, if the gibs are set right so the head does not rotate, and if you have sufficient light and magnification to read the vernier properly. Probably 30+ years old, but in very good condition. A few scratches here and there, but no noticeable wear to the jaws and no sign of having been dropped. I'm assuming that you are not calling dial calipers "vernier". Just to be sure, I'll cover them too. They're genuine verniers. Then your 2 thou is likely more hopeful. Get a pair of dials, boy! They're less easy to misread. I forgot you were talking about verniers. Got a good magnifying glass? -- "Just think of the tragedy of teaching children not to doubt." -- Clarence Darrow |
#20
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Vernier caliper accuracy
On Sun, 21 Feb 2010 08:31:27 +1100, "Grumpy"
wrote: I would suggest that you calibrate it against a new bearing bore. The accuracy that those are ground to is amazing. It is pretty amazing what you get for your money when purchasing bearings. But even though the vast majority of bearings will likely be better, the bore of a bearing in this size range could be close to ..001 low and another .001 out of round. As you might expect, thin section bearings have a wider roundness tolerance than the standard 62xx and 63xx series. So, trust, but verify. g -- Ned Simmons |
#21
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Vernier caliper accuracy
On 2010-02-22, Christopher Tidy wrote:
Don Foreman wrote: Hi Don, Sorry to everyone for the slight delay in replying. No. Calipers are not as accurate as micrometers because they spring more and provide less "feel". Their value is wide range and quick operation for ballpark measurements to within a coupla thou. That's often quite sufficient, certainly in roughing or intermediate operations. That was about the accuracy I was guessing. As calipers go, these are about as stiff as you can get. Probably weigh between 1 and 2 lbs. But obviously there's no mechanism to ensure a constant closing force, like a micrometer thimble. Indeed -- you need to develop a feel for the sliding force on the caliper jaws once closed. (And, of course, the jaws are not carbide faced, so they will wear more rapidly than most micrometer jaws.) I figure that as I'm not reboring an engine (I just want to know how severe the wear on each part is, so I can decide what to replace), a measurement to a couple of thousandths is good enough for me. After all, the smallest oversize piston I've seen is +0.010". But if anyone thinks this is a bad plan, do let me know. Probably adequate -- especially as you are closing the calipers to a given setting (using the adjustment screw with the extra traveling head clamped down) and then using it as a reference for the dial gauge. If you had a set of gauge blocks, you could close it to a light sliding fit on those (to free yourself from the possible errors in the vernier and in reading it) and hold it in a vise to eliminate the problems from hand heat causing expansion of the beam. I've found the Asian import micrometers to be very good value, and some come with a reference with which to check them. Don't know about sources in the UK but an Asian 3-4" mike can be bought here for about $35. I have some good mikes (Etalon, Starrett, Fowler) and some Asian imports. They agree to well under .001", usually to better than half a thou. The better mikes do have better ratchets or friction thimbles. I prefer a friction thimble, not found on cheap mikes. I've never seen a micrometer without a thimble. My 0.0001" Tesa micrometer (Swiss I think) has a friction thimble and my cheap Draper metric micrometer still has a ratchet thimble. My first one from about 1960 (long gone, and I don't remember the brand) had only a small diameter spinner, not a ratchet or friction thimble, and I developed a feel for letting my fingers slip on the knurled portion of the man thimble. I've got others with various designs, including a 0-6" Brown & Sharpe set which still have no torque limiting features, along with others with very good friction thimbles. What do people think of micrometers with interchangeable anvils, to give several measurement ranges? So for example you have four anvils which fit a 4" micrometer frame to give measuring ranges of 0" to 1", 1" to 2", 2" to 3" and 3" to 4"? My gut reaction is that they won't be as consistent as a single range micrometer, but for brand new ones, Mitutoyo's website claims this isn't the case. Remember that you have to zero them against a standard each time you change the anvils -- or for that matter if you pick it up a week later and want to measure -- the room temperature might have changed between the zeroing and the time of the intended measurement. My main consideration of the problems with the multi-range micrometers is that you have the large C frame so there is more metal to expand as your hand warms it, thus more error from the thermal expansion. If you can prevent this (including hand warming of the standards you use when you zero the micrometers) you should be OK. Often a bench clamp stand for the micrometer is indicated. If calipers are good to a couple of thousandths, my inclination is to use them for the moment. And potentially good for better than that as you will be using them in zeroing the bore gauge. If you use gauge blocks to set the calipers, you will be better than the caliper. But then, if you have a stack of gauge blocks, and two longer blocks at the ends, and you have a setting reference which won't need the calipers at all. There are devices designed for just this purpose -- a rectangular tube to hold the blocks, a pair of long blocks for the ends, and provisions for clamping it down firmly. Good Luck, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
#22
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Vernier caliper accuracy
On 2010-02-22, Christopher Tidy wrote:
Ed Huntress wrote: Interchangeable anvils are fine if you keep them very clean, and if you check them against gage blocks. Sounds like I should avoid them unless I buy the gauge blocks then. They *should* come with standards for zeroing the micrometer after changing the anvils -- as many standards as you have anvils. These should be enough to assure accuracy at the zero point at least, and you can use gauge blocks to check for errors in mid spindle travel, but this should not be a problem with new micrometers anyway -- only after a lifetime of use by you, or someone else. Enjoy, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
#23
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Vernier caliper accuracy
On 2010-02-22, Christopher Tidy wrote:
Ed Huntress wrote: Hi Ed, The reason is thermal expansion of the caliper. If you're pushing for the best accuracy, and particularly if the room is cold, holding it in your hand for a few minutes can make a difference. If you warm a three-inch-long piece of steel by 30 deg. F, from your 40 deg. shop to 70 deg., it will expand by almost 0.001". If the piece you're measuring is the same temperature as the caliper, and if they're both steel, the actual temperature matters little, but a difference in their temperatures, if it's more than a few degrees, can result in inaccurate measurement. Right. I rarely wear gloves except for particularly dirty jobs. I prefer barrier cream. Gloves are a *very* bad idea when operating machine tools, but when measuring with micrometers or calipers are a good way to reduce thermal transfer resulting in errors. (Of course -- the thermal errors can be in the workpiece as well -- if you have just turned a steel workpiece in the lathe, it will measure significantly larger than after it has cooled for a couple of hours -- which can lead to fit problems when fitting a backplate to a lathe chuck for example. Finish the rough turning, go eat dinner and read a book or watch a TV show, and come back later to measure it and take the final passes to get the desired size. [ ... ] But it depends on whether you're measuring *relative* dimensions or *absolute* dimensions. If it's the former, you don't need a well-calibrated gage. If it's the latter, you'll never know for sure how accurately your gages measure unless you check them from time to time against a gage block (or a stack) that's somewhere in the middle of the gage's range, and another one near its largest opening. For a 3" - 4" mike, I'd want at least a 3" block (or a stack to make that dimension) and a 4" block or stack. I'd like to have a 1/2" block, too, to wring with the 3" block to test the midrange. What's a stack? Multiple gauge blocks wrung together to make up a precise size. A good set of blocks will have something like: 1.000" 2.000" 3.000" 4.000" 0.100" 0.200" 0.300" 0.400" 0.500" 0.600" 0.700" 0.800" 0.900" 0.110" 0.120" 0.130" 0.140" 0.150" 0.160" 0.170" 0.180" 0.190" 0.101" 0.102" 0.103" 0.104" 0.105" 0.106" 0.107" 0.108" 0.109" 0.1001" 0.1002" 0.1003" 0.1004" 0.1005" 0.1006" 0.1007" 0.1008" 0.1009" And -- in a separate box, I also have: 0.10000" 0.10001" 0.10002" 0.10003" 0.10004" 0.10005" 0.10006" 0.10007" 0.10008" 0.10009" "Wringing" two blocks together involves cleaning the surfaces about to mate, crossing them at right angles, and rotating them until the two blocks are parallel. A good block will cling to its neighbor, and you can progress to a fairly long stack of blocks which can be lifted by the top-most block and they will all stay together. (The cheap Chinese sets, supposedly accurate to 0.000050", tend to not have a good enough finish to bond together properly -- at least my set does not. But I have a good B&S/"Jo"hansen block set which does this well, and which comes with a certificate of calibration listing the actual size of each block. The combination of multiple blocks will allow you to build up almost any dimension as long as it is shorter than the multiplicity of ones which are just above '0.10000"' (they don't often make thinner ones because they can warp more easily). As a result, some sine plates have an extra section ground 0.20000" or 0.30000" below the main surface, so you can build a stack of blocks which will achieve the small angle you want to make. If any of this is unclear, ask, and I or someone else will explain. FWIW, most home-shop work doesn't require accurate measurement of absolute dimensions. Usually we're trying to make two things fit together, and what you need to know for that is their *relative* dimensions. If that's the case, forget the gage blocks for now. In this case, I think it's the absolute dimensions. The engine's piston wobbles noticeably in the bore. It's an aluminium piston in a cast iron bore, so I suspect there could be much more wear on the piston than the bore (the bore looks good, without a ridge at the top). Then again, softer materials tend to embed abrasive particles so they wear away the harder material against which they are run. This is the principle of a "lap". At a guess, I would expect the measurement down into the bore at right angles to the crankshaft axis to measure larger than the dimension at that height parallel to the axis. (The forces from the crankshaft and connecting rod would tend to apply more force along that cross axis.) So I want to know how well a brand new piston will fit in the existing bore, before I buy one. Understood -- and also to discover whether you need to bore 0.100" oversized to fit the next size piston up. Note that the skirts of some pistons are designed to move with temperature to fit well at operating temperature. The solid part near the top remains more constant in dimensions than the bottom of the skirts. Good Luck, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
#24
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Vernier caliper accuracy
Ed Huntress wrote:
It would really help to have a good engine man chime in here. There are several around; try a new thread with a title like "Measuring engine bores" Might do that, but I'm going to try taking the measurements first. I have the urge to get into the workshop :-). Many of us can help you with handling gages but engine cylinders have other issues, like taper and ovality, etc. If it's an old engine, the pistons may be cylindrical. If it's a newer one, they're probably elliptical ("oval"). And they're tapered along their lengths, too. Interesting. Why are pistons intentionally made elliptical? I've heard of pistons where the top land is of a smaller diameter (apparently it reduces wear because the lubrication is poorer at the top), but I've not heard of an elliptical piston. I'm surprised it doesn't increase the wear on the sides due to the reduced surface area, and I'd have thought it could allow the piston to vibrate in an angular sense about the gudgeon pin. Any more information, Ed? Best wishes, Chris |
#25
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Vernier caliper accuracy
Ed Huntress wrote:
I'd avoid them unless you really need them. Full disclosure -- Mitutoyo was my client for many years, and I wrote all of their articles during those years and some of their instructional materials. They're quite honest about what they claim. Just be aware that things like interchangeable-anvil micrometers sacrifice some assurance for the sake of convenience. They can be as accurate as any mike; you just have to be a bit more careful. Thanks. I'll remember you're the guy to ask about Mitutoyo gear! The interchangeable anvil micrometer I saw advertised doesn't include all the calibration standards Don mentioned, so I'll avoid it. Best wishes, Chris |
#26
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Vernier caliper accuracy
Larry Jaques wrote:
Don't go by the piston, go by the bore. It sounds like your engine is in fairly good shape, but check for elongation perpendicular to the crankshaft. Bores become oval from wear, where the connecting rod pushes 'em up and drags 'em down the opposite sides. If you bore it out, you'll need all new pistons by default. The piston is wobblier perpendicular to the crankshaft that it is in the parallel direction, which suggests to me that there's some significant wear. Also, the compression isn't great. But the bore itself looks fine, hence the bore gauge purchase. Chris |
#27
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Vernier caliper accuracy
DoN. Nichols wrote:
"Wringing" two blocks together involves cleaning the surfaces about to mate, crossing them at right angles, and rotating them until the two blocks are parallel. A good block will cling to its neighbor, and you can progress to a fairly long stack of blocks which can be lifted by the top-most block and they will all stay together. (The cheap Chinese sets, supposedly accurate to 0.000050", tend to not have a good enough finish to bond together properly -- at least my set does not. But I have a good B&S/"Jo"hansen block set which does this well, and which comes with a certificate of calibration listing the actual size of each block. Thanks for the explanation. Won't a stack be somewhat less accurate than a single block manufactured to the right size? Or is the tolerance on gauge blocks so small that it doesn't matter? The combination of multiple blocks will allow you to build up almost any dimension as long as it is shorter than the multiplicity of ones which are just above '0.10000"' (they don't often make thinner ones because they can warp more easily). As a result, some sine plates have an extra section ground 0.20000" or 0.30000" below the main surface, so you can build a stack of blocks which will achieve the small angle you want to make. Just briefly, what's a sine plate used for? Understood -- and also to discover whether you need to bore 0.100" oversized to fit the next size piston up. I've not seen +0.100" oversize pistons. For this engine the options are +0.020" or +0.040". Note that the skirts of some pistons are designed to move with temperature to fit well at operating temperature. The solid part near the top remains more constant in dimensions than the bottom of the skirts. I haven't removed the piston yet. The wobble I can see is adjacent to the solid part, at the top. Best wishes, Chris |
#28
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Vernier caliper accuracy
Ned Simmons wrote:
The Starrett 123 series calipers have adjustable scales and are as good as verniers get. The 50 division scales with the vernier and main scale in the same plane make them very easy to read. I can read them without glasses in a pinch, though I don't recommend it. http://www.starrett.com/download/62_123_caliper.pdf Thanks. I'll bear them in mind if I ever need another set. Chris |
#29
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Vernier caliper accuracy
DoN. Nichols wrote:
Well ... the ones which I have are quite old. These days, most people buy either dial or digital calipers. Dial is nice if you can keep chips out of the rack, but Digital (if good) is far more convenient, including the ability to zero at any point (such as on what you are fitting to) and then measure how much more needs to be removed to reach the proper dimensions. Also, measuring the distance between the centers of two holes of identical size by zeroing it while measuring the ID of one hole, then shift to measuring the distance between two opposite sides of the two holes in question. This subtracts the diameter of one hole from the final measurement which is the sum of the center distance and half of each hole's diameter, giving the actual center-to-center distance. I chose the vernier calipers because I wanted both imperial and metric on the same tool, and I wanted them to last. I hate replacing tools. O.K. But it misses three-lobed bores, which can be in a shape which actually measures the same between any two opposite points, but still is potentially seriously out of round. (This is more likely to be formed by certain machining operations -- including centerless grinding for OD shapes, and in a used automobile engine, the ovality is more likely, and for that your bore gauge is probably quite adequate. I've not seen a three-point bore gauge intended for measuring engine cylinders. All the gauges I found on the market were two-point with a centring device. I picked the one I mentioned because it's complete with all the anvils, locking nuts and the spanner, and is in good condition. There were more accurate gauges available (measured down to 0.0001" instead of 0.0005"), but they were much more worn and had missing parts. Also, I figured that for investigating wear as opposed to reboring, having a 40 thousandths range on the dial might be more useful than a 10 thousandths range. If people are interested, I can take a picture of the bore gauge and calipers. Best wishes, Chris |
#30
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Vernier caliper accuracy
DoN. Nichols wrote:
Well ... this one is for setting an air gauge, so it has to be pretty close to the diameter of the probe. An air gauge is hollow with both ends sealed, and air feed in through one end, with a hole of a specific size (or maybe more holes? -- I haven't actually seen one -- just read about them in books). The air goes out the hole, and flows out between the probe walls and the ID of the bore being checked, and the pressure built up in the interior of the gauge is measured and is a very good indication of the difference between the OD of the gauge and the ID of the bore -- over a fairly narrow range. So -- this ring was for setting something quite close to 16.8349 mm --- maybe 16.8350 mm is the actual target size. Anyway -- the rings are made too small, hardened, and then ground to a diameter near what is needed, and then marked as measured. They may be lapped as a final finishing pass. Thanks. That's interesting. I wasn't sure what an air gauge was. A lot of the variation in calipers comes from a loose fit of the head to the bar, allowing it to tilt when pressure is put on the jaw tips. If you have it pretty snug, you can keep this from being a problem. And the closer to the bar you do the measurement, the less the problem from a tilting head and jaws. Good tip. But fortunately the jaws on my calipers are snug. If the image which I saw was yours, the traveling body is long enough to minimize the jaw tilt which I was worrying about. I've seen others which were much shorter (including the digitals which I have) which make the gib setting more critical. That picture isn't actually my set of calipers, but is a very similar set. Same brand, but shorter and perhaps made a little earlier. Chris |
#31
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Vernier caliper accuracy
Larry Jaques wrote:
Then your 2 thou is likely more hopeful. Get a pair of dials, boy! They're less easy to misread. I forgot you were talking about verniers. Got a good magnifying glass? Looks like I might regret buying verniers as I get older :-). Chris |
#32
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Vernier caliper accuracy
"Christopher Tidy" wrote in message ... Ed Huntress wrote: It would really help to have a good engine man chime in here. There are several around; try a new thread with a title like "Measuring engine bores" Might do that, but I'm going to try taking the measurements first. I have the urge to get into the workshop :-). Many of us can help you with handling gages but engine cylinders have other issues, like taper and ovality, etc. If it's an old engine, the pistons may be cylindrical. If it's a newer one, they're probably elliptical ("oval"). And they're tapered along their lengths, too. Interesting. Why are pistons intentionally made elliptical? Because the thicker sections, which are the boss areas for the wrist pins (piston pins) expand with much more force than the thin sections. So the pistons have a smaller diameter across the boss area. I've heard of pistons where the top land is of a smaller diameter (apparently it reduces wear because the lubrication is poorer at the top), but I've not heard of an elliptical piston. Almost all production automobile pistons made today are elliptical. In fact, they're often elliptical with the major axis in one direction at the top of the piston, and in the other direction at the bottom. The bottom ellipse is for better sealing, to meet emission requirements. It has to do with differential friction and heating between the neutral axis, which is parallel to the crankshaft, versus the other axis. When I was at Wasino we had some drawings from Ford that actually had three different ellipses along their length, from top to bottom, and they had to blend into each other. I'm surprised it doesn't increase the wear on the sides due to the reduced surface area, and I'd have thought it could allow the piston to vibrate in an angular sense about the gudgeon pin. Any more information, Ed? If you don't get an expert to chime in here, I'll see what I can dig up for you. There is one guy who stops in here from time to time who is an engineer for one of the world's top piston manufacturers; you won't get any better info than that from him. If you're eager to search on it yourself, try both "elliptical piston" and "oval piston." They're often, incorrectly, called "oval pistons" in the trade. -- Ed Huntress |
#33
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Vernier caliper accuracy
"Christopher Tidy" wrote in message ... Larry Jaques wrote: Then your 2 thou is likely more hopeful. Get a pair of dials, boy! They're less easy to misread. I forgot you were talking about verniers. Got a good magnifying glass? Looks like I might regret buying verniers as I get older :-). Chris You'll get in the habit of wearing a swing-away loupe on your glasses when you're reading gages, after you pass a certain age. g You original reasons for buying a vernier caliper were good ones. Dial calipers are no more accurate; they're just easier to read. The same is true for the digitals. I use my TESA vernier caliper when I'm not in a hurry and I want to keep up the skill of reading them. But if I'm doing a lot of measuring, I'll pull out one of my digitals. I've never owned a dial caliper. -- Ed Huntress |
#34
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Vernier caliper accuracy
On Tue, 23 Feb 2010 05:04:18 +0000, the infamous Christopher Tidy
scrawled the following: Larry Jaques wrote: Then your 2 thou is likely more hopeful. Get a pair of dials, boy! They're less easy to misread. I forgot you were talking about verniers. Got a good magnifying glass? Looks like I might regret buying verniers as I get older :-). We all do. -- "Politics is the art of looking for trouble, finding it whether it exists or not, diagnosing it incorrectly, and applying the wrong remedy." -- Ernest Benn |
#35
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Vernier caliper accuracy
On 2010-02-23, Christopher Tidy wrote:
DoN. Nichols wrote: Well ... the ones which I have are quite old. These days, most people buy either dial or digital calipers. Dial is nice if you can keep chips out of the rack, but Digital (if good) is far more convenient, including the ability to zero at any point (such as on what you are fitting to) and then measure how much more needs to be removed to reach the proper dimensions. Also, measuring the distance between the centers of two holes of identical size by zeroing it while measuring the ID of one hole, then shift to measuring the distance between two opposite sides of the two holes in question. This subtracts the diameter of one hole from the final measurement which is the sum of the center distance and half of each hole's diameter, giving the actual center-to-center distance. I chose the vernier calipers because I wanted both imperial and metric on the same tool, and I wanted them to last. I hate replacing tools. O.K. There *are* dial calipers with dual scales, and two separately geared pointers -- but you still have the problem of the pinion skipping a tooth shifting the zero point either from a shock or from chips getting into the rack gear in the bar. Digital are nice for switching between metric and imperial, but have the problem of keeping fresh cells around to power them, as some will kill their cells in six months, and I think a year and a half is pretty long for one to last. And -- they are more easily damaged -- things like the liquid crystal display are rather fragile -- behind the clear plastic window. O.K. But it misses three-lobed bores, which can be in a shape which actually measures the same between any two opposite points, but still is potentially seriously out of round. (This is more likely to be formed by certain machining operations -- including centerless grinding for OD shapes, and in a used automobile engine, the ovality is more likely, and for that your bore gauge is probably quite adequate. I've not seen a three-point bore gauge intended for measuring engine cylinders. For checking *wear* in the cylinders (as you want) what you got is better -- quicker to use and all. And it lets you measure parallel to and at right angles to the crankshaft to check for oval wear. For checking a reboring job, I would prefer the three-point, since the boring had *better* be cylindrical. :-) But since this is going to be in an automobile, and you have dissimilar metals between the cylinder and the piston, you have differing thermal coeifficents of expansion, and the temperature range between sitting outside on a really cold day (maybe -40 in some areas, where special lubricants and coolants are also needed, and a bit over 212 F (100 C) would really require a good starting clearance, or it will seize at one extreme or the other. All the gauges I found on the market were two-point with a centring device. I picked the one I mentioned because it's complete with all the anvils, locking nuts and the spanner, and is in good condition. There were more accurate gauges available (measured down to 0.0001" instead of 0.0005"), but they were much more worn and had missing parts. Any idea what the required starting clearance is between the pistons and the bores? *That* would settle how accurate you need the measurement to be for checking a rebore. Also, I figured that for investigating wear as opposed to reboring, having a 40 thousandths range on the dial might be more useful than a 10 thousandths range. If people are interested, I can take a picture of the bore gauge and calipers. If so -- post it to the dropbox, or on a private web site and post the URL to find it. Enjoy, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
#36
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Vernier caliper accuracy
On 2010-02-23, Christopher Tidy wrote:
DoN. Nichols wrote: "Wringing" two blocks together involves cleaning the surfaces about to mate, crossing them at right angles, and rotating them until the two blocks are parallel. A good block will cling to its neighbor, and you can progress to a fairly long stack of blocks which can be lifted by the top-most block and they will all stay together. (The cheap Chinese sets, supposedly accurate to 0.000050", tend to not have a good enough finish to bond together properly -- at least my set does not. But I have a good B&S/"Jo"hansen block set which does this well, and which comes with a certificate of calibration listing the actual size of each block. Thanks for the explanation. Won't a stack be somewhat less accurate than a single block manufactured to the right size? Or is the tolerance on gauge blocks so small that it doesn't matter? As someone else mentioned, the joint between a properly wrung pair of blocks is on the order of two microinches (0.000002"), so only with the highest grade blocks do you need to take account of the interface thickness. The combination of multiple blocks will allow you to build up almost any dimension as long as it is shorter than the multiplicity of ones which are just above '0.10000"' (they don't often make thinner ones because they can warp more easily). As a result, some sine plates have an extra section ground 0.20000" or 0.30000" below the main surface, so you can build a stack of blocks which will achieve the small angle you want to make. Just briefly, what's a sine plate used for? It is a plate (or a bar -- the more common ones are sine bars) which has a pair of cylindrical surfaces at each end, separated by a precise center distance. The most common is 5.000", though I have one at 2.500", and have seen some offered at 10.000"). For a sine bar, there is no captive base plate, so you set it on a surface plate, and with both cylinders in contact, its top is parallel to the surface plate. Now -- let's say you want a precise fifteen degrees. O.K. Look up the sine of 15 degrees (0.258819045) and multiply by the length of the bar (5.000"), so you get 1.294095226". Wring a stack of gauge blocks to get 1.2941" and you will get very close to 15 degrees. Calculating back from that, I get 15.000056 degrees +/- a bit given the accuracy of the gauge block set. I stopped the blocks at 1.2941" assuming a cheap Chinese set with +/- 0.000050 accuracy. You can get greater precision with the more expensive and accurate sets. But -- to get that 1.2941" -- we need to build a stack. Let's see -- start with a 0.1001" block, add a 0.1040" block, then a 0.1900" block, so we are up to 0.3941" and need only 0.9000" to make up our total size. When calculating/building a stack, always start with the last decimal place and work backwards. Here, for example, if you had started at the big end, you would have picked up a 1.0000" block, and when you got the lesser digits you would have discovered that the total was too long. Now -- a sine plate is like a sine bar, except that it is wider (the sine bar may be 1" wide) and is captive to a base, so you can build the angle and lock it in and then carry it to the magnetic chuck of a surface grinder to grind the desired angle on something mounted to the top (angled) plate. To see a sine bar -- here is one on MSC's site: http://www1.mscdirect.com/CGI/NNSRIT?PMPXNO=17520867&PMT4NO=80436460 Or MSC part number 85005502 in case the url above turns out to be a temporary one built by my search. The toe on one end is to keep the workpiece from sliding off the end while measuring. An example sine plate (much larger and *much* more expensive than the one which I have) is MSC item 08020216 http://www1.mscdirect.com/CGI/NNSRIT?PMPXNO=1778994&PMT4NO=80436812 You can see the near roll under the top plate in the image, and a raised block for the zero point, which is a precise height above the base plate. So you can either build blocks above the raised block, or above the base plate - whichever lets you reach your desired height more easily. Note that there are double sine plates -- a second one hinged at right angles to the first to allow compound angles. I've used mine to make Acme threading tools to fit a boring bar. I first used the smallest sine bar that I have (2.5" long between centers) to machine a 14 degree angle plate (half of an Acme) guide to hold a HSS tool bit at that angle in a small vise, then mounted the vise on the sine plate, and set the gauge blocks under it for the desired side relief on one side of the bit. This went onto the surface grinder, and was used to make the desired angle on that side. Then I reversed the bit and angle plate, and built a different stack of gauge blocks to provide the different relief angle on the other side of the bit. (This was calculated based on the helix angle of the thread. After this was complete, I put the bit upright in the vise and set a nose relief angle to grind while I ground the nose back for the proper nose width for that particular Acme thread pitch. Understood -- and also to discover whether you need to bore 0.100" oversized to fit the next size piston up. I've not seen +0.100" oversize pistons. For this engine the options are +0.020" or +0.040". Sorry -- yes, 0.100" is a bit large for automotive pistons at least. :-) Note that the skirts of some pistons are designed to move with temperature to fit well at operating temperature. The solid part near the top remains more constant in dimensions than the bottom of the skirts. I haven't removed the piston yet. The wobble I can see is adjacent to the solid part, at the top. O.K. Good Luck, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
#37
Posted to rec.crafts.metalworking
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Vernier caliper accuracy
On Feb 23, 5:26*pm, "DoN. Nichols" wrote:
On 2010-02-23, Christopher Tidy wrote: DoN. Nichols wrote: ... Just briefly, what's a sine plate used for? ... * * * * Now -- let's say you want a precise fifteen degrees. *O..K. *Look up the sine of 15 degrees (0.258819045) and multiply by the length of the bar (5.000"), so you get 1.294095226". *.... * * * * * * * * DoN. Nice description. A sine bar can also be used to measure an unknown angle, such as the taper on a shaft. Lay the taper on a flat surface and clamp the sine bar on top of it, rolls up. A ground toolmakers vise works well for this. Measure the difference in the heights of the rolls. If you have only a short-range 0.0001" test indicator and can't measure that much distance, tweak an adjustable parallel to make up the height difference, so the indicator reads the same on both, then measure the parallel with a micrometer. jsw |
#38
Posted to rec.crafts.metalworking
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Vernier caliper accuracy
On 2010-02-23, Jim Wilkins wrote:
On Feb 23, 5:26*pm, "DoN. Nichols" wrote: On 2010-02-23, Christopher Tidy wrote: DoN. Nichols wrote: ... Just briefly, what's a sine plate used for? ... * * * * Now -- let's say you want a precise fifteen degrees. *O.K. *Look up the sine of 15 degrees (0.258819045) and multiply by the length of the bar (5.000"), so you get 1.294095226". *.... Nice description. Thanks! A sine bar can also be used to measure an unknown angle, such as the taper on a shaft. Lay the taper on a flat surface and clamp the sine bar on top of it, rolls up. A ground toolmakers vise works well for this. Measure the difference in the heights of the rolls. If you have only a short-range 0.0001" test indicator and can't measure that much distance, tweak an adjustable parallel to make up the height difference, so the indicator reads the same on both, then measure the parallel with a micrometer. Aha! A nice trick which I had not thought of. I've got one much smaller sine bar -- 1.000" between rolls -- which is mounted on a micrometer, with a bar of the same length as the anvil, so it can be used to measure the sine of existing angles within a limited range of diameters. Of course -- you lose the multiplier effect of a 5" or 10" sine bar, so you don't get the accuracy that you can with one of those, but it is still quite good and a lot more convenient for quick readings. Enjoy, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
#39
Posted to rec.crafts.metalworking
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Vernier caliper accuracy
DoN. Nichols wrote:
Hi Don, Thanks for the description of the sine plate. Sorry I've taken a few days to reply. Bad week! Just briefly, what's a sine plate used for? It is a plate (or a bar -- the more common ones are sine bars) which has a pair of cylindrical surfaces at each end, separated by a precise center distance. The most common is 5.000", though I have one at 2.500", and have seen some offered at 10.000"). For a sine bar, there is no captive base plate, so you set it on a surface plate, and with both cylinders in contact, its top is parallel to the surface plate. Now -- let's say you want a precise fifteen degrees. O.K. Look up the sine of 15 degrees (0.258819045) and multiply by the length of the bar (5.000"), so you get 1.294095226". Wring a stack of gauge blocks to get 1.2941" and you will get very close to 15 degrees. Calculating back from that, I get 15.000056 degrees +/- a bit given the accuracy of the gauge block set. I stopped the blocks at 1.2941" assuming a cheap Chinese set with +/- 0.000050 accuracy. You can get greater precision with the more expensive and accurate sets. But -- to get that 1.2941" -- we need to build a stack. Let's see -- start with a 0.1001" block, add a 0.1040" block, then a 0.1900" block, so we are up to 0.3941" and need only 0.9000" to make up our total size. When calculating/building a stack, always start with the last decimal place and work backwards. Here, for example, if you had started at the big end, you would have picked up a 1.0000" block, and when you got the lesser digits you would have discovered that the total was too long. Now -- a sine plate is like a sine bar, except that it is wider (the sine bar may be 1" wide) and is captive to a base, so you can build the angle and lock it in and then carry it to the magnetic chuck of a surface grinder to grind the desired angle on something mounted to the top (angled) plate. To see a sine bar -- here is one on MSC's site: http://www1.mscdirect.com/CGI/NNSRIT?PMPXNO=17520867&PMT4NO=80436460 Or MSC part number 85005502 in case the url above turns out to be a temporary one built by my search. The toe on one end is to keep the workpiece from sliding off the end while measuring. An example sine plate (much larger and *much* more expensive than the one which I have) is MSC item 08020216 http://www1.mscdirect.com/CGI/NNSRIT?PMPXNO=1778994&PMT4NO=80436812 You can see the near roll under the top plate in the image, and a raised block for the zero point, which is a precise height above the base plate. So you can either build blocks above the raised block, or above the base plate - whichever lets you reach your desired height more easily. Note that there are double sine plates -- a second one hinged at right angles to the first to allow compound angles. I've used mine to make Acme threading tools to fit a boring bar. I first used the smallest sine bar that I have (2.5" long between centers) to machine a 14 degree angle plate (half of an Acme) guide to hold a HSS tool bit at that angle in a small vise, then mounted the vise on the sine plate, and set the gauge blocks under it for the desired side relief on one side of the bit. This went onto the surface grinder, and was used to make the desired angle on that side. Then I reversed the bit and angle plate, and built a different stack of gauge blocks to provide the different relief angle on the other side of the bit. (This was calculated based on the helix angle of the thread. After this was complete, I put the bit upright in the vise and set a nose relief angle to grind while I ground the nose back for the proper nose width for that particular Acme thread pitch. Not what I was expecting! I had imagined a steel plate with a surface shaped like a sine wave, sitting on a table (though what you'd use that for, I don't know). Thanks for the explanation. Some day I'll probably need one! Best wishes, Chris |
#40
Posted to rec.crafts.metalworking
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Vernier caliper accuracy
DoN. Nichols wrote:
For checking *wear* in the cylinders (as you want) what you got is better -- quicker to use and all. And it lets you measure parallel to and at right angles to the crankshaft to check for oval wear. For checking a reboring job, I would prefer the three-point, since the boring had *better* be cylindrical. :-) But since this is going to be in an automobile, and you have dissimilar metals between the cylinder and the piston, you have differing thermal coeifficents of expansion, and the temperature range between sitting outside on a really cold day (maybe -40 in some areas, where special lubricants and coolants are also needed, and a bit over 212 F (100 C) would really require a good starting clearance, or it will seize at one extreme or the other. Actually, it's a big motor lawnmower (80 mm bore). All the gauges I found on the market were two-point with a centring device. I picked the one I mentioned because it's complete with all the anvils, locking nuts and the spanner, and is in good condition. There were more accurate gauges available (measured down to 0.0001" instead of 0.0005"), but they were much more worn and had missing parts. Any idea what the required starting clearance is between the pistons and the bores? *That* would settle how accurate you need the measurement to be for checking a rebore. I've found that figure in the manual. I'll post it along with my measurements in a new thread shortly. Also, I figured that for investigating wear as opposed to reboring, having a 40 thousandths range on the dial might be more useful than a 10 thousandths range. If people are interested, I can take a picture of the bore gauge and calipers. If so -- post it to the dropbox, or on a private web site and post the URL to find it. Here's a picture of my actual calipers: http://www.mythic-beasts.com/~cdt22/...r_calipers.jpg Best wishes, Chris |
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