Early surface plates: How were they made?
Chris Lindquist wrote: I've been trying to find out exactly what process was used for originating a surface plate in the good old days. I expect it involved careful hands and a large amount of scraping, but what provided a reference for "flat"? And how flat was flat around the turn of the century? I'm not planning to try this at home, of course. My Chinese granite plate is plenty flat enough, thanks. But I've been going through my books looking for an answer to this chicken-and-egg question without finding a solution. Can anyone help? Thanks! Greetings, You don't make one plate, you make 3 of the same size. Match plate A to B, B to C, and A to C. It's an iterative process, bringing down the high spots on each plate a bit at a time. The same method can also be used to generate straight edges, and with some variation master precision squares. Cheers, Stan |
Early surface plates: How were they made?
Yeah, and it was being done a lot further back than "the turn of the
century". Sir Joseph Whitworth was one of the first to publicize flat and straight edge making, but it didn't originate with him, probably. For details, get one of Lindsay's books, "English and American Tool Builders"/ Bob Swinney "Dave Baker" wrote in message ... Subject: Early surface plates: How were they made? From: (Chris Lindquist) Date: 21/08/03 20:43 GMT Daylight Time Message-id: I've been trying to find out exactly what process was used for originating a surface plate in the good old days. I expect it involved careful hands and a large amount of scraping, but what provided a reference for "flat"? And how flat was flat around the turn of the century? I'm not planning to try this at home, of course. My Chinese granite plate is plenty flat enough, thanks. But I've been going through my books looking for an answer to this chicken-and-egg question without finding a solution. Can anyone help? By lapping 3 plates against each other with grinding paste until all three are flat. The same way as reference plates are made now. The ancients could make a plate as flat as we can now. The technique requires no special technology. Dave Baker - Puma Race Engines (www.pumaracing.co.uk) I'm not at all sure why women like men. We're argumentative, childish, unsociable and extremely unappealing naked. I'm quite grateful they do though. |
Early surface plates: How were they made?
In article , Dave Baker says...
By lapping 3 plates against each other with grinding paste until all three are flat. The same way as reference plates are made now. The ancients could make a plate as flat as we can now. The technique requires no special technology. Not strictly true, Dave. Read the description about flat surface generation in Moore's book, they go into considerable detail on this. 1) they use cast iron plates, specially ribbed and supported. 2) the square plates are spotted against each other with a marking medium, and are hand scraped to each other. 3) the exact sequence of operations matters, and there is 90 degree rotation included between each cycle. This prevents a saddle error from developing. 4) once the plates are spotted and hand scraped as well as possible, each plate is then futher corrected using several additional steps, to get down to roughly one micron flatness level. Unless one includes these steps, they say that ten or so microns is all that can be achieved. Probably the *most* important technologies that we have, that were not available to the 'ancients' are a) more accurate metrology, and b) temperature controlled environments for doing the measuring in. The second is probably the most important. Moore's book give considerable engineering detail about what is now pretty trivial stuff, but when the book was written is was state of the art, he talks about feedback loop control of HVAC systems in their plant. Jim ================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ================================================== |
Early surface plates: How were they made?
I read that scraping results in better accuracy when making true planes,
than does surface grinding. I find that hard to understand. Can someone explain why that would be so? Jordan |
Early surface plates: How were they made?
In article ,
(John Flanagan) wrote: Yes, in fact a quartz (?) sphere (12" diameter) was hand made by the chinese I believe over 1000 years ago and is very nearly perfect. It's in the Smithsoanian. Very interesting to imagine how the did it. Something similiar is done in the mountains by hillbillies. It involves a small stream of water falling into a 'pot' in the rock and a stone in the pot that turns in response to the water flow. -- free men own guns - slaves don't www.geocities.com/CapitolHill/5357/ |
Early surface plates: How were they made?
How perfect is perfect? Somebody can consider that a 1/32" accuracy is
perfect enough whil another isn't happy with an accuracy of a 1/4 wavelength of green light. Making a sphere isn't a hard chore at all. Rubbing another piece of material over the surface will quickly produce a spherical surface to the size of the grit used and gradually to a fair bit more accurate than that. -- Bob May Losing weight is easy! If you ever want to lose weight, eat and drink less. Works evevery time it is tried! |
Early surface plates: How were they made?
In article , Bob May says...
How perfect is perfect? One micron rms, over four feet square. Jim ================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ================================================== |
Early surface plates: How were they made?
jim rozen wrote:
In article , Bob May says... How perfect is perfect? One micron rms, over four feet square. Read "The Perfect Machine: Building the Palomar Telescope" |
Early surface plates: How were they made?
In article , Jim Stewart says...
One micron rms, over four feet square. Read "The Perfect Machine: Building the Palomar Telescope" Right, but could they put a one hundred pound straight edge on the mirror and still have it hold tolerance? Jim ================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ================================================== |
Early surface plates: How were they made?
On Fri, 22 Aug 2003 10:28:26 +0100, Jordan wrote:
I read that scraping results in better accuracy when making true planes, than does surface grinding. I find that hard to understand. Can someone explain why that would be so? Jordan PRO:- the table on a surface grinder follows the ways to some extent and will also vary in height if the oiler has been used. Grinding also produces heat which will distort the object being ground, Scraping three plates against each other is a primary method rather than a secondary method i.e. It is not dependant on the accuracy of any other piece of equipment. Scraping isn't limited by the size of your surface grinder. CON:- If the piece will fit the grinder at work then I can get better results with an hour of surface grinding than I can with a week of evenings spent scraping. I burnt my hand on a carbide scraper blade that I was using (hard) for some rough scraping last week :-( For true planes you have to go to the primary method of generation which is the theory that the only surface which can be congruent to an identical surface in all orientations is the plane surface and the corollary that the only surface which can be congruent to its reflection in all orientations is a plane surface. This means scraping three surfaces against each other. Anything else is an approximation.. Mark Rand RTFM |
Early surface plates: How were they made?
Subject: Early surface plates: How were they made? From: (Chris Lindquist) Date: 21/08/03 20:43 GMT Daylight Time Message-id: I've been trying to find out exactly what process was used for originating a surface plate in the good old days. I expect it involved careful hands and a large amount of scraping, but what provided a reference for "flat"? And how flat was flat around the turn of the century? I'm not planning to try this at home, of course. My Chinese granite plate is plenty flat enough, thanks. But I've been going through my books looking for an answer to this chicken-and-egg question without finding a solution. Can anyone help? During my apprenticeship I had the 'priviledge' of resurfacing a number of 4'x6' cast iron surface plates. (1 was standard, I was the bosses 'favorite'). * We were able to get a good start by cutting below the patina of the badly warped plates on a single point planer. Then they were left to soak and settle for a couple months. * For the plates in better shape, we just started in. Using three plates (five is better, I'm told) the program says that you blue one plate to another, and scrape away the blue on one plate. Then take that plate and blue it to the third plate and scrape that one. Then take the third and blue it to the first one and scrape the first one. Then you turn one of the plates 180 degrees and start all over. This continues until all three blue evenly to each other in all orientations. Then you usually flake the surface to break it up to keep it from being too smooth (and to give a place for minute dirt to collect). * Now - this takes a long time. Especially when the boss loans out the power scraper. It took two of us 6 weeks to hand scrape approximately .003. A paper coffee cup of shavings was a good days work. * I still have the scrapers I made for all that. Drew out some 6150 to about 1" X 24" X ~ 3/16 and brazed some carbide on the end. Made about a half dozen to get one with just the right feel. |
Early surface plates: How were they made?
In article , TreeMoose says...
Then you turn one of the plates 180 degrees and start all over. I always thought it had to be 90 degrees. A saddle error will not resolve for a full 180 rotation, right? Jim ================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ================================================== |
Early surface plates: How were they made?
In article , Mark Rand says...
For true planes you have to go to the primary method of generation which is the theory that the only surface which can be congruent to an identical surface in all orientations is the plane surface and the corollary that the only surface which can be congruent to its reflection in all orientations is a plane surface. This means scraping three surfaces against each other. Anything else is an approximation.. The 'in all orientations' part is quite critical. This is why a) surface plates generated this way are either round or square, not rectangular. And b) why there has to be a 90 degree rotation during the scraping/spotting cycle. Jim ================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ================================================== |
Early surface plates: How were they made?
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Early surface plates: How were they made?
"Fdmorrison" wrote in message
... jim rozen TreeMoose Then you turn one of the plates 180 degrees and start all over. Jim I always thought it had to be 90 degrees. A saddle error will not resolve for a full 180 rotation, right? Well, the old, old texts don't have any answer. Jim is right, if you get the rotations wrong in a certain way, you wind up with anticlastic saddles. I made a model of this once, in thin cardboard, and wrote down the required rotations. I think it's 180 deg. between one and two and one and three, and then 90 deg first (and then 180 deg) between two and three. Or something like that. g My uncle made a set of three aluminum plates, 6 in. square, to demonstrate this. You can make the saddle quite pronounced if you work at it. But you have to be a real bungler to do it by accident. Ed Huntress |
Early surface plates: How were they made?
On 21 Aug 2003 21:30:24 -0700, jim rozen
scribed: Hey all: Great thread! When I worked in Switzerland as an apprentice, we would lap Stainless Steel height gage bearing surfaces down to near millionths flatness using a chunk of (relatively flat) cast iron with some deep file scores in it... And diamond paste... Think of a cast iron gauge stand, take off the column, scratch a few deep lines in it with a file edge, criss-cross, slap some diamond paste and kerosene on the work surface and go to town... Took a few hours or so, but with the fine paste, kerosene as a lubricant, we could achieve some pretty good results... A nearly mirror finish, with exceptional flatness. 1st hour was getting all the high spots, 2nd hour was to polish it with the slurry, last hour was to dilute the paste enough to get a nice polish on the column. Goal was to get 1um flatness over 600mm in the checking fixture... OBT Priceless: Cleaning the lapping slurry out of every nook and cranny of your body after lapping a few of these a day...Ugh... Best, Fred In article , Dave Baker says... By lapping 3 plates against each other with grinding paste until all three are flat. The same way as reference plates are made now. The ancients could make a plate as flat as we can now. The technique requires no special technology. Not strictly true, Dave. Read the description about flat surface generation in Moore's book, they go into considerable detail on this. 1) they use cast iron plates, specially ribbed and supported. 2) the square plates are spotted against each other with a marking medium, and are hand scraped to each other. 3) the exact sequence of operations matters, and there is 90 degree rotation included between each cycle. This prevents a saddle error from developing. 4) once the plates are spotted and hand scraped as well as possible, each plate is then futher corrected using several additional steps, to get down to roughly one micron flatness level. Unless one includes these steps, they say that ten or so microns is all that can be achieved. Probably the *most* important technologies that we have, that were not available to the 'ancients' are a) more accurate metrology, and b) temperature controlled environments for doing the measuring in. The second is probably the most important. Moore's book give considerable engineering detail about what is now pretty trivial stuff, but when the book was written is was state of the art, he talks about feedback loop control of HVAC systems in their plant. Jim ================================================= = please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ================================================= = |
Early surface plates: How were they made?
Tony's precision scraping page:
http://www.csgnet.net/toolroom/scrape1.htm http://www.csgnet.net/toolroom/scrape2.htm http://www.csgnet.net/toolroom/power.htm |
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