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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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#81
Posted to rec.crafts.metalworking
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Which tool is needed. . . ?
"Jim Wilkins" wrote in message ... On Nov 28, 11:19 pm, "Ed Huntress" wrote: "Jim Wilkins" wrote in message ... I'm sure there are many possible solutions. ... Ed Huntress The problem is making the first headstock spindle without another lathe. Once you have it you can machine a better one. In my case someone would likely offer me a good lathe cheap *after* seeing the one I struggled to make. jsw I wouldn't attempt this without access to another lathe, unless someone made it a group or club project and made the necessary machined parts available for a reasonable price. -- Ed Huntress |
#82
Posted to rec.crafts.metalworking
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Which tool is needed. . . ?
On Nov 29, 9:20*am, "Ed Huntress" wrote:
"Jim Wilkins" wrote in message ... On Nov 28, 11:19 pm, "Ed Huntress" wrote: "Jim Wilkins" wrote in message ... I'm sure there are many possible solutions. ... Ed Huntress The problem is making the first headstock spindle without another lathe. Once you have it you can machine a better one. In my case someone would likely offer me a good lathe cheap *after* seeing the one I struggled to make. jsw I wouldn't attempt this without access to another lathe, unless someone made it a group or club project and made the necessary machined parts available for a reasonable price. -- Ed Huntress I think it could be achieved starting with a simple machine that's adjusted into place. For example my dead-center lathe could bore the headstock pipe for your cast concrete one. Slide the headstock down the ways over a long fixed boring bar. The practical application is temporary oversized equipment to recondition old worn machines. I'd like to rig up a milling head with enough X and Y travel to clean up the ways of my surface grinder. It only needs to slide along one axis while cutting, and can rest on parallels for the other axis. jsw |
#83
Posted to rec.crafts.metalworking
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Which tool is needed. . . ?
On Sat, 28 Nov 2009 23:08:15 -0500, "Ed Huntress"
wrote: The HLVH layout is extreme, but some space between the front bearing pair is not unusual. I'm looking at a cross section of a 10EE headstock and it appears the spacers are about 2-1/2" long. The support at the tail is an unspaced pair of angular contact bearings. Top speed of an EE is about 1000RPM higher than an HLVH. The bearings at the nose of a Bridgeport spindle are separated perhaps 1-1/2". In this case there's a single deep groove bearing at the top of the quill. A BP spindle running at top speed gets much hotter than an HLVH. Grinder spindles typically have the bearings pairs mounted directly back-to-back. -- Ned Simmons That generally agrees with what I've seen, although I haven't had any spindles apart for a few decades. Thirty degrees F produces about 0.001 in. of growth in about 5 inches of length. One thing that we've neglected here is that this is, at least potentially, a self compensating system. As the spindle warms up and expands the preload drops, reducing the heat generated in the bearing. The problem is coming up with a design that will settle at a reasonable equilibrium under the normal range of operating speeds and loadings. It seems Hardinge has been able to do this. That shouldn't be a problem for ordinary bearings, which are less that perfect all around; there's a little room for elastic compression. As it's been explained to me, the problem becomes more critical as the bearing class goes up. The Class 9 bearings in a Hardinge HLVH must be very touchy in terms of the growth they'll tolerate. I've never heard that and find it hard to swallow. If a lower class bearing has imperfections that allow it to deflect more easily, that implies there are areas of high stress that would be more sensitive to damage. I can see where a bearing with more accurate geometry might be stiffer as a result of better stress distribution, but I'd expect that would make it more robust, not less. -- Ned Simmons |
#84
Posted to rec.crafts.metalworking
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Which tool is needed. . . ?
"Ned Simmons" wrote in message ... On Sat, 28 Nov 2009 23:08:15 -0500, "Ed Huntress" wrote: The HLVH layout is extreme, but some space between the front bearing pair is not unusual. I'm looking at a cross section of a 10EE headstock and it appears the spacers are about 2-1/2" long. The support at the tail is an unspaced pair of angular contact bearings. Top speed of an EE is about 1000RPM higher than an HLVH. The bearings at the nose of a Bridgeport spindle are separated perhaps 1-1/2". In this case there's a single deep groove bearing at the top of the quill. A BP spindle running at top speed gets much hotter than an HLVH. Grinder spindles typically have the bearings pairs mounted directly back-to-back. -- Ned Simmons That generally agrees with what I've seen, although I haven't had any spindles apart for a few decades. Thirty degrees F produces about 0.001 in. of growth in about 5 inches of length. One thing that we've neglected here is that this is, at least potentially, a self compensating system. As the spindle warms up and expands the preload drops, reducing the heat generated in the bearing. The problem is coming up with a design that will settle at a reasonable equilibrium under the normal range of operating speeds and loadings. It seems Hardinge has been able to do this. That shouldn't be a problem for ordinary bearings, which are less that perfect all around; there's a little room for elastic compression. As it's been explained to me, the problem becomes more critical as the bearing class goes up. The Class 9 bearings in a Hardinge HLVH must be very touchy in terms of the growth they'll tolerate. I've never heard that and find it hard to swallow. If a lower class bearing has imperfections that allow it to deflect more easily, that implies there are areas of high stress that would be more sensitive to damage. There are. That's why they don't last as long if both types are properly applied. Unless it's overloaded, a Class 9 bearing will run until hell freezes over, while a lesser bearing will eventually spall and fail. That assumes that they aren't abused and brinelled, or otherwise damaged. I can see where a bearing with more accurate geometry might be stiffer as a result of better stress distribution... Yes. but I'd expect that would make it more robust, not less. It will last longer in proper service. It also is more susceptible to overloading from thermal growth, misalignment, etc. If you're going to use Class 9, everything in the setup had better be perfect. If it is, it will outlast a lesser-quality bearing. -- Ed Huntress |
#85
Posted to rec.crafts.metalworking
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Which tool is needed. . . ?
On Sun, 29 Nov 2009 16:58:29 -0500, "Ed Huntress"
wrote: "Ned Simmons" wrote in message .. . On Sat, 28 Nov 2009 23:08:15 -0500, "Ed Huntress" wrote: That shouldn't be a problem for ordinary bearings, which are less that perfect all around; there's a little room for elastic compression. As it's been explained to me, the problem becomes more critical as the bearing class goes up. The Class 9 bearings in a Hardinge HLVH must be very touchy in terms of the growth they'll tolerate. I've never heard that and find it hard to swallow. If a lower class bearing has imperfections that allow it to deflect more easily, that implies there are areas of high stress that would be more sensitive to damage. There are. That's why they don't last as long if both types are properly applied. Unless it's overloaded, a Class 9 bearing will run until hell freezes over, while a lesser bearing will eventually spall and fail. That assumes that they aren't abused and brinelled, or otherwise damaged. Not quite. Unless very lightly loaded, all bearings will eventually fatigue and fail by spalling. Very light loads will cause problems related to skidding of the balls. I can see where a bearing with more accurate geometry might be stiffer as a result of better stress distribution... Yes. but I'd expect that would make it more robust, not less. It will last longer in proper service. It also is more susceptible to overloading from thermal growth, misalignment, etc. If you're going to use Class 9, everything in the setup had better be perfect. If it is, it will outlast a lesser-quality bearing. This doesn't make sense to me. If a high ABEC class bearing will outlast a lower class bearing under ideal conditions, what's the mechanism that will cause it to fail sooner in a less than ideal installation? -- Ned Simmons |
#86
Posted to rec.crafts.metalworking
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Which tool is needed. . . ?
Ned Simmons wrote:
I can see where a bearing with more accurate geometry might be stiffer as a result of better stress distribution... Yes. but I'd expect that would make it more robust, not less. It will last longer in proper service. It also is more susceptible to overloading from thermal growth, misalignment, etc. If you're going to use Class 9, everything in the setup had better be perfect. If it is, it will outlast a lesser-quality bearing. This doesn't make sense to me. If a high ABEC class bearing will outlast a lower class bearing under ideal conditions, what's the mechanism that will cause it to fail sooner in a less than ideal installation? Well, he didn't say fail catastrophically. It could be that it degrades in performance and doesn't meet class 9 specs any longer. |
#87
Posted to rec.crafts.metalworking
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Which tool is needed. . . ?
On Sun, 29 Nov 2009 21:17:00 -0800, Jim Stewart
wrote: Ned Simmons wrote: I can see where a bearing with more accurate geometry might be stiffer as a result of better stress distribution... Yes. but I'd expect that would make it more robust, not less. It will last longer in proper service. It also is more susceptible to overloading from thermal growth, misalignment, etc. If you're going to use Class 9, everything in the setup had better be perfect. If it is, it will outlast a lesser-quality bearing. This doesn't make sense to me. If a high ABEC class bearing will outlast a lower class bearing under ideal conditions, what's the mechanism that will cause it to fail sooner in a less than ideal installation? Well, he didn't say fail catastrophically. It could be that it degrades in performance and doesn't meet class 9 specs any longer. Perhaps, but that's not how I read it. Clearly it doesn't make sense economically to stick an expensive bearing in an inferior gadget, but I can't come up with any reason it wouldn't last as long as an ABEC 1 bearing. -- Ned Simmons |
#88
Posted to rec.crafts.metalworking
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Which tool is needed. . . ?
"Ned Simmons" wrote in message ... On Sun, 29 Nov 2009 16:58:29 -0500, "Ed Huntress" wrote: "Ned Simmons" wrote in message . .. On Sat, 28 Nov 2009 23:08:15 -0500, "Ed Huntress" wrote: That shouldn't be a problem for ordinary bearings, which are less that perfect all around; there's a little room for elastic compression. As it's been explained to me, the problem becomes more critical as the bearing class goes up. The Class 9 bearings in a Hardinge HLVH must be very touchy in terms of the growth they'll tolerate. I've never heard that and find it hard to swallow. If a lower class bearing has imperfections that allow it to deflect more easily, that implies there are areas of high stress that would be more sensitive to damage. There are. That's why they don't last as long if both types are properly applied. Unless it's overloaded, a Class 9 bearing will run until hell freezes over, while a lesser bearing will eventually spall and fail. That assumes that they aren't abused and brinelled, or otherwise damaged. Not quite. Unless very lightly loaded, all bearings will eventually fatigue and fail by spalling. Very light loads will cause problems related to skidding of the balls. I can see where a bearing with more accurate geometry might be stiffer as a result of better stress distribution... Yes. but I'd expect that would make it more robust, not less. It will last longer in proper service. It also is more susceptible to overloading from thermal growth, misalignment, etc. If you're going to use Class 9, everything in the setup had better be perfect. If it is, it will outlast a lesser-quality bearing. This doesn't make sense to me. If a high ABEC class bearing will outlast a lower class bearing under ideal conditions, what's the mechanism that will cause it to fail sooner in a less than ideal installation? -- Ned Simmons There's nothing much to "crush." A given amount of displacement of one race relative to the other can produce a substantially higher preload in a higher-class bearing. The difference may be slight, but small variations in the percentage of yield strength that a bearing is subject to will produce large variations in its fatigue life -- in other words, the time it takes for the bearing balls or the race to spall. -- Ed Huntress |
#89
Posted to rec.crafts.metalworking
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Which tool is needed. . . ?
"Jim Wilkins" wrote in message ... On Nov 29, 9:20 am, "Ed Huntress" wrote: "Jim Wilkins" wrote in message ... On Nov 28, 11:19 pm, "Ed Huntress" wrote: "Jim Wilkins" wrote in message ... I'm sure there are many possible solutions. ... Ed Huntress The problem is making the first headstock spindle without another lathe. Once you have it you can machine a better one. In my case someone would likely offer me a good lathe cheap *after* seeing the one I struggled to make. jsw I wouldn't attempt this without access to another lathe, unless someone made it a group or club project and made the necessary machined parts available for a reasonable price. -- Ed Huntress I think it could be achieved starting with a simple machine that's adjusted into place. For example my dead-center lathe could bore the headstock pipe for your cast concrete one. Slide the headstock down the ways over a long fixed boring bar. The practical application is temporary oversized equipment to recondition old worn machines. I'd like to rig up a milling head with enough X and Y travel to clean up the ways of my surface grinder. It only needs to slide along one axis while cutting, and can rest on parallels for the other axis. jsw Maybe. I've thought about some of this in the past, and I don't see being able to bore the headstock from the bed without a pretty fancy, and strong, temporary boring rig. If it was just a straight bore, maybe. But I've changed my thinking on that to include a tube bored on another lathe; a careful setup to cast it in place when the headstock is cast; and a honing/lapping rig mounted on the new lathe's bedways, rather than boring, to finish it off. The loads will be much less and you won't need a controlled feedrate. The whole affair would be simpler. But I'm not saying I have all the answers for this. It's just a lot of thinking and speculating on my part. Nor would I want to discourage anyone else who wants to give it a try. Viva the experiments. As for finish-machining bedways, you might like to see my idea for a right-angle grinding head that moves on ordinary, low-accuracy ways (Thompson round ways), with two axes of stepping motors that respond to optical drives that follow a laser beam -- or maybe you wouldn't want to see it, come to think of it. It was pretty rough and crude, but there's an idea there. (No, I don't have any CAD files of it. I sketched it around 30 years ago.) -- Ed Huntress |
#90
Posted to rec.crafts.metalworking
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Which tool is needed. . . ?
On Mon, 30 Nov 2009 09:59:17 -0500, "Ed Huntress"
wrote: "Ned Simmons" wrote in message .. . This doesn't make sense to me. If a high ABEC class bearing will outlast a lower class bearing under ideal conditions, what's the mechanism that will cause it to fail sooner in a less than ideal installation? -- Ned Simmons There's nothing much to "crush." A given amount of displacement of one race relative to the other can produce a substantially higher preload in a higher-class bearing. The difference may be slight, but small variations in the percentage of yield strength that a bearing is subject to will produce large variations in its fatigue life -- in other words, the time it takes for the bearing balls or the race to spall. Right. But I understood you to say that the imperfections on the contact surfaces of a low class bearing will cause it to fail earlier than a high class bearing when they are both properly mounted. On the other hand, you also seem to be saying that those imperfections are *protecting* the low class bearing in a poor mounting. If you imagine looking at only a very small patch on the bearing race, there's no way to tell whether the bearing is mounted properly or not, all you can determine is the contact pressure as a ball passes. If there are imperfections in the surface of the low class bearing's race, there will be local peaks in the contact stress, regardless of the how the bearing is mounted. Re the temperature compensation business, I was looking thru some of my references and found this: http://tinyurl.com/ya7hvm4 There's about a half page missing, but the jist of it is there. -- Ned Simmons |
#91
Posted to rec.crafts.metalworking
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Which tool is needed. . . ?
"Ned Simmons" wrote in message news On Mon, 30 Nov 2009 09:59:17 -0500, "Ed Huntress" wrote: "Ned Simmons" wrote in message . .. This doesn't make sense to me. If a high ABEC class bearing will outlast a lower class bearing under ideal conditions, what's the mechanism that will cause it to fail sooner in a less than ideal installation? -- Ned Simmons There's nothing much to "crush." A given amount of displacement of one race relative to the other can produce a substantially higher preload in a higher-class bearing. The difference may be slight, but small variations in the percentage of yield strength that a bearing is subject to will produce large variations in its fatigue life -- in other words, the time it takes for the bearing balls or the race to spall. Right. But I understood you to say that the imperfections on the contact surfaces of a low class bearing will cause it to fail earlier than a high class bearing when they are both properly mounted. On the other hand, you also seem to be saying that those imperfections are *protecting* the low class bearing in a poor mounting. Right. Both. Local overloads are what cause a lower-class bearing to fail sooner than a high-class bearing, given a good mounting. But the presence of anomalous bumps and so on are also what give it some "crush" room. A low-grade bearing will fail sooner than a high-class one in a good mounting. It will fail even sooner in a bad mounting. Depending on the nature of the "bad" mounting, however, it can last longer than a high-class bearing in the bad mounting. Some of the anomalies in a lower-class bearing don't result in premature spalling of the balls or races; they may just displace locally. That's the "crush" room. If you imagine looking at only a very small patch on the bearing race, there's no way to tell whether the bearing is mounted properly or not, all you can determine is the contact pressure as a ball passes. If there are imperfections in the surface of the low class bearing's race, there will be local peaks in the contact stress, regardless of the how the bearing is mounted. Right. But even when they fail, the spalling may not spread around. If the load on these "points" is very high, they may not spall at all: the points will just displace plastically, or fracture off from local overload. Then some of the preload is relieved; the bearing runs loose; but the mean load on the bearings is reduced. A high-class bearing, poorly mounted, will subject the balls and/or spots on the races to continual overload at certain points in their rotation. There's nothing much to "crush," so nothing will relieve the overload; they'll spall sooner, depending again on how the mounting is "bad," than the lower-class bearings. You know, all of this is from memory, based on explanations derived from practice and perhaps from theory as well, passed along to me by bearing specialists many years ago. I had the job of dealing with lubrication issues when I was at _American Machinist_, and in those days, that meant listening to some really boring stuff in interviews. g The guys at Timken were great; they spent hours explaining things to me about bearings in the real world. That's where I got all this stuff. My memory for these things usually is Ok, but I'm reconstructing it. In general, the idea that good bearings can go to pot quicker than poorer-class bearings in a bad setup, with a poor mounting, is clear in my memory. Re the temperature compensation business, I was looking thru some of my references and found this: http://tinyurl.com/ya7hvm4 There's about a half page missing, but the jist of it is there. Well, right through page 542, there's most of the story. I didn't follow the relative radii between balls and races in detail, but I see the picture. Finite-element analysis and bench-testing a prototype sound like a good idea. g I've never touched thermal FIA so I don't know how predictable the bearing and spindle temperatures are, but Slocum does identify some problems that have to be tested. Very interesting, Ned. Thanks. -- Ed Huntress |
#92
Posted to rec.crafts.metalworking
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Which tool is needed. . . ?
On Tue, 1 Dec 2009 01:01:12 -0500, "Ed Huntress"
wrote: "Ned Simmons" wrote in message news On Mon, 30 Nov 2009 09:59:17 -0500, "Ed Huntress" wrote: "Ned Simmons" wrote in message ... This doesn't make sense to me. If a high ABEC class bearing will outlast a lower class bearing under ideal conditions, what's the mechanism that will cause it to fail sooner in a less than ideal installation? -- Ned Simmons There's nothing much to "crush." A given amount of displacement of one race relative to the other can produce a substantially higher preload in a higher-class bearing. The difference may be slight, but small variations in the percentage of yield strength that a bearing is subject to will produce large variations in its fatigue life -- in other words, the time it takes for the bearing balls or the race to spall. Right. But I understood you to say that the imperfections on the contact surfaces of a low class bearing will cause it to fail earlier than a high class bearing when they are both properly mounted. On the other hand, you also seem to be saying that those imperfections are *protecting* the low class bearing in a poor mounting. Right. Both. Local overloads are what cause a lower-class bearing to fail sooner than a high-class bearing, given a good mounting. But the presence of anomalous bumps and so on are also what give it some "crush" room. A low-grade bearing will fail sooner than a high-class one in a good mounting. It will fail even sooner in a bad mounting. Depending on the nature of the "bad" mounting, however, it can last longer than a high-class bearing in the bad mounting. Some of the anomalies in a lower-class bearing don't result in premature spalling of the balls or races; they may just displace locally. That's the "crush" room. If you imagine looking at only a very small patch on the bearing race, there's no way to tell whether the bearing is mounted properly or not, all you can determine is the contact pressure as a ball passes. If there are imperfections in the surface of the low class bearing's race, there will be local peaks in the contact stress, regardless of the how the bearing is mounted. Right. But even when they fail, the spalling may not spread around. If the load on these "points" is very high, they may not spall at all: the points will just displace plastically, or fracture off from local overload. Then some of the preload is relieved; the bearing runs loose; but the mean load on the bearings is reduced. A high-class bearing, poorly mounted, will subject the balls and/or spots on the races to continual overload at certain points in their rotation. There's nothing much to "crush," so nothing will relieve the overload; they'll spall sooner, depending again on how the mounting is "bad," than the lower-class bearings. OK, I see what you're saying. But to allow that a bearing that has permanently deformed to the degree necessary to relieve an overload is still OK is rather generous. But I suppose if it still runs without making nasty noises... You know, all of this is from memory, based on explanations derived from practice and perhaps from theory as well, passed along to me by bearing specialists many years ago. I had the job of dealing with lubrication issues when I was at _American Machinist_, and in those days, that meant listening to some really boring stuff in interviews. g The guys at Timken were great; they spent hours explaining things to me about bearings in the real world. That's where I got all this stuff. My memory for these things usually is Ok, but I'm reconstructing it. I'm afraid those days are gone, at least for us peons. As recently as 5 years ago I could still speak directly to someone at SKF or Timken or Fafnir who was willing to answer questions that weren't covered in the literature. I recently had a very simple question about the strength of the cast housings of mounted bearings relative to the load capacity of the inserts. The know-nothing I spoke to at Fafnir said he'd try to get an answer by emailing the tech guy, who was in a time zone remote enough that their workdays didn't ovelap. I never did get my answer. In general, the idea that good bearings can go to pot quicker than poorer-class bearings in a bad setup, with a poor mounting, is clear in my memory. Re the temperature compensation business, I was looking thru some of my references and found this: http://tinyurl.com/ya7hvm4 There's about a half page missing, but the jist of it is there. Well, right through page 542, there's most of the story. I didn't follow the relative radii between balls and races in detail, but I see the picture. Finite-element analysis and bench-testing a prototype sound like a good idea. g I've never touched thermal FIA so I don't know how predictable the bearing and spindle temperatures are, but Slocum does identify some problems that have to be tested. Very interesting, Ned. Thanks. Well, thanks for sticking with me on this. It may not have much practical value -- I'm not planning on installing $300 bearings where $8 units will do, but it's good exercise. Now back to the birthers... -- Ned Simmons |
#93
Posted to rec.crafts.metalworking
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Which tool is needed. . . ?
On Tue, 1 Dec 2009 01:01:12 -0500, "Ed Huntress"
wrote: "Ned Simmons" wrote in message news On Mon, 30 Nov 2009 09:59:17 -0500, "Ed Huntress" wrote: "Ned Simmons" wrote in message ... This doesn't make sense to me. If a high ABEC class bearing will outlast a lower class bearing under ideal conditions, what's the mechanism that will cause it to fail sooner in a less than ideal installation? -- Ned Simmons There's nothing much to "crush." A given amount of displacement of one race relative to the other can produce a substantially higher preload in a higher-class bearing. The difference may be slight, but small variations in the percentage of yield strength that a bearing is subject to will produce large variations in its fatigue life -- in other words, the time it takes for the bearing balls or the race to spall. Right. But I understood you to say that the imperfections on the contact surfaces of a low class bearing will cause it to fail earlier than a high class bearing when they are both properly mounted. On the other hand, you also seem to be saying that those imperfections are *protecting* the low class bearing in a poor mounting. Right. Both. Local overloads are what cause a lower-class bearing to fail sooner than a high-class bearing, given a good mounting. But the presence of anomalous bumps and so on are also what give it some "crush" room. A low-grade bearing will fail sooner than a high-class one in a good mounting. It will fail even sooner in a bad mounting. Depending on the nature of the "bad" mounting, however, it can last longer than a high-class bearing in the bad mounting. Some of the anomalies in a lower-class bearing don't result in premature spalling of the balls or races; they may just displace locally. That's the "crush" room. If you imagine looking at only a very small patch on the bearing race, there's no way to tell whether the bearing is mounted properly or not, all you can determine is the contact pressure as a ball passes. If there are imperfections in the surface of the low class bearing's race, there will be local peaks in the contact stress, regardless of the how the bearing is mounted. Right. But even when they fail, the spalling may not spread around. If the load on these "points" is very high, they may not spall at all: the points will just displace plastically, or fracture off from local overload. Then some of the preload is relieved; the bearing runs loose; but the mean load on the bearings is reduced. A high-class bearing, poorly mounted, will subject the balls and/or spots on the races to continual overload at certain points in their rotation. There's nothing much to "crush," so nothing will relieve the overload; they'll spall sooner, depending again on how the mounting is "bad," than the lower-class bearings. OK, I see what you're saying. But to allow that a bearing that has permanently deformed to the degree necessary to relieve an overload is still OK is rather generous. But I suppose if it still runs without making nasty noises... You know, all of this is from memory, based on explanations derived from practice and perhaps from theory as well, passed along to me by bearing specialists many years ago. I had the job of dealing with lubrication issues when I was at _American Machinist_, and in those days, that meant listening to some really boring stuff in interviews. g The guys at Timken were great; they spent hours explaining things to me about bearings in the real world. That's where I got all this stuff. My memory for these things usually is Ok, but I'm reconstructing it. I'm afraid those days are gone, at least for us peons. As recently as 5 years ago I could still speak directly to someone at SKF or Timken or Fafnir who was willing to answer questions that weren't covered in the literature. I recently had a very simple question about the strength of the cast housings of mounted bearings relative to the load capacity of the inserts. The know-nothing I spoke to at Fafnir said he'd try to get an answer by emailing the tech guy, who was in a time zone remote enough that their workdays didn't ovelap. I never did get my answer. In general, the idea that good bearings can go to pot quicker than poorer-class bearings in a bad setup, with a poor mounting, is clear in my memory. Re the temperature compensation business, I was looking thru some of my references and found this: http://tinyurl.com/ya7hvm4 There's about a half page missing, but the jist of it is there. Well, right through page 542, there's most of the story. I didn't follow the relative radii between balls and races in detail, but I see the picture. Finite-element analysis and bench-testing a prototype sound like a good idea. g I've never touched thermal FIA so I don't know how predictable the bearing and spindle temperatures are, but Slocum does identify some problems that have to be tested. Very interesting, Ned. Thanks. Well, thanks for sticking with me on this. It may not have much practical value -- I'm not planning on installing $300 bearings where $8 units will do, but it's good exercise. Now back to the birthers... -- Ned Simmons |
#94
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Which tool is needed. . . ?
On Dec 2, 5:01*am, Ned Simmons wrote:
Well, thanks for sticking with me on this. It may not have much practical value -- I'm not planning on installing $300 bearings where $8 units will do, but it's good exercise. Now back to the birthers... -- Ned Simmons It may not have any value at all. The $8 bearing has a minimum tolerance. There is no guarantee that it will have characteristics that Ed says will make it last longer in a poor mounting. The $300 bearings are selected after manufacture from the lot that has the $8 bearings. So if the demand for $300 bearings isn't very high, you may get a high precision bearing from the $8 bin. Also bearing manufacturing has improved in the last thirty years. So more of the $8 bearings are closer to meeting the specs of the $300 bearings. Granted not all manufacturers have tighter control on their production. Dan |
#95
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Which tool is needed. . . ?
On Wed, 2 Dec 2009 06:01:43 -0800 (PST), "
wrote: On Dec 2, 5:01*am, Ned Simmons wrote: Well, thanks for sticking with me on this. It may not have much practical value -- I'm not planning on installing $300 bearings where $8 units will do, but it's good exercise. Now back to the birthers... -- Ned Simmons It may not have any value at all. The $8 bearing has a minimum tolerance. There is no guarantee that it will have characteristics that Ed says will make it last longer in a poor mounting. The $300 bearings are selected after manufacture from the lot that has the $8 bearings. That may be true of resistors, but not bearings. For example, Barden makes *only* precision bearings. Precision bearings also have different cages than the bearing you get if you simply ask for a 6206. So if the demand for $300 bearings isn't very high, you may get a high precision bearing from the $8 bin. Also bearing manufacturing has improved in the last thirty years. So more of the $8 bearings are closer to meeting the specs of the $300 bearings. Granted not all manufacturers have tighter control on their production. This is true. I was told by an SKF engineer that most of their ABEC 1 deep row bearings will meet ABEC 5 standards, and I've verified this in a couple cases where I built very low speed spindles with sub-tenth runout using ABEC 1 bearings. The fallback plan was to replace the bearings with precision units, but it wasn't necessary. -- Ned Simmons |
#96
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Which tool is needed. . . ?
On Dec 2, 2:31*pm, Ned Simmons wrote:
That may be true of resistors, but not bearings. For example, Barden makes *only* precision bearings. Precision bearings also have different cages than the bearing you get if you simply ask for a 6206. I think it is true for most manufacturers. It has been sometime since I read whatever I read. I may have been reading about roller bearing at the time with the emphasis on using the sizes that are relatively cheap because they are manufactured for use on semi-trucks. This is true. I was told by an SKF engineer that most of their ABEC 1 deep row bearings will meet ABEC 5 standards, and I've verified this in a couple cases where I built very low speed spindles with sub-tenth runout using ABEC 1 bearings. The fallback plan was to replace the bearings with precision units, but it wasn't necessary. So if most meet ABEC 5, what are the chances that some meet ABEC 7 or 9? Dan -- Ned Simmons |
#97
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Which tool is needed. . . ?
"Ned Simmons" wrote in message ... On Tue, 1 Dec 2009 01:01:12 -0500, "Ed Huntress" wrote: "Ned Simmons" wrote in message news On Mon, 30 Nov 2009 09:59:17 -0500, "Ed Huntress" wrote: "Ned Simmons" wrote in message m... This doesn't make sense to me. If a high ABEC class bearing will outlast a lower class bearing under ideal conditions, what's the mechanism that will cause it to fail sooner in a less than ideal installation? -- Ned Simmons There's nothing much to "crush." A given amount of displacement of one race relative to the other can produce a substantially higher preload in a higher-class bearing. The difference may be slight, but small variations in the percentage of yield strength that a bearing is subject to will produce large variations in its fatigue life -- in other words, the time it takes for the bearing balls or the race to spall. Right. But I understood you to say that the imperfections on the contact surfaces of a low class bearing will cause it to fail earlier than a high class bearing when they are both properly mounted. On the other hand, you also seem to be saying that those imperfections are *protecting* the low class bearing in a poor mounting. Right. Both. Local overloads are what cause a lower-class bearing to fail sooner than a high-class bearing, given a good mounting. But the presence of anomalous bumps and so on are also what give it some "crush" room. A low-grade bearing will fail sooner than a high-class one in a good mounting. It will fail even sooner in a bad mounting. Depending on the nature of the "bad" mounting, however, it can last longer than a high-class bearing in the bad mounting. Some of the anomalies in a lower-class bearing don't result in premature spalling of the balls or races; they may just displace locally. That's the "crush" room. If you imagine looking at only a very small patch on the bearing race, there's no way to tell whether the bearing is mounted properly or not, all you can determine is the contact pressure as a ball passes. If there are imperfections in the surface of the low class bearing's race, there will be local peaks in the contact stress, regardless of the how the bearing is mounted. Right. But even when they fail, the spalling may not spread around. If the load on these "points" is very high, they may not spall at all: the points will just displace plastically, or fracture off from local overload. Then some of the preload is relieved; the bearing runs loose; but the mean load on the bearings is reduced. A high-class bearing, poorly mounted, will subject the balls and/or spots on the races to continual overload at certain points in their rotation. There's nothing much to "crush," so nothing will relieve the overload; they'll spall sooner, depending again on how the mounting is "bad," than the lower-class bearings. OK, I see what you're saying. But to allow that a bearing that has permanently deformed to the degree necessary to relieve an overload is still OK is rather generous. But I suppose if it still runs without making nasty noises... You know, all of this is from memory, based on explanations derived from practice and perhaps from theory as well, passed along to me by bearing specialists many years ago. I had the job of dealing with lubrication issues when I was at _American Machinist_, and in those days, that meant listening to some really boring stuff in interviews. g The guys at Timken were great; they spent hours explaining things to me about bearings in the real world. That's where I got all this stuff. My memory for these things usually is Ok, but I'm reconstructing it. I'm afraid those days are gone, at least for us peons. As recently as 5 years ago I could still speak directly to someone at SKF or Timken or Fafnir who was willing to answer questions that weren't covered in the literature. I recently had a very simple question about the strength of the cast housings of mounted bearings relative to the load capacity of the inserts. The know-nothing I spoke to at Fafnir said he'd try to get an answer by emailing the tech guy, who was in a time zone remote enough that their workdays didn't ovelap. I never did get my answer. In general, the idea that good bearings can go to pot quicker than poorer-class bearings in a bad setup, with a poor mounting, is clear in my memory. Re the temperature compensation business, I was looking thru some of my references and found this: http://tinyurl.com/ya7hvm4 There's about a half page missing, but the jist of it is there. Well, right through page 542, there's most of the story. I didn't follow the relative radii between balls and races in detail, but I see the picture. Finite-element analysis and bench-testing a prototype sound like a good idea. g I've never touched thermal FIA so I don't know how predictable the bearing and spindle temperatures are, but Slocum does identify some problems that have to be tested. Very interesting, Ned. Thanks. Well, thanks for sticking with me on this. It may not have much practical value -- I'm not planning on installing $300 bearings where $8 units will do, but it's good exercise. I don't know if I've ever touched a $300 bearing. Well, maybe -- I've handled some all-ceramic bearing sets, and the ones with ceramic races, as well as ceramic balls, cost like crazy. Or they did. But anything I'm likely to work on will get along with cheap. In fact, I kind of like plain bearings...g Now back to the birthers... Yes, on to the birthers... -- Ed Huntress |
#98
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Which tool is needed. . . ?
On Dec 1, 1:01*am, "Ed Huntress" wrote:
... Right. But even when they fail, the spalling may not spread around. If the load on these "points" is very high, they may not spall at all: the points will just displace plastically, or fracture off from local overload. Then some of the preload is relieved; the bearing runs loose; but the mean load on the bearings is reduced.... Ed Huntress Are you suggesting that lower grade bearing components have less stringent heat treatment? jsw |
#99
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Which tool is needed. . . ?
Ned Simmons wrote:
This is true. I was told by an SKF engineer that most of their ABEC 1 deep row bearings will meet ABEC 5 standards, and I've verified this in a couple cases where I built very low speed spindles with sub-tenth runout using ABEC 1 bearings. The fallback plan was to replace the bearings with precision units, but it wasn't necessary. Don't worry. It's probably only a matter of time before they start relabeling and selling genuine ABEC 1 bearings from China... |
#100
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Which tool is needed. . . ?
On Wed, 2 Dec 2009 08:02:47 -0800 (PST), "
wrote: On Dec 2, 2:31*pm, Ned Simmons wrote: That may be true of resistors, but not bearings. For example, Barden makes *only* precision bearings. Precision bearings also have different cages than the bearing you get if you simply ask for a 6206. I think it is true for most manufacturers. It has been sometime since I read whatever I read. I don't know for sure one way or the other. But besides the matter of the cages I mentioned before, it seems marking would also be a problem. Marking the part number would certainly have to be done before final grinding of the assembled bearing, and more likely even before heat treat of the components, which I assume is done after rough turning but before the races are ground. That's pretty early in the process to be selecting components. I may have been reading about roller bearing at the time with the emphasis on using the sizes that are relatively cheap because they are manufactured for use on semi-trucks. This is true. I was told by an SKF engineer that most of their ABEC 1 deep row bearings will meet ABEC 5 standards, and I've verified this in a couple cases where I built very low speed spindles with sub-tenth runout using ABEC 1 bearings. The fallback plan was to replace the bearings with precision units, but it wasn't necessary. So if most meet ABEC 5, what are the chances that some meet ABEC 7 or 9? I wouldn't be surprised if the occasional bearing meets at least some of the specs. My understanding is that the geometry and finish requirements to meet electric motor bearing standards, which are for the most part quietness specs, are the same things required to make a true running bearing. On the other hand, EM quality does not require especially tight tolerances on the overall dimensions of the bearing, so standard bearings may be less likely to exceed their class in that regard. Like Ed, I've formed these impressions based on conversations I've had with various tech support persons over the years, so take them with a grain of salt. -- Ned Simmons |
#101
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Which tool is needed. . . ?
On Wed, 2 Dec 2009 11:50:25 -0500, "Ed Huntress"
wrote: "Ned Simmons" wrote in message Well, thanks for sticking with me on this. It may not have much practical value -- I'm not planning on installing $300 bearings where $8 units will do, but it's good exercise. I don't know if I've ever touched a $300 bearing. Well, maybe -- I've handled some all-ceramic bearing sets, and the ones with ceramic races, as well as ceramic balls, cost like crazy. Or they did. They still do. But even a pair of Bridgeport spindle bearings costs close to $300. -- Ned Simmons |
#102
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Which tool is needed. . . ?
"Ned Simmons" wrote in message ... On Wed, 2 Dec 2009 11:50:25 -0500, "Ed Huntress" wrote: "Ned Simmons" wrote in message Well, thanks for sticking with me on this. It may not have much practical value -- I'm not planning on installing $300 bearings where $8 units will do, but it's good exercise. I don't know if I've ever touched a $300 bearing. Well, maybe -- I've handled some all-ceramic bearing sets, and the ones with ceramic races, as well as ceramic balls, cost like crazy. Or they did. They still do. But even a pair of Bridgeport spindle bearings costs close to $300. Jeez. I'm glad I don't own anything newer than about...oh, 1950. g I need to buy a new set for my Walker-Turner drill press. You're making me nervous. -- Ed Huntress |
#103
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Which tool is needed. . . ?
"Jim Wilkins" wrote in message ... On Dec 1, 1:01 am, "Ed Huntress" wrote: ... Right. But even when they fail, the spalling may not spread around. If the load on these "points" is very high, they may not spall at all: the points will just displace plastically, or fracture off from local overload. Then some of the preload is relieved; the bearing runs loose; but the mean load on the bearings is reduced.... Ed Huntress Are you suggesting that lower grade bearing components have less stringent heat treatment? jsw No, I wasn't suggesting that, Jim. I don't recall the ABEC specifications on heat treatment, but the point here is that imperfect balls and races will have high points, where the specific load will exceed the compressive strength of the metal, and will get squashed down or broken off. -- Ed Huntress |
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