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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
Posted to rec.crafts.metalworking
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Millrite X-axis thrust bearings were frozen
On my old (built in 1965) Millrite MVI vertical mill, one annoyance is the
difficulty setting the table to a specified X (side-to-side) location. One would overshoot, in both directions. My first theory was that this was because the X-axis feeedscrew and nut were worn, but I wondered if there was an adjustment needing attention, so I got a bright light and looked at the screw as I cranked the table back and forth. I could see that things were moving a bit at the left end, where the leadscrew is fixed to the table by two opposing thrust ball bearings, so I decided to take this assembly apart and de-spooge it. This assembly has never before been disassembled, I think. The three hex socket cap screws that hold the left end "bell" to the table were glued in place by well-hardened spooge, and took some force to disassemble, and there were lumps of spooge everywhere. Oddly, the deep blind threaded holes into which these cap screws go were filled with oily swarf. Cleaned everything out. It turned out that one of the thrust ball bearings was caked with hardened grease, being unable to move, and so the whole assembly rotated, forcing the preload nut to turn and loosen, so everything could move. This was a major cause of lost motion. Soaking the two thrust bearings in acetone for four hours dissolved the caked grease and allowed free rotation and full cleanout. Bearings looked OK, so packed them with Mobil-1 synthetic grease and reassembled the end assembly. The preload nut is round and engages threads machined into the feedscrew, rotation being prevented by a setscrew in the nut. I didn't like the idea of mashing a cup-point setscrew down on and mangling those threads, so I put a little piece of annealed copper in under the setscrew, so the copper would mash and conform to the steel threads. I tightened the nut first by hand, and then by an added 1/8 turn with a pin spanner wrench, only then driving the setscrew home, so there is a slight drag when cranking the screw. The lost motion is now about 0.025", which isn't much better than what it was before, but it does seem easier to set the table to a desired location. I'll use the mill for a while and see if this is really true. With a DRO, the real issue is ability to set to a desired location, not the accuracy of the screw. Both the leadscrew and matching nut (5 tpi) are made of steel, but the nut (being far shorter) should have suffered more wear than the screw. Joe Gwinn |
#2
Posted to rec.crafts.metalworking
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Millrite X-axis thrust bearings were frozen
On Sun, 28 Mar 2010 20:12:33 -0400, Joseph Gwinn
wrote: On my old (built in 1965) Millrite MVI vertical mill, one annoyance is the difficulty setting the table to a specified X (side-to-side) location. One would overshoot, in both directions. My first theory was that this was because the X-axis feeedscrew and nut were worn, but I wondered if there was an adjustment needing attention, so I got a bright light and looked at the screw as I cranked the table back and forth. I could see that things were moving a bit at the left end, where the leadscrew is fixed to the table by two opposing thrust ball bearings, so I decided to take this assembly apart and de-spooge it. This assembly has never before been disassembled, I think. The three hex socket cap screws that hold the left end "bell" to the table were glued in place by well-hardened spooge, and took some force to disassemble, and there were lumps of spooge everywhere. Oddly, the deep blind threaded holes into which these cap screws go were filled with oily swarf. Cleaned everything out. It turned out that one of the thrust ball bearings was caked with hardened grease, being unable to move, and so the whole assembly rotated, forcing the preload nut to turn and loosen, so everything could move. This was a major cause of lost motion. Soaking the two thrust bearings in acetone for four hours dissolved the caked grease and allowed free rotation and full cleanout. Bearings looked OK, so packed them with Mobil-1 synthetic grease and reassembled the end assembly. The preload nut is round and engages threads machined into the feedscrew, rotation being prevented by a setscrew in the nut. I didn't like the idea of mashing a cup-point setscrew down on and mangling those threads, so I put a little piece of annealed copper in under the setscrew, so the copper would mash and conform to the steel threads. I tightened the nut first by hand, and then by an added 1/8 turn with a pin spanner wrench, only then driving the setscrew home, so there is a slight drag when cranking the screw. The lost motion is now about 0.025", which isn't much better than what it was before, but it does seem easier to set the table to a desired location. I'll use the mill for a while and see if this is really true. With a DRO, the real issue is ability to set to a desired location, not the accuracy of the screw. Both the leadscrew and matching nut (5 tpi) are made of steel, but the nut (being far shorter) should have suffered more wear than the screw. Joe Gwinn The usual procedure is to make all final adjustments from one direction which negates any looseness in fit between the lead screw and the nut. Most old guys do it without thinking - back it off a half turn too far and go back 'till you get where you want to be for the next cut. John B. Slocomb |
#3
Posted to rec.crafts.metalworking
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Millrite X-axis thrust bearings were frozen
In article ,
John B. Slocomb wrote: On Sun, 28 Mar 2010 20:12:33 -0400, Joseph Gwinn wrote: On my old (built in 1965) Millrite MVI vertical mill, one annoyance is the difficulty setting the table to a specified X (side-to-side) location. One would overshoot, in both directions. My first theory was that this was because the X-axis feeedscrew and nut were worn, but I wondered if there was an adjustment needing attention, so I got a bright light and looked at the screw as I cranked the table back and forth. I could see that things were moving a bit at the left end, where the leadscrew is fixed to the table by two opposing thrust ball bearings, so I decided to take this assembly apart and de-spooge it. This assembly has never before been disassembled, I think. The three hex socket cap screws that hold the left end "bell" to the table were glued in place by well-hardened spooge, and took some force to disassemble, and there were lumps of spooge everywhere. Oddly, the deep blind threaded holes into which these cap screws go were filled with oily swarf. Cleaned everything out. It turned out that one of the thrust ball bearings was caked with hardened grease, being unable to move, and so the whole assembly rotated, forcing the preload nut to turn and loosen, so everything could move. This was a major cause of lost motion. Soaking the two thrust bearings in acetone for four hours dissolved the caked grease and allowed free rotation and full cleanout. Bearings looked OK, so packed them with Mobil-1 synthetic grease and reassembled the end assembly. The preload nut is round and engages threads machined into the feedscrew, rotation being prevented by a setscrew in the nut. I didn't like the idea of mashing a cup-point setscrew down on and mangling those threads, so I put a little piece of annealed copper in under the setscrew, so the copper would mash and conform to the steel threads. I tightened the nut first by hand, and then by an added 1/8 turn with a pin spanner wrench, only then driving the setscrew home, so there is a slight drag when cranking the screw. The lost motion is now about 0.025", which isn't much better than what it was before, but it does seem easier to set the table to a desired location. I'll use the mill for a while and see if this is really true. With a DRO, the real issue is ability to set to a desired location, not the accuracy of the screw. Both the leadscrew and matching nut (5 tpi) are made of steel, but the nut (being far shorter) should have suffered more wear than the screw. Joe Gwinn The usual procedure is to make all final adjustments from one direction which negates any looseness in fit between the lead screw and the nut. Most old guys do it without thinking - back it off a half turn too far and go back 'till you get where you want to be for the next cut. Yep. Though I'm still trying to achieve true old-guy machinist status. I had come to the go-one-way solution, but cutting in one direction but not the other (even with the X-axis clamped) still caught my attention. Joe Gwinn |
#4
Posted to rec.crafts.metalworking
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Millrite X-axis thrust bearings were frozen
On Mon, 29 Mar 2010 00:02:04 -0400, Joseph Gwinn
wrote: In article , John B. Slocomb wrote: On Sun, 28 Mar 2010 20:12:33 -0400, Joseph Gwinn wrote: On my old (built in 1965) Millrite MVI vertical mill, one annoyance is the difficulty setting the table to a specified X (side-to-side) location. One would overshoot, in both directions. My first theory was that this was because the X-axis feeedscrew and nut were worn, but I wondered if there was an adjustment needing attention, so I got a bright light and looked at the screw as I cranked the table back and forth. I could see that things were moving a bit at the left end, where the leadscrew is fixed to the table by two opposing thrust ball bearings, so I decided to take this assembly apart and de-spooge it. This assembly has never before been disassembled, I think. The three hex socket cap screws that hold the left end "bell" to the table were glued in place by well-hardened spooge, and took some force to disassemble, and there were lumps of spooge everywhere. Oddly, the deep blind threaded holes into which these cap screws go were filled with oily swarf. Cleaned everything out. It turned out that one of the thrust ball bearings was caked with hardened grease, being unable to move, and so the whole assembly rotated, forcing the preload nut to turn and loosen, so everything could move. This was a major cause of lost motion. Soaking the two thrust bearings in acetone for four hours dissolved the caked grease and allowed free rotation and full cleanout. Bearings looked OK, so packed them with Mobil-1 synthetic grease and reassembled the end assembly. The preload nut is round and engages threads machined into the feedscrew, rotation being prevented by a setscrew in the nut. I didn't like the idea of mashing a cup-point setscrew down on and mangling those threads, so I put a little piece of annealed copper in under the setscrew, so the copper would mash and conform to the steel threads. I tightened the nut first by hand, and then by an added 1/8 turn with a pin spanner wrench, only then driving the setscrew home, so there is a slight drag when cranking the screw. The lost motion is now about 0.025", which isn't much better than what it was before, but it does seem easier to set the table to a desired location. I'll use the mill for a while and see if this is really true. With a DRO, the real issue is ability to set to a desired location, not the accuracy of the screw. Both the leadscrew and matching nut (5 tpi) are made of steel, but the nut (being far shorter) should have suffered more wear than the screw. Joe Gwinn The usual procedure is to make all final adjustments from one direction which negates any looseness in fit between the lead screw and the nut. Most old guys do it without thinking - back it off a half turn too far and go back 'till you get where you want to be for the next cut. Yep. Though I'm still trying to achieve true old-guy machinist status. I had come to the go-one-way solution, but cutting in one direction but not the other (even with the X-axis clamped) still caught my attention. Joe Gwinn I apparently didn't read about cutting in one direction but if that happens there must be some play somewhere. Climb milling will certainly pull the work into the cutter but that is usually obvious when it happens and of course, if there is play somewhere, the opposite cutter rotation will push the work out of the way. John B. Slocomb (johnbslocombatgmaildotcom) |
#5
Posted to rec.crafts.metalworking
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Millrite X-axis thrust bearings were frozen
In article ,
John B. Slocomb wrote: On Mon, 29 Mar 2010 00:02:04 -0400, Joseph Gwinn wrote: In article , John B. Slocomb wrote: On Sun, 28 Mar 2010 20:12:33 -0400, Joseph Gwinn wrote: On my old (built in 1965) Millrite MVI vertical mill, one annoyance is the difficulty setting the table to a specified X (side-to-side) location. One would overshoot, in both directions. My first theory was that this was .... [big snip] The usual procedure is to make all final adjustments from one direction which negates any looseness in fit between the lead screw and the nut. Most old guys do it without thinking - back it off a half turn too far and go back 'till you get where you want to be for the next cut. Yep. Though I'm still trying to achieve true old-guy machinist status. I had come to the go-one-way solution, but cutting in one direction but not the other (even with the X-axis clamped) still caught my attention. I apparently didn't read about cutting in one direction but if that happens there must be some play somewhere. Climb milling will certainly pull the work into the cutter but that is usually obvious when it happens and of course, if there is play somewhere, the opposite cutter rotation will push the work out of the way. Yes, there was play. Two things were wrong. First, the saddle-knee gib needed to be tightened. This solved the cut-in-one-direction problem. As it happened, it was climb that didn't make contact, but climb-versus-conventional was not the issue - the problem was due to the table cocking one way then the other way. Self-feeding was not the problem, for lack of contact. Then, the thrust bearings at the left end of the table were cleaned, greased, installed, and preloaded. This greatly reduced the difficulty in setting the table to a specified X-location on the DRO. Next will be to tighten the table-saddle gib, but this is a big deal (as removal of the table-saddle assembly is required) and so it may be a while. Joe Gwinn |
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