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This tale is about replacing the worn cross slide and compound leadscrew nuts on a Clausing 5900 lathe, using the popular
HSM 'Evanut' acetal nut concept that made the rounds around 2010. To wit:
https://bbs.homeshopmachinist.net/fo...ay?view=thread
Version V1 was in keeping with the Evanut procedure of clamping cylindrical acetal blanks around a hot leadscrew.
But the result was not so grand, mostly because the smallish volume of the Clausing nuts does not give much plastic
"meat" to the final product. So, skipping pics of that attempt, and on to the next.
To make the process simpler and to get more "meat," I chose instead to go the route of fabbing a complete AL
housing/nut configured as the melting mold. I sampled melting various plastics, and settled on HDPE (#2 recycle)
chips from your typical plastic bucket as yielding the best combo of toaster-oven compatible low-temp melting and
high melt flow index (MFI). Maybe I should have continued the acetal route this time, but I did not.
HDPE seemed to promise low friction, was plentiful, and melts at about the same temperatures as acetal/delrin.
My 2nd iteration was much too hokey. And convoluted in its attempt to address the high coefficient of thermal expansion
of plastics relative to steel "shrinkage" yielding a nut too tight (by completely splitting the nut to avoid having to chase the
threads for clearance.) The last photo in this submission is a picture of that forgettable V2 attempt.
I moved on to V3 after a few days:
Steps in the 3rd Evolution (with still no thread chasing step needed):
1) Machine a solid Al facsimilie of a Clausing cross slide nut housing. (Made wider/longer as would fit inside the slide.)
2) Thru drill the housing to the leadscrew diameter.
3) Hollow out the insides for a plastic cavity, leaving just a short annular ring of leadscrew-diameter on both ends.
This is to preserve alignment/fit during molding.
4) Drill a port into the side to allow pressing of melting HDPE (or acetal) chips into the interior.
5) Wrap leadscrew with 6-10 wraps of teflon tape. This helped counter the too-tight shrinkage.
6) Heat assembled housing and leadscrew (in toaster oven) to 400-450 degF, progressively melting and pressing chips of
HDPE into it until oozing out the ends. Let cool.
7) Remove leadscrew; pick the teflon shreds out of the plastic -- it takes a while.
8) Saw-split the housing and plastic on one side. Install jack screws; adjust for fit.
Casting for the compound nut was similar. Made the nut a little longer for more thread engagement. Did not put any
adjustment method on compound nut...figured easy enough to remove and "re-heat&press" if the need arises.
The original screws were not too badly worn, while the nuts were. I reduced the 0.045" floppy Clausing nut carriage backlash to 0.004"
with the V3 HDPE one. Tighter than that resulted in too much friction to turn the crank freely.
Longer term: After several months use, the cross-slide nut backlash has increased to 0.014", but I note that with plastic,
the handwheel still "feels" firm and does not have the "floppy loose" region of a worn brass nut. Dial position stays put.
So I have not resorted to re-adjustment (yet). Maybe need to compare to an acetal re-melt someday.
Pros: zero $; relatively "easy" method; an alternative when "original" or machining is not.
Cons: Not expected to be a long-term nor adjustment-free solution. Also, the HDPE scheme has more "compliance," I think,
than anything metal/brass (or even acetal). So you have to recognize that cutting forces will cause deflections...allowing
for spring passes will always be in the equation. And you gotta figure a significant crash will probably compromise the nut.
The 'real' solution in my lathe case will probably be something like a housing retaining a brass/bronze two-piece
nut with an easily accessible backlash adjusting scheme...
The I don't want to think about it V2 kludge:
HSM 'Evanut' acetal nut concept that made the rounds around 2010. To wit:
https://bbs.homeshopmachinist.net/fo...ay?view=thread
Version V1 was in keeping with the Evanut procedure of clamping cylindrical acetal blanks around a hot leadscrew.
But the result was not so grand, mostly because the smallish volume of the Clausing nuts does not give much plastic
"meat" to the final product. So, skipping pics of that attempt, and on to the next.
To make the process simpler and to get more "meat," I chose instead to go the route of fabbing a complete AL
housing/nut configured as the melting mold. I sampled melting various plastics, and settled on HDPE (#2 recycle)
chips from your typical plastic bucket as yielding the best combo of toaster-oven compatible low-temp melting and
high melt flow index (MFI). Maybe I should have continued the acetal route this time, but I did not.
HDPE seemed to promise low friction, was plentiful, and melts at about the same temperatures as acetal/delrin.
My 2nd iteration was much too hokey. And convoluted in its attempt to address the high coefficient of thermal expansion
of plastics relative to steel "shrinkage" yielding a nut too tight (by completely splitting the nut to avoid having to chase the
threads for clearance.) The last photo in this submission is a picture of that forgettable V2 attempt.
I moved on to V3 after a few days:
Steps in the 3rd Evolution (with still no thread chasing step needed):
1) Machine a solid Al facsimilie of a Clausing cross slide nut housing. (Made wider/longer as would fit inside the slide.)
2) Thru drill the housing to the leadscrew diameter.
3) Hollow out the insides for a plastic cavity, leaving just a short annular ring of leadscrew-diameter on both ends.
This is to preserve alignment/fit during molding.
4) Drill a port into the side to allow pressing of melting HDPE (or acetal) chips into the interior.
5) Wrap leadscrew with 6-10 wraps of teflon tape. This helped counter the too-tight shrinkage.
6) Heat assembled housing and leadscrew (in toaster oven) to 400-450 degF, progressively melting and pressing chips of
HDPE into it until oozing out the ends. Let cool.
7) Remove leadscrew; pick the teflon shreds out of the plastic -- it takes a while.
8) Saw-split the housing and plastic on one side. Install jack screws; adjust for fit.
Casting for the compound nut was similar. Made the nut a little longer for more thread engagement. Did not put any
adjustment method on compound nut...figured easy enough to remove and "re-heat&press" if the need arises.
The original screws were not too badly worn, while the nuts were. I reduced the 0.045" floppy Clausing nut carriage backlash to 0.004"
with the V3 HDPE one. Tighter than that resulted in too much friction to turn the crank freely.
Longer term: After several months use, the cross-slide nut backlash has increased to 0.014", but I note that with plastic,
the handwheel still "feels" firm and does not have the "floppy loose" region of a worn brass nut. Dial position stays put.
So I have not resorted to re-adjustment (yet). Maybe need to compare to an acetal re-melt someday.
Pros: zero $; relatively "easy" method; an alternative when "original" or machining is not.
Cons: Not expected to be a long-term nor adjustment-free solution. Also, the HDPE scheme has more "compliance," I think,
than anything metal/brass (or even acetal). So you have to recognize that cutting forces will cause deflections...allowing
for spring passes will always be in the equation. And you gotta figure a significant crash will probably compromise the nut.
The 'real' solution in my lathe case will probably be something like a housing retaining a brass/bronze two-piece
nut with an easily accessible backlash adjusting scheme...
The I don't want to think about it V2 kludge:
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