MWF FEED
30th December 2021, 11:41 PM
A forum member sold me a nice 4.5" Taylor conical lathe chuck, on a Hercus style back plate.
Its jaws feel tight, with very little slop against the scroll, so it should be much better than my worn out Pratt 4.25", or my "has runout from new" TOA 125mm.
However, when mounted up on my Hercus 9C, it consistently has 7 thou run out. I marked the side that is high. I can remove it from the spindle, clean the threads, spin it back on, and that marked side is still 7 or 8 thou high.
So, time to investigate. The back of the plate has a nick where some of the iron has been chipped away:
IMG_2328.jpg (https://metalworkforums.com/attachment.php?attachmentid=395507&d=1640867175)
so I thought that might just need truing up. Take it off the chuck:
IMG_2329.jpg (https://metalworkforums.com/attachment.php?attachmentid=395508&d=1640867200)
It was a good tight fit. Strangely, there was lots of oil in there!
Note that the bolt holes are not symmetrical. Note also the inside of the chuck:
IMG_2331.jpg (https://metalworkforums.com/attachment.php?attachmentid=395509&d=1640867229)
It has a raised lip near the shoulder edge, that the flat of the back plate locates onto.
Stamped into the chuck is PLATE MUST CLEAR THIS FACE.
I screw the back plate onto the spindle, and do some tests:
IMG_2330.jpg (https://metalworkforums.com/attachment.php?attachmentid=395510&d=1640867287)
50 microns axial run out on the edge of the spigot. So, that might be 2 of my 7 thou?
I also measure the flatness of the outer face, where it bolts onto the back of the chuck. 180 microns, or 7 thou wobble. OK, that is the issue. I could just machine it flat now, but I figure the chip on the back should come out first, so screw the back plate on backwards...
Except that it won't screw on all the way. Too tight.
Only goes on about 3/8" before I decide to stop forcing it. I check the wobble:
IMG_2332.jpg (https://metalworkforums.com/attachment.php?attachmentid=395492&d=1640861512)
55 microns. Different to when screwed on using the register.
For a while, contemplate machining that little surface with the plate only half screwed on, but decide on a plan B - the surface grinder...
IMG_2333.jpg (https://metalworkforums.com/attachment.php?attachmentid=395493&d=1640862931) 30 microns removed
IMG_2334.jpg (https://metalworkforums.com/attachment.php?attachmentid=395494&d=1640863057) 50 microns
90 microns IMG_2335.jpg (https://metalworkforums.com/attachment.php?attachmentid=395495&d=1640863180) and it is flat, relative to the other side.
Try back on the spindle:
IMG_2336.jpg (https://metalworkforums.com/attachment.php?attachmentid=395496&d=1640863494) IMG_2337.jpg (https://metalworkforums.com/attachment.php?attachmentid=395497&d=1640863752)
60 microns axial wobble (slightly more than the 2 thou before), and 80 microns lateral wobble (down from 180).
The lateral wobble is easy to correct - just machine off in the lathe. The axial wobble is a little harder. I'm trying to avoid machining too much off the face, so I try to correct the wobble by grinding a slight slope on the register-locating face of the back plate.
66234400554__15326891-F9F8-46A0-88E1-12B28BBA429C.jpg (https://metalworkforums.com/attachment.php?attachmentid=395498&d=1640864869)
Note the sheet of paper on one side. Sadly, this actually made the axial wobble worse -
I think I might have been removing metal from the wrong side - so I had to re-do it.
Sadly, it made no difference. Still 2 thou axial wobble on the locating spigot. Sigh. Go home for the day.
Going to have to do it the sensible way. Re-machine the bolt-attaching face:
IMG_2339.jpg (https://metalworkforums.com/attachment.php?attachmentid=395499&d=1640865411)
mount the chuck up to test. Just how tight should I torque a vintage chuck? :U
IMG_2340.jpg (https://metalworkforums.com/attachment.php?attachmentid=395500&d=1640865522)
About 6 thou TRO. Not much better.
Going to have to re-cut the spigot:
IMG_2345.jpg (https://metalworkforums.com/attachment.php?attachmentid=395501&d=1640865618)
I made the bare minimum cut - about 1mm off the outside, and 0.5mm from the spigot face.
Re-mount the chuck. Two of the bolts aren't going in smoothly - the two that were on the high side:
IMG_2346.jpg (https://metalworkforums.com/attachment.php?attachmentid=395502&d=1640865822)
I wonder if that was a problem all along, twisting the chuck a tiny bit?
File the holes a little, find 3/8 NC tap and die to clean the bolts and chuck threads. Attach chuck.
There is about 21 thou gap between the chuck and the part of the back plate where the bolts attach, which I might later correct (by machining 17 or 18 thou off the flat of the locating spigot), but this does allow me to spend time carefully tightening the bolts to minimise run out.
I started by correcting the chuck body, then refined with a ground rod in the chuck.
End result:
IMG_2351.jpg (https://metalworkforums.com/attachment.php?attachmentid=395503&d=1640865986)
23 microns. Less than a thou!!!
So, this is a pretty good old chuck, but I am perplexed that the back plate fitted so badly.
Then I had the thought to check the register.
Using an old (uncalibrated?) 2" mic., my Hercus spindle is 1.471":
IMG_2348.jpg (https://metalworkforums.com/attachment.php?attachmentid=395504&d=1640866530)
but this back plate's register is a little larger:
IMG_2349.jpg (https://metalworkforums.com/attachment.php?attachmentid=395505&d=1640866568) IMG_2350.jpg (https://metalworkforums.com/attachment.php?attachmentid=395506&d=1640866606)
at 1.488",
so I wonder if this was from a Southbend, Myford, or Boxford?
Attached Images
https://metalworkforums.com/images/attach/jpg.gif IMG_2331.jpg (https://metalworkforums.com/attachment.php?attachmentid=395509&d=1640867229) (256.0 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2351.jpg (https://metalworkforums.com/attachment.php?attachmentid=395503&d=1640865986) (152.9 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2348.jpg (https://metalworkforums.com/attachment.php?attachmentid=395504&d=1640866530) (218.0 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2349.jpg (https://metalworkforums.com/attachment.php?attachmentid=395505&d=1640866568) (205.6 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2350.jpg (https://metalworkforums.com/attachment.php?attachmentid=395506&d=1640866606) (261.9 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2330.jpg (https://metalworkforums.com/attachment.php?attachmentid=395510&d=1640867287) (172.0 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2337.jpg (https://metalworkforums.com/attachment.php?attachmentid=395497&d=1640863752) (147.4 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2336.jpg (https://metalworkforums.com/attachment.php?attachmentid=395496&d=1640863494) (161.4 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2335.jpg (https://metalworkforums.com/attachment.php?attachmentid=395495&d=1640863180) (166.6 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2339.jpg (https://metalworkforums.com/attachment.php?attachmentid=395499&d=1640865411) (162.9 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2329.jpg (https://metalworkforums.com/attachment.php?attachmentid=395508&d=1640867200) (206.4 KB)
https://metalworkforums.com/images/attach/jpg.gif 66234400554__15326891-F9F8-46A0-88E1-12B28BBA429C.jpg (https://metalworkforums.com/attachment.php?attachmentid=395498&d=1640864869) (207.3 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2332.jpg (https://metalworkforums.com/attachment.php?attachmentid=395492&d=1640861512) (166.0 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2333.jpg (https://metalworkforums.com/attachment.php?attachmentid=395493&d=1640862931) (155.5 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2334.jpg (https://metalworkforums.com/attachment.php?attachmentid=395494&d=1640863057) (172.4 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2340.jpg (https://metalworkforums.com/attachment.php?attachmentid=395500&d=1640865522) (208.8 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2345.jpg (https://metalworkforums.com/attachment.php?attachmentid=395501&d=1640865618) (155.7 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2346.jpg (https://metalworkforums.com/attachment.php?attachmentid=395502&d=1640865822) (170.2 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2328.jpg (https://metalworkforums.com/attachment.php?attachmentid=395507&d=1640867175) (162.0 KB)
Read the full thread at metalworkforums.com... (https://metalworkforums.com/showthread.php?t=207519&goto=newpost)
Its jaws feel tight, with very little slop against the scroll, so it should be much better than my worn out Pratt 4.25", or my "has runout from new" TOA 125mm.
However, when mounted up on my Hercus 9C, it consistently has 7 thou run out. I marked the side that is high. I can remove it from the spindle, clean the threads, spin it back on, and that marked side is still 7 or 8 thou high.
So, time to investigate. The back of the plate has a nick where some of the iron has been chipped away:
IMG_2328.jpg (https://metalworkforums.com/attachment.php?attachmentid=395507&d=1640867175)
so I thought that might just need truing up. Take it off the chuck:
IMG_2329.jpg (https://metalworkforums.com/attachment.php?attachmentid=395508&d=1640867200)
It was a good tight fit. Strangely, there was lots of oil in there!
Note that the bolt holes are not symmetrical. Note also the inside of the chuck:
IMG_2331.jpg (https://metalworkforums.com/attachment.php?attachmentid=395509&d=1640867229)
It has a raised lip near the shoulder edge, that the flat of the back plate locates onto.
Stamped into the chuck is PLATE MUST CLEAR THIS FACE.
I screw the back plate onto the spindle, and do some tests:
IMG_2330.jpg (https://metalworkforums.com/attachment.php?attachmentid=395510&d=1640867287)
50 microns axial run out on the edge of the spigot. So, that might be 2 of my 7 thou?
I also measure the flatness of the outer face, where it bolts onto the back of the chuck. 180 microns, or 7 thou wobble. OK, that is the issue. I could just machine it flat now, but I figure the chip on the back should come out first, so screw the back plate on backwards...
Except that it won't screw on all the way. Too tight.
Only goes on about 3/8" before I decide to stop forcing it. I check the wobble:
IMG_2332.jpg (https://metalworkforums.com/attachment.php?attachmentid=395492&d=1640861512)
55 microns. Different to when screwed on using the register.
For a while, contemplate machining that little surface with the plate only half screwed on, but decide on a plan B - the surface grinder...
IMG_2333.jpg (https://metalworkforums.com/attachment.php?attachmentid=395493&d=1640862931) 30 microns removed
IMG_2334.jpg (https://metalworkforums.com/attachment.php?attachmentid=395494&d=1640863057) 50 microns
90 microns IMG_2335.jpg (https://metalworkforums.com/attachment.php?attachmentid=395495&d=1640863180) and it is flat, relative to the other side.
Try back on the spindle:
IMG_2336.jpg (https://metalworkforums.com/attachment.php?attachmentid=395496&d=1640863494) IMG_2337.jpg (https://metalworkforums.com/attachment.php?attachmentid=395497&d=1640863752)
60 microns axial wobble (slightly more than the 2 thou before), and 80 microns lateral wobble (down from 180).
The lateral wobble is easy to correct - just machine off in the lathe. The axial wobble is a little harder. I'm trying to avoid machining too much off the face, so I try to correct the wobble by grinding a slight slope on the register-locating face of the back plate.
66234400554__15326891-F9F8-46A0-88E1-12B28BBA429C.jpg (https://metalworkforums.com/attachment.php?attachmentid=395498&d=1640864869)
Note the sheet of paper on one side. Sadly, this actually made the axial wobble worse -
I think I might have been removing metal from the wrong side - so I had to re-do it.
Sadly, it made no difference. Still 2 thou axial wobble on the locating spigot. Sigh. Go home for the day.
Going to have to do it the sensible way. Re-machine the bolt-attaching face:
IMG_2339.jpg (https://metalworkforums.com/attachment.php?attachmentid=395499&d=1640865411)
mount the chuck up to test. Just how tight should I torque a vintage chuck? :U
IMG_2340.jpg (https://metalworkforums.com/attachment.php?attachmentid=395500&d=1640865522)
About 6 thou TRO. Not much better.
Going to have to re-cut the spigot:
IMG_2345.jpg (https://metalworkforums.com/attachment.php?attachmentid=395501&d=1640865618)
I made the bare minimum cut - about 1mm off the outside, and 0.5mm from the spigot face.
Re-mount the chuck. Two of the bolts aren't going in smoothly - the two that were on the high side:
IMG_2346.jpg (https://metalworkforums.com/attachment.php?attachmentid=395502&d=1640865822)
I wonder if that was a problem all along, twisting the chuck a tiny bit?
File the holes a little, find 3/8 NC tap and die to clean the bolts and chuck threads. Attach chuck.
There is about 21 thou gap between the chuck and the part of the back plate where the bolts attach, which I might later correct (by machining 17 or 18 thou off the flat of the locating spigot), but this does allow me to spend time carefully tightening the bolts to minimise run out.
I started by correcting the chuck body, then refined with a ground rod in the chuck.
End result:
IMG_2351.jpg (https://metalworkforums.com/attachment.php?attachmentid=395503&d=1640865986)
23 microns. Less than a thou!!!
So, this is a pretty good old chuck, but I am perplexed that the back plate fitted so badly.
Then I had the thought to check the register.
Using an old (uncalibrated?) 2" mic., my Hercus spindle is 1.471":
IMG_2348.jpg (https://metalworkforums.com/attachment.php?attachmentid=395504&d=1640866530)
but this back plate's register is a little larger:
IMG_2349.jpg (https://metalworkforums.com/attachment.php?attachmentid=395505&d=1640866568) IMG_2350.jpg (https://metalworkforums.com/attachment.php?attachmentid=395506&d=1640866606)
at 1.488",
so I wonder if this was from a Southbend, Myford, or Boxford?
Attached Images
https://metalworkforums.com/images/attach/jpg.gif IMG_2331.jpg (https://metalworkforums.com/attachment.php?attachmentid=395509&d=1640867229) (256.0 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2351.jpg (https://metalworkforums.com/attachment.php?attachmentid=395503&d=1640865986) (152.9 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2348.jpg (https://metalworkforums.com/attachment.php?attachmentid=395504&d=1640866530) (218.0 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2349.jpg (https://metalworkforums.com/attachment.php?attachmentid=395505&d=1640866568) (205.6 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2350.jpg (https://metalworkforums.com/attachment.php?attachmentid=395506&d=1640866606) (261.9 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2330.jpg (https://metalworkforums.com/attachment.php?attachmentid=395510&d=1640867287) (172.0 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2337.jpg (https://metalworkforums.com/attachment.php?attachmentid=395497&d=1640863752) (147.4 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2336.jpg (https://metalworkforums.com/attachment.php?attachmentid=395496&d=1640863494) (161.4 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2335.jpg (https://metalworkforums.com/attachment.php?attachmentid=395495&d=1640863180) (166.6 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2339.jpg (https://metalworkforums.com/attachment.php?attachmentid=395499&d=1640865411) (162.9 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2329.jpg (https://metalworkforums.com/attachment.php?attachmentid=395508&d=1640867200) (206.4 KB)
https://metalworkforums.com/images/attach/jpg.gif 66234400554__15326891-F9F8-46A0-88E1-12B28BBA429C.jpg (https://metalworkforums.com/attachment.php?attachmentid=395498&d=1640864869) (207.3 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2332.jpg (https://metalworkforums.com/attachment.php?attachmentid=395492&d=1640861512) (166.0 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2333.jpg (https://metalworkforums.com/attachment.php?attachmentid=395493&d=1640862931) (155.5 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2334.jpg (https://metalworkforums.com/attachment.php?attachmentid=395494&d=1640863057) (172.4 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2340.jpg (https://metalworkforums.com/attachment.php?attachmentid=395500&d=1640865522) (208.8 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2345.jpg (https://metalworkforums.com/attachment.php?attachmentid=395501&d=1640865618) (155.7 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2346.jpg (https://metalworkforums.com/attachment.php?attachmentid=395502&d=1640865822) (170.2 KB)
https://metalworkforums.com/images/attach/jpg.gif IMG_2328.jpg (https://metalworkforums.com/attachment.php?attachmentid=395507&d=1640867175) (162.0 KB)
Read the full thread at metalworkforums.com... (https://metalworkforums.com/showthread.php?t=207519&goto=newpost)