Dear all,
please assist on this, I am really puzzled.
I have started on making a backplate, to fit a 4-jaw I recently got my hands on, on my old italian PAV lathe, threaded spindle. I will admit that I overshoot the backplate register ID, so it is not a tight fit on the spindles register, BUT, I still have the spindle's shoulder to register. So far so good.
So, I mounted the backplate on the spindle and started facing. Of course, all I need to be true is the surface the mates with the chuck, but anyhow, I faces the spiggot as well. Not sure why, I setup to measure run out on the chuck mating surface on the backplate but first I measured runout on the spiggot face. Got around 0.03 mm or runout (more than 0.001''). So I faced the spiggot again and remeasured. Same result. Did some extra runs, increasing depth of cut, trying manual cross-feed, nothing, same runout.
Here is a video on this:
So, ok, it has to be the spindle bearing. Tightened the plain taper bushing a bit so that I can't measure more than 0.01 mm of radial movement while trying very hard to pull the spindle up, tried everything again, still getting the same runout.
Checked it also on the granite surface plate. While left-hand side face of the backplate is nice and flat, opposite face, the prpoblematic one, still has the same runout as the one I am measuring on the lathe. Blue test on the surface plate was not good at all...:
The thing is that I cannot understand how a lathe could have runout on a faced surface. I can understand taper on the face if cross slide is not perpendicular to the spindle. I can understand gaps or whatever if crosslide is very worn and has inconsistent travel. However I cannot understand runout. A lathe should face anything, no matter how crazy it turned to begin with, to a taperred surface with, ideally, 0 taper angle....And I think it also can't have something to do with runout on the spindle shoulder.
Any ideas guys? I can't even say 'get a new lathe' since I can't identify the root cause for this...
Thanks in advance for any help.
BR,
Thanos
please assist on this, I am really puzzled.
I have started on making a backplate, to fit a 4-jaw I recently got my hands on, on my old italian PAV lathe, threaded spindle. I will admit that I overshoot the backplate register ID, so it is not a tight fit on the spindles register, BUT, I still have the spindle's shoulder to register. So far so good.
So, I mounted the backplate on the spindle and started facing. Of course, all I need to be true is the surface the mates with the chuck, but anyhow, I faces the spiggot as well. Not sure why, I setup to measure run out on the chuck mating surface on the backplate but first I measured runout on the spiggot face. Got around 0.03 mm or runout (more than 0.001''). So I faced the spiggot again and remeasured. Same result. Did some extra runs, increasing depth of cut, trying manual cross-feed, nothing, same runout.
Here is a video on this:
So, ok, it has to be the spindle bearing. Tightened the plain taper bushing a bit so that I can't measure more than 0.01 mm of radial movement while trying very hard to pull the spindle up, tried everything again, still getting the same runout.
Checked it also on the granite surface plate. While left-hand side face of the backplate is nice and flat, opposite face, the prpoblematic one, still has the same runout as the one I am measuring on the lathe. Blue test on the surface plate was not good at all...:
The thing is that I cannot understand how a lathe could have runout on a faced surface. I can understand taper on the face if cross slide is not perpendicular to the spindle. I can understand gaps or whatever if crosslide is very worn and has inconsistent travel. However I cannot understand runout. A lathe should face anything, no matter how crazy it turned to begin with, to a taperred surface with, ideally, 0 taper angle....And I think it also can't have something to do with runout on the spindle shoulder.
Any ideas guys? I can't even say 'get a new lathe' since I can't identify the root cause for this...
Thanks in advance for any help.
BR,
Thanos