Rd14x40 Bed Twist

Astjp2,
Thank You for the supportive posts. All of you have been helpful. I like the discussion.
I see from your pictures that you also have a RD lathe. My saddle does not rock any that I can easily detect. I did take it off and clean the apron gearbox and the saddle. There was wear on the saddle surfaces but not so much. Did you happen to see the measurements I posted on the other thread (under scraping forum)? There was ,what I
feel like, very little wear. Not enough wear to cause this rather large taper effect. I most likely will get a test bar. I know that the test bar will give a spindle reference. If I use the carriage to measure against the test bar, I will get a combination error. But, that will be interesting as a starting point. I will also go to the effort of taking the head off and re-seating it based on what the test bar shows. Then I will start digging into the Connley book. I do not want to "live with" this kind of error.

My way measurements in this post thread:
http://www.hobby-machinist.com/threads/map-the-errors-on-a-older-lathe.39504/page-3

Thank You all.
 
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wa5cab said:
Hermetic,

No. Given: That the cross slide moves exactly perpendicular to the longitudinal axis of the lathe (bed) and that the spindle axis is twisted slightly toward the rear of the machine and therefore not parallel to the lathe axis and not perpendicular to the cross slide path.

To produce an eliptical end on a workpiece mounted in or to the spindle, you would have to have a motor mounted on the cross slide turning something like a face mill and do the cut with the spindle locked. If you turn the spindle and use a normal cutter in the tool post, you will cut a convex cone. Twist the headstock so that the spindle is pointed slightly toward the front of the bed and you will cut a concave cone.
Click to expand...


Damn, yer right! that has spun my head completelyI am not back at my workshop yet, so no access to a lathe, I have been sitting here with an AA battery and a screwdriver trying to mock it up, and finally the penny dropped, thanks for persisting with me!!
  • :afro:
 
This is fun, hang in there guys!


Sent from my iPhone using Tapatalk
 
JJTGRINDER,

No, a 6x18 wouldn't work. Even if you had some way to hold it, you couldn't rotate the spindle. And actually, the same is true of the 12x12 and probably of the 10x10 as the diagonal dimension is 14.14". It might just barely clear the inner edges of the bed but it might not. So probably a 9x9 would be safe.

Tim,

No, I was working up to proposing a method to determine whether or not the cross slide was perpendicular to the spindle. Admittedly, if it isn't, the method wouldn't tell you where the problem was, but only that the two axes were not perpendicular. At that point, the problem could still be headstock misalignment or bed wear. Or some of both.
 
hermetic,

That's OK. I've done the same sort of thing. In fact just did last night when I asked jjtgrinder whether or not he had a 10x10 or 12x12 surface plate and a 4-jaw large enough to mount either. Obviously even if he did, he wouldn't be able to turn the spindle because the diagonal it too large. :oops:

EDIT: And in my statement about cutting a concave cone, I should have added "until the cutter passes the center point of the workpiece". Because shortly after that you will have a crash probably preceded by some gouging as the underside of the cutter begins to rub.
 
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Tim /
I weren't so old and lazy, I would dive into the whole re-scrape project. Maybe when I retire in the near future. For now I am going to re-seat the head-stock and see what happens.
 
I think that is what I would do first as well, although I can't really see it being a problem, unless it has been slung from the headstock at some time, the bolts have been loose, and swarf or cutting fluid has got under it. I will say this though, when you strip a lathe, you find fine swarf in the damndest of places and wonder "How the devil did that get there"!
Phil
 
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