Sergei Slovenija
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To repair a lathe, you need another lathe. And another milling machine, and another grinder, and another...You could replace it with anything you want for argument’s sake.
You likely won’t notice any difference in use but you may find the tolerances are slightly larger in an acme / trapezoidal thread and my have slightly more backlash.
Ideally, replace it with a ball screw for ultimate accuracy and ease of use
I am newbie. It's too early to sharpen something, it's more difficult than washers, bars, etc. Trimming blades have not yet begun to buy.I don't agree, you have a lathe that would work when put back together! Lathes are amazing, they can make parts to fix themselves!
...replace it with a ball screw for ultimate accuracy and ease of use
The screw is assembled on two thrust bearings, and two powerful Belleville springs provide preload. This is how all the screws of the caliper and tailstock of the lathe are made. There is a large backlash in bronze nuts, about 5 (or more, I don’t remember) divisions of the limb. The wear of the transverse screw is visible through the eyes (waist).On a manual lathe, a ball screw is not the best idea as it will backdrive. Another hurdle is the relative size of a ball nut compared to an ACME or trapezoidal nut.
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To the OP. ACME is an imperial standard. In your place, trapezoidal (TR) thread (effectively a metric version of ACME) might be more easily available. However, trapezoidal thread is only available off the shelf in limited pitch and diameter combinations, so you need to check what you have and see if it is available or the graduations on the dials will not match the movement of the screw.
Have you confirmed that the play is between screw and nut and not between screw and its housing?
Good point, ignore that comment!On a manual lathe, a ball screw is not the best idea as it will backdrive. Another hurdle is the relative size of a ball nut compared to an ACME or trapezoidal nut.
Is it possible to replace this thread profile with the Acme profile? What could be the disadvantages of such a solution?
View attachment 359764
I think the line below "prostoliniowość mm/300mm" (which is covered by the green circle) is the accuracy (50 microns per 300mm). Sorry to drop into imperial units, but I think that is roughly 0.002" per foot (100 microns is about 0.004"). According to this place (https://www.helixlinear.com/blog/acme-screws/what-puts-the-precision-in-precision-acme-lead-screws/), that puts it better than 'standard rolled' but not as good as 'precision rolled'. I do not know if that is considered acceptable for a lathe application so do some research. If they are not accurate enough, you might have to look for ground trapezoidal stuff rather than rolled.
I think the line below "prostoliniowość mm/300mm" (which is covered by the green circle) is the accuracy (50 microns per 300mm). Sorry to drop into imperial units, but I think that is roughly 0.002" per foot (100 microns is about 0.004"). According to this place (https://www.helixlinear.com/blog/acme-screws/what-puts-the-precision-in-precision-acme-lead-screws/), that puts it better than 'standard rolled' but not as good as 'precision rolled'. I do not know if that is considered acceptable for a lathe application so do some research. If they are not accurate enough, you might have to look for ground trapezoidal stuff rather than rolled.
Another thing to find out is the dimensions of the nut and see what would need to be done to it to make it fit the lathe.
You would need to think about the handle end of the screw - maybe drill and ream the new one, cut down and turn down the old one and loctite together.
I was a newbie with a clapped out lathe, you can make reasonable parts on a worn machine, there's play, but you can learn to make it work. It would seem impossible at first, but you take up the slack when you move the dial or the "steering wheel"!I am newbie. It's too early to sharpen something, it's more difficult than washers, bars, etc. Trimming blades have not yet begun to buy.
I see a big play on the steering wheel and understand what to do about it.
Do not go anywhere. I will now shoot a short video, what kind of play is in a screw + nut pair.I was a newbie with a clapped out lathe, you can make reasonable parts on a worn machine, there's play, but you can learn to make it work. It would seem impossible at first, but you take up the slack when you move the dial or the "steering wheel"!
All the best, Matthew