linear rails on lathe?

[Liron Alm]

hi guys,

i'm having problems with the finish on parts i'm making on my C3 lathe..
it seems that i'm expiriancing vibrations - small in amplitude and high frequency. i've been trying different feed rates and spindle RPMs, but it seems that the best finish still shows the vibrations...

i think i tracked it down to the guids. its a simple dove tail guids. i have some linear rails in hand and i want to mount them on the lathe, eliminating the dove tail methid.
the problem is that i never saw a lathe iwth linear rails before.. is there a good reason not to do the mod?

please let me know what you think

Thanks
Liron

[acondit]

First problem that comes to mind is that you will probably lose turning diameter by adding linear rails and bearings.

Check the bearing preload on your spindle before making any changes, then make sure that you have the gibs properly tightened on your dovetails, both cross-feed and compound. Also check and make sure that the clamps that hold the saddle down onto the ways aren't allowing a bunch of lift on the front or back of the saddle.

If none of these solve your problem, there are a few lathe builds here on the zone where people have used linear rails, however, they are usually scratch builds, not modifications to an existing lathe.

Alan

[Rube]

Liron...there have been several scratch built lathes using linear rails on this site. This is a small CNC one that my friend Steve built here;
http://www.cnczone.com/forums/showthread.php?t=40584

I'm sure you tried adjusting the gibs to eliminate any slop in the system? I'm not a machinist, so I cant tell you all the factors that can contribute to surface finish, but I'm sure someone will. My guess is that you should be able to get a good surface without resorting to that major modification.

[Liron Alm]

thanks for the reply...
how do i check the spindle bearing preload?
as for the gibs, i tried to adjast them, but they are as close to optimal as i can get them...
if i tighten them a bit more they lock.

as for loosing turning diameter, do you refer to the increase in height?

thanks..
Liron

[acondit]

I have a 9x20, so I suspect the preload steps would be slightly different, but only slightly. I will attach part of an thread from the 9x20Lathe group, and you can read through the discussion about setting the preload on the 9x20, then look at your manual and the parts breakdown. I think you will find them very similar (different part numbers and different bearings). I would also suggest doing a search on the web for Sieg C3 spindle bearing preload.

As to your second question, yes I am talking about the increase in height.

Alan

[Tony611]

hi Liron,

I to have a small lathe and sometimes I run into problems such as you described. First, what type of material are you turning? Second, what type of tool are you using, high speed steel, carbide, colbalt etc? If your tool has a sharp point or a small radius on the end it can cause vibration or chatter as it is sometimes called. Try grinding a larger radius on the nose of the tool and also check the angles they should be around 5 degrees. Also check to see that the tool does not stick out too far, this will allow the tool itself to flex and cause chatter. Hope this helps you.

Tony