Ball feed screws

[John Collins]

Has anyone converted the cross feed screw in a Chinese lathe (Grizzly)? It seems to me the this would be a great improvement. (I hope I haven't posted this before and forgot - senior moment)

Thnx - John C

[steamin10]

The biggest thing with ball feed screws is they are so efficient, if they are not driven by power drives, they have to have very good table locks, as the act of machining may be enough to move the screws and allow the table to drift. It is less a problem with drives but still a point to consider.

good luck.

[Mcgyver]

John, to what advantage? a ball screw offers a number of advantages, but it does leap out at me what they'd be in this application. Backlash is one for example, not sure why reducing backlash would matter for the cross slide. And like Dave said, the cutting force could easily drive the screw. Unless you are going for a very expensive ground screw, it won't by as accurate as a well made ground acme screw. if you question the accuracy of the existing set up, consider a high quality acme screw

[Harold_V]

if you question the accuracy of the existing set up, consider a high quality acme screw

Makes me wonder. Is the idea one that, perhaps, is intended to avoid the effects of backlash?

If so, that's a mistake. Until a person running machine tools understands the proper procedures for working with backlash, they can expect to make scrap on a regular basis.

Harold

[JimGlass]

John:

I'm with the others as to your expected benefits of a ball screw in your lathe cross slide.

I have a JET 13 X 40 lathe made in good old China. I bought the lathe new in 1999. Since I retired a year ago I have since concluded the JET lathe has better capability than I first thought.

It is all about finish pass technique which I call 5-2-2. Rough the work piece down to about .010 oversize. Then take a .005 pass then a .002 pass and measure the results with a micrometer. AT this point all tool and workpiece deflection should be accounted for.

Next, dial in the remaining amount (up to .003") and the dialed in amount should be the exact size (+/_ .0002) after the cut is taken.

Jim

[Mcgyver]

if you question the accuracy of the existing set up, consider a high quality acme screw

Makes me wonder. Is the idea one that, perhaps, is intended to avoid the effects of backlash?.

Harold

what makes you wonder? you quoted my recommendation that, speculating that if the problem is accuracy in the screw, a quality ground screw might make sense (as opposed to a ball screw) then you went on to talking about eliminating backlash....what does accuracy have to do with backlash Eliminating backlash would accomplish nothing as i said in my post.

he's got some shortcoming in mind....curious what this is.

[steamin10]

No, I think I see Harolds point here of an underlying accuracy problem, that may stem from feeding the tool in the wrong direction, and lash may be orking things up.

I work with very small mill cutters at times, and if the table hiccups, 'bing' either the part or more usually the cutter is history. Controlling the slop or lash in the table drive is everything here.

[Mcgyver]

I work with very small mill cutters at times, and if the table hiccups, 'bing' either the part or more usually the cutter is history. Controlling the slop or lash in the table drive is everything here.

that's a good point Dave , when i was thinking backlash in the cross feed shouldn't matter i was stuck in my paradigm - how i use the lathe. I can see if you are milling in the lathe there would be advantages in eliminating, or rather drastically reducing backlash.....all this speculation, come on John tell us the problem you're trying to solve ;D

[Bill Shields]

OK, ignoring all the good advice that you have already gotten from everyone about using ball screws, let's assume that you want to go ahead with this idea.

Take a good look at just how big in DIAMETER the ball screw 'nut' actually is before you seriously consider spending any time or $$ on this project.

There are very few lathes, not designed for ball screws, that can accomodate the diameter of a ball screw 'nut', plus the mount needed to hold it in place, in the carriage.

The lack of space makes the entire concept very unworkable.

[John Collins]

Thanks very much for all your input. I don't have a serious problem with backlash in my machine, but I know that over time my backlash will slowly increase. I read some where that ball screws had little or no backlash and I thought I would ask if anyone had done this. I have decided that, based on all the good input I got, that this is not that good of an idea.

Thnc - John C

[Steamin]

After the fact point: Even ballscrews wear, just maybe not as fast a plain screws. Although it is a mill not a lathe, the ballscrews on my table are plum wore out after years of commercial use. I have lash, heavy cuts push the table around and it is loose in the middle but stiff at the ends of the travel. Just like a plain screw!

[someonesdad]

All feed screws (ball or otherwise) are going to have some level of backlash. And, over time, it will vary, depending on the level of wear. As steamin10 said, it can lead to the "ting" of little mills or jumps in the table when cutting.

For the original poster, it probably should be mentioned that this can be somewhat controlled by adjusting the table gibs and, temporarily at least, clamping down on the feed direction's lock (although this typically isn't available in e.g. lathe crossfeeds).

And, as Harold_V mentioned, make sure you know how to deal with backlash, as you can't avoid it. If you're not sure, please post and you'll get plenty of good suggestions.