Is 0.005-0.010” of backlash with an Acme Screw acceptable?

[MrRage]

I’m rebuild an old mill and while inspecting the leadscrew I noticed that over almost the entire length of the screw the unit had about 0.005-0.010” of backlash. However the ends of the screw I was getting closer to 0.002”, so this must have been the part of the screw that was rarely used it looks like. I might have taken down these numbers incorrectly because when the nut was not bolted down when I was inspecting it so it was free to move side to side.

I’m going to pricing out new parts on Monday, I just wanted to know if these tolerances were acceptable or not.

[NC Cams]

What is acceptable for one person may prove to be categorically unacceptable to another.

If you plan to use the machine as a drill press, it is probably fine. For simple milling and facing, you could probably live with it. If you will do precise hole location drilling, groving, slotting or other work needing precise table positioning for size control, it is unacceptable.

For example, we had 0.001 backlash on our ball screw equipped machine. It was ok for general machine work. We then tried to precise form milling (putter heads) and the B/L left "flats" at direction change points which ruined appearance.

With gib adjustments and ball screw bearing shimming, we got B/L accelptable for putter milling but it was still too much at 0.0003" for master form shape milling.

We then had the ball screws reworked and replaced ball screw bearings with special ABEC 7's with high preload ones. Now we have B/L comp'd out to near zero.

We still see a 0.0001 error at direction changes while profile milling but it is "acceptable" but not what we ultimately hoped for.

At this point, however, we'll need to change software, servo encoders, ball screws (from rolled thread to precision ground) and PC and controller card to noticeably improve performance. Since this will involve close to a $10k investment (to eliminate a 0.0001 error that we can live with), we've stopped making improvements for the time being.

Ultimately, YOU will have to decide if the backlash you're seeing is "acceptable". For our use, however, it would be about 100 times too much.

Drill press or precision mill - the choice is yours and the ca$h therapy applied to turn one into the other is the controlling differential between the two.....

[AMCjeepCJ]

I posted this elsewhere but if you need to get by with those lead screws that far out of whack for awhile here is a good method to try so you can even climb cut with them bad... I always cut this way because control triples at least!!

((((Not sure if this will help at all or not but if you'd like to climb cut and bury the cutter on a manual mill, lock the gibbs down pretty snug and put a 3/4" box wrench on the nut at the handle... This will give you incredible leverage to override the gibbs being snug and you can climb cut, not to mention get a sick finish compared to conventional milling. The point being your cutter can't jerk the work into your cutter and snap it... I like to think of it as 'poor mans ballscrews'... I've done it on a manual lathe too and it knocked down chatter considerably when coupled with a small stick rubbing on the part~

I agree with Ken though, waaaay to many variables, I go by feel normally, or if I get a good cut on my cnc's write down what works for a ball park reference next time and adjust in 10% increments...

ps
lock your gibbs in both X & Y or you'll regret it, chances are you'll break some cutters learning this method, so don't try it on something important...))))