Rent Mill & Lathe DVDs at Smartflix | Great aluminum & steel prices at OnlineMetals

BACKLASH AND LEAD ACCURACY

What is backlash and why does it matter? What about lead accuracy? How does it affect me and my machine? Or in other words... "In search of 'perfection'"

Also: Ballscrew and ACME Leadscrew Accuracy Charts

1. PREFACE
2. INTRODUCTION
3. BACKLASH IN A MANUAL WORLD
4. CNC TO THE RESCUE?
5. EXPECTATION
6. A PERFECT CIRCLE
7. OTHER DESIGN CONSIDERATIONS AND THE PROS AND CONS
8. CONCLUSION
9. RESOURCES

EXPECTATION

Since this site focuses mainly on the Sieg-made mills of the mini (and soon the small) size, we'll use this as our frame of reference.

You bought the mini-mill for under $500 and now want to go down the path to upgrade your manually-operated machine to CNC so that you can cut complex 3D shapes and 2D circles and such. But you also expect that if you tell the machine to go 1" in some direction, it better well do just that! (Not to mention that you also want it to come back home just as accurately).

While you can achieve just that, it most likely won't happen without great expense and some major work to your machine.

So... If you can "deal" with errors of +/- 0.005" (get out your digital caliper and measure that distance), you can have a really pleasant experience without feeling too light in the checkbook.

To give you an idea of just how much precision you can get, semi off-the-shelf screws can have lead accuracies of 0.0005 in./ft. This means that in a span of 12 inches (or 1 foot), your actual distance traveled could be 1" - 0.0005" = 0.9995". Time to get your digital caliper out again and measure 0.0005"! If you're digital caliper is like mine (the cheap import from China sold by Harbor Freight - there's nothing wrong with that...), the scales' accuracy is +/- 0.001" and you really won't be able to read that tiny, tiny linear increment even though the stated resolution is 0.0005".

The point here is that while you can certainly get very accurate, it all depends on how much you want to spend and to what lengths you're willing to go to in order to achieve that. Not an easy decision but an important one to make before you start spending your money.