New Lead Nut For Old Import Mill

[knots43]

I own an old import vertical mill which has close to .025 backlash in both the x and y axis. It was even more until after I worked the lead nut mountings over.

I don't use the mill except for my own needs fabricating jigs and such. But I feel the need to repair this machine to reduce the backlash and improve its performance .

My plan is to purchase a clyndrical ACME nut from a supplier , such as Roton Products, and fabricate a holding fixture to hold the nut. This assembly would then replace original nut.

I have checked the original acme feed screw which appears to be in good condition, and as far as I can tell true to acme screw tolerance. I suspect that the nuts were originally machined out of tolerance.

Have any of you repaired your mill using this method ? Comments ?

[squirrel]

I own an old import vertical mill which has close to .025 backlash in both the x and y axis. It was even more until after I worked the lead nut mountings over.

I don't use the mill except for my own needs fabricating jigs and such. But I feel the need to repair this machine to reduce the backlash and improve its performance .

My plan is to purchase a clyndrical ACME nut from a supplier , such as Roton Products, and fabricate a holding fixture to hold the nut. This assembly would then replace original nut.

I have checked the original acme feed screw which appears to be in good condition, and as far as I can tell true to acme screw tolerance. I suspect that the nuts were originally machined out of tolerance.

Have any of you repaired your mill using this method ? Comments ?

Most of the leadscrews are worn and a new nut might help alot. Can you post a pic of the nut, I only ask because most have an threaded insert inside of casting so you might only need to make a nut. If you have a lathe thats not hard to do.

[knedvecki]

.025 inch backlash is pretty minimal and probably not worth messing with. You should always rotate yours screws in the same direction when going to position , and it should repeat within .001 inch. This IS standard procedure for a conventional mill.

[knots43]

Thank you both for your response.

No picture is available. The machine is reassembled. However the nut is machined from a single bronze block. It has a cylindrical boss machined into the bottom of the block which is set into a hole in the knee casting, abd fastened from below with a cap screw. One problem was that the hole was about .006" oversize which allowed the nut to wallow around when machining. I have improved that condition with stainless steel shim stock around the boss.

The screw is uniformly within .003" of the recommended major diameter recommended for the ACME screw size. I have miked the screw all along it's length. These measurements remarkably uniform along the entire length of the screw. The backlash is uniform no mater where the table is positioned.

Yes I can make a new nut. There are a couple of reasons That I am considering the commercial cylindrical nut set in a fabricated or machined fixture: First I can purchase the nut for less than $40 USD which is far less than I can buy a lump of bronze bearing stock of the size needed to machine a new nut.
Second Once the fixture is prepared future nut replacements will be a simple task. Third after mikeing and checking the entire length of the screw with an ACME screw thread gage it looks to me like the screw is still good if not excellent condition.

There is the possibility that the missing .003" of major screw diameter is at least part of the problem ( even with the original nut). If so the measuring the backlash between the commercial nut on the existing screw will quickly reveal that fault. If that turns out to be the case I will have one extra ($40) nut in my GOK bucket and will chalk the failed experiment up a as worthwhile attempt.

The original question remains: Has anyone out there done anything like this?

A new question is: Should I decide to machine a new nut what is a good , economical source of a good grade of machine-able bearing bronze.

[PrecisionSpindle]

Bronze nuts of flange style and pillow style are available from stock, as well as various sizes, pitches and lengths of stock lead screw in LH thread and RH thread. The bronze nuts are stocked as blanks, and typically are finish threaded to fit the screw that is shipping.
For more information, contact:

Precision Spindle & Accessories Inc.

www.precisionspindleinc.com tel. 519 671 3911
haviland@precisionspindleinc.com fax. 519 652 5994