New lead screws and nuts for SX3 mill

Home Model Engine Machinist Forum

Help Support Home Model Engine Machinist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.


Project of the Month Winner !!!
Jan 29, 2013
Reaction score
Mossyrock Washington
I have been using my SX3 bench top milling machine for a little over two years now. I installed DROs at the get-go so the machine has been usable BUT, there has been a lot of slop that got acute in the past few weeks. After tearing down the machine I found the lead screw nuts for the X & Y axis to be nearly worn away. After cleaning and inspecting the threaded rods with a magnifier I could see that the rod was actually a file. So just replacing the worn nuts was not going to make my mill any better for very long.

I have a CNC router that has been in service for almost 15 years. It has ultra-smooth Acme threaded rod and the self-adjusting nuts on it are still tight. So I replaced the SX3’s lead screws with the ultra-smooth Acme rod and self-adjusting nuts. It was a simple conversion and the result is fantastic. My table now glides almost effortlessly yet has a very positive Feel. The backlash was reduced to .001” and all of that is at the thrust bearings. No lubrication is needed and if and when the nuts need to be replaced it will only take a few minutes and not require the table to be disassembled. I also replaced the funky oiler fittings with oilers with spring loaded lids.

I used the old worn lead screw nuts for anchors for the new acme nuts. The Y axis needed a 2” longer lead screw. The X axis lead screw I made a little shorter because I eliminated the slip joint that allowed the crank wheel to disengage. I did that so that I could make it possible to adjust the tension on the thrust bearings. Total cost was $270 USD.

Mark T


Great post.
Would like to do this mod to my Chester 836 (mini Bridgeport) but my screws and nuts are just fine at the moment.
I am sure this could be done to the majority of mills that have a similar problem.


Hi dnalot (Mark)
Thanks for an interesting post and sharing great information. I also have a SX3 with some backlash in the leadscrews which I would like to eliminate.

Can you please answer a few Q's.

Does the ACME threaded rod come in metric 2mm pitch to match the SX3 leadscrews? There seems to be metric ACME rod available but no info on Self adjusting nuts metric or otherwise.

Do the self adjusting nuts effectively prevent backlash sufficient to permit climb milling?

Does fitting the Self Adjusting Nut in the shown manner/position restrict the amount of either X or Y travel?

Finally A search has not turned up anywhere to buy the ACME ultra smooth threaded rod with Self Adjusting Nuts. Where did you obtain yours?

Thanks in advance
Ron, you are unlikely to find ACME threads with metric pitch but if you search for "Trapizoidal Lead Screw" or similar you should come up with the 30deg trapizoidal screws which are the metric equivalent. Though I don't think 2mm is a standard pitch:(

Like Bogs I'll bear it in mind if my X3 nuts get too sloppy.
Hi Ron

I bought my ultra smooth threaded rod and nuts from McMaster Carr. My SX3 had 10 threads per inch and I was able to replace with the same. There was no loss of travel on the X or Y axis. And YES I can climb cut without any problems. It transformed a rather pathetic machine into a machine that is a joy to use. I have DRO's but with the new rod & nut a person could actually use the the machine without. My power feed also works much better. The 5/8" rod was .001 smaller in diameter than the original.

The other improvement I made to the SX3 was adding a regulated air cylinder to the Z axis. It works far better than a counter weight and it is adjustable. My Z travels as easily up as down. Link to my post on that mod is here ->

Mark T
Hi Jasonb
thanks for the info on searching for "Trapizoidal Lead Screw". I have now found Metric ACME with the right size & pitch and even anti backlash nuts. Just have to enquire about price & Shipping

Mark T
Also thanks and apologies. I didn't think that you might have a imperial leadscrew machine and that my request regarding Metric ACME was inappropriate.

I have now located Metric ACME ( Trapizoidal - they are slightly different thread form to Imperial) in the right size & pitch 16 x 2 mm and anti backlash nuts to suit. Have to find out price & shipping from wherever. Checked my machine and realised that the threads are actually Left handed. i.e. X table movement is away from winder when winder is rotated clockwise. Is this correct?

I have included links for any one else who is interested

Prices for teh stock size screws look very reasonable just hope the 16x2 in not disproportionally more.

Keep us posted.