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chucketn
08-20-2017, 11:39 AM
Successfully made a lead nut for a 1/2" x 10tpi lead screw for a cnc router project, following Evan's thread from 2010. It's 7/8" in dia and 1 1/8" long, it fits the lead screw snugly with no backlash. The nut is quite hard to turn on the screw with my hands. How can I lessen the torque required to turn it? I don't have a matching tap, and I really don't want to cut a notch/tooth in the lead screw. Any suggestions?

lakeside53
08-20-2017, 11:48 AM
You could use a grinding paste but you don't want to do that on your lead screw either!

- Notch just the very first thread on your screw. Won't hurt functionality.
- Buy another short length of lead screw and notch away -assuming it's a 'std' size.
- Try different lubes

RichR
08-20-2017, 12:00 PM
Bore it out 5 or 10 thousands larger. Now the flat topped peak of the nut won't rub against the flat bottom valley of the screw. That should
lower the friction some. If you're really good, you could grind a right angle flat tipped tool to skim a few thousands off of the flat bottomed
valley of the nut.

Toolguy
08-20-2017, 12:10 PM
You can lightly knurl a short section of the leadscrew on the end where the nut will never go when in service. Run the nut back and forth over the knurled part. It should relieve a lot of the pressure without affecting the backlash. Boring the nut will probably help some too.

alanganes
08-20-2017, 01:04 PM
Any chance you could make a small matching section of 1/2-10 lead screw that you could notch or use as a lap to open up the nut? It would not necessarily even need to be steel, you could make it of brass or maybe aluminum, just for a one-time use? Thinking out loud...

RichR
08-20-2017, 01:29 PM
... If you're really good, you could grind a right angle flat tipped tool to skim a few thousands off of the flat bottomed
valley of the nut.

If you mount the tool in a decent handle and your lathe has a slow speed in the 30 to 60 RPM range, you just need something to rest the
tool on, like a wood turner does. The thread will guide the tool and all you need is to apply a slight pressure into the valley. You probably
want a flat topped tool so it scrapes but doesn't try to dig in.

chucketn
08-20-2017, 01:50 PM
Thanks, folks. I set the lathe up for 10 tpi, found an internal threading tool in my collection with an acme form, ran that through several times. Also bored a bit through to trim the thread peaks off the nut. Still not a free as I want, but much better.

Magicniner
08-20-2017, 07:47 PM
following Evan's thread from 2010.

Using a procedure he poached and never credited the originator for!

strokersix
08-20-2017, 09:01 PM
Squeeze the nut in a 7/8 collet, run the screw in and out a few times, then release the collet. Maybe warm things up a little too.

darryl
08-20-2017, 10:13 PM
I've ended up making a tap from a short section of the lead screw and running that through several times. The other way to deal with it is to split the nut lengthwise to allow it to expand slightly. You could make the slit on only one side, and perhaps tuck a wedge into the gap to aid in this. Piece of popsicle stick maybe. This way you don't damage the finish inside the nut, and you retain a higher degree of contact between the nut faces and the lead screw. What has always worked for me is potting the prepared nut into a holder, which you design to fit. Epoxy has always worked for me, although there are other potting compounds which would work well also- perhaps even better. One that comes to mind is AnchorFix, a Sica product. That is some tough stuff, and if the outside of the nut is prepared with lots of tooth, you end up with a nut that can't deform or shift in any way inside of the holder. You won't have any way of adjusting backlash, but you won't have any for a long time.

I agree with RichR also- bore the nut out a little before doing anything else. The material you're removing isn't in the load-bearing area, but it adds unwanted friction because it's still in intimate contact with the bottom of the threads of the lead screw. Eliminate that, why not.

RichR
08-20-2017, 11:13 PM
Thanks, folks. I set the lathe up for 10 tpi, found an internal threading tool in my collection with an acme form, ran that through several times. Also bored a bit through to trim the thread peaks off the nut. Still not a free as I want, but much better.

Glad to hear it's moving better. I think what's happening is as the Acetal cools and solidifies it shrinks more than the screw does resulting in a
tight fit. Essentially the peaks and valleys of the nut are just clamping down on the screw and adding friction, so opening them up makes sense.