Need Help!- Acme screw issue, need suggestions

[pencilneck]

Brief background... purchased two 3 foot and one 6 foot acme screws from McMaster-Carr. Purchased bearing blocks and 1/2-10 ACME Nut, 5 Start from CNC Router Parts.

When I got those items in along with other goodies, I bench top rigged up some of my parts using one of the 3ft acme screws and was able to slide the bearing blocks along the screw, and without much effort twist on the acme screw.

But when I cut the 6ft screw down to the needed length and then tried to slide the bearing blocks on it, they slide over the screw a little then bind up. You can barely slide then down the bearing by hand until they bind, and then I have to basically hammer then free. The acme screw is VERY snug when trying to twist it onto the shaft, way more effort needed to twist the nut on the screw as compared to the 3ft one.

It is almost like this acme screw is a hair over sized. But I used my caliper tool and checked it out, .4995" everywhere I checked it, same as the 3 foot acme screw that I have no issues with. I tried different bearing blocks on the 6 foot acme screw, no help.

I can see "spots" in random locations along the acme screw, but can't feel anything if I twist it between my fingers.

Right now I'm thinking about scrubbing down this screw with steel wool or something in hopes of cleaning it up and seeing what happens. I'm kind of screwed (no pun intended) because I found this problem after I cut it.

Anyone run into bearings binding when trying to slide the acme screw though them? Any fixes?

Thank you for any help you can offer.

[louieatienza]

I would suppose you want them as snug as possible, as any play can cause problems down the road. Though I've heard of guys doing stuff like sizing the threads down with 600 grit to using dry ice to "shrink" the screw slightly...

[ger21]

I chucked mine in a drill and wrapped some sandpaper around it until I could get a bearing around it. I have 3 "identical" screws, and some needed sanding, but some didn't.

[johnmac]

You mentioned cutting the 6' down. If the cutoff is scrap, try what ger21 said on it first.

John

[1armsbandit]

I had the same issue on mine. I took a very fine file the length of mine and test fit the bearing as I went; it took a couple of hours but it worked. Good luck

[pencilneck]

Got it fixed now. I rigged it up so that the stepper motor would run at a steady pace, about 2 turns per second. Used a medium grit sand paper and went over it several times then cleaned off with a micro fiber cloth. After a several runs and test fits, I was happy with my results.

Thank you for the input.

Up next, putting the gantry back on and getting it squared up.