Friction - tight 5 start acme nut

[CountyK]

Hello cnc zoners ,

I've just finished building my CNC machine and my stepper motors (200 oz in.) are not able to turn any of the 3 axis. I can barly turn the acme screws by hand. I know most of the friction is coming from the acme nuts as the machine is pretty smooth without the screws attached. Are the nuts on the acme screws supposed to be extremly tight or should I wear down the nuts somehow (by turning them on the acme screw by hand before assembly)?

The acme nuts are 5 start acme nuts from cnc router parts: http://cncrouterparts.com/product_in...products_id=36

[fretsman]

I actually have this same issue with DumpsterCNC delrin nuts as well using the McMaster black oxide screws (McMaster part number that DumpsterCNC refers to on his site).

If this is normal, how do you all go about resolving this? I'm guessing one of 2 things. Send them back and have them cut correctly or open them up by cutting notches in the end of a screw (like a tap) and opening them up?

Thanks,
Dave

[jalessi]

Spin them back and forth a few dozen times with a cordless drill.

Much cheaper than shipping them back to the USA.

Jeff...

[fretsman]

Originally Posted by jalessi Spin them back and forth a few dozen times with a cordless drill. Much cheaper than shipping them back to the USA. Jeff...

That doesn't work, Jeff, been there, tried that-

Dave

[ger21]

You can cut a few slots in some scrap (or the end where it's not used) and run the nut over it a few times to open it up. Be careful it doesn't get too loose. It shouldn't take much to make them looser.

I got 3 screws from MSC, and the outside diameter on 2 of them was more than 1/2", which made the nuts tighter. I lightly sanded the outside diameter and the nuts got a bit looser. Once I had them installed and lightly oiled them, I didn't have a problem.

[fretsman]

Thanks Gerry, mine are exactly .500, right on the money, so I think I'm going to open the nuts up a bit after I hear from Tim over at DumpsterCNC.

Dave

[ger21]

I made a jig with 1/2" ID bearings to grind the ends down on mine, and they wouldn't fit in the bearings. That's why I sanded them down originally.
http://www.cnczone.com/forums/showthread.php?t=86180

[fretsman]

Nice work there, Gerry, and I love your delta saw with the outfeed table setup you did.

Wish I had that much room, lol!

Thanks for sharing-
Dave