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? On acme screws and nuts

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azscooby

Swarf
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#1
My new Benchmaster is coming along great, but I've found there is quite a bit of backlash on the y axis, and some on the x axis due to excessive wear on the leadscrew nuts.

I've tried the Delrin nuts, with minimal success, mostly I can't seem to get them "loose" enough.

So, I bought a RH and LH 5/8x10 ACME threaded cylinder from http://www.greenbaymfgco.com/ACME-nuts.php since they weren't too expensive. I was then planning to build housings for them as others have done.

However, when I got them, they don't want to thread on the screws. They do start nicely but they only go on about 1/8", but are extremely tight. I haven't tried to really force them on, which I think they would, but it just feels way too tight, something isn't right. I've verified the tpi, both 10, and both .625" so I'm not sure where I've gone wrong.

I'm beginning to wonder if it has something to do with "square threads" vs "modified square threads"...or some other nuance that I've not considered with my minimal machining knowledge.

Any ideas?
Thanks
 

azscooby

Swarf
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Dec 21, 2013
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#2
Or.....(as I do some googling.....) Double lead vs. single?

I'm missing something here for sure. I'm at work now, but I'll check the threads again for single lead vs. double lead now that I understand that concept.

The items I purchased, the ACME nuts, should be single lead. I never bothered to check the screws, but I wouldn't think they would use a double lead screw. I do think the screws have been replaced. I'll try and get some pics up later.
 

f350ca

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#3
You may have a metric thread form inch acme screw. Isn't that an example of non-standardization. I had a crash on my Summit lathe, built in Poland. Basically the machine is metric with inch lead screws for the North American market. The lead screw in the compound was bent. When I measured it up to build a new one the lock threads for the bearings were metric and the acme was inch standard but 30 degree thread angle not the standard 29. I wanted to use the old two piece adjustable nuts, so I cut the new thread with a 30 degree cutter.

Greg
 

azscooby

Swarf
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Dec 21, 2013
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#4
Thanks for the reply. I doubt it would be metric, but who knows. But being American iron, built in California, I wouldn't think so....but surely a possibility.
 
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