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Question for forum machinists

DShortt

DShortt

Gold $$ Contributor
I need to make a square thread nut but I do not have the leadscrew in my possession. The nut has been recast with an epoxy that I believe to be JB weld. I plan to recut a replacement nut from bronze round stock, but I want to check the fit before returning it. The nut is for an obsolete vice that used a non-standard thread. Closest I can figure is 7/8"-4 and the thread width and depth appears to be non-standard as well.
So. I was thinking of casting an epoxy pattern leadscrew around a dowel but I don't want something that will shrink or swell more than necessary. Any suggestions? I'd thought about using soft lead around steel round stock but I don't think the JB weld can survive the heat.

Thanks in advance
 
It does look like JB Weld. I think that'll withstand like 600 degrees F. Roto metals has a low temperature casting alloy similar to Cerrosafe that melts at 158 degrees F. It's on Amazon. I would probably do the entire cast of thos allow rather than casting around a dowel. I think it would fill out much better that way. I'd get some light oil, a very small amount, into all the threads first before casting and then before the alloy cools and hardens get something into it to use as a handle to screw it out...a hex rod, heck even a screwdriver.
 
AccelR8 said:
It does look like JB Weld. I think that'll withstand like 600 degrees F. Roto metals has a low temperature casting alloy similar to Cerrosafe that melts at 158 degrees F. It's on Amazon. I would probably do the entire cast of thos allow rather than casting around a dowel. I think it would fill out much better that way. I'd get some light oil, a very small amount, into all the threads first before casting and then before the alloy cools and hardens get something into it to use as a handle to screw it out...a hex rod, heck even a screwdriver.
Click to expand...
Sounds like a good suggestion. Thank you!
 
I don't have an answer but aren't there at least a few different "square" threads? You might do a cast and split it just to identify what you're working with first, then a cast to trial fit. Tough with nothing to go by and non-standard. It might be that "good enough" is great to the end user too, but maybe not.
 
I don't have the lead screw. No idea what the original length or dimensions are which is why I want to make a casting to check fit. It's for a vice and they don't use Acme thread. They use square threads. The nut was completely stripped out and the JB cast insert was made around the original leadscrew by the vice owner. Not myself. Yes, it's a lot of trouble for an old vice but I'm trying to repay a couple of personal favors. I've already bought a piece of bronze round stock of sufficient size to completely remake the nut, I just need to make sure the leadscrew will fit the new nut.
 
look up the Evanut. Basically take two pieces of plastic and heat them then sandwich them over the rod
Id think you could then measure the nut. Could probably do the same thing with a casting from lead or epoxy and spliting it.
 
There is a paragraph about square thread forms in the Machinery's Handbook I will post it in case you dont have it. If you decide to remake the screw and nut you can produce it to the standardized spec. Based on the condition of the nut, I would venture a guess that the screw is worn as well and if you produce a new nut it may have tight and loose spots along travel. That may not matter but my ocd is showing itself. My .02... I would cut a thread .875 X 4 tpi square thread to the book then make a matching nut. Sounds like it would be a fun little project lol

IMG_7151 (1).jpg
 
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