How worn are your half-nuts?

12bolts

12bolts

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On my Hercus 9" the last couple of threads I cut, I had problems with the half nuts skipping and causing me untold grief trying to get the job finished.
After removing the half nuts from the apron and cleaning them up it seems that the bottom half is pretty badly worn all over, and the top half is badly worn on the flanks.
botthalf_zps7577897c.jpg tophalf_zps43c725bc.jpg

So now I'm at a crossroads as to what to do here.
Replace with new,...... iffy given the age of the machine and availability of spares.
Cast new ones from bronze or aluminium,...going to be difficult to chase the threads without a tap.
Cut off the thread portion and affix a "*insert substitute here*" into place.
split_zps831d93b2.jpg closed_zps2efa22c6.jpg

Open to suggestions..........

Cheers Phil

botthalf_zps7577897c.jpg tophalf_zps43c725bc.jpg split_zps831d93b2.jpg closed_zps2efa22c6.jpg
 
Re: How worn are your nuts?

The easiest way I can come up with is to see if you can find an Acme nut of the correct pitch, cut out the old threads, machine the new nut to fit, and braze it into place. Then split the halves, and finish brazing. File to fit.

Or buy a tap and braze up the existing threads.
 
Re: How worn are your nuts?

This could be an interesting CNC exercise, milling the threads rather than tapping them.
 
Re: How worn are your nuts?

JimDawson said:
The easiest way I can come up with is to see if you can find an Acme nut of the correct pitch, cut out the old threads, machine the new nut to fit, and braze it into place. Then split the halves, and finish brazing. File to fit.

Or buy a tap and braze up the existing threads.
Click to expand...

This is pretty much what I would do. I would avoid brazing though and see if I could attach the new inserts by bolting them in. This would mean that replacements in the future would only require unbolting and attaching new blanks.

Paul.
 
Re: How worn are your nuts?

You can start with a chunk of bronze. Chuck it up offset in the 4-jaw on your lathe. Do you have another lathe?

Drill and single point thread the acme thread. Then mill the chunk to similar dimensions and slit it down the middle.

I just made an acme nut for my crosslide on one of the lathes. It wasnt a split nut, but the split part is no big deal really.
 
Re: How worn are your nuts?

I believe I've seen people describe fixing half nuts with a product called moglice. Where they coat a portion of the lead screw with the least amount of wear with a release agent. Then using an injector of some sort. injecting the moglice into the half nuts so that it thoroughly filled the area. Obviously more release agent and clay dams would need to be in place to keep the stuff from blowing out the ends of the nuts and to allow the nuts to separate after it had set up. The basic premise is that you would build up the nuts to their original depth using the lead screw as a mold. I couldn't quickly put my finger on an article/post showing the repair. Their website http://www.moglice.com has some examples of fixing everything from ways to nuts. I have absolutely no idea how much the stuff costs, but I get the impression it isn't very cheap.

Sincerely
Mark R. Jonkman
 
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