Advice on an Internal Acme Thread

You're correct Daryl it won't work, at least with the nut I linked. The gear is only 2" in diameter.
I guess you could turn the nut down.
Maybe use part of the old screw as an arbor.
 
Cast, bronze or acetal I think are the only choices. It will be interesting when I get the old gear out to see if there is an insert in the gear.
 
A for real surface grinder needs a precision lead screw and nut in the Y axis (yes, Y, spindle up and down). You need to be able to accurately raise or lower the spindle a tenth or two at a time. Something cobbled together will give you fits. Of course, not all surface grinders are used for accurate work and that changes things...
 
Have you considered single point threading the gear on your lathe (I assume you have one)? I've threaded small acme nuts by welding/brazing/silver soldering HSS tool bits onto the end of small diameter bars. You need to take light cuts, but it has worked out for me. It will probably also depend on what material that gear is made out of (how tough/hard it is).

Just throwing some thoughts out there,
Ted
 
Have you considered single point threading the gear on your lathe (I assume you have one)? I've threaded small acme nuts by welding/brazing/silver soldering HSS tool bits onto the end of small diameter bars. You need to take light cuts, but it has worked out for me. It will probably also depend on what material that gear is made out of (how tough/hard it is).

Just throwing some thoughts out there,
Ted
I have yes. The gear is not hardened. I believe it is 1020 steel. All I know for sure is it is .2%
https://www.amazon.com/gp/product/B004N62R76/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1
 
A for real surface grinder needs a precision lead screw and nut in the Y axis (yes, Y, spindle up and down). You need to be able to accurately raise or lower the spindle a tenth or two at a time. Something cobbled together will give you fits. Of course, not all surface grinders are used for accurate work and that changes things...
That's why I'm leaning towards ordering a precision screw with the same fit nut. The nuts come large so you can turn them to your dimension. Is press fitting a nut into a bored hole on the gear considered cobbled together?
The grinder is a Sanford SG-48. Very precise for it's size when it was made. I do not doubt there is probably a fair amount of wear in the ways. I'd love to do a complete restoration but I have never learned how to scrape. There is a fair amount of backlash in the Y direction that would be nice to eliminate. Also, in the X direction but that is an easy fix with a small gear and rack.
The handle for the Y direction is graduated in .0005" increments. Sufficient for my needs I believe.
 
Since the gear isn't hardened, I'd use a shrink fit. You stand a much beter chance of getting it concentric to the nut and once cooled it would never slip.

Greg
 
If you have clearance above the gear you could what I did on a repair. Buy a precision lead screw from McMaster Carr. Then make a bronze nut to fit the screw. Turn and thread the OD of the nut on one end with a fine thread. Bore and thread the gear to screw onto the nut so it is flush with the other side of the gear. On the bottom, drill and tap a small hole on the seam and put a set screw on the seam to lock the nut and gear together. I t will look like it was made that way.
 
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