T-nut Fit

T. J.

T. J.

H-M Supporter - Gold Member
H-M Supporter Gold Member
Joined
Oct 31, 2015
Messages
462
Is there a guideline for how close a T-nut should fit in a lathe's compound rest? I'm setting up to machine the nut on a Phase II QCTP to fit my Logan/Powr-Kraft lathe. I assume that it isn't critical to get a precise fit, but assumptions have led me astray before...;)
 
The fit does not need to be critical to work. If the fit is too close, it interferes with sliding the tool post to one side of the compound or the other for getting into tight places. If it is too loose the tool post will move around when you loosen the top nut to swivel the tool post. Just make the t-nut so it nearly fills the available space, and make sure the top surface of the t-nut is below the top of the compound when tightened down or it will only be tightened to itself, not tightened to the compound like it should be, there needs to be a gap between the t-nut and toolpost.
 
Thanks!
 
Agreed, but be sure the flats of the T are a fairly good fit to the slot, I blued and scraped mine in so the pressure's even on the slot's upper inside face with the stud dead square to the topslide surface - I'm not sure it needs to be that good a fit, but it means the forces are evenly spread on the T slot and are less likely to cause a fracture, I think? And it agrees with my engineering sensibilities!

Dave H. (the other one)
 
Your instincts are exactly correct, Other Dave.
 
Make sure that the top of the 'T' nut "flange" has a small chamfer to clear any small radius in the compound slide . This to ensure the 'T' nut sits flat against the underside of the slot and not against any radius.
 
In case you're unsure how to get it dead square, clamp the stud lightly in a V-block then use a spacer and nut on top of the block to pull it up (again quite lightly) against the T-slot, then a couple of short strokes sliding the V-block on the topslide will mark through the blue, scrape the bright spots! I went to about 25 spots / inch square and fairly even marking, seems to fit quite well...

Dave H. (the other one)
 
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