VN #12 Table Screw

[Scra99tch]

Well I wanted to get my X-Axis threaded nuts replaced this week but ran into a snag. Instead of trying to remake the nuts from scratch where there is some 2-3/8 16TPI thread for adjusting backlash out integrated I figured I would just bore out the existing threads and order some 1-5TPI nuts from Roton. They came in and I am at a loss as to why they are not fitting. It looks to me like the Root and Crest of the nut clear the screw and when I blue up the nut the first bit of interference I get is wholly on the flanks. I can't even get a 1/4 of a turn on the nut before it stops cold. I even bore the root off about .2" of the nut and .01" off the table screw OD and still did not budge.

Is a Van Norman Thread not 29 degrees? I have the screw apart and will take it to work tomorrow to confirm its 29.

The table dial is .200/Rev which does indicate a 5TPI thread form. Anyone know if I am way off?

Thanks

 

[Scra99tch]

I did confirm that the screw is RH and I ordered RH nuts.

 

[Scra99tch]

So my next step is to grind a 29 degree single point internal HSS tool. Then try to pick up the middle of the nut thread in the lathe, and cut both sides at depth until it "fits".

Any tips on picking up the thread with my lathe threading dial locked in place?

Thanks

 

[Scra99tch]

Alright well guess there is not much of an issue. I bored out .1" to find the major of the nut and tried putting the screw in and found that with just a little more torque the threaded rod started. After it got past the mangled (cleaned up) threaded portion it went on just fine. I am a little worried though that when these two nuts are together in the backlash assembly that it will bind up.

 

[tekym]

Can you post some pictures? I've read through several times and can't really picture what you're running into.

 

[Scra99tch]

Can you post some pictures? I've read through several times and can't really picture what you're running into.

Was at a loss of why the nut would not at least start more than a 1/2 a turn or so. The shaft threads were mangled and after cleaning them up on my lathe the nut was struggling to go on.

I finally chucked the nut up in the lathe spindle and hand fed the screw through after a bit of difficult turning it eventually went past a "burr" and was good to go.

I was searching all over the shop getting ready to try and grind or substitute a 14.5 degree cutting face to trim off some flank of the thread of the nut. What I am worried about now is making sure that the backlash assembly is not out of round and binding up when put together on the screw. As these nuts have minimal radial and axial play in them to begin with.

 

[tekym]

Too late now that you've cut into it, but my first suggestion would have been to double check that they actually sent you a 1-5 nut like you ordered, if it didn't fit.

I'd say put the backlash adjuster in your lathe and use an indicator to check roundness. This is the part that I'm confused about - were you boring out the backlash adjustment nuts for some reason?

 

[Scra99tch]

Yeah I'll take a picture. I am removing the old threads and boring it oversized. Taking the new nuts and turning them down to press fit, glue, and pinned into the assembly.

I counted and used my thread gage to double check they were correct.