Dismantle rear shocks on 1966 Scrambler

Snakeoil · Post by **Snakeoil** » Sat Jan 07, 2012 10:56 am

That's a nice looking shock upgrade, G-man. Someday I may get my shocks rechromed.

Might as well post the threading technique here. I'm sure there are other hobby machinists that will read this and can learn from this.

Learned this when I did my apprenticeship back in the early 70's.

Set the compound at 29-1/2 deg with your starting point (zero) set at 90 deg to the ways and with the front of the compound pointing towards the headstock/chuck as you rotate it. In other words a 1/2 deg less than your thread profile angle.

Touch off on the work piece and zero the dial on the cross slide. This will be your return point for every new cut.

I like to use the same number on the threading dial to eliminate any wear issues in the lathe. Run the carriage back to the end of the work, crank a few mils for the cut depth on the compound and wait for the number to come up on the thread dial. When you get to the end of the thread, quickly back off the cross slide and disengage the feed at the same time. Run the carriage back past the workpiece, bring the cross slide back to zero and crank a few more mils on the compound and make your next cut.

This will give you a thread that is a little tight and makes up for an error in grinding your tool or slop in the machine. We even did this with carbide threading tools which are dead on, angle-wise.

What this also does is slowly takes a cut off just the one face of the tool, which puts less pressure/strain on the tool. You only cut the full face width on one side of the tool. The other side is just taking the few mils you cranked on the compound. I'm sure you know what I mean here or you will when you set up your machine and see what is actually going one.

If you feed the tool with the cross slide you are plunging the tool into the work, cutting on both faces of the tool bit and setting you up for higher risk of tearing the material or chattering.

regards,
Rob

G-Man · Post by **G-Man** » Sat Jan 07, 2012 1:55 pm

Rob

Thanks for that. Good to have it spelled out. I have a faint recollection of being taught that method back in he day and I'll try it when I do my next screw cutting job.

I'll have to check my screwcuttingbtoolsvas those good old Whitworth (and maybe BSF) threads have a 55 degree angle.

Thanks again.

G