How to determine anvil or shim angle for single pointing an acme thread with a lead angle of 5.59 degrees

[WobblyHand]

Is it possible your work piece rotated in the chuck? If it did during the heavier cuts, then I think it might look like that. Maybe try another one and use a Sharpie to make a mark on it relative to the chuck jaws and see if it is moving.

When troubleshooting, one can't leave anything out. I'll mark the piece and see. The work piece was in an ER40 collet, so it's possible if I forgot to tighten it sufficiently.

 

[RJSakowski]

When troubleshooting, one can't leave anything out. I'll mark the piece and see. The work piece was in an ER40 collet, so it's possible if I forgot to tighten it sufficiently.

I would think that if the work rotated in the chuck, the depth on the right side wouldn't be as great.

 

[WobblyHand]

I cut the 60 degree threads 0.1" deep at 5 TPI. Looks pretty clean to me. Yeah it's 1" 6061 aluminum, didn't want to use steel. Maybe I'm reducing the load. Went in r = 0.1/cos(30) = 0.1/0.866 = 0.1154"

Threads look ok to me. I only used a chip brush to clean it, didn't do anything else. I marked the chuck and work piece, nothing moved for the V threads. Used my AXA-8 and roughly set the lead angle of the blade. Thread has nice sharp vee. It hasn't wandered. Chuck flank is not as smooth as the tail stock side, but serviceable.


Set the compound to 14.5 degrees, sort of. It's close anyways. Then played around with the cross slide and compound to sync the tool to the thread when the dial is on #1. The banding is the LED light vs the phone camera.

Hoping to cut the Acme threads and see what happens.

 

[mmcmdl]

That a boy ! The Acme tool will clean out the 60 degree thread and you won't be cutting full form .

 

[WobblyHand]

Well, I learned something today. You get some very fine advice on this forum! Thank you so much.

I don't know exactly what happened previously, (bad technique, I'd guess) but when you "chase" the thread with a Vee, and then thread with the Acme, it comes out fairly well. I still have an undersized lathe for this kind of work, but, I learned the technique. I had the lathe spindle motor stall at the very end on the last cut, which was ambitious for being near the end. (I took 0.005" full form.) But no harm to the work piece. The VFD on my lathe has little torque at it's lowest speed. I had to really pay attention for 5 TPI, things happen pretty quickly at 100 RPM. Would be nice to drop the speed to 50, guess I would need to make a pulley for that.

Now this looks like an acme thread form. It's not useful for me, (wrong diameter and material) as it was just a test piece, but it was an invaluable lesson in technique! Thank you all for your help.

I used my original acme tool I ground with 15 degree relief angles on all cutting edges. Didn't even hone the tool, just straight off the belt grinder (36 grit ceramic). I'll probably grind another, better (smoother) tool sometime soon.

Same ELS, thread TPI as before, but it came out much much better, at least in terms of the thread form. Surface finish? Well, I'm going slow, with minimal lube, on a small lathe that is rated for 8 TPI stock, using roughly ground HSS tooling. Still, pretty pleased with doing this.

 

[Illinoyance]

On Acme threads I always flank feed. It is essential the tip be of the correct width. When calculating the pitch angle based on the minor diameter of the thread. To this I add 8* to get the desired clearance angle on the leading edge of the tool. This is especially important on multiple stary threads.