Turning threads off rod fine but now rod advances out of chuck.

[whitmore]

Are you saying it's better to pinch just the front of the work near cutter? With a straight rod I would want maximum engagement in the holder wether it's in a jaw, collet or coupling. Standard disclaimer here, I am not an engineer!

Yes, that's what I say; the issue is that you want the threaded workpiece NOT to shift, so any torsion caused by the cutter should
not twist the work, which is what the distal-end clamping encourages. Proximal-end clamping means the torsion
only acts on the extended work (where the cutting forces occur) and that keeps the springiness of the workpiece out
of the problem.

Work holding is most effective near the cut location. Holding elsewhere encourages deflection.

 

[helmbelly]

Do you have any concentricity requirements? If you don't really have super concentricity requirements (you were using a 3 jaw after all), I don't see why using a coupler nut and a top side jam nut wouldn't work. The chuck grabs the coupler nut, the jam nut is external and possibly sacrificial. If you need to flip the part, I'd put on a second jam nut on the coupler (other side) or totally remove that one, so the stud is held near where the turning is.

Threads can be tricky to remove, been burned a couple of times. But locking up the jam nut is pretty effective, as is using a tool with a greater nose radius (at least until some of the thread has been shaved off). Small nose radius tools tend to want to follow the thread. Once the tops of the thread have been knocked down, a smaller radius is fine.

Thanks the earlier term "wide" threw me off for some language barrier reason. Blunt nose- thanks I had not thought of that and I ground one a couple years back that should be perfect.

No concentricity to speak of, I'm just making bolts to fit into a tubular arm that I'm brazing to the bolt shaft later. Yes the jam nut would be fine and I'll use them if I get any slip, just shying away bc it's fiddly and time consuming if I need to make a few hundred. I made a second crunch bushing thats smooth bore and it is holding well, immediate change overs. Delrin, best invention since the crotch !

 

[helmbelly]

Work holding is most effective near the cut location.

Sounds right, guess I could wrap the part near the cutter in a turn of tape or paper.

 

[WobblyHand]

Thanks the earlier term "wide" threw me off for some language barrier reason. Blunt nose- thanks I had not thought of that and I ground one a couple years back that should be perfect.

No concentricity to speak of, I'm just making bolts to fit into a tubular arm that I'm brazing to the bolt shaft later. Yes the jam nut would be fine and I'll use them if I get any slip, just shying away bc it's fiddly and time consuming if I need to make a few hundred. I made a second crunch bushing thats smooth bore and it is holding well, immediate change overs. Delrin, best invention since the crotch !


View attachment 469768

Looks good. Don't think it would last for hundreds though.

 

[WobblyHand]

This is just so you don't mark the parts? Obviously, you can just chuck them in a 3 jaw... Do you have a collet chuck available?

Delrin sure machines nice, doesn't it?

 

[helmbelly]

Looks good. Don't think it would last for hundreds though.

I'll put $20 on her making a thousand! But if it dies after 50, it's about 2 mins to make the next one!

 

[helmbelly]

This is just so you don't mark the parts? Obviously, you can just chuck them in a 3 jaw... Do you have a collet chuck available?

Delrin sure machines nice, doesn't it?

I starting out making custom camera parts and used Delrin for almost everything, I'd melt in threaded inserts for repeat fasteners it needed to accept, polish in up on a buffer. A wood lathe for rpm with 1500 grit paper gives it a nice shine, needs to develop heat to get the sheen. I love it. I use liquid dish detergent for cutting lube and don't tap it, just drill the diameter small and let the fastener cut it's own way.

 

[helmbelly]

This is just so you don't mark the parts?

No collet chuck - 120 yr old Seneca Falls 9" swing. Leather belt power. It's threaded just don't want to gank up the threads.

 

[helmbelly]

Got 10 made got tuckered out and quit. Lotta set up time and fussing around. Here they are, I added a bevel to take the braze silver. Thx Wobbly for the advice of using a bull nose. Never tried my new m-Carbide bit. I will say that it also cut well with a triangular insert bit just coming straight down the ways at the thread. I'd recco a crush bushing like this cause it does the job and it's super fast to reload. Thanks Wolves for the relief cut idea and to Mr. York for the added relief, it's working like a champ.

 

[Sticks]

I did not read the entire thread, and this may have been suggested..

Make a collet that is drilled and tapped, then split it. The internal threads should give it more bite to hold on w/o slipping.

Make a steel collet that is drilled and tapped (not split), use a jam jut on the cut side to lock in at desired length + .125, then put a dial indicator on the ways for your carriage to give you precise Length Of Cut

Make a collet that is drilled and tapped, with a cross drilled hole for a pin or bolt at each desired depth for LOC.