another pen and ruined threads???

[watch_art]

So I turned a cap a few nights ago - and aside from the material doesn't really go with the pen body.
Turned a section out pretty quickly tonight - very happy with it.
Turned a barrel out. Very happy with it.

Started to cut the threads with the 1/2" die I have and it just destroyed the threads instead of cutting them!! When I took the die back I could see that the last couple of threads looked fine but from the barrel lip up a bit was ruined. What the heck man!?

What did I do and what should I do??

Resized to 94% (was 1000 x 681) - Click image to enlarge




Resized to 94% (was 1000 x 750) - Click image to enlarge

[skiprat]

First off, wow for the size of your post !!! Did you copy it from another forum?

I would say there are one of two things happening here.
1st you didn't back off and clean the die and it didn't have sufficient lube. Perhaps a hard chip got stuck in the die and ripped up the threads as it got to them.

My money is on the die not being perfectly aligned with the workpiece. Either the tailstock is off or the die is not seated properly in the die holder.

[gawdelpus]

A couple of things come to mind for that sort of effect, the major dia of the thread was too big so cutting too much material, did you wind the die on by hand and lubricate it ,did you do a couple of turns then wind back to clear the chips ,even on most metals you have to wind back after a couple of turns to break the chips and stop buildup,if you dont you will just tear the material being either tapped or threaded ,any acrylic or similar material is quite soft and will tear very easily . Shame about the pen was looking good till that point .Was it a dedicated tap for pen threads or off the shelf die,does make a difference :( Hope that is some help to you ,I have not made threads in plastic, but as a fitter and turner I have done most threads in a varied selection of materials ,and unless you are doing production work ,the old couple of threads in then back off to break up the swarf in the tap or die is the tried and true method . cheers ~ John

[watch_art]

Ugh! Yes - copied. DIdn't mean to get all that junk in there. Sorry bout that.

Maybe a kind mod could delete the excess junk out?? :)

I took the die out and cleaned it up and started again, that's when I went as far as in the picture. At first it wasn't cutting - didn't feel like it was cutting - so I pulled it off and noticed that I only had 2 threads and a bunch of ruined plastic. When I tried again it gave me the same thing. I guess I didn't get it clean enough. I ran it through the ultra sonic and hopefully that and a toothbrush will get it good again.

I don't think the tail is off b/c I cut all the other threads last night inside the barrel, on the section, and they turned out fine. I'm getting much better at all this. :D

Thanks!

[Rich L]

Don't know how you're holding your die, but:

clogged die
major diameter too big
wobbly die
something holding the die back from following its feed path (stuck tailstock?)

Cheers,
Rich

[watch_art]

I'm gonna go with dirty. At least I'm hoping that's all it was. I cleaned it and the die holder out really good so --- here's hoping.

Thanks all for your suggestions.

[watch_art]

What about tail stock sliding resistance? I cleaned the bed off so it was nice and dry before I started turning last night. Could it have just been fighting friction?

[skiprat]

Originally Posted by watch_art

What about tail stock sliding resistance? I cleaned the bed off so it was nice and dry before I started turning last night. Could it have just been fighting friction?

Mmmm, but then ALL the threads would be wrecked, not just the trailing ones. This theory also degates some of the other possibilities too.

If you are relying on the tailstock to slide on the bed, then it really is time you got a proper die holder. They are not expensive and worth their weight in gold.

Another possibility is a chipped tooth on the die. I have chipped a few on stainless but these dameged ones can still often ( but not always )be used by reversing the die in the holder. Dies used to have a front and a back end. The front was the side with the writing on it. But I believe just about all dies can be used from either end now. You can tell just by looking at the cutting angles but it's worth a try anyway.