My first internal thread- and a tricky one

[markba633csi]

I wanted an ER16 collet chuck for my Unimat so rather than try to thread the collet chuck itself I did it this way:
The Unimat spindle is 12MM x 1 and the collet chuck has a 10MM bore. I hand ground the bit to cut the threads.
I used my "Big" lathe (Atlas MK2) to fab the adapter. I put a sharpie mark on the way to show me when to stop the
machine and pull out. Fits like a glove- haven't measured the runout yet but looks to be less than a thou- good enuf

I did the final cuts on the 10mm arbor section on the Unimat itself for the best accuracy
Gotta make a knurling tool one of these days

 

[ChazzC]

The thread looks good, but I'm fascinated by the tool bit you ground: did you get any significant flexing during the cuts? I've never seen a lathe bit made from a flat tool steel blank.

 

[WobblyHand]

Single pointed a M8x1 internal thread on this. Used a Micro100 LH threading bit. There's no visibility on a M8 internal thread! Threaded away from the chuck. Make a mistake with a carbide tool this size and it snaps instantly. BTDT. Had a different boring tool and it lasted less than 5 minutes. Fortunately I hadn't paid full price, but still...

The M8x1 threads onto an airgun barrel. Comparatively speaking, single pointing the 1/2-20 thread was easy! This was a fun project.

 

[markba633csi]

ChazzC: It's a 1/4" HSS bit with cobalt- looks flat in the photo but it's square. Tip of tool just slightly above center, 30 thou or so
The small endmill in the photo is a broken one I used to make a relief tool for the bottom of the hole

I had to pick up the thread again once when I opened the half nuts too soon- thought I was done but wasn't deep enuf
That was the tricky part- with half nuts re-engaged I used the cross slide and compound to get the threading tool approximately
in the right place and backlash removed, then loosened the tool bit in the holder and wiggle till it snapped into place. Voila!

Atlas lathes cut an approximate metric thread, but for short threads like this (7-8) it works fine
Backgears and variable speed really helps- I wouldn't want to attempt this without those unless the lathe is fully automatic/CNC
You want the spindle just crawling... 30 rpm or so

 

[ChazzC]

ChazzC: It's a 1/4" HSS bit with cobalt- looks flat in the photo but it's square.

Thanks for the clarification, Mark: zooming in on the original photo and understanding the angle I can see it now.