My Projects‎ > ‎

Trigger Adjuster

This was a project I did a while ago but just getting around to posting it.  It is a trigger adjuster for a kit gun my brother built.  We were yacking on the phone one day and he was telling me about the project and wondered if I could do this little thing for him..."of course", I said mouth insert foot.  Basically it is a 1/4-28 SHCS center drilled and then tapped for a 6-32 set screw.

I knew it would have some challenges with the hardness of the SHCS but there were more.  The bushing in the picture above was built along the way in order to hold the 1/4-28 securely for drilling and tapping.  Center drilling the screw on the mini worked pretty well using a center drill and then a cobalt drill for the tap size and the counter bore...slow going with lots of cutting fluid, blowing it out and cooling it down every so often.

The trick was the tapping!  SHCS' are RC35-42 out of the box and the type of steel varies a bit based on the manufacture.  Normal HSS 3-4 flute taps don't have much of a chance based on this and the standard #36 tap drill, plus how many threads needed for this job.  At .437 the 6-32 will use about 14 threads.  I had a couple of plug taps and one taper tap.  I started with the taper to ease into it.  It worked barely to get going into it, maybe 3-4 threads.  Then blew it out and cooled it down, more tap fluid and then switched to the plug tap to open it up a bit...then back and forth until I was almost through...then...the almighty - BINK!  %*(#)&@^%%!! 

Bottom line is I went through all 3 of my taps, having to start over each time with drilling and counter boring.  Even tried a 18-8 SS 1/4-28 thinking it might be a bit softer...but nope!  Now being 6-32 tap-less, I did some research on spirals to find one that was willing to work on RC35-42 and long enough to reach through from the top.  Finally found a couple that I could afford...pricy little beggars.  One was a Morse I found on eBay and the other a YG-1 on Amazon.  They were both plug type and coated but HSS, figuring the spiral would at least eject the chips better.  The Hi-Zute ones were out of my league in the $40-$60 range...but of course I had gone through 3, $6-$8 ones and all the futzing time...@¿ maybe should have.

Also did some more research on annealing the screw, but didn't find much.  So, I just decided to try it "home brew".  I drilled out a couple of screws to get ahead of the game and took one to try and anneal.
  All I did to anneal it was to bring it up to dark to medium orange and held it there for a minute or two then backed the flame away a bit at a time, but kept it on the part and further and further away, until I thought it was about right (about 3-4 more minutes total).  Then let it cool down to ambient.  Not a lot of mass in a drilled out 1/4-28 was my thought and didn't want to distort it, At All!

Somewhere in waiting for the taps to arrive I had stopped by a local hardware and picked up a couple of Vermont taper taps and proceeded to try it on the annealed piece.  It did seem easier but still BINKED as it was about to go through.  So I stopped at that to save a standard for my kit and waited for the new spirals to arrive.

When they arrived I had thought further that .438 was way more thread than necessary.  I talked with my brother and agreed to reduce it to .375, meaning only 12 threads.  I also decided after consulting the Machinery Handbook that I could go to a #35 drill and still have decent engagement.

Bottom line it took annealing, less threads and larger tap drill with Medium-Zute spiral taps to "Getter Done".  However I only got one made and really wanted to make a couple for him.  The Amazon YG-1 BINKED on the second one...So I stopped for now...still pondering how to get this done consistently without breaking taps.

Overall it was a fun, but large learning curve project for my fine brother and I did "Getter Done" as Keith Fenner says!  After this time has passed I am thinking this project is Not for the faint of heart nor small pocket book, home shop!  If any of you master wizards out there have any thoughts of how to do this better on a budget, I'd love to hear from you.