Tuning Tip Threads

[Paul Chick]

Subject: Re: Tuning Tip Threads

> Both Ron. The stripped threads are in the head to shaft joint. But 
> additionally, I find that some tips will fit one extension, but not the 
> other.....
> 
> Terry Farrell

Ok, head to shaft. I've had occasional failures there, and 
determined it was just because the joint wasn't tight. If it's 
not cranked down, any movement in the threads will eventually 
tear them up. I like the tapered pipe thread because it jams 
in very solidly. In your case, I'd start with a new head, and 
re thread the shaft. Then you may have to make modifications 
to make it work. The shaft has to go in deep enough to jam the 
threads. If it bottoms out in the hole, it won't tighten. 
Likewise, if the head contacts the end of the threads in the 
shaft, it won't tighten. In either case, it will soon be loose 
and fail before you're ready. 

The threads in question here are 1/8"x 27 pipe thread. I solved this problem
with a tap and die from the local hardware store. Before any threads were
chased (redone with the tap or die),IU put the shaft together then marked
the shaft at the joint with the head with tape; removed the shaft to see the
threads.  I cut a piece of tag board to the profile of the threaded end of
the shaft then trimmed it to the minor diameter of those threads. Now I have
a gage, which I marked with the distance from the end of the threads to the
piece of tape. By inserting this gage into the head, I could see how deep
the shaft threads reached.  If it was shallow, I re-tapped the head about 1
turn, removed the tap, cleaned the head, inserted and tightened the shaft,
remarked it with tape and repeated the process.  Before the re-tapping step,
I ground the lead off of the tap to make it a plugging/bottoming tap, so I
had threads all the way to its tip.
 If the gage went into the head all the way to the end of its threads, I
ground off the end of the shaft and did the gage step again.  This got me to
the point where the end of the shaft was almost touching the bottom of the
hole in the head when TIGHT, chasing the head and/or the shaft.  If you want
interchangeable heads and shafts, this will get you there with a tight fit
every time. It took less time to perform than it did to write this message.
I carry tip mounted heads for various tuning pin types and sizes. The tips
are fitted and tightened to the heads so the star pattern is always lined up
with the center line of my tuning lever.  This keeps me from fumbling around
for tuning pin flats. (Someone suggested a better pair of bifocals.)...hope
this helps.
Paul C