I bought a commercial tension compression tapper for use on my
non-C-axis CNC mills. Took me only one buggered hole to get timing
right so it would work. No compression, and very little extension
testing on aluminum with good spiral point taps in sizes I commonly use.
Then it took me only a couple tries to create a style in my style
library that will produce good tapping code for it in my CAM software
using a "scripted" drilling operation.

You would think that would be enough, but lately I've found myself
tapping three different sizes commonly. My newest mill takes advantage
of the tool table heights and does a good job, but if I am constantly
swapping taps int he TC tapper I can't set the tool height in the table.

My solution. Make a couple more TC tappers. The first two blanks I
destroyed on the lathe by trying to shade tree it. Nothing is really
critical except that the bore for the tap holding collet chuck and the
shaft of the TC tapper are concentric. Well on the third one I had some
success, but I failed to get the proper alignment turning concentric.
The tip of the tap orbits around the center of rotation. Its to much to
just let slop in the TC tapper account for it. I actually tapped a
couple test holes in aluminum with it, and it tapped them... over sized.
LOL.

Mine is in front:
http://bbs.homeshopmachinist.net/att...7&d=1543523014

Anyway, I thought about my steps and processes and I know how to make
the next one better. Now I am thinking about materials. The first ones
were all made out of 304 stainless except the straight shank collet
chuck which is some sort of modestly hard steel or so says my drill
bits. I didn't pick 304 stainless because I thought it was good for the
application. I picked it because it was the cheapest stock I had on
hand that was the right size to start with. I've got some 4140QT TGP on
hand. Its good stuff for making tools, but its a bit expensive to
waste. My local metal yard (the one I like) has 1018, I think 1035, and
1144 Stressproof (tm) on hand along with oodles of 304 stainless. There
really isn't going to be a lot of stress on the shank. The tap will
likely break before anything slips. Still I'd like to use something I
can put in the machine that isn't going to mess it up, but that I can
machine without having to send out to heat treat. I'm leaning towards
the 1144 stress proof. Its pretty strong, and it machines very nicely.