On 7 Mar 2018, at 06:28, Erik Christiansen wrote:

> On 07.03.18 00:58, Gene Heskett wrote:
>> And the grub screws stayed tight?

I made a whole tapping system for my pillar tool, for small taps, using the 
4-grubscrew technique, and I have used it successfully for years. I only use it 
for threads below M3, though, and only for manual tapping. One flaw is that 
although the grubscrews stay fairly tight, most of the time, they do have a 
tendency to work loose because of the angle of the twisting force, which is 
roughly parallel to the flat of the squares, at the tangent point of the 
imaginary same-diameter circle.
Another more annoying problem is that there is nothing much to stop the tap 
from tending to slip along its long axis, as the screws slacken slightly. What 
they need is a conical hole, a vee or a flat with shoulders ground into the 
shank, to stop the sliding.
For larger taps, that would be easier to arrange, but I suspect the forces 
involved with those larger taps would tend to magnify the problems.

Is the answer not to use a thread mill? Expensive - yes - but more controllable 
and easier to cut the thread in several passes, I think. I've no experience, 
except of looking at my shockingly expensive thread mill cutter and wondering 
about its life expectancy.


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