Pin torque - project

[Ron Nossaman]

>To me, the interesting thing about these torque measurements is that in some 
>cases the larger bits produced a hole with higher torque than smaller bits, 
>pointing out that rotation and feed speed, as well as drill 
>sharpness/straightness and flute design can have more effect than a bit size 
>change. DRILL TEST HOLES EVERY TIME.
>Bob Davis

Hi Bob,
It looked to me like there was a generally reasonable and logical
correlation between bit size and torque in all the medium and lower density
blocks. The ones that were the most erratic initially were the high density
blocks like Delignit, Falconwood, and the Baldwin block. These blocks are
very unforgiving, and it's not necessarily the drilling method that
accounts for the torque differences. Even with perfectly uniformly drilled
holes, there is enough difference in diameter from tuning pin to tuning pin
in the average set, to account for these kind of torque differences. Mike
didn't say whether they mic'd all the pins for the test, did he? Also, with
these dense blocks, as the hole gets smaller than about 0.015" less than
the pin diameter, the torque readings don't continue to climb predictably
because you are past the springback limit of the material.

Of the three dense blocks, after three years, the Falconwood was the most
erratic, with readings very high and not correlating to hole size. The
Baldwin block, after three years, settled to a remarkably uniform torque
irregardless of the original bit size. The only dense block that showed a
logical gradient was the Delignit, which demonstrated a logical torque
gradient from the smaller largest bit, to the smallest. 

The less dense blocks showed general torque gradients proportional to the
bit size at the three year point.

What the chart tells me is that, choice of bit sizing, drilling technique,
and pin uniformity will show up most immediately after pinning. In the long
run, however, the thing that seems to be critical is the original choice of
pinblock material, and not drilling the hole too big in the first place.

Thanks for the information Mike. It answered some questions for me and blew
out some residual chaff.


Ron N