Sorry to hear about all the effort in drilling this material.
The last time I did it was going through 1/2" wall and it took less than 10
minutes for the pilot hole and the final hole.
The key is the way the bit is ground, plus the drill speed, pressure and
oil. We actually sharpened the bit before going up the tower. It needs to be
a shallow angle, so the chip load is very light. Using a slow speed and good
oil, plus adjusting the feed rate (pressure) will keep it cutting smoothly.
I used a 1/8" pilot hole and finished from both sides with the larger bit.
The drill motor is a double handle 1/2" drive, running at about 300 rpm. The
reason to go from both sides is that when the bit goes through one side and
strikes the concave inside of the tube, it can easily dull/chip the flutes
of the bit, as they hit immediately. After going through both sides, the bit
can be carefully run through both to make a straight hole.
One caution when using a double handle 1/2" drive drill motor. These larger
motors will not stop when you release the trigger. The gearing is such that
they will continue with the existing energy, so if you have the bit grab, it
will test your arm strength. A friend of mine was using the same motor and
got caried away - had a splint on both forearm/wrists for 3 weeks.
Have a good day and 73,
Force 12 Antennas and Systems
(Home Page http://www.QTH.com/force12 )
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