On Sat, 24 Apr 2010 13:16:58 -0700, "Jon Danniken"
wrote:
Don Foreman wrote:
A hole saw with plenty of cutting fluid will be the lowest-torque
approach. Next would be a step bit, last choice would be a 1" dia
twist drill. The twist drill would be better for production rate in
heavier material with suitable machinery driving it, but hole saws and
step drills (unibit) work much better when the dia of the hole is
considerably larger than the thickness of the material.
1/4 hp at 620 RPM is 25.4 in-lbf of torque. That might drive a good
holesaw if nothing binds up due to deflection. It would help a lot if
you could change pulleys to get the speed down. That would increase
your torque and decrease heating.
At 620 RPM a 1" hole saw will have a tooth speed of 162 SFPM, which is
on the high side of the range for bimetal cutting mild steel but not
absurdly out of the ball park. The range generally goes from 80 to
200 SFPM. Use lots of juice. Slower would be better.
Thanks Don, I appreciate it. Right now 620RPM is the slowest speed the
drillpress will go down to, with 3 7/8" OD pulley on the quill and 1 1/2" OD
pulley on the motor shaft.
BUT: I dug around in the shop and found my old compressor, with the 1hp
motor (not compressor duty) motor still attached to it. If I can make an
adaptor plate between the 1hp motor and the drill press mount, it *will*
fit.
The only rub is that it has a 5/8" shaft (3/16" keyway), and the smallest
single pulley with those dimensions from McmasterCarr has an OD of 1 3/4".
I'm guessing that extra 1/4" inch will multiply the RPM by 1.75/1.5 (if that
is the correct formula), and I will end up with about 725RPM at 1hp.
That's a fair bit faster, but with the extra torque perhaps I could then use
the 1" silver/demming drill bit with coolant and crank it hard through the
workpiece.
Hmmm....
Please re-read guidance several have offered, then do as you will.
A 1" drill bit, silver demming or otherwise, is not a good choice for
11 gage steel, and it's a particularly bad choice in a lightweight
drillpress.
I have a Bridgeport mill and I have a 1" silver-deming drillbit with
1/2" shank. If I were drilling 11 gage, I'd use a holesaw or a step
drill whether in a drillpress or in the mill.
Harbor Freight offers a pair of stepdrills for $14.99.
http://www.harborfreight.com/cpi/cta...emnumber=96275
These work quite well in a hand-held drillmotor. Drill 1/2" pilot
holes on your DP, then enlarge them to suit with a step drill in a
handheld that has the low-speed high-torque to get it done.