For What Its Worth
Drilling out hard materials
In some
of the
1-2nd gen disk brake conversion kits The
original steering arms are used but the 7/16 holes have to be opened to
1/2
inch.
I don't
have a
drill press so I took them to my local machine shop (Hopefully Santa
can think
drill press this year). He called a
while later and said he had burned up his new 1/2 drill Tin coated $$$
drill
bit. They were too @#$ hard.
When I
stopped by
to pick up my unfinished parts I looked at the drill.
He had it set to 920 RPM. In
short this is too fast for hard
material. I suggested the lowest 460
RPM on the belts, but he wasn't interested in trying again.
I took
them home,
stuck them in a vise, pumped the holes full of grease and used my 3/8
(10mm) hand drill
with a cheap high speed steel drill. As
long as I kept the RPM down it cut fine, but stalled out the drill a
lot. I had to free run the drill from time
to time
to cool it off. The grease in the
holes
is a coolant not lubricant. When the tip
got hot the grease would melt and flow and help cool the cut down. Made it through 2 1/2 of the 4 holes
before I got
carried away with the RPM and melted the tip off the drill. Ground a new tip on the grinder and finished
in a few
minutes. Carbide tip drills work
well
as long as the part is held firm and you don't chatter/crack the tip. I used a carbide tip cement drill to finish
the one hole started at the shop, but it didn't have enough support for
the tip
and chipped/broke right at the end.
When cutting hard
metals remember, heat kills and speed makes heat. You don't have to
have
expensive tools, just patience.
