According to B.B. u:
OK, let's say you're given the task of making a 5/8" hole in a truck
frame (heat treated alloy steel) rail. You have at your disposal a
center punch, an air drill and what ever the hell you can chuck in the
end of it. 1/2" chuck. As a metalworker, how would you go about it?
Any torching is a big no-no.
I center punched, drilled a little hole, enlarged it to a 3/8 hole,
then used a "bridge reamer" to make it a 5/8" hole. This was a
Hmm ... I would check to see whether a step drill (UniBit is one
maker -- the first, I think) would work. It starts out pretty small,
and increases in steps. It has a single flute to do the cutting, and
something around 3/4 of the circumference rides in the hole as a guide.
The trick is to have a step drill either with steps as long as
the thickness of your metal, or with the maximum diameter matching the
target size. Some step drills have fairly short steps, but a lot of
them -- good for something like holes in 16 ga steel or aluminum of
similar thickness. Others have longer steps -- over 1/8" (but not as
many steps). I suspect that the latter is what you would need.
One thing to consider is that you will probably want to reduce
the RPM as the drill moves up to larger steps, or you risk running too
fast and overheating the drill -- step drill or normal style.
harrowing experience because it was a mother****er to put that initial
hole in there, (had to apply a lot of pressure from a really
uncomfortable stance) and that reamer (on loan and rather pricey) had a
nasty habit of grabbing if I didn't hold it exactly straight through the
entire cut.
Any kind of tapered reamer is nasty that way -- either the
bridge reamers (which I have never used), or the T-handled reamers by
General (and probably others) which I have used many times to make holes
in electronics chassis.
I made it without hurting the reamer or breaking my wrists,
but I'd like to know if there is a better way.
Also, one hole was stubborn. I was going to enlarge it one more time
to a half inch, but about half way though the hole I suddenly stopped
making progress. For the life of me I could not make the damn drill cut
no matter how much pressure I applied.
What RPM were you running? I suspect that you may have
overheated the bit. And also, as you increase the diameter (assuming
constant sized steps) you need more force to keep it cutting properly.
Just in case there was something
wrong with the bit that I couldn't see visually, I tried another, but it
wouldn't cut either. The original bit in another hole cut just fine.
Work hardening of the workpiece, then.
HSS drill bit. The reamer (also HSS) handled that stubborn hole just
fine.
Different angle of cut (as was mentioned by another), and you
are running it at a much slower speed (manual power, instead of air or
electric drill).
So, what the hell? Did it harden on me?
I suspect so.
I wasn't building up
much heat at all.
Work hardening does not need much heat.
I could pull the drill out of the hole and grab the
bit and while hot, it didn't burn me.
BTW, my "cutting fluid" was 50wt transmission oil because that's all
I had, and was recommended by the guy who loaned me the reamer. It
worked, but probably isn't optimal. For next time, what (obtainable)
fluid is suggested?
Not sure for the bridge reamer, but I would probably use
Molly-Dee (Molybdenum Disulfide in oil) with the step drill.
Good Luck,
DoN.
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