My guess is that you work hardened the surface. The different cutting angle
on the reamer got you through.
For a 5/8th hole I would have drilled a 3/16 for your pilot and gone
directly to a 5/8th Prentice bit ( stepped shank ). When you go in
gradual steps you just dull the drill bit because the cutting edge is almost
instantly overloaded cutting on the rim of the bit.
The procedure I have done is that the 5/8th hole is drilled with an
electric drill having a half inch chuck and lots of torque. One person
holds the drill and the other has a pipe extension held to take the torque
reaction. Without a helper you face the possibility of a broken arm/wrist.
The ideal way is with a magnetic base drill.
I have become partial to something called Anchorlube for slow drilling
and tapping.
Randy


"B.B." u wrote in message
news 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
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. 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. 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.
HSS drill bit. The reamer (also HSS) handled that stubborn hole just
fine. So, what the hell? Did it harden on me? I wasn't building up
much heat at all. 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?

--
B.B. --I am not a goat! thegoat4 at airmail dot net