Hard Spot when Drilling?

Yes, work hardening. An old German engineer/ machinist I worked with would yell "STAY IN THE CUT" when someone was drilling steel and looked like they were easing up on the pressure.

Use oil to keep things cool and keep the pressure up so that you're always peeling off steel and cutting new material.

HRS or CRS I'm sure will be asked...

I've never had any problem with HRS from Ace Hardware (expensive as it is), FWIW.

OT-ish, I did, however, try annealing an in-situ broken tap (it got to brown temper before the block of aluminum starting softening) and drilling it out, but the HSS bit just bounced off it and started going sideways though the clay-like aluminum...

Tim

Don't try to anneal steel taps in aluminum, dissolve them with nitric acid which doesn't attack aluminum.

Dick I bet you were working with some of that exquisite imported steel from the Orient. I have some DOM tubing that I use in my shop to make gun parts from and while milling or turning it, I invariably find hard spots in it. I looked at the labelling on it and Sho' Nuf, it's from Japan. Paid $1.52 per foot for it, instead of $2.35 for American stuff.

The joy of low price sure won't last as long as the bitterness developed from the poor quality.

Or someth>I had an odd experience when drilling some 5/8 inch steel plate, unknown

My brother told me of some Asian iron he was machining that had a partially-melted tap embedded in it. That would be some hard spot!

I hate to say it but most "mild steel" these days is made from melted-down cars. You probably ran into a bit that used to be a ball bearing or something.

- GWE

Richard Ferguson wrote in news:3FF0FDA7.1738C082 @att.net:

I've seen this in cheap steels. I have also see this where the steel had been previously flame cut.

Or if it's a tiny tap, and the part isn't too big, boil it in water with alum disolved in it.

Jeff