On Wed, 12 Nov 2014 07:58:44 -0500, "Pete C."
wrote:


Stuart Wheaton wrote:

Drilling into the end of a large threaded rod, centered, punched and
drilled starting at 1/8" worked up to 3/8". 3/8" is about 1/4 of the
way into the hole and quit cutting, Either I hit a hard spot in the
steel, or it got work hardened, I was using coolant, but not flood.

Swapped to a new and sharp HSS bit, no joy at all.

Suggestions?

I can:

1. Try a masonry bit, 3/8 is something I have in the shop.
2. Heat it with a plumbers torch and see if I can temper the hole.
3. Go get a TiN or Cobalt bit...

I need to finish the 3/8 and then drill it to 13/32nds, then tap, so I'm
close, but I'm worried about the tap and the hard spot too.

Any help would be great!

Stuart

Where did you get the TR? The stuff found in short lengths in the big
box stores is total crap and you have no idea what you'll find in it.
The stuff found in 10' lengths and not galvanized in the electrical area
next to the Unistrut is normally much higher quality and the stuff you
see hanging 300# transformers over your head.

The lowest grade threaded rod, even from a reputable supplier
(McMaster calls it "low strength threaded rod"), machines like crap.
Grade B7 is made from 4140 and is only a bit more expensive in small
sizes. It's stronger, has good machinability, and better form and
finish on the threads. It may well be what's sold for use with
Unistrut.

--
Ned Simmons