Helo, all,

I have a set of the 3/8" square lathe toolholders for triangular carbide
inserts with the 1/4" inscribed circle. I used them on a 10" Atlas, and
later on a 12" Craftsman, for over 15 years. I broke a few inserts, and
wore out or chipped quite a few, over the years. This past weekend, I
was doing some heavy turning on my 15" Sheldon lathe, and broke
the nose off one of the holders. It cracked across the front, splitting
at the threaded hole, so the front point of the holder dropped off.
Amazingly, the screw and the insert didn't break, just the holder!
It had a very nodular-looking fracture, like cast Iron, not like some
ductile steel. What are these things supposed to be made of?
I got this set at the same time I got my original QC toolpost from
Enco. The toolpost was a Phase-II, I don't remember if the holders
were also from Phase-II or not.

Any comments? (I'm going to try to get a better set on eBay, and
in the 1/2" holder size, with 3/8" IC inserts. I assume the larger
holder has to be a little stronger, just because of the vertical
dimension, if nothing else.)

Anyone have any comments on the strength and reliability of the
5-pc holder sets that everybody sells? Also, does anyone have
any recommendations for a general-purpose insert, chipbreakers,
positive or negative rake, etc? I have been using a couple of different
inserts that I managed to get at a good price, all positive rake with
molded-in chipbreaker. Now that I have a lathe with the power and
rigidity to use negative rake tooling, does anyone have any recommendations
for those? (I'm a bit leery of buying a bunch of inserts at $9.50 ea
with toolholders running $50 - 100 at the usual machinist supply
outfits like J&L and MSC without some word on others' experiences
with them.)

I do a LOT of aluminum, but I do some tools and fixtures, etc. in
mild and tool steels.

Oh, one other thing. I got a little plastic gadget some time ago that
had a Vee, a flat and a bubble level that was used to make the cutting
tool even with the center of the workpiece on the lathe. It seems to have
gone with my last lathe. I'm trying to find a replacement, but can't
seem to find them in the catalogs. What do they even call these
things? I think mine was listed as something like a "lathe tool height
setting gauge". I couldn't find any on eBay, either, under any name
I could think to search for.

Thanks much in advance!

Jon