Jim Wilkins wrote:
On Mar 19, 6:33?pm, Cydrome Leader wrote:
I finally attached the thread cutting kit to a sherline lathe. The kit
came with a 60 degree carbide cutter.

Even with 1/4" brass rods, that broke in probably minutes, followed by the
spare I had.

the cuts looked like **** too. They weren't really shiny and the "feel"
from the handcrank on the headstock/gear train didn't seem right. I was
only cutting 2 to 3 mils per pass.

I decided to gring my own with 1/4" HSS steel blanks on a Tormek knife
sharpener.

That worked much much better. The cuts look nice and shiny.

So what's the deal with the ugly finish I was getting with carbide? I
think I know why the tips snapped off, but the finish part I don't
understand. A mild steel rod looked awful with the carbide cutter too. It
looked like there was more tearing or smearing than cutting going on.

Carbide is a matrix of grains glued together, like concrete, and it
doesn't take as sharp an edge as HSS. I doubt you'll ever need carbide

I though they were giant crystal or something like that. The "like
concrete" part makes sense.

on a lathe with so little power anyway. It's likely that if the
material was that difficult to cut the lathe would twist away when you
tried to force a carbide bit into the work.

High Speed Steel will cut stainless steel and Grade 8 hardened bolts,
it just dulls quickly.

Does HSS leave nicer finish when sharp than carbide on these materials?
Considering tiny pieces of the tips broke off the carbide cutters I have,
I can't really test this anymore.