On Sat, 19 Mar 2011 23:37:11 -0400, "Tom Gardner" w@w wrote:


"Cydrome Leader" wrote in message
...
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.

I much prefer HSS to carbide for a lot of jobs and especially threading. You have to
have rigidity squared to use carbide well and horsepower too. Great for removing a
lot of material quickly or production jobs. I've got a 7.5 HP Reed Prentice with the
rigidity and HP and only use carbide 25% of the time.

NOT, repeat NOT for the original poster. I recently bought carbide
threading inserts for my CHNC lathe. WHAT AN IMPROVEMENT! On a machine
built for it, these are great. Of course, I never thread at less than
500 RPM on larger diameters and into the 1000s if going under one
inch. Don't know if the reflexes could ever be fast enough on a manual
machine.

Karl