Ideally, I'd like to be able to use one tool to take a heavy cut
followed by an acceptable finishing cut. Is that possible with
carbide on a 9A?
You and Ondrej recommend 400-600 sfpm with carbide. I take it
carbide cuts better at a faster sfpm? Maybe I misunderstood carbide
usage. I thought it was capable of faster cutting, but faster
cutting was not essential for a good cut. I know the speed effects
the chipbreaking, but I did not know slower cutting will actually
make the finish worse. So will cutting at a lower sfpm lead to the
tearing finish that I wrote about originally?
I have about 100# of various carbide inserts, so I'd really like to
find something I can use rather than buying something else.
Mike
On 7/14/2022 10:10 AM, Bill in OKC too
via groups.io wrote:
I'm afraid that you need a much sturdier/more massive
lathe than the lighter SB lathes. My experience is with
Clausing-Colchester 13 & 15 inch school lathes. The
smaller 13" lathe weighs about 2700 pounds, the 15" lathes
about 3800lbs. My Heavy 10L weighs just over a third of what
the smaller CC lathe weighed and about has to be a great
deal less stiff. Mild steel, in our class was specified
90SFPM for HSS, and 400SFPM for carbide tooling. I could get
a mirror finish on the 13" lathe. I've not gotten to use my
SB yet, just the Atlas. It's about a quarter the weight of
the SB. Pretty much spaghetti comparatively. Unless your SB
is one of the newer lathes and a 14" or larger you're going
to need slower speeds and feeds, and shallower cuts to make
up for the lesser stiffness.
You could use carbide for roughing cuts, and HSS for
finish cuts if you really need or want the fine finish. You
can diamond hone HSS & carbide if you need it sharper,
but that can mess up your repeatability with indexable
inserts.
Arwarnerco.com sells HSS indexable inserts which the
folks who use 7x mini-lathes a lot seem to find very
helpful. LittleMachineShop.com sells the smaller sizes
appropriate for the 7" and similar machines, and in smaller
quantities IIRC.
HTH!
Bill in OKC
William R. Meyers, MSgt, USAF(Ret.)
Aphorisms
to live by:
Good judgement comes from experience.
Experience comes from bad judgement.
SEMPER GUMBY!
Improvise,
Adapt, and Overcome.
Physics
doesn't care about your schedule.
The
only reason I know anything is because I've done
it wrong enough times to START to know better
On Wednesday, July 13, 2022 at 09:46:54 PM CDT, Mike
Poore
<mpoore10@...> wrote:
I am sure this is not
the first time for this topic, but I'd like to know what
setup, if any, anyone has found that provides a good
surface finish using carbide on 1018?
I have acquired a lot of carbide inserts and holders
along with my QCTP. I have negative rake and no rake
holders. I have chipbreakers and flat carbide. I turned
some aluminum after rebuilding the lathe and the surface
finish was as good as one could expect so far as it was
nearly a mirror finish using the slowest feed. Then I
tried 1018 with the same tooling and ended up with a
fairly rough finish. It looked and felt like the metal
was tearing rather than cutting. I have tried other
combos and nothing yet is satisfactory. I have a diamond
disc sharpener, but I think the carbide is sharp enough
to do better than it is. There is plenty of HSS laying
around that could be used, but the idea of indexable
carbide would be preferred if I can make it work.
There is plenty of experimenting left to do. I was
hoping someone could give me a starting point as far as
insert shape, rake, speeds (I am guessing it might be a
little different than what the book says for an old WWII
cast iron bearing lathe.), and tool angle. Thanks for
any help.
