In article ,
(DoN. Nichols) wrote:

In article ,
B.B. u wrote:

[ ... ]

Harold, When you wrote "Can I assume the mandrel is ½?" that last
character came out as Pi on my screen, and I have no idea what you meant
by it.

It comes out as "1/2" on some screens, but since it is a part of
the extended ASCII character set, there are no promises that it will
show up the same on all. This is a primary reason for sticking to only
the characters which show on the tops of your keyboard keys. Anything
which requires fancy keyboard tricks to generate (e.g. Compose-1-2 on my
Sun keyboard) will not mean the same to everybody in this newsgroup with
mixed systems in mixed locations around the world. (And it even chances
on some of them when you change the characterset used by the program.

But, bar stock, pressed the mandrel in with an arbor press.

Hmm ... bar stock? Not turned to have a very slight taper?
That could be part of the problem. I think that the typical taper on an
arbor for turning between centers is 0.001 inch/foot, but I'm sure that
Harold will correct me if I am wrong.

Oh, the mandrel itself is tapered--it's a pre-made mandrel out of a
box. I thought Harold was asking if I was turning my part from either
cast or bar stock. I'm turning from bar stock, and the part is pressed
onto a mandrel. Hope that clears it up.

We're using general-purpose indexable carbide tools on all of the
lathes, but I have a fresh bit of tool steel and I'll see about making
my own tool to play with.

That could help, as typically a carbide insert is not as sharp
as a frechly ground and honed HSS bit.

Note that I have some very nice sharp solid carbide inserts
(1/4" IC 55 degree diamond *without* TiN coating or the like, which I
use when I want a sharp tool but am too lazy to grind my own. :-)

I did find (counter-intuitively) that running
on the high side of the cutting speeds helped.
I'll likely settle on the heat & press method suggested by
PrecisionMachinist. Class is on monday--I'll let you know how it goes.

If your arbors *do* have a taper, it should get it that much
tighter. (Also note that the heat generated by turning could expand the
aluminum and loosen the grip on the steel arbor, which would make the
typical carbide insert the poorer choice here.)

Yeah, maybe I'll just turn it until it starts slipping and then run
it over to the press while still hot.

--
B.B. --I am not a goat! thegoat4 at airmail dot net
http://web2.airmail.net/thegoat4/