On Monday, January 9, 2017 at 1:34:52 PM UTC-5, Jim Wilkins wrote:
wrote in message
...
On Monday, January 9, 2017 at 11:29:51 AM UTC-5, Phil Kangas wrote:
"whit3rd" wrote in message
...
On Sunday, January 8, 2017 at 7:35:01 PM UTC-8, James
Waldby wrote:
On Sun, 08 Jan 2017 19:23:11 -0800, whit3rd wrote:

On Sunday, January 8, 2017 at 5:42:13 PM UTC-8, Phil
Kangas wrote:
I've been presented with an unusual project involving
cutting a 2 deg taper on one side of a disk. The part
is mild steel, 3/8 thick, 5" O.D., with a 3" hole in
the
center. Guy wants a 2 deg tapered face

So, bore the hole 2.5", hold from inside, complete the
taper,
hold from outside, and finish boring the hole.

Is that intended for lathe setup, or mill? Why not just
cut the
3" ID in the first place?

I was thinking 'taper' meant making the disk into a cone.
So, my answer was for a reversible jaw 3-jaw chuck and
workholding
on the lathe to avoid cutting the jaws.

If it means a wedge, the lathe isn't the easiest tool for
the facing cut
(though a faceplate and a backing wedge could be
arranged).

This is not a cone, it is a wedge. The cut is only on one
face
of the disk. The cut face is 2 deg off perpendicular to the
center
axis of the hole. It's a nasty work holding situation.


As I read the question, the disk will end up 0.375" thick
at
one point, and about 0.2005" at a point 5" from the first
point.

Yup, you see it correct.
Perhaps one way to do it would be to make a work holding
ring long enough to hold in the mill somehow and cut a
2 deg face on one end. Then tack weld this ring to the
disk of interest and cut that face with the lathe. Make
sense?
More taper disks could then be cut with this setup.

If I'm thinking about the geometry correctly, this is how I'd do it:
I'd mount it on a lathe faceplate with one edge propped up, and a
drawbar pulling a bolt-like piece through the through-hole. Face the
disk as close as you can to the central clamp -- whatever you're
pulling with the drawbar. Then, without changing the setup, I'd clamp
the disk at three or four points around the edge, and withdraw
whatever I was holding with the drawbar. Then I'd finish facing the
area around the hole.

Or did I just crash something I hadn't thought of? d8-)

--
Ed Huntress

===========

The prop could be a #17 or 11/64" drill bit. I'd want two more props
at right angles to stabilize the disk from wobbling, and something
(wire?) to independently hold the props in place if it does anyway.
You can't tighten the drawbar to clamp everything together while the
faceplate is flat on the bench being assembled.
-jsw

True, which is why I have a stub "fake" spindle (made by my uncle, before he passed his SB 10L on to me) that I clamp in my big vise to do faceplate setups. I have four faceplates, two of them custom-cast, and I used to do a lot of faceplate work when I was doing a lot of home machining, 20 years ago.

Get the setup right in that setup rig, and then take it off the stub and mount it on the lathe. Re-set the drawbar as you had it set up in the vise.

It sounds like a lot of tedium, but if you don't have a mill (I didn't in those days, and I've scrapped the one I did have since), faceplate jobs like that come naturally.

This piece, being only 3/8" thick and 5" diameter, is going to spring if you don't have it well propped-up in the faceplate. It would be a little tricky but a few small scraps of metal, well-placed, should do the job.

--
Ed Huntress