On 2018-01-08, Bob La Londe wrote:

On 1/7/2018 9:09 PM, Gunner Asch wrote:
On Sun, 7 Jan 2018 12:25:04 -0700, Bob La Londe
wrote:

After much adieu over nothing I suppose (since at the moment I only have
one to do) I decided to turn a tapered mandrel between centers. The
first one turned out pretty good except I screwed up the finish pass(es)
and came in under sized. No I can't just shorten it up. So I still
have just one to do. LOL.

[ ... ]

The taper is pretty shallow. .157 over 10 inches.


What grease are you using? White lithium isnt going to cut it on this
sort of job...just saying...

Red Lead or a really good axle grease...

[ ... ]

At 115 RPM plane old waterproof wheel bearing grease worked ok. The job
took a couple hours at that speed, but the bearing didn't start to get
really hot until about 3/4 of the way through the job. I replaced the
bearing and the grease and finished the job. It was pretty frustrating
to go so slow. This was a 416 stainless shaft, and it will actually
machine much faster.

One problem with turning between centers is that the workpiece
length increases as it heats up. A setting which is right at the start
of the job can be too tight part way along.

If you can make the center both a ball bearing mounted center,
and spring loaded to keep about the same pressure throughout the job,
you probably won't get the overheating you've observed, and maybe can
run faster, too.

Such centers are made for cylindrical grinding (where the
workpiece is more likely to heat up and seize if the spring loading is
not provided. Of course, these centers are likely not made for offset
turning -- though there may be some for grinding tapers like Morse Taper
shanks.

Enjoy,
DoN.

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