On 1/7/2018 2:47 PM, David Billington wrote:
On 07/01/18 19:25, 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.

I picked up one of those little offsettable centers and it worked well
enough, except the tip melted. I kept it lubricated, but it might
have just been to high of an rpm for the method. I can turn it
slower, but if I get to do more of these I sure don't want to go slower.

I have two thoughts:

I can offset the tail stock and use a ball bearing center.

I can machine off the melted center, center drill it, and insert a
ball bearing between it and the center drill on that end of the
stock. The ball bearing certainly won't melt, and it will more evenly
distribute the load from the stock to the center. It would also have
more contact with the drilled out center. It would also allow me to
have a small reservoir of grease behind the bearing.

I really don't have a strong feeling for which approach will work out
better other than I dislike the time spent adjusting my tailstock back
in. I can leave the offset center setup for this taper indefinitely.
Ok, maybe I hope the ball bearing method will work out atleast as well.

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



Bob,

I think it was me that suggested those offsettable centres so shame the
centre melted. I think if it was me I would try and modify it to have a
rotating centre. Maybe you can fit a housing to the movable part to
support the outer races of a couple of ball races back to back and fit a
centre into those so you'll have a well supported rotating centre. I've
done similar before but not for a centre application but the application
is still going well, it was actually the rotating mass bearings for a
vibratory table, the housing was fixed to the vibrating table and the
centre shaft connected to the motor via a bit of flexible hose.

Its ok. They atleast paid lip service to it needing to be hard. Based
on how it machines it was case hardened. Very hard start, and then
right through for a pretty face. Its a neat idea, but the boring head
might have been better. The offset center tool is really wide for what
it is and you have to use longer than ideal tool stick out from the tool
post. I have no hard feelings about it. I learned quite a bit in a
very short time by using it.

I socketed the center for a ball bearing and got the job done using some
waterproof wheel bearing grease. I may never use it again, but then...
I might. LOL. I've mentioned two or three times now. If I have to
turn a lot of tapers I'm going to invest a day into making a proper
linear rod taper attachment.