You might be able to obtain an assembly with allowable run out by
welding an over sized shaft as accuratey as possible to the bottom of
your bowl. The end of the shaft to be welded to the bowl should be
milled square, so the bowl will have best chance of being perpendicular
to axis of the shaft. To eliminate any offset between shaft and bowl
axes, place the weldment in a 4 jaw chuck on a lathe. Adjust 4 jaw chuck
till you reduce runout at bowl edge to an acceptable level. You can now
turn the shaft down to your bearing size and the axis of the bowl should
coincide with the new shaft axis.
As an alternative you might design a coupling element to use between
bowl and shaft that can adjust offset and tilt. It could be as simple as
a long oversized collar with 8 set screws. Kind of like a Chrismas tree
stand.
--
D. Miller
"BR" wrote in message
...
Your idea sounds like a good one except I'm not sure I'll make it with
little runout. I made some spherical speaker enclosures using a
rounter mounted on a turntable setup, but don't have that anymore.
Though it may cost some, a metal spinner could make the tank. They'll
make it more precisely in terms of TIR than anything
I could do.
The stepping motor may work but I'm concerned with torque ripple
transmitted to the tank contents, although less thru a gear reduction.
It's unfortunate that servodisc motors are so expensive since they
have no cogging and are brushed dc motors. Well, it's just like
anything - it'll take some experimenting to see what effects things
like cogging have on the contents. Perhaps it won't be a problem due
to its mass, just like platters used for record turntables. I'm just a
bit paranoid about building this contraption, because it's then a lot
of trial and error for a certain pattern.
The only other possibility is using say, three small motors with
rubber tires around the circumfrence to turn a mixing bowl floating in
a larger bowl of water. Just thinking out loud....
""Paul E. Bennett"" wrote in message
Make yourself a wooden mould for the bowl shape, a wooden ring and
make the bowl in fibre-glass. The wooden ring would form the basis
for the shaft attachment. Keep application of the fibre-glass and
resin even around the shape. A rotating flat table (with suitable
clamps) and a sander held at a fixed point will assist in making
the outside smooth (the inner would be smooth from the mould form).
On the drive side, a stepper motor (at least 100 steps per rev) with
worm drive gearing to the base gear wheel would provide a quite
smooth
rotation which you have total control over. The drive electronics
would be quite simple.
--
************************************************** ******************
Paul E. Bennett
Forth based HIDECS Consultancy .....http://www.amleth.demon.co.uk/
Mob: +44 (0)7811-639972 .........NOW AVAILABLE:- HIDECS COURSE......
Tel: +44 (0)1235-811095 .... see http://www.feabhas.com for details.
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk..
************************************************** ******************