Re: Homemade 2 spindle lathe preliminary results

In article <48c5f851.1975069439@xxxxxxxxxxxxxxxx>, <etpm@xxxxxxxxxxx>
wrote:

On Sun, 7 Sep 2008 14:39:53 -0700, "William Noble"
<nobody@xxxxxxxxxxx> wrote:

Greetings Don,
The two spindles will be at the same speed. What I need is to make
sure that whatever speed the master spindle is turning at the slave
will match. If the part swap from the master spindle to the slave
spindle happens fast enough the part won't be scratched. So I really
don't care if the slave lags one encoder count as long as it lags
consistantly. And it appears that is happening right now. I will need
to take some pictures with a fast shutter to see if the marks always
line up.
Eric

Eric - what you need to consider is dynamics, not just statics - it is not
clear from your limited requiements statement what kind of dynamic tracking
is required. I will absolutely guarantee however that under dynamic
conditions the two will not track. The amount of error depends on the
specific servo loop and its response time (and power) - whether the error is
a problem depends on your needs. I had suggested collecting the standard
frequency response data so you could evaluate this mathamatically. If
you'd rather not do that, then try this - mount an L shaped item (such as a
heavy allen wrench) in the main chuck. set up a a steel block so the L will
hit the block in about 1/2 revolution from "zero". Set the thing to zero,
fire off your high speed camera and hit the L as hard as you can with a
hammer (to make the main chuck rotate) - reveiw the high speed camera data
to see how good tracking is.


** Posted from http://www.teranews.com **
Greetings William,
The goal is to drive two spindle mounted chucks at the same speed so
after a part is machined on one end in the master chuck the slave
chuck can grab it. After the part is clamped in the slave chuck the
master chuck releases it. Then the rest of the work can be done on the
other end of the part. So the two chucks must be spinning at pretty
close to the same speed when the swap occurs. So if the master is
spinning at a certain fairly steady rate and if the slave can then
spin at the same rate I'll be OK. I realize that the slave will always
lag a little as far as angular position goes. But as long as the lag
is unchanging then the two spindles can match speeds.
Eric

That's really neat and elegant. Hope it works!
-j
.

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