Re: Couplings

"Alfredo Sola" alfredo@... alfredosola wrote: Good day Johann et
al, Following your advice on couplings, I found this. It's Chinese but
looks pretty decent:
<http://cgi.ebay.de/3x-Kupplung-Drehstarre-fuer-Schrittmotor-1-4-NEU_W0QQitemZ160382401978QQcmdZViewItemQQptZMotoren_Getriebe?hash=item2557893dba#ht_3281wt_912>
Also the price can't be beaten at 9,90 euros for 3 units! what do you
think?

Hi Alfredo;

If those are meant to couple a motor to a leadscrew, I don't think much
of them. Unless your alignment is absolutely perfect, a solid coupling
like that can break the end off your motor, or the stem off your
leadscrew. What you want for a situation like that is some kind of
flexible coupling, which will allow for some imprecision in the
positioning of the two shafts being joined. There are several basic
designs for this sort of thing; such as the "Lovejoy" type, which has a
pronged head for each shaft and a rubber "spider" that fits in between
them, or one that has a helical slot cut in the middle, which acts like
a spring, or one that has metal ends but a solid rubber center portion.
The Taig mills I sell have metal cylinders on the end of the motors and
leadscrews, which are bored with four facing holes with stiff nylon
tubes making the connection. Any of these solutions would be better
than what you're looking at on Ebay.

Also, the simple set-screw attachment will tend to give you problems
over time. A better design is the clamp-type connection, which uses a
screw to compress the split end of the coupling over the shaft. This is
less likely to loosen, and if it does, it won't make a gouge in your
shaft that makes the coupling very difficult to remove. Yes, you can
save some money going with those cheap solid couplings, but you'd be
setting yourself up for losing a lot more down the line, not to mention
the frustration factor of ruining parts and having to tear your machine
apart to repair it and wait for parts to arrive before you can get back
to work. I'm not sure who sells couplings in Europe, but I'm sure you
can find some like this:

http://www.anaheimautomation.com/products/coupling/flexible-coupling.php?tID=114&pt=t&cID=32

Good luck;

Andrew Werby
www.computersculpture.com