On 29/01/15 22:17, Terry Coombs wrote:
David Billington wrote:
On 29/01/15 18:18, Terry Coombs wrote:
Tim Wescott wrote:
On Wed, 28 Jan 2015 22:58:41 -0600, Terry Coombs wrote:

Got any stepper motors for cheep? I think nema 34's will work , I
want to power the X axis and maybe the Y on my benchtop mill . I
have (or have components to build) controllers and power supplies ,
can fabricate mounts and the rest in house . I actually had an 18v
HF drill motor all but mounted , using a PWM controller and a 13.5
volt supply . At the speeds I need it didn't have enough torque -
though I may revisit that setup now that I can cut gears .
And speaking of cutting gears , how about cutting pulleys for
cogged belts
, anybody got experience doing that that they'd like to share ?
Having worked with stepper motors in space- and power-constrained
devices, I am highly prejudiced against them. That doesn't mean
they won't work -- it just means that I've had bad experiences. I
much prefer a servo motor driven by a feedback loop (at least, when
I get to design the controller).

Check with Herbach & Rademan (http://www.herbach.com) for motors.
They may not have what you want, but they have lots of stuff in that
sort of size.

For pulleys and belts and whatnot, check Stock Drive products. They
aren't a surplus place, but they have fair to middlin' prices on
fair to middlin' stuff, and they'll have the same thing next year. I've
had good success tossing together mechanisms using their parts.
Thanks , I'll check that supplier for motors . As far as gears
and pulleys , I'm equipped to make those , from casting the blank in
aluminum or brass to final machining . I have lots more time than
money ... and a big pile of casting stock .

Do you heat treat the aluminium at all as my limited experience with
as cast items is it is soft and gummy and not nice to machine. A mate
that worked as a designer at a company the made a number of products
with aluminium castings said they always heat treated them, not for
strength reasons, but for machinability as the surface finish
achieved was much better and some other benefits.
My experience has been that extruded stock makes gummy castings . Material
that was originally cast usually machines just fine . My usual practice is
to dunk the casting in water as soon as it comes out of the mold , this both
helps machineability and helps get residual molding sand off the piece .
Letting a casting stand for a few days also helps , as I understand it
aluminum gets some temper from just aging .

Sounds like you are doing a basic post cast heat treatment with that
procedure. The castings I've had done were done commercially with a
standard casting alloy, LM25?, and were soft and not nice to machine.