Re: [CAD_CAM_EDM_DRO] tuff enuf?

jmw@... wrote:

> Over the weekend I found some nice looking PMDC motors at C&H. I
> bought a pair of GE units rated at 100VDC, 8.1A. The maker's plate
> also had a box labelled heat or duty, I forget which said 2 MIN. I
> assume this means two minutes of max output. No speed on the plate,
> but one of the old motor hands fired it up and felt the spinning
> shaft and pronounced it "about 2000." The plate also mentions 75
> ft/oz. The things have a 5/8" keyed shaft and a smaller tach or
> encoder shaft in back. One motor had a hockey puck sized device made
> by Siganltronics coupled to its back shaft. The motors themselves are
> aobut the size of one pound coffee cans.
>
> So, my question to you who've been there before, does this sound like
> enough for a Bport-class hobby shop conversion?

Probably, depending on the speed, however. I am running 75 V, 1.54A
rated motors on mine, with a peak current of about 5-6 Amps. These motors
have a rating point of 1/8 Hp at 1725 RPM. Extrapolating from these numbers,
I figured out that at 5 A (assuming armature reaction is negligible), and with
a 2.5:1 belt ratio to a 5 TPI ballscrew, I should get 1000 Lbs of linear
force at the table. This seemed like enough to me.

> It sounds like enough
> to me, especially after taking into account a 1:2 or 1:3 belt ratio.
> But C&H has a 10 day return policy, so ... keep em or return em for
> something bigger? BTW, C&H says they sold "hundreds" of these and
> have three left.

Well, it might be a good idea to connect a photocell or other arrangement
to measure speed, and put a known voltage on it. Assuming the speed at
100 V is not too much above 2000 RPM, that should work fine with just
a modest belt reduction.

>
> Also got a nice 90VDC 7 AMP motor for the quill, also with a
> backshaft extension for tach/encoder. Plenty of these two, plus a
> half size version that runs at (as I recall) 35VDC.
>
> Finally, there were some very fancy looking things about half the
> size of a soda can, and really heavy. Markings just serial and part
> numbers. I asked, "Are these DC tachs," and the man said "Yep," so a
> bought three at $10 each. Plently more of these, too.

Sounds good!

Jon