Re: CNC Servo motor gear ratio: overheating. EMC step rate. Tablespeed

Just thought id mention that I considered these motors for a mini
mill (taig) and abandoned the idea and went with larger motors. You
may want to do the same if planning on 3/4 inch endmills.

Mark

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
>
>
> Tim Goldstein wrote:
>
> >Jon,
> >
> >We discussed these particular motors previously on this group. The
> >consensus was that these motors were not a good selection for
direct
> >drive on most mills. The only specs that are on the Camtronics
website
> >are:
> >
> >These motors have a 5/8 diameter shaft 1.75L. The bodies are 4"
diameter
> >and 4.5" long. It has a standard 3.250 DBC on the front face.
about 50
> >oz in per amp torque and RPM is about 900. 36 VDC PM brush ball
> >bearing.
> >
> >So at 25 rpm for his 5 ipm which I am assuming is a speed he
plans to
> >actually cut something at I think he will be risking getting very
hot
> >motors and potentially frying them.
> >
> >
> Yes, I think I misunderstood his original post. I thought the 25
Lbs
> of linear force to move the table was the total force he needed,
but
> he doesn't actually say that. he gives no indication whatsoever
of what
> cutting forces will resist table movement. I think it is safe to
say
> that these motors COULD handle the 25 Lbs force without trouble,
> but if he is cutting metal, that is another story. With a 900 RPM
> limit, he is limited on what he can do in the way of reduction,
> although 450 RPM on a 5 TPI screw is still 90 IPM, so maybe
> a 2:1 reduction would still be acceptable. I also suspect these
motors
> could be run over 900 RPM (over 36 V) without harm. If these are
> the Ametek motors that have flooded the surplus market, the 4 Ohm
> (or worse) armature resistance is the bad news on them. That makes
> them VERY prone to overheating on any continuous load.
> On any servo application where motors are drawing over a couple of
> amps, I really hate to see over one Ohm of resistance.
>
> Jon