Re: Timing Pulley Accruacy and Servo shaft runout

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Polaraligned"
<polaraligned@...> wrote:

>
>
> > 5 thou ? on a new motor ? I shudder to think that is even possible !
> >
> > I would think that is scrap from the trash bin of the QC department.
> > or it fell on the floor from the top of the rack.
> >
> > Dave
>
>
> Well Dave, I retested the motors. The worst was .005" the best was
> .0002". The best was a new Ametek motor.
> Many were .002" runout (I tested 5 Baldors)and these new Baldor motors
> came to me in a sealed factory box. The motor was shrunk wrapped to a
> plywood bottom.
> Boxes are in fine shape, no damage here. The Ametek that tested
> so nice has a short 1.5" shaft that appears well machined.
> The Baldor servos have longer 2.25" shafts that don't have nearly
> as nice a finish as the Ametek servos. But the runout is there
> regardless of the surface finish. The .002" motors are the ones
> I plan on using on my machine and I am struggling to see if that
> runout can cause any significant error. I would think that as
> the belt gets tighter and looser the teeth engage a bit deeper, or
> a bit shallower and that error would be a function of the tooth and
> how deep it is going into the pulley. I would imagine that a spring
> loaded tensioner would eliminate the runout as a source of error.
> How far off base am I here?
>
>
> Scott

I don't think you'll find any noticable error from the 0.002" runout.

The motor would appear to have moved to the side by 0.001", then to
the other side by the same.

the shaft centers would be the long side, the diameter the short side
and then calculate the hypotenuse by the +/- 0.001"

that would yield somewhere around 0.0002". then calculate how much
rotation occurs with that movement on your driven pulley. then divide
that by how many TPI your screw is.

I still find it hard to imagine such error on a motor. But, I have to
believe your measurements.

Dave