Re: My Sherline speed

Hi,

If I calculated correctly, the speed at which you begin to miss steps
is 800 full steps per second (4 revs / sec). This speed is a little
tricky because it may be at the very edge of the motor's start/stop
speed so several different causes may be at play here. To tell which
one:

When you say it misses steps, does the motor stop or continue on?

If it continues on, "ragged" step pulses may be the cause. Try CNC
pro and see if it makes a difference. It has extrordinarily smooth
step pulse timing.

Also if it continues on, listen to the motor. If there is a "popcorn"
type sound, you may want to check your grounding and wiring because
that would indicate noise getting into your step pulse line. Noise
shows itself by moves being longer than they should be.

If the motor stops, it could be midband instability. Your motor
current and power supply voltage makes this a possibility too. Again
listen to the motor. If the motor makes a descending pitch "growl"
just before it stalls, then it is midband instability. Sometimes it's
difficult to catch because the "growl" lasts less than 1/2 second
before a stall.

You can sometimes accelerate thru the resonance region (4 to 15 revs
per second) at a higher rate of acceleration to reach the stable
region beyond. Midband instability is most severe just past the speed
where torque just begins to drop off.

Mariss

--- In CAD_CAM_EDM_DRO@y..., Randy Gordon-Gilmore <zephyrus@r...>
wrote:

> Thanks for the replies, Chris and Al and Tim
>
> The Sherline stepper motor is a Shinano Kenshi SST57D3201. Data

sheet is at

>
> http://www.shinano.com/pdf/SST57D.pdf
>
> It is a 3.2V, 2-amp size 23 motor, double 1/4" shaft, 134 oz-in

holding

> torque and about 95 oz-in pull-in torque. I have it hooked up

using half

> the coils (one end plus center tap) and the resistance is called

out as

> 1.6ohm per phase. The chart shows it keeping its full torque out

to about

> 1200pps with a 24V, 2A chopper drive.
>
> The computer is a P100, with no provision physically in the case

for a

> CD-ROM, and I don't plan to use one.
>
> The Sherline leadscrews are 20tpi, so 8000 half-steps are an inch.

I

> should have full torque at 9ipm, and it feels like it. I'm nowhere

near

> maxing out the speed that DeskNCrt is capable of with this

processor, but

> at say 12ipm the mill will miss steps occasionally and randomly.

Maybe I'm

> just hitting a resonance at that speed? I've been sneaking up in

speed,

> but this weekend I'll just try a significantly higher rapid speed

and see

> what happens.
>
> But from your post, Al, it sounds like CNCPro would be a good and

tested

> choice. :-)
>
> Best regards,
>
> Randy
>
>
> Randy Gordon-Gilmore ,----.___________ ______________

_________________

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