Re: Sherline CNC stepper motors getting "stuck"

Sounds like electrical noise from the spindle motor is causing
interference. I'm reading between the lines here and guessing you
had it off while setting the max speed - then turned it on to make
the part? I've heard of this happening to other Sherline owners as
well.

If so, you'll need to work on shielding the logic cables, adding
pull-up resistors to the port lines, or running the wires a bit
differently.

It sounds counter-intuitive, but more current can reduce the top
speed available with a stepper motor. I'm no expert on the subject,
but I believe it has to do with the pole pieces being magnetized more
strongly under high currents - making it harder for them to rapidly
switch polarity.

Lastly, if 100mm is long enough to reach the top speed, then yes,
it's a valid check on the speed settings to try and jog that
distance. The max speed will never be exceeded in a program, no
matter what the F-word is set to (at least in TurboCNC).

Dave Kowalczyk
Everett WA

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "builder4wd
<builder4wd@y...>" <builder4wd@y...> wrote:

> Thanks for the responses.
>
> When I jog my motors, I set the jog increment to 100 or 50mm, and
> with 20000 Hz acceleration, I can see the motors spin up to max

speed

> at 18000 Hz with no problem. The issue arises when I try to run the

g-

> code. The weird thing is, the part is only a 1mm deep cut in soft
> wood, with a 1/8" size endmill. It's only about 1" square, so the
> motors never really see full speed. The g-code is set to about 11

ipm

> feed. I get this problem even with the motors set to 8000 Hz

movement

> and 5000 Hz acceleration! Do I really have to set my machine to

move

> even slower? My motors are rated at 191 oz-in.
>
> Also, if by jogging motors 100 mm is not a good way to test maximum
> motor speeds, how can I do it? How would I find the optimum current
> settings for the motor? From my observation, it seems that with

less

> current, the faster I can move the motors. With more current would

I

> get more torque, but less max speed?