Re: which steppers to buy?

CNC List:

At 11:25 PM 5/27/01 -0400, Chris wrote:

>.....snip.....
>Now mulitply by (as a guess) about 4 if you
>want any feedrate at all from a stepper. Scale by any reduction...
>.....snip.....

It seems losing steps on a CNC stepper system is a bad thing. A real bad
thing. So, for CNC applications, does anyone have a rule of thumb for
motor torque versus maximum torque to be controlled? Is 4 as mentioned a
reasonable number? I've also heard 8 or 10. I assumed the 8 or 10 was for
static motor torque (no motion) to account for any drop in motor torque
with speed.

What would be a reasonable number if you knew the velocity
required? Knowing this and having the motor curves you could determine the
motor torque for that speed. What would be a reasonable ratio between
motor torque and required machine torque at a given velocity to guard
against missing steps?

I like the idea of testing rapid and cutting torques with a lever arm and
weights. I've also heard you can use a torque wrench. But once you have
these two numbers, you still need some idea on how much buffer (safety
factor) between the actual numbers and motor torque is needed.

Thanks.

Hugh Currin
Klamath Falls, OR
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Hugh & Denise Currin
currin@...
Klamath Falls, Oregon USA
541/884-3023
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