Re: [CAD_CAM_EDM_DRO] How fast is too fast on a Bridgeport?

Hi Jeff,

Are you sure the table really is moving at 1200ipm? Assuming you have
your steppers direct coupled and are using 5 turn per inch ball screws
i.e. 0.2" per rev then 20ips=1200ipm=1200/0.2=6000RPM - this is pretty
darn speedy for any steppers I've ever heard of on this planet -
particularly in the NEMA42 size. Keeping in mind steppers lose power at
speed, I seriously doubt you are spinning your steppers at 6000RPM.
Double check your calculations.

I have a BP clone with NEMA42 servos and am quite happy with rapids in
the 100-120ipm range. I can go faster but it gets too scary and I'm not
doing high speed machining - i.e. fast feed rates. I've found the
biggest limitation to high speed machining is my spindle speed
limitation - even with a VFD - I can't get much more than about 4800RPM
before real funny noises start emanating from the belts. This limits
feed rates with typical tools to about 24-30 ipm on relatively light
cuts. So blazing fast rapids don't really get you much more
productivity if you're only cutting at 24ipm...

As for your question about the table continuing to move after you
release your finger - it is due to momentum and inertia type issues.
From whatever your rapid speed is, it takes a finite amount of time to
decelerate your big mass of iron. Based on the accel/decel settings you
have entered into Mach2, this will result in a short or long decel time.
When you release your finger, Mach2 will produce a controlled slowing
down step rate (decel) based on your settings. If you try to accel or
decel too fast your table momentum will simply overpower your motors
holding torque and you will lose steps.

Cheers, Peter



washcomp wrote:

>I'm tuning my NEMA 42 stepper motors with MACH2 and find that I can
>make the table on my Bridgeport move at blindingly scary speeds (in
>excess of 20 ips). I've slowed it down, but don't have a clue what
>is an approprite speed and accelleration setting for the X, Y and Z
>axis? I'm currently running 1000 steps per inch. The table also
>seems to continue to move (from momentum, inertia) after I release my
>manual jog button. Is this normal?
>
>Thanks and regards,
>Jeff
>
>
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