Ignoramus6705 wrote:

On 2010-07-29, RogerN wrote:

"Ignoramus6705" wrote in message
...
My friend told me that he saw something written somewhere that
Bridgeport Interacts cannot mill (bore) a precisely round hole,
because of stretch on the servo motor timing belts. What do you think
about this statement.

i

I would think it is minimal since an entire turn of the handwheel is 0.2" or
so. I would guess belt stretch to make less than a half thou difference.
But if it does affect your parts, you have the capability to put DRO scales
on your mill and use them with EMC2 instead of the motor encoders. That's
what my mill has, an Anilam control with Anilam DRO scales , the motors have
tachometers on them, they are stable even with backlash.

Roger, there is no handweel attached to the ballscrews.

No, but his point was the one full revolution of the ballscrew is a
pretty small movement, and any belt stretch issues aren't likely to
cause more than a couple degrees of ballscrew position error. I think
you said 2.5mm ballscrew pitch, so perhaps something like 0.0006"
positioning error under belt stretch? Backlash and proper backlash
compensation will be a much bigger factor in accurate circular
interpolation.