Re: [CAD_CAM_EDM_DRO] Re: Bridgeport servo motors

doug98105 <DougR@...> wrote:

I don't have the specs of my $800 Baldor servos handy, but I know
they're rated 40 in-pound torque. These are on a knee mill a bit
larger than a conventional 42" table B'port. They drive the lead
screw through a cogged belt at 1:1 ratio. I don't know the lead
screw pitch offhand, but it's about 1-1/4" diameter, so maybe 4 o 5
tpi. The machine rapids at 300ipm max.

This talk of reduction ratios to the lead screw got me thinking. I
don't recall seeing anything other than 1:1 on commercial CNC's.

/// One thing to keep in mind about "Commercial" products, they are designed by people too. Doesn't mean they are neccessarily correct. Like the old Allen-Bradley control that was on my mill originally. It never worked reliably from the day it was new. The Z drive board had been replaced countless times. Someone miscalculated. A 3000 RPM servo on a 5 tpi ballscrew needs a reduction. Just the cold facts of belting a servo to anything. Just because something works for a week or more doesn't mean it will work for 6 months. And you're buying servos. Start with 80% of the servos attainable RPM and design the transmission of power from there considering the target linear speed. Of course, we scavenger/builders have to use what we can find and often these servos are limited in terms of voltage by the drives available. Then we use the limited RPM attainable and design the transmission from there. /// Ron




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