Re: [CAD_CAM_EDM_DRO] Motor drive belt tightness

I have always relied upon the calculated center to center distance based
on the pitch diameters and belt length. this values are given bythe
manufaturrs and generally you can find the ctc values for given
combinations intables suplied by he manufacturers. Terms like "tight" or
"really tight" are subjective.

I have used this method sucessfully for a lot of years going back to the
"Good old days" of NC. (BTW - anyone who speaks affectionately of the
"Good Old Days" either wasn't there or will also lie about other
things). I have fitted timing belt reductions to Planer Mill Conversons
driving large tables with excellant results. One machine fitted 14 years
ago and still running 24/7 is on a G.A. Gray 24' Planer conversion. The
4 axis CNC control drives the table using an Allen Bradley Servo Drive
and Motor. The Servo Motor output is 410 FT-Lbs, this is coupled to a
compouded timin belt reducton with a final ratio of 10:1. This drives a
4" Diameter ball screw positioning the 45,000 pound table at 200
Inches-per-Minute. Positioning control is done using a 240 Line pe
Revolution Encoder mounted on the dead end of the screw so that it
doesnot see the drive train torsional windup.

This timing belt reduction runs in an oil bath similar to a conventional
gearbox and stills uses the original bearings and belts instlld 14 years
ago althougth the ball screw has been rebuilt several times and replaced
once due to wear.

gary

CalBoy101 wrote:

>I bought a retrofitted Bridgeport clone mill that has size 42 stepper
>motors on it. The controller was blown up and in the process of trying
>to debug it the previous owner had loosened up all the belts on the
>machine.
>
>It has 5/8" wide Gates type cogged belts on X and Y and a 3/8" wide
>Gates belt on the Z axis.
>
>Is there a "rule of thumb" for how tight these belts should be?
>
>Thanks,
>
>Paul T.
>
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