RE: [CAD_CAM_EDM_DRO] Belt tensioners on toothed belts

>
> I just finished helping a customer with a servo driven plasma
> table and I was surprised to see spring loaded idler wheels
> on swing arms (like the old reel-to-reel tape drives) being
> used to tension the belts on the toothed pulleys. The
> tension mechanism was a coil spring and was not very taunt so
> that when the motors changed direction the belt would bow out
> or in, depending on the direction. Seems to me the flexing
> of the belt would introduce some errors. Do any of you have
> any experience with a design of this type? Seems like a way
> to move the motor to maintain belt tension would be a better
> approach. I guess if the belt tension was strong enough it
> might be a better solution (?)

By coil spring do you mean like you'd find in a clock?

If so, these are negator springs. The reason they are used is the tension
is constant, unlike other type of springs. To increase the force, you can
'wind them up' a bit, that may help.

The springs are used in cable winders, clocks, and tapes measures, oddly
enough. Grab a tape measure, pull out a bit & measure the force. Pull out
more of the tape and measure it again, it'll be the same.

If you have a need for a small constant force, use a tape measure. Reducing
backlash on a small mill (say doing PCBs) comes to mind.

Tony