Re: Belt tensioners on toothed belts

The error introduced is directly related to the slackness of the belt,
the diameter of the pullies and the screw pitch. For acme threads it
will be negligible and I don't think it is worth bothering with
tensioning at all, for ballscrews the error would be more significant.

IMHO a better solution than sprung idlers or moving the motor would
be adjustable, but non sprung idlers. A couple of bearings (depending
on the size of the belt, cheap skate bearings would do) on a sliding
mount would be my prefered method

Chris

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "caudlet" <thom@...> wrote:
>
> 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 (?)
>
> I do know that in this circumstance it ended in disaster. The pivot
> arm became loose and the arm got cocked at an angle. It was okay with
> the axis running in one direction but it acted almost as a brake in
> the other direction and since the motors were large it just ran until
> the fuse blew (about 30 msec after the servo drive blew!).
>
> Tom Caudle
>