pulley center distance vs. belt tension

I'm using a HTD5 15mm belt to join a big stepper with a shaft, I've used belt / pulley calcs available here:

SDP/SI

I've left 15mm of space on both sides of the stepper, to pull it back a bit and have some tension on the belt. Is that normal practice, or should the pulleys be at precisely the distance shown by the calculator? I'm asking as I've pulled the belt a bit to have less slack on the belt, but after some running, there's tiny bits of rubber under the belt, as if something is rubbing or stressed too far. The belt is not pulled too hard, I'd say it's medium tension, I can still pull it with my finger and it will give slightly. Just wondering if tiny rubbery residue under the belt is normal or not.

Regards,
dsc.

Puller centre distance isn't an exact science.
The most accurate way to set tension is by harmonics aka you ping the belt and measure the frequency at which it resonates.

For something non-critical, I'd probably verge on the side of lose rather than tight. I wouldn't worry too much about little bits of rubber during initial use, however I'd keep an eye just to make sure the belts not wearing unevenly.

Cheers m_c, helpful as usual.

Regards,
dsc.

According to one supplier's bumph I read, belt should be tight enough to stall the stepper rather than skip teeth.. so some trial n error testing needed (and maybe a sacrificial belt!). Can't find the reference at the mo tho :(

For this application I might just do it 'tight enough' and keep my fingers crossed:)

Cheers irving2008.

Regards,
dsc.

I always like to set the belt tension so that I can just about twist it between my fingers 90 degrees in the centre of the run. It won't twang like a guitar string, but equally doesn't sag under its own weight.