Here is an easy belt tensioner I designed that helped quiet my bed resonance. I removed the belt springs and had this installed in a few minutes. In a departure from the metric sizes, I decided to go with a #8-32 x 1 1/4" hex socket cap head screw and an 11/32" nylon stop nut as my tensioner screw. It is just a little bigger than an M4 of the same type. It has proven to work beautifully. The slide is a perfect fit and incorporates angled guides to prevent pop out.
Printed with 5mm brim and a speed of 35 mm/s.