Idler Wheel and detail of fixed end of idler assembly

 

The idler wheel has been turned from a piece of beech and is fitted with a brass bush.   The rod is of 5mm diameter plated steel (an odd piece I found in my junk-box - I seldom throw anything away!)  The wheel end of the rod is reduced in diameter and has a 4BA thread, (3mm would do just as well), but is plain where it goes inside the bush, with lock-nuts to allow free running.   A self-locking nut would be better but I didn't have one at the time. Note - Never make the spindles and bearings of similar materials, they will wear quite quickly.  A steel spindle and brass or even better, phosphor-bronze bush are to be preferred.  Furthermore, never use aluminium. The diameter of the wheel is not important but should be close to the dimension given in John's plans otherwise a change will have to be made to the position or diameter of the primary drive wheel.  I used the vacuum-cleaner belt as John suggested although any rubber or perhaps plastic ring of circular or square cross-section would suffice. The detail picture shows the fixed end mounted in a rubber grommet.  This allows vertical movement of the idler for disengagement with the drive wheel.   Longitudinal movement is prevented by a screw and washer on the outside (the end of the rod is tapped 6BA), and a collar inside.  This arrangement keeps the idler-wheel spaced from the pressure-box side thus removing the need for an anti-friction washer.