How to assemble a tensioning pulley?

[GGA]

I want to assemble a self-standing pulley to apply side force to my turntable belt.

I found a miniature precision brass pulley with a 1/4" bore and 2" diameter that looks like it would work fine as a pulley, however, I can't figure out how to assemble it into a self-standing unit.

I'll need a vertical shaft but what will hold the pulley up? Also I'll need to attach the shaft to a heavy base and make sure it is 90 degrees.

I also found a grooved pulley with the same specs and a set screw. The screw would allow the pulley to be fixed to the shaft but now the shaft needs to spin.

Anybody got any ideas?

[454Casull]

If your belt is positive-drive, you can try one of the spring tensioners from McMaster-Carr.

Aesthetics may not be ideal.

[Soundminded]

Originally Posted by GGA

I want to assemble a self-standing pulley to apply side force to my turntable belt.

I found a miniature precision brass pulley with a 1/4" bore and 2" diameter that looks like it would work fine as a pulley, however, I can't figure out how to assemble it into a self-standing unit.

I'll need a vertical shaft but what will hold the pulley up? Also I'll need to attach the shaft to a heavy base and make sure it is 90 degrees.

I also found a grooved pulley with the same specs and a set screw. The screw would allow the pulley to be fixed to the shaft but now the shaft needs to spin.

Anybody got any ideas?

The pulley shaft needs to be supported by a journal bearing. A sleeve bearing or bushing is another choice but the shaft will have to ride on a support from below. This could be a low friction teflon or nylon plate or block anchored to the base, possibly with a hemispherical cup drilled in it acting as an end bearing.

If you want to adjust the tension manually you'll need to mount it on an adjustable base which can position it with a long screw. If it is to be self tensioning then a spring should apply tension between the pully assembly and the fixed outer housing. The pully assembly would have to be able to slide usually by means of a pin in a slot on a base plate or pivoted by a tensioning arm. This is the same principle used for tensioning on some magnetic tape decks for maintaining tape tension. Spring tension is very critical to be certain the belt is kept sufficiently taught but not overstretched. If you have a machine shop you should be able to fabricate this yourself. Otherwise a commercial machine shop and mechanical designer should have no problem producing it for you. It may not be cheap.

The tensioning pully, motor, and turntable should all be mounted on a common base to maintain the same geometric relationship and keep the adjustable pulley from moving independently of the other two. That would defeat its purpose.