Mike,

You don't need an idler. You need to get the right type of belting. I
recommend what they call flat transmission belting. You can get it from
MCMaster-Carr.

http://www.mcmaster.com/

It's less then a buck a foot. The bigger cost is getting a clipper
lacing tool, or you could use alligator lacing. The trick is trying to
figure out the right length. I normally rap the belt around the pulleys
and pull it tight. I mark the length on the belt, and then subtract out
the length of the clipper lacing, then I subtract out another .5" to 1"
and cut the belt. If it is to lose, then cut off just the clipper
lacing from one end and try again.

If the tension is right, then you don't need any dressing.

Vince




wrote:

Anyone here familliar with flat belt drives? I have an old-style floor
drill press that uses a flat belt to drive the pulley on the upper
cross shaft from the lower one and I want to put it back into running
condition. The belt has a tendency to slip under load and so I added an
adjustable idler near the lower driving pulley, on the side of the belt
that goes down as it is running, but now the belt wants to slip
sideways off the lower pulley when the idler is on. The belt tracks ok
when the idler is not in contact and I tried shimming first one side of
the idler shaft and then the other, thinking the alignement was off,
but this only seemed to make things worse. The idler shaft is paralell
to, and level with, the driving and driven shafts so far as I can tell.
Does it matter which side of the belt the idler is on? The original
belt was missing so I used one made from what looks like black rubber,
1 3/4" wide and 1/4" thick, and running at about 300 rpm. So maybe
rubber is not suitable for this application? Any advice appreciated.
Mike