Crowned Pulleys

| April/May 2000

492 Congress Street Fairfield, Connecticut 06430

A story that has always intrigued me is the comments that occasionally show up in GEM regarding the function of the crowned pulley as used on flat belt drives.

I got involved with crowned pulleys quite a few years ago. I was living in an old house heated by a cast-iron kitchen range. It seemed I spent all my spare time cutting and splitting wood, which usually was damp and hard to get going. After going through one winter this way, I decided to make an effort to build a cord wood saw rig. This was during the late Depression period and scrap parts were plentiful and cheap.

It didn't take long to locate several saw mandrels, some saw blades, belting, and a very nice one-cylinder upright engine of about 5 HP. I believe the engine was a Fairbanks-Morse, but I can't be sure. I remember how well the engine ran and how it would throttle down. Of course, it was a four-stroke water-cooled design.

Among the parts I had accumulated was a very nice crowned pulley that was a perfect fit on the gas engine. I was a little puzzled by the crowned pulley, as to the reason for the crown, but since it fit on the shaft okay, I decided to use it. Of course, as soon as I started the rig up, the belt came flying off. Since I was anxious to get going and cut some wood, I put a stake alongside the belt. This worked, but I could see it wasn't very good and was tough on the belt.

After some more shuffling of pulleys, I came up with a flat pulley for the engine and decided to try the crowned pulley on the saw mandrel. Of course, this worked very well. The crowned pulley kept the belt right in the middle and I was slightly mystified. But since I needed wood, I thought I'd try to figure it out later.