By Daniel Ouellet, originally from an owwm.org forum postA while ago I
posted a question about crowning bandsaw tires, wondering why most people use an inverted V-shaped crown instead of a rounded crown as you see on commercial machines. The low-down on the answers I got is basically that a V-shaped crown is easy to produce and works fine for blade tracking. Bob Vaughan also issued a challenge, or at least, that’s how I took it :-)
“If there was a way to get the round crown EASILY with stuff a woodworker might have in his shop, then that would be the norm.
Come up with a plan, execute it, and get back to us with photographs. We all may learn something.”
I’m happy to report that I found a pretty easy way to get the job done. A picture is worth a thousand words:
It is basically a two part cradle. The fixed cradle can be clamped on a disk sander table. The second cradle is attached to the fixed one via two bolts so that it can swing. The bandsaw wheel mounts on a shaft that sits in the middle of the swinging cradle. The trick to a perfect rounded crown is to get the center plane of the wheel at the same level as the axis of the cradle. I did this by getting the wheel to rest on a wood block that I shaved down until it was the right thickness. The hydraulic jack under the jig is a nice help to keep things steady. Pump it up a couple of times, then get the wheel to go around two full turns, and repeat until you are done.
The horizontal distance from the sanding disc to the axis of the cradle determines the radius of the crown. I used a 5 inch radius as it matches quite closely what I have on an 18” Taiwanese bandsaw (that will soon be up for sale). The Crescent 20” that I’m rebuilding came with old tires that had never been crowned, which gave me an opportunity to test the set up without fear of wrecking a brand new tire. The results are excellent:
For the record, I used an 80-grit disc.