Why crowned pulleys and bandsaw wheels?

[Moby Duck]

Great explanation on why pulleys need to be crowned, I understand at last.
Now can you tell me which wheels on a 2" x 72" Belt Grinder with 4 wheels, (2 on the platen, 1 for tracking, and 1 being the driven wheel),need to be crowned. There is much debate on this on the web. Some say all 4 wheels, some say just the tracking wheel, some say just the driven wheel and some say both the driven and tracking wheels need to be crowned.

[tonyfoale]

Great explanation on why pulleys need to be crowned, I understand at last.
Now can you tell me which wheels on a 2" x 72" Belt Grinder with 4 wheels, (2 on the platen, 1 for tracking, and 1 being the driven wheel),need to be crowned. There is much debate on this on the web. Some say all 4 wheels, some say just the tracking wheel, some say just the driven wheel and some say both the driven and tracking wheels need to be crowned.

There is always some misalignment between pulleys due to manufacturing tolerances etc, so if you crown them all then each will be trying to align the belt on itself. So you'll end up with the effects from each pulley fighting the effects from the others, thereby putting some unwanted and unnecessary stress in the belt.
If you only crown one then that one will align the belt which will then find its own position on the other pulleys provided that they are wide enough. Of course with a tiltable tracking wheel you can adjust the belt centrally over the other pulleys.
So which wheel track with? I think that the answer now becomes clear, it is unlikely to be a good idea to use a crown wheel to align the belt and other to then realign it elsewhere.
So it's one crowned pulley which has the tracking control.

Strange that this topic came up yesterday, because then I pulled that little Burgess saw apart (which features at the beginning of this topic) to give it a 50 year service. The drive belt which the blade runs on is badly chewed up and the top pulley has seen better days. 2 new belts should arrive today, they should see me OK good for the next 100 years. The wheels are made of a hard plastic with no rubber tyres so I shall machine the rims smooth again and glue on some tyres cut from an inner tube. I'll only be crowning the top wheel.

[Moby Duck]

Thanks, you have confirmed what I already believed about the best wheel to crown but I needed your opinion to be sure.

I shall watch for the Gyro post.

[tonyfoale]

Thanks, you have confirmed what I already believed about the best wheel to crown but I needed your opinion to be sure.

I shall watch for the Gyro post.

The gyro explanation has been posted here http://www.homemadetools.net/forum/g...ut-maths-65745