Re: Belt pulley and belt care

Posted by Rod (NH) on September 01, 2003 at 22:40:02 from (12.148.160.138):

In Reply to: Belt pulley and belt care posted by Wayne M Kittler on September 01, 2003 at 18:31:09:

Hi Wayne,

I don't know about the feed mill but perhaps I can help on the cordwood saw.

Circular saws cutting wood are best run between 6000 and 9000 surface feet per minute (sfpm). Don't ask where this comes from. I don't know. It's just been my understanding for a long time. Maybe Dad told me. Whatever.

The cordwood saw on my AC-B is run between 7000 and 8000 sfpm, depending on throttle position. I generally run it at half engine throttle when using the saw and that puts it up around 7700 sfpm. It has worked fine at that speed for many years.

You take the desired sfpm and divide by the saw circumference (in feet) to get saw rpm. e.g. [sfpm]/[saw diameter, ft x 3.14] = saw rpm. Given the saw rpm, multiply it by the ratio of the driven pulley diameter to that of the drive pulley (tractor belt pulley) to get the required speed of your belt pulley.

The following would be an example:

saw diameter = 30" = 2.5 ft
saw circumference = 2.5 x 3.14 = 7.85 ft
desired saw sfpm = 7000
desired saw rpm = 7000/7.85 = 892
belt (drive) pulley diameter = 9.5"
driven pulley diameter = 8"
ratio of driven to drive pully diameters = 8/9.5 = 0.84
required belt pulley speed = 892 x 0.84 = 750 rpm

You will need to check your tractor belt pulley speed spec to see if the calculated speed is possible with a reasonable throttle position. If not, you may have to juggle the saw sfpm some or, more preferably, the driven pulley size to get a workable combination. Don't forget that your belt pulley speed spec is likely given at wide open engine throttle, a condition that you probably would not want to run at while sawing. I calculate my actual belt pulley speed using the stated spec from the manufacturer and determining what it would be at about half engine throttle. That puts the engine about halfway between idle and full throttle speeds and the belt pulley speed is reduced accordingly at that throttle setting.

Rod

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