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RPM pulley size question


Oct 16, 2016
My Delta table saw has a 5" pulley on a 1725 RPM motor and a 2.5" pulley on the table saw shaft, this will yield the desired 3100 RPM for optimal performance.

My 1725 motor is no good anymore and I have a 3450 RPM motor that would make a great replacement.

How do I achieve the desired 3100 RPM from a 3450 motor?
Ha, that's exactly the ratio and pulleys that I have on my 1971 10" Delta Contractor's Saw. Works great ror 3,100 rpm.

Interestingly enough my 9" Delta Contractor's Saw had the same combo but reversed. This was factory ratio with an optional 1 HP motor. Worked great with 1" stock or less but if routinely cutting thicker hardwoods a slower rpm would have been in order. Since I rarely cut thicker stock I never changed it.
Well...it is a Delta saw so one must wonder if anything really matters. But, one must also question why it was built the way it was built....there must be a reason they used a higher cost 4 pole motor instead of a lower cost 2 pole motor.

My guess is a 2 pole motor would turn the saw into one of those tools where it starts up (notably more miserable with a 2 pole motor) and sounds great until you stuff some wood into the blade at which point it bogs down and gets unhappy. Chances are it's already borderline unhappy even with the 4 pole motor.

All this is assuming the unknown HP of said saw is around 1HP, and it is a single phase motor. If it is a 3 phase saw of 50HP or so, you probably won't notice any bogging.
Twice the motor speed, you need half pulley dia, simple.

As an aside, I was cutting up some rough lumber for firewood. I hated to use a decent 10" blade, so I used an old 7-1/4 skilsaw blade. I was amazed how well it cut. I've never put the 10" blade back on the saw.

If I'm doing a job that requires me to cut quality plywood I'll "splash out" on a new narrow kerf 40 tooth blade for about $10, from HD. A new one for each major project. Beautiful cuts !

Very narrow kerf, low hp requirements. It'll cut 1-1/2 inch thickness.

I've never worried about speeds, just did it.

Try it.
For V-belt pulleys I think the "effective diameter" of the belt is closer to the middle of the belt so the ratio may work out a bit differently than using the pulley OD. Might be a bit getting a bit OCD here...
Tip speed is more relevant than rpm. You run 9" blades faster than 10", 10" faster than 12", you get the picture. I'm not sure 3100 rpm is optimum for a small diameter blade. I think that may more to have to do with the build of the trunnions, yoke, and pulleys to not over stress the machine. If the saw is stout and higher speed or HP were options, I'd run the blade a little faster. If not, I'd hesitate unless I was sure the machine could handle the additional load. Dave