pulley question?

larry merlau

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Delton, Michigan
in another thread i saw where jim delany had told the person the speed at which his bandsaw would run properly due to pulley size configuration.. wel this is for jim or anyone that understand the ratios i have 2.5" pulley on a 1725 rpm motor running a 6.5" pulley on a 12" Bsaw.. am i in the right speed range or should i change a pulley for better use? it seems to be cuttin ok :dunno:

thanks for the help from where ever it comes.
 
hey bart think i need to do something else???? i know that its gong fast than 1725.. i have a 1725 pushing a 2.5 pulley that is connected to a 6.5 pulley that is driving a 12" wheel some how the wheel size needs to enter in a some point if i was using just a 2 to 2 on a shaft it would be running at 4 times the moter speed right:huh: as i see it then its running at arond 630rpm??? thats not even close to what i though was normal speed.. so what do i need to get to get i running upto speed?
 
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Here's the formula:

Drive pulley diameter / driven pulley diameter * input RPM = OUTPUT RPM

So for yours it should be:

2.5 / 6.5 * 1725 = 664

12 / 6.5 * 664 = 1225

Edit...sorry had 6 in vs. 6.5...also the shaft for the 12" is moving the same speed as the 6.5", so it should be swapped in the formula above.
 
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Larry, I think this is how it works. I'm using * for multiplication and / for division.

driven pulley speed = motor speed * (motor pulley circumference / driven pulley circumference)

Note that circumference is linear with respect to either diameter or radius, so either of these measurements may be substituted for circumference as long as you're using the same measure for both pulleys.

To go from rpm to fpm on a bandsaw we remember that the bandsaw wheel rpm is equal to the driven pulley rpm since it is a one piece construction.

bandsaw fpm = driven pulley speed (rpm) * bandsaw wheel circumference

In this calculation circumference must be used, as the circumference is the translation between rotational speed to linear speed by definition.

A quick reminder:

circumference = pi * 2 * radius = pi * diameter

So, for your saw:

driven pulley speed = 1725 rpm * 2.5 / 6.5 = 663 rpm

circumference = 3.14 * 1 = 3.14 (12" is 1 foot even in MI, right? :rofl: )

bandsaw fpm = 663 * 3.14 = 2084 which seems slow (I used many more decimal places for pi and the driven motor speed, so if you come up with 2082 or 2083 fpm just accept this as rounding error) for hardwoods. If Larry mistyped and meant he had a 14" bandsaw his fpm would be 2430. If Larry has had too many beers already and meant he had a 17" saw the fpm would be 2951, about right for hardwoods.

I hope this helps and that I didn't screw up my physics or math.
 
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well darren the driven pulley is 6.5 and reguardless of the differnece there it isnt going very fast???? i am pretty sure that its set up the way it was intended yearas ago its a 40's model of a atlas and cuts ok but i thouhgt jim delany said the rpm or blade speed should be around 3ooo rpm???? if thats the case i am going way to slow.. what are most pulley configs on a 14 " saw?

motor pulley size and wheel pully size?
 
no beers today actuall been a week plus,, saving room for the good stuff coming up:) so it is a 12" mark.. and it is old. older than me even:) thanks for the help so mark do me a favor,, play with the link wes gave us and figure out what pulleys i need to get tyhe right spped on this thing,, 12" wheels i got to make saw dust so i can take a trip soon:)
 
Ok, you're at 2k and you want 3k fpm.

Your motor pulley / driven pulley ration is now 2.5 / 6.5 = 0.38. To get to 3K fpm, you want to increase this ratio by 3/2 (3000 / 2000) which gives a target ratio of 0.58.

There are three ways to do this.

Change the motor pulley:

x / 6.5 = 0.58 ==> x = 6.5 * 0.58 = 3.77" pulley - 3 3/4" will be close enough

Change the driven pulley:

2.5 / x = 0.58 ==> x = 2.5 / 0.58 = 4.3" - 4 1/4" should be good.

Change both pulleys:

new motor pulley size / new driven pulley size = 0.58 - you need to do your own math here.
 
Royall, that wasn't part of Larry's question, so I'm not accepting any responsibility for that. :rofl: Besides, he's a big fella with a bigger beard than me, so I'm sure he can figure it out. :thumb:
 
ok royal your always lookin fer my pitfalls ,,thanks someone has to the motor is a 40's version of a 1/3 hp.. will go get the amps from the tag... so you can tell me if i should or not.. ok its a dual voltage motor,,110 or 220. the amps are 6.1 on 110 and 3 on 220.. its a 116g frame motor.. so there yu have it now what do i do royall???:)
 
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thanks mark, i will get me a 3.75 for the motor..the one onthe saw is original for sure and the motor pulley must have been changed out..

As Mark Said, a 3.75" motor pulley will be about right. It'll get you about 3125 fpm blade speed.

You'll notice a bit of a power loss in resaw type cutting, but probably wont even notice it for 'flat work.'
 
An executive drove from home at an average speed of 30 mph to an airport where a helicopter was waiting. The executive boarded the helicopter and flew to the corporate offices at an average speed of 60 mph. The entire distance was 150 miles; the entire trip took three hours. Find the distance from the airport to the corporate offices.

A car and a bus set out at 2 p.m. from the same point, headed in the same direction. The average speed of the car is 30 mph slower than twice the speed of the bus. In two hours, the car is 20 miles ahead of the bus. Find the rate of the car.

A passenger train leaves the train depot 2 hours after a freight train left the same depot. The freight train is traveling 20 mph slower than the passenger train. Find the rate of each train, if the passenger train overtakes the freight train in three hours.
 
ok royal your always lookin fer my pitfalls ,,thanks someone has to the motor is a 40's version of a 1/3 hp.. will go get the amps from the tag... so you can tell me if i should or not.. ok its a dual voltage motor,,110 or 220. the amps are 6.1 on 110 and 3 on 220.. its a 116g frame motor.. so there yu have it now what do i do royall???:)

I'm far far from being an expert. Just an old ex-mechanic:D BUT, I would run the motor on 220v and please I'm not looking for the 110/220v debate here, but with my BS I had problems the the motor acting like it was under powered and the lights would dim when I started it. The old WW up the street came down one day and was watching me and then looked over the BS. He said "let me try something" and he switched the wires in the motor, and we took the 220v plug off the TS and put it on the BS. Geez, what a difference!! the BS started so much faster and when I cut another piece of the wood I was working on the lights didn't dim and the motor didn't bog down anymore. That is when I became a believer of running all the tools on 220v if it was capable of it. YMMV:dunno:
 
As Mark Said, a 3.75" motor pulley will be about right. It'll get you about 3125 fpm blade speed.

You'll notice a bit of a power loss in resaw type cutting, but probably wont even notice it for 'flat work.'

dont use it for rersawing at all, just curve work. so am i hurting myslef by changing the pulleys? i can cut 8/4 cherry as it is but did get some burning but thats common for cherry..have cut some 8/4 white oak as well, got some junky walnut coming up on the list soon.. so whats your opinion jim? leave it or change it?
 
Whoa, hold on a sec.

According to my calculations, if Larry is running his saw with a 2.5" motor pulley to a 6.5" saw pulley, he should be at 2083 fpm.

Changing the saw pulley only to a 4.5" would get him to 3009 fpm.

Running a 3.75" motor pulley to a 4.25" saw pulley would put him at 4779 fpm.

Running a 3.75" motor pulley to a 6.5" saw pulley would get him to 3125 fpm.

Am I correct? I suggest Larry, that you change only the saw pulley, OR the motor pulley, not both. JMNSHO.

I would agree with you Royall, on one thing, taking the bandsaw off the same circuit as your lights, would stop them from dimming when you run the saw, Putting it on a 220 circuit might help, but your table saw is probably on a dedicated circuit alone, so it gets full power.

Aloha, Tony
 
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