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How to determine pulley size?

Started by sawyerkirk, February 06, 2003, 03:11:38 PM

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sawyerkirk

I'm trying to  determine what size pulley s I need for a "thing" I'm building. I have a 1/2 hp 175 rpm motor that I want to turn a shaft at 50 rpm, and am looking for the formula to determine what size pulleys to put on each shaft. Any thoughts?

Ron Wenrich

Here's how I figure it:  You need to reduce your speed by 175/50 = 3.5 ratio.  Your drive pulley should be smaller than your driven pulley in order to slow it down.  A 2":7" pulley arrangement should work.  
Never under estimate the power of stupid people in large groups.

Rick Schmalzried

Sawyerkirk,
Is that 175 RPM or 1750?  It will make a big difference in Ron's calculations if 1750.  In that case you would need a 1750/50 or 35:1 ratio.  A car tire driven off the 1/2" shaft would get you close.
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sawyerkirk

It was definately 175 rpm, it's some kind of funky low speed high torque motor I got at at an auction some years ago, and never had a use for it. Thanks for the help on the ratio.

Kevin_H.

OK, OK, OK,
You have got to tell us what this "Thing" is...
Got my WM lt40g24, Setworks and debarker in oct. '97, been sawing part time ever since, Moving logs with a bobcat.

Mark M

Ja! - was ist das thing?

I am building a thing too (yankee yarder) and trying to figure out how much I can pull with an 8 hp Honda 6:1 motor after it goes through a couple of pulleys and a couple of gears.

Mark

LeeB

somewhat along the same line; how much hp would i lose by stepping up a 1hp,1750rpm to 3500rpm by changing pully sizes? LeeB
'98 LT40HDD/Lombardini, Case 580L, Cat D4C, JD 3032 tractor, JD 5410 tractor, Husky 346, 372 and 562XP's. Stihl MS180 and MS361, 1998 and 2006 3/4 Ton 5.9 Cummins 4x4's, 1989 Dodge D100 w/ 318, and a 1966 Chevy C60 w/ dump bed.

sawyerkirk

If y'all remember back, a month or so ago I was asking about air staplers to attach plastic film to stakes for silt fencing, well that little project is progressing nicely, but we had been using a hand crank to roll them up with. Now that I know we can do it effectively I want to increase production and decrease labor,so I'm putting a motor on the roller. Hopefully it will work. I'll see if I can't brek out the camera when it's complete. Thanks for the help

pigman

LeeB
 The hp will be the same ( if you negelect any small changes in the friction of the pulleys and belt) but the torque will be 1/2. I am sure some of the ungineers here can explain it better. :P ;D
Things turn out best for people who make the best of how things turn out.

LeeB

would that not in essence give me 1/2 hp? LeeB
'98 LT40HDD/Lombardini, Case 580L, Cat D4C, JD 3032 tractor, JD 5410 tractor, Husky 346, 372 and 562XP's. Stihl MS180 and MS361, 1998 and 2006 3/4 Ton 5.9 Cummins 4x4's, 1989 Dodge D100 w/ 318, and a 1966 Chevy C60 w/ dump bed.

Stephen

LeeB,
HP=force X speed=550 foot pounds per second
You would still have 1hp, twice the speed, but at 1/2 the torque. You are correct in that the torque would be about the same as that of a 1/2hp motor operating at 1750rpm.

MarkM,
You must first determine what your line speed will be. (adjust numbers where necessary and anyone please correct me where I am wrong) example: engine rpm=3600 divide by 6 for output shaft speed(6:1 gear box)=600rpm X first (drive) pully size (2in) divide by next (driven) pully (6in) X sprocket teeth (10) divide by next sproket (30 teeth)=67rpm X circumference of cable drum (8in) = 533 feet per minute.
Since 1hp=550fps, you could pull 60lbs 550 feet in 1minute, or 60 X 550/533(your speed)= 62lbs pull X 8hp(your engine)= 495 lbs pull.
Sounds way too fast, and each winding of cable will be faster with less pull.
Back to the drawing board!
If you use different pullys and gears and drum size to reduce your speed by 1/4, you will 4 times your pull. ie 1980lbs at 133 feet per minute or 2 feet/second.

Think about a farm tractor winch: 40hp will pull about 8,000lbs. You have 8hp (1/5), therefore, at the same line speed you will also pull 1/5 of the load, or 1600lbs. How fast is a tractor winch at 540rpm? (2 feet/second?) Anyone know?

Keep me posted about this winch, I have had plans for one for about 10 years but been scared to try it out.

Stephen

1994 WoodMizer LT40G18. 69 acres mixed wood. 1952 ford tractor, Norse 290 winch, studed Norse ice chains. 45-66DT Fiat.

Bro. Noble

Lee,

The Hp stays the same-------it will only move half as much but it will move it twice as fast.

Noble
milking and logging and sawing and milking

Mark M

LeeB

I've always been a little confused by this too and I've never been good at physics (that's why I am a chemist) but I'll try to explain the little I know. If I say something wrong someone please correct me.

Horse power relates to moving a certain weight a certain distance in a certain time (I think it's 1 pound - 550 feet - in 1 second, but I'm not sure). This tells how much  work we can do. With motors we also have torque that tells us about the twisting force.

By changing the gear ratio you can change the amount you can lift and the speed you lift it, but you can't increase the amount of work you do because work relates to the amount of effort used to move a certain amount of weight a certain distance. In other words you can spend more time lifting more weight or less time lifting less weight, but to lift the same weight in less time would require more power.

Hope this doesn't leave you more confused.

Mark

woodmills1

that is right on.  torque is what moves something.  thats why big trucks and your fathers oldsmobile had a big torquey engine.  more horse power equates to more speed, that is less time taken to do the same job.
James Mills,Lovely wife,collect old tools,vacuuming fool,36 bdft/hr,oak paper cutter,ebonic yooper rapper nauga seller, Blue Ox? its not fast, 2 cat family, LT70,edger, 375 bd ft/hr, we like Bob,free heat,no oil 12 years,big splitter, baked stuffed lobster, still cuttin the logs dere IAM

LeeB

sawyerkirk, sorry . I sorta hijacked your thread. Never meant to do that. Appreciate all the answers from everyone though. LeeB
'98 LT40HDD/Lombardini, Case 580L, Cat D4C, JD 3032 tractor, JD 5410 tractor, Husky 346, 372 and 562XP's. Stihl MS180 and MS361, 1998 and 2006 3/4 Ton 5.9 Cummins 4x4's, 1989 Dodge D100 w/ 318, and a 1966 Chevy C60 w/ dump bed.

sawyerkirk

Glad to get it started, and I learned more than I had planned.

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