HP rating for pulleys

[stuckmotor]

I'll need two pulleys for a project that I plan to drive with a 13 hp engine. The specs for pulleys of the right diameter that I've found at Surplus Center say they are for fractional hp applications. I can't even find hp specifications on pullies from most other companies. What I can sometimes find, is an industry number. I suspect there's something in that number that specifies hp rating. Can anyone tell me if my guess is right or how to determine what horse power a pulley will carry.
Thanks,
Stuck

 

[CalG]

Simply, ...It's not that simple.

Horse Power is a function of speed as well as torque. That means that a power transmission system that is designed around high speeds in it's shafts, gears, belts, or chains can make use of smaller components and still transmitt equal HP as it's bulky, slower moving counterpart.

Use the pulley hole size as an indication of it's possible capacity. Construction can be a tip off as well. Spot welded, stamped steel "halves" won't last long in hard service.

But, 13 hp isn't much. That's whats on the walk behind lawn mower I've got. That unit is fitted with cast iron pulleys with engine shaft diameter bores for power transmission, and stamped steel for idlers and guide pullys.

Big reason for pully failure? Over tensioning the belt because of undersizing the requirement. An "A" belt won't carry much hp. B belts carry more, and doubles or triples do weally well.
(triple "B" belts transmit the 23 hp to the pto on the Bolens HT)

'hope it helps

 

[Baby Grand]

Here's a reference with lots of interesting reading:

http://www.bandousa.com/html/pdfs/bu-143manual.pdf

 

[SPYDERLK]

I'll need two pulleys for a project that I plan to drive with a 13 hp engine. The specs for pulleys of the right diameter that I've found at Surplus Center say they are for fractional hp applications. I can't even find hp specifications on pullies from most other companies. What I can sometimes find, is an industry number. I suspect there's something in that number that specifies hp rating. Can anyone tell me if my guess is right or how to determine what horse power a pulley will carry.
Thanks,
Stuck

Well, Whats your guess? ... I can tell you from experience that a 4.5" cast iron "A" pulley at 3600RPM will transmit 13HP durably to another pulley at least as large. Go up an inch on both ends for a good safety factor if you have room. Avoid multi belts. Youll do better replacing one belt twice as often.
larry

 

[BHD]

belts are usually what is rated, but diameter of the pulley is also important. for example one could use a 2 inch diameter pulley and would not transmit very much HP, but if one used say 5 inch diameter pulleys the power that would be able to be transmitted, would be more than double and possibly up to 4 times more,

on v belts the V sides are the griping part, the belt should not be touching the bottom of the pulley, and with tension the belt grips the sides, on a small pulley first there is not much surface area, and the tight bend is not working in your favor, or the belts, on the larger pulley much more surface area, and longer V section to grip into,

both set up would be turning the shafts the same speed,

here is some info from gates, the design info is about page 20 -34 or so, http://industrialbeltdrives.com/wp-content/uploads/2012/05/20070_V-BELT_DDMANUAL_ENGISH.pdf

when you get done reading and understanding it, you will know more about V belts than you thought was out there,

 

[stuckmotor]

Thanks to everyone for your wisdom. I especially like CalG's opening statement, "Simply, ...It's not that simple" and, I'm afraid he's right.
It'll take me a while to digest the information you've all given me, then, maybe I'll know what to look for.
Stuck

 

[Baby Grand]

You could always use the size of the pulleys on a professional grade 4 or 5 foot finish mower deck as a start ... they should handle 13 HP, all day, without breaking a sweat.

 

[LD1]

Perhaps tell us what this project is and we may be able to offer some more insight? Are you trying to change speeds? or just simply transfer power?

And yes, it isnt simple. While size is certainly important, thats the easy part. Without trying to decode every manufactures number, construction type is the hardest to figure out. Take a simple 4" A-section pulley. There are many styles and likely ranging from a few bucks to $50+ Some are the stamped halves. Some have welded in hubs, some are a "pot metal", and some are quite stout or even a solid piece.

 

[Brad_Blazer]

This reference from Grainger looks easy enough to follow. http://static.grainger.com/tps/powe...nce.pdf?cm_sp=TPS-_-VBeltReferenceGuide-_-Top

McMaster-Carr USA Bearings and Belts www.vbeltsforless.com are vendors I have had good luck with.

 

[BHD]

also most gasoline small engines are over rated in the Hp they produce, (if you noticed many no longer rate the power in horse power),

(it is my understanding the way the old system worked was to use a brake and to get the max HP, that meant to kill the engine, by over load),

in the past, one could usually safely replace a gasoline engine with an electric motor in the 1/2 to 2/3 range and usually no have any problems,

or if one was replacing an eclectic motor it was normally suggest you double the gas engines HP,

so I really doubt if you engine can continue to run and produce the 13 HP, most likely it really only has the ability to produce about 6 to 8 true horse power,

(one quick example is a generator, say a 13 HP engine is used to run a generator, most are only about 5500 watt normal out put generators (alternators actually), a horse power is said to be, 745 watts, take that 5500 and divide by is 7.3 (horse power), yes I know there is some losses, but 5.7 HP in losses, I doubt it,

https://www.google.com/search?num=1...-1.1.0....0...1c.1.42.serp..1.0.0.rYnzlbsZI1s

 

[stuckmotor]

LD1
I'm trying to make a 4 stroke chainsaw mill. From what I've read I need to approximately double the speed of the engine to achieve satisfactory speed on the chain. I'm thinking about a 6" pulley on the engine and a 3" pulley on the drive shaft for the chain sprocket. I know a bandmill would be faster and that's in the works but, for right now, I want to work out a verticle cut chainsaw mill with the engine that will eventually power the bandmill.
I like the Surplus Center prices but can't see a pulley rated for fractional hp holding up to a 13 hp engine. I'd like to be proven wrong.

Perhaps tell us what this project is and we may be able to offer some more insight? Are you trying to change speeds? or just simply transfer power?

And yes, it isnt simple. While size is certainly important, thats the easy part. Without trying to decode every manufactures number, construction type is the hardest to figure out. Take a simple 4" A-section pulley. There are many styles and likely ranging from a few bucks to $50+ Some are the stamped halves. Some have welded in hubs, some are a "pot metal", and some are quite stout or even a solid piece.

 

[Brad_Blazer]

I went over the Grainger sheet and going with 2bk sheaves at USA Bearings and Belts you can get one each 2bk50 and 2bk100 pulleys (sheaves) and a pair of bx belts. Cogged/Notched B V-Belts
Horsepower is limited by the smaller sheave and a BX belt on the 4.75 sheave is good for about 7.5hp so the doubles will get you there. Just over $100 with belts. These will be imported goods. The bearings I've gotten there have been very good and the prices are hard to beat.

Going with a 3" sheave you would barely get there with a triple. It will cost more and be less efficient.

 

[BHD]

for example most better lawn tractors use a magnetic (electric clutch) to run the mower deck

I have 16hp Briggs on my mower, the drive pulley (which is the smaller) is about 5" in diameter, most are using 5/8" belt,

by looking at the clutches most range in the 5" to 6" area, Genuine Warner Electric & Ogura PTO Clutches

most riding lawn mowers are coming out with 16 to 20 hp engines and they are not tearing up belts,
(I am sure there stresses some from time to time), but do hold up well under the larger engines,

would think a trip down to the home depot and look at the lawn tractors and see what the smallest pulley they have on there deck drive and consider it as your smallest pulley size for design proposes,

you do not have to reinvent the wheel, or even reengineer it,

and the post above by going with doubles your for sure to do the job,

I have a 218 Ohan engine on my home made band saw mill, I really wish I had used a magnet clutch instead of the hand unit I came up with, off the engine I used a double pulley about 4" in diameter,

and as far as chain speed, you may want to do some more research on the subject,

a number of years the electrical company came by to trim some limbs by the power lines, and they pulled out this chain saw, and it was hydraulic, driven and it was low speed, it worked beautifully, better than my gas saws, for the most part, but the thing was it was low speed, and I asked about it and said they get about four times the chain life over a gas saw and it need to be sharpened much less, and works better, It just purred and out cam nice full chips, (I think many chain saws, run so fast they do not have time to cut and all they do is heat up and burn, the chain),

(I know to rip logs your chains well need to be sharpened differently over cross cut, sawing,

but I do not know if the RPM is do to the needs of a two stroke engine to make power, or for the design of the chain, (I think the chain is made to stand up to the engine, not the other way around).
years ago, they had some mini saws, that had a small chain, and they finally out lawed them do to the speed of the chain, and the danger they were if the chain broke,

if the engine is at 3600, doubling it is about 7200,
my chain saw book basically said max rpm is 10,000 farm boss by stihl

I think your on the right track, do some eBay shopping some times one can even yet come up with a deal, (harder now than a few years ago)

like said your belts and RPM are more the problem than the sheaves, if they have the correct size order and try it out,

I do not like to waste money either, but not every project will work the first, or even the second try, usually they will work, if you keep at it, (Oh that power the house out of a bread box project has yet to work for me), but
the best I can say is to copy a know design or guts of a know working design,

if your coming up with this all on your own then expect some do overs, it is all part of the game,
If it works most likely your saving a considerable amount over the manufactured counter part, so if you end up buying pulleys and belts a few times, so be it,

what is called fractional horsepower is more of a name like George or Pete, it is an identification for a type of belt and pulley, if you look at the design manuals you can see a given belt may only carry a 1/4 hp at one diameter and speed where the same on larger pulley and different RPM can carry possibly up to 16 hp

no I would not suggest the light weight aluminum pulleys like used in dryers and washers, machines,

post the URL for the pulleys or number from surplus center, and people will give there opinion on if they will do the job or not since now you have told us what your trying to do,

I would suggest the cast iron pulley or billet steel

 

[Tractor Seabee]

In general, I have always considered die cast and stamped steel pulleys a fractional HP and light duty. They are low cost and destroy themselves under heavy loads taking the belt(s) with them.

Multiple HP and heavy loads always use cast iron. They are expensive but never wear out. Drives with small drive end pulleys and large load end pulleys will always wear out belts fast as they slip and heat up on the small pulley. Ir you have the space it is better to have a jack shaft and do the ratio in two steps. Alignment is another belt life issue, use a straight edge across the full width of both pulleys. As the load goes up you need parallel belts. For parallel belts always change all at once and use matched sets. I used to work on large ammonia compressors and ran across "C" width belts up to 8 belts wide. These were around 200 HP.

Like was already stated, what is you project all about? Running time is a big factor in the economic decision making. Continuous/long terms -one scenario, intermittent like a mower- whole new ball game.

Ron

Ron

 

[CalG]

In general, I have always considered die cast and stamped steel pulleys a fractional HP and light duty. They are low cost and destroy themselves under heavy loads taking the belt(s) with them.

Multiple HP and heavy loads always use cast iron. They are expensive but never wear out. Drives with small drive end pulleys and large load end pulleys will always wear out belts fast as they slip and heat up on the small pulley. Ir you have the space it is better to have a jack shaft and do the ratio in two steps. Alignment is another belt life issue, use a straight edge across the full width of both pulleys. As the load goes up you need parallel belts. For parallel belts always change all at once and use matched sets. I used to work on large ammonia compressors and ran across "C" width belts up to 8 belts wide. These were around 200 HP.

Like was already stated, what is you project all about? Running time is a big factor in the economic decision making. Continuous/long terms -one scenario, intermittent like a mower- whole new ball game.

Ron

Just a note regarding "matched sets"....

Most, if not all the "big" manufacturers have dropped the notion of "matched belts", citing the precision and quality of the manufacturing process assuring that all the belts of the same size come out "close enough".

But,... I needed to replace the drive belts on a German lathe I have in the shop. The spindle needs to be pulled to replace these belts, and that is no small task with a $600 spindle bearing on the line if things go sour. I wanted to do it right.
After getting the latest information from Gates regarding the "matching" thing, I ordered belts from MSC ...qty 2. The belts arrived in good fashion, but they were from two different manufacturers , made in two different countries, and one looked a lot like the milk man. ;-)

I called to get a return authorization and was pleased to learn that MSC offers an "engineering service", whereby someone with more than half a wit, will take a look at what is pulled from the stock room to see if everything makes sense. Good service I would say!

Well, the two replacement belts arrived. Both from the same maker, and only two serial numbers apart! (Note: Belts are produced in wide bands, sequentially numbered, then cut off as individual belts.) Adjacent bands would have been a matched set prior to the refinement of mfg..

I'm happy, and the lathe turns smooth as glass ;-)

 

[Brad_Blazer]

Looks like Surplus Center does have the cast iron doubles for a significantly lower price. The "fractional horsepower" in the description is probably from lazy editing since it doesn't make sense but you can call them to verify.
4.75 O.D. 1 BORE 2 GROOVE PULLEY
9.75 O.D. 1 BORE 2 GROOVE PULLEY

Edit - I just realized my error: Those HP ratings are for the smaller sheave turning 1750RPM. Your small sheave will turn at 4x that speed so in theory will transmit 4x the horsepower. That means a single 3" pulley and BX belt will get you there. I would still recommend stepping up the diameter a little to reduce hysteresis heating and power loss at your high speeds.


If you need a clutch you could go with something like this on the motor. 12 VDC WARNER CLUTCH 1" BORE 7.25" SINGLE B PULLEY
And this on the saw: 3.75 O.D. 1 BORE 1 GROOVE PULLEY

The plain motor pulley would look like this: 7.25 O.D. 1 BORE 1 GROOVE PULLEY

I've been selecting 1" bore because that's what the Predator engine has. not sure what you need on the saw pulley.

 

[BHD]

Multiple HP and heavy loads always use cast iron. They are expensive but never wear out. Drives with small drive end pulleys and large load end pulleys will always wear out belts fast as they slip and heat up on the small pulley.
Like was already stated, what is you project all about? Running time is a big factor in the economic decision making. Continuous/long terms -one scenario, intermittent like a mower- whole new ball game.

Ron

Ron

I have seen many a steel or cast pulley wear out, yes they do wear slowly and last a long time, but can and do wear out, but most will out last most machines they are on,

 

[BHD]

Like was already stated, what is you project all about? Running time is a big factor in the economic decision making. Continuous/long terms -one scenario, intermittent like a mower- whole new ball game.

Ron

Ron

yes some mowers are intermittent, but many mowers are ran 8 to 10 hours a day continually, when we mow we have 7 acres on the farm that is in yard and building sites, , when many times have mowed that in a day with a small lawn tractor, that is not intermittent use, and when I worked for a collage in Montana, we use used the mower daily for hours a day, summer and winter,
many areas I know of use there mowers very hard. many many hours a day over many acres,

yes many people only mow a few thousand SQ feet, but some mow acres and acres with there mowers

 

[stuckmotor]

Hi guys,
I haven't been able to respond to your kind advice sooner because I'm away from the internet several days a week. I really appreciate so many responces.

BHD,
It's good to hear from someone who's actually built his own mill and I may PM you when I begin my band mill. After reading your message, I think I need to quit planning and begin building. If I end up with several pulleys that don't work, my wife can sell them at that estate auction when I die. I may even get the cheaper spot welded pulleys to begin with, to work out the best ratio and upgrade if they don't hold up. Here are links to a couple of Surplus Center pulleys that I'm interested in, 3.95 O.D. 1 BORE 2 GROOVE PULLEY
7.75 O.D. 1-7/16 BORE 2 GROOVE PULLEY
They look pretty substantial to me and with two belts, I don't know why they are only rated at fractional HP.

Brad
Thank you for loging onto Surplus Center and having a look. l didn't see any pulleys rated at multiple HP, no matter what the size and may take your advice and call the company.

I noticed a question linked below titled Pulleys and " Pulleys and Sheaves" the OP was having trouble finding multi HP pulleys too. I wonder whether he was checking the same suppliers I am.

 

[SPYDERLK]

-- Single groove cast iron pulleys will handle the power you have. Multiple belting will waste power and should only be used if you have space constraints preventing a 4.5" or larger small pulley. Browning makes some very good adjustable pulleys and they cover the 4 to 5" range well. Theyre not cheap ~$90, but you should be able to get away with just the small one adjustable and save when tuning your setup. P/N- 6205K57 will get you to the correct page in McMaster-Carr online catalog.