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pulley sizes for 22 hp saw motor?

Started by SineWave, March 06, 2017, 04:03:22 PM

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SineWave

Hey, guys,

I'm going to put together a bandmill using a Linn Lumber super sawframe for Model 1900 (36" max log diameter) like this:

http://www.linnlumber.com/wpimages/wp0067fd21_06.png

and a 22 hp Harbor Freight motor.

Can I get the full 22 hp out of a single pulley system to pull the blade, or should I use a double sheave setup?

Also, I see that the Linn rig normally comes with a 14" diameter driven pulley attached to a 19" diameter bandwheel. So that I can calculate the proper size clutch pulley on the engine, can anyone tell me what blade speed I should shoot for with a 22hp engine? I plan to cut everything from loblolly pine to white oak.

(If I use a clutch with a 4" diameter sheave, I calculate that the blade speed – assuming a 14" diameter driven sheave attached to a 19" diameter bandwheel – will be 1445 feet/minute. Is that about right for a 22 hp motor?)

If a single belt is OK for 22 hp going through a 3600rpm faster shaft (which I'm led to believe is OK, and definitely OK with a "B" belt), then I was considering a clutch with a 4" diameter sheave, like this:

http://www.ebay.com/itm/CENTRIFUGAL-CLUTCH-SINGLE-GROOVE-24-HP-HEAVY-DUTY-1-STRAIGHT-KEYED-BORE-NEW/351449693432

Thanks in advance for any information.

Kbeitz

With a large diameter pulley you can handle 22hp.
The problem is that you will need a small diameter pulley.
So your going to need double sheave or more.
The smaller the pulley the more groves you will need.
Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

SineWave

Hang on...I think I screwed up the math (again)...

muggs

In my opinion, you need at least 2 belts. With a single belt, it would have to be so tight to prevent slipping that your bearings would wear out very fast. I have built lots of machinery, I always figured about an A belt for every 5 HP.   Muggs

SineWave

Let me try the math again. I screwed something up...

If engine running speed is 3600 rpm and
clutch (driving) sheave is 4" diameter and
driven sheave is 14" diameter then
driven sheave speed will be (4/14) x 3600 rpm = 1028 rpm

If bandwheel is 19" diameter, then blade speed will be (1028 rpm) x (19 x 3.14)/12 = 5,110 feet per minute

(assuming no slip)

Cook's Saw at

http://www.cookssaw.com/index.php/increase-portable-sawmill-profits-a-production/how-fast-should-a-bandwheel-turn

says that for a 22 hp motor, I should shoot for a blade speed of about 4,600 feet/minute.

Is 5,110 feet/minute too fast for a 22 hp engine to pull the blade?

To get 4,600 feet/minute with a 14" diameter driven sheave and 19" bandwheels, I would need to have a clutch sheave of about 3.6" diameter if my calculations are correct.

Or else use the 4" diameter clutch sheave and substitute a driven sheave of 15.5" diameter...

I'm thinking best bet would be to just go with the 4" clutch sheave and 14" driven sheave, and slow down the feed rate


SineWave

Quote from: muggs on March 06, 2017, 04:45:55 PM
In my opinion, you need at least 2 belts. With a single belt, it would have to be so tight to prevent slipping that your bearings would wear out very fast. I have built lots of machinery, I always figured about an A belt for every 5 HP.   Muggs

Thanks, Muggs. I suspect you're right. I found an engineering guide at

http://www.baldor.com/mvc/DownloadCenter/Files/MS4050

but I'm having a devil of a time making sense of it...

Den-Den

My experience is that a 5" dia pulley for "B" section belt is barely adequate to load a 23 hp Briggs engine and that the belt does not last as long as it should.  For a 4" diameter pulley, you definitely will need a double groove to utilize 22 hp.
You may think that you can or may think you can't; either way, you are right.

KirkD

If you go up to the top of the page and click on Extras and then tool box you will find a band speed calculator.
Wood-mizer LT40HD-G24 Year 1989

SineWave

Thanks for the replies, everyone. I'll go with the double-groove pulleys.

Does that suggested band speed of 4600 feet/minute sound about right for 22 hp?

I would have expected the band speed to remain the same no matter what size motor was pulling it ... I thought this was governed by the tooth geometry and that the only thing more horsepower did for you was allow you to pull it through the log faster ... but now that I think about it, I realize the only way you can pull the saw through the log faster is to speed up the blade! Doh!

Sorry if these are dumb questions...I'm feeling my way around in the dark, here.

Rougespear

Cooks has some nice short videos, but it is my understanding that higher horsepower allows greater feedspeeds, which in turn allow faster rpms because more wood is being exposed to the teeth... for what its worth, aiming for the largest chips flying horizontally out of the dust chute seems to be the ticket.
Custom built Cook's-style hydraulic bandmill.

KirkD

Quote from: KirkD on March 06, 2017, 08:43:21 PM
If you go up to the top of the page and click on Extras and then tool box you will find a band speed calculator.

If you go up to tools and use the calculator it will answer a lot of your questions

>You are shooting for a MINIMUM of 4500 surface feet per minute up to 5800 for a maximum. This is for Timberwolf blades from Suffolk Machinery.
Wood-mizer LT40HD-G24 Year 1989

JRWoodchuck

I run a single A type belt on my home built mill with a 19hp diesel and have not experienced slip yet.
Home built bandsaw mill still trying find the owners manual!

Clover

I've got a thirty hp Kohler (overblown 27?) I had two b-belts on a three and twelve inch pully set up. My band speed was on the slow side but the biggest limiting speed cutting factor was belt slippage. Go to any belt supplier web site (gates?) and they will have hp ratings for each belt and reductions for each inch smaller pulley you go down to. The 3" was not capable of holding that much power so I've now upgraded to a 5" and 16" double set up. Don't waste your money doing it twice just get the biggest driver pulley from the start and properly tension it. Your going to have plenty other problems to resolve building your own mill. Don't know if it was mentioned but you need to pull the blade through the cut. Disregard if you already knew that and have fun with the build.
The reason a lot of people do not recognize opportunity is because it usually goes around wearing overalls looking like hard work. --Tom A. Edison

Home made 30 hp sawmill all hydraulic, stihl 026, 170, pioneer 65, John Deere 955 with home made forks. And a whole slew of other tools

Clover

I went to the baldor website and checked my two pulley sizes for hp transfer.
Look at line 461 and you will see approximate to my 3" and 12" pulley sizes. It lists a 3.4" driver and a 12.4" driven pulley set as only being able to transfer 3.84 hp per b belt.
On line 440 it lists a 5" driver and a 16" driven pully set capable of transferring 8.18 hp per b belt.
The limiting factor for driver sizing is the terminal speed for the driven pulley. As the pulley gets bigger it's max rpm's lower. The pully would fly apart if you went beyond its design speed.
I hope this helps with your decision making.
The reason a lot of people do not recognize opportunity is because it usually goes around wearing overalls looking like hard work. --Tom A. Edison

Home made 30 hp sawmill all hydraulic, stihl 026, 170, pioneer 65, John Deere 955 with home made forks. And a whole slew of other tools

FloridaMike

When using the calculator, do you use the pulley's OD or B belt datum dia.?  It makes quite a big difference in the band speed calculation. 

Also does everyone run their gas motors at the maximum rpm?  Would backing down 100 rpm result in longer service life, with minimal hp loss?
Mike

Clover

Floridamike I used 5" and 16" for my calculations then ordered those sizes. Getting into the b belt datum is a whole other subject.

My mill runs at 3650 rpm's blade engaged but not cutting. I push it until the rpm's drop to 3450 to 3500 when cutting. My belt is slipping at the lower rpm though. I will push it harder now that I've got the bigger pulleys as my actual peak torque is 45 at 2400 rpm's. Obviously not going to go that low but we really don't use a gasoline engines full potential at higher rpm's. My target rpm's at 3300 to 3400 while cutting.
The reason a lot of people do not recognize opportunity is because it usually goes around wearing overalls looking like hard work. --Tom A. Edison

Home made 30 hp sawmill all hydraulic, stihl 026, 170, pioneer 65, John Deere 955 with home made forks. And a whole slew of other tools

KirkD

The 22HP Predator max RPM is 4000 but it says on the spec's "Maximum Torque (ft. - lbs.)    45 NM @ 2500 RPM" So to me that means max torque is at 2500 RPM?
Wood-mizer LT40HD-G24 Year 1989

Clover

Kirkd the 45 nm is metric newtons. The foot pounds would be less than that. And yes maximum power output is at 2500 rpm's. After that it just drops off to a certain extent. Some manufacturers will list an average torque output over a broader rpm range allowing the user to better apply the engines use. Just as a heads up you can't measure horsepower only torque. Hp is a mathematical equation. For some reason we all want to know hp numbers but it's actually torque doing the work.
The reason a lot of people do not recognize opportunity is because it usually goes around wearing overalls looking like hard work. --Tom A. Edison

Home made 30 hp sawmill all hydraulic, stihl 026, 170, pioneer 65, John Deere 955 with home made forks. And a whole slew of other tools

SineWave

Quote from: Clover on March 07, 2017, 06:59:02 PM
Kirkd the 45 nm is metric newtons. The foot pounds would be less than that. And yes maximum power output is at 2500 rpm's. After that it just drops off to a certain extent.

Torque might peak at 2500 rpm but I doubt that power (torque x rpm) peaks at 2500 rpm.

Between 2500 and 3600 rpm, the rotational speed increases by almost 44%. For the power to peak at 2500 rpm would require the torque to decrease by at least 44% between 2500 and 3600 rpm...

Thanks for pointing out those numbers in the Baldor book, Clover. You helped it make sense to me. Discouraging sense, but sense...

My lawnmower with 54" cutting deck runs on a 26 hp motor and a single belt/pulley to the deck. I suspect that according to the Baldor book, this is impossible...


Clover

Sinewave I apologize for the use of the word "power" in my explanation. When I think of power I'm thinking about torque not horsepower. Horsepower is not measurable and the numbers sometimes get tweaked to suit a manufacturers purpose.
I tried to upload a graph of my engine yesterday and for some reason it kept corrupting my phone. I gave up trying and didn't look for the predator motor. The Kohlers torque curve is very flat from 2200 to 3400 rpm's. I've got my blade speed pretty close where I want it. At maximum rpm's I'm a bit over suggested blade speed but as I push into the cut getting closer to my working rpm's it will still be in the proper range without dropping below the suggested fpm. I will also be closer to a good torque range for my motor.

As for your lawnmower, the reason it only has one belt is that it doesn't require the full engine hp to turn the blades. You also need hp to move the tractor through hills, wet grass etcetera. I looked into electronic clutches for my set up but decided against it. Most of the ones on eBay are for lawnmowers and the math for a blade to slice through grass is totally different than a blade cutting wood. 

One last thing. When looking at hp charts for most industrially used thing (belts, pulleys, hydraulics ect) they are shown for electric motor hp. A gas engines hp has to be derated 20-30 percent to compare apples to apples.

So a 22 hp predator engine derated to 16-18 hp should run perfect with two b-belts on a 5" driver pulley. As per my earlier post to b's on 5" is equal to about 17 hp.

Hope this helps a bit to clear things up.
The reason a lot of people do not recognize opportunity is because it usually goes around wearing overalls looking like hard work. --Tom A. Edison

Home made 30 hp sawmill all hydraulic, stihl 026, 170, pioneer 65, John Deere 955 with home made forks. And a whole slew of other tools

Don P

Would motorcycle parts do any good?

Clover

Ok I'm not done yet LOL just a little more food for thought. Let's not think about engine hp or torque let's imagine your band blade as a set of brakes on your car. The band blade is applying a braking force to your engine. You now know from the baldor charts that a 5" properly tensioned pulley with one b-belt is around 8.2 hp. So the band blade can brake your engine to 8.2 hp before the belts start to slip or fail. As you hear that belt slipping you back off on the cut to the point it's not anymore. You are only using 8.2 hp of your engines 22 hp. Make sense? With two belts you are able to put the brakes on your engine to 16.4 hp. Clearer?
You could run one belt and not Have it slip but would have wasted you money buying that 22 hp engine when you could have gotten away with less than half of that. All because the belt didn't have enough power the put the brakes on your engine 
Your 22 hp engine or my 30 hp engine is not producing that amount while it's running. They will both only produce the amount of power required that the belt or belts brake them to.
The reason a lot of people do not recognize opportunity is because it usually goes around wearing overalls looking like hard work. --Tom A. Edison

Home made 30 hp sawmill all hydraulic, stihl 026, 170, pioneer 65, John Deere 955 with home made forks. And a whole slew of other tools

Remle

IMHO, Quit trying to engineer this, the engineering has already been done. If you are buying the head kit from Lynn, just ask them for their recommendation on motor and belt/pulley size. Or even better buy the components from them.

Clover

That's why I built my own mill, to engineer it!!! Lol
The reason a lot of people do not recognize opportunity is because it usually goes around wearing overalls looking like hard work. --Tom A. Edison

Home made 30 hp sawmill all hydraulic, stihl 026, 170, pioneer 65, John Deere 955 with home made forks. And a whole slew of other tools

Kbeitz

Horsepower is continuous torque. New engine is sometimes rated
at flywheel horsepower not continuous. I cant see how they can rate
the horsepower of a pulley with out knowing the OD of it.
The bigger the OD the less pull on the belt. It's like a longer
pipe wrench. The top pulleys in the drawing can handle much more
horsepower than the bottom pulleys. Both will turn the same RPM.



 

Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

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