# chain rpm's



## bstall (Jan 21, 2009)

I have been thinking about building a csm with a 17 hp 4 stroke that i have lying around thats in perfect condition.Ive pretty much got the design nailed down from looking at many other mills im just not sure how many rpm's are sufficient.Ive noticed most chainsaws run 10,000 or more and i can accomplish this easily with a jackshaft i just dont know what rpm's to shoot for.


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## ShoerFast (Jan 21, 2009)

Slower milling speed would not be the worst thing in the world, things just last longer. 

You might be able to put a bigger sprocket on the drive, there are a few that race bike-saws here, they might have a few ideas where and how to set the drive up to increase the chain speed.


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## BlueRider (Jan 21, 2009)

*chain speeds on my saws*

To figure out chain speed you multiply the pitch of the chain by 2 and then multipy that by the number of teeth on the sprocket. now multipy by the rpm of the saw and then devide by 12. This will give you the chain speed in feet per minute.

My 075 has .404 pitch chain on an 8 pin rim sprocket and the saw runs at 9,000rpm. [.404x2x8x9,000]/12= 5,280 f/m 

In contrast my 038M is running .375 pitch chain on a 7 pin rim sprocket and the saw runs at 13,500 rpm. [.375x2x7x13,500]/12= 5,906 f/m

those numbers would sugest that the 038M cuts slightly faster than the 075. What those numbers fail to show is that the 075 is almost 40cc larger and actually has the torque to maintain that rpm/ chain speed while the smaller saw cant even come close to running at its max rpm when milling. 

I have no idea what the amximum chain speed would be for milling or if it would come down to swarf clearance for the tooth design or maximum power/ load on the chain. someone up at Madsons may be able to help you with the info as well as some of the parts for the chain drive on your mill.


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## treecycle (Jan 21, 2009)

*4-stroke chain rpm*

Maybe with a 14 or 16 pin it would work. If your motor turns at about 3 to 3.5 K rpm I would love to know if that would rip boards. What kind of clutch are you planning on? 

www.lmsaws.com 

has some neat videos to check out. They have a 20 horse honda hooked up to a 5 ft bar that looks similiar to what a milling saw could be, sorta. A lucas has some sorta jack shaft pully gearing, but I wonder if you could go right off the crank if you had a big enough sprocket?

cheers Peter

www.treecycleseattle.com


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## BobL (Jan 22, 2009)

When you have low revs and plenty of grunt you can also compensate for slow revs by dropping the rakers a little more. I think Will Malloff uses 0.045" on his 090.


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## bstall (Jan 23, 2009)

thanks for all the info.do chains designed for ripping do better at low or high speed.i understand how to set the saw up for any speed needed i just dont know what the optimum speed is.


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## slabmaster (Jan 24, 2009)

Ripping chain is the best for ripping.As for rpm.You want the highest rpm you can get without looseing too much power.


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## Brmorgan (Jan 24, 2009)

slabmaster said:


> Ripping chain is the best for ripping.As for rpm.You want the highest rpm you can get without looseing too much power.



Or without risking chain breakage if there's a jam - a 17HP 4-stroke has enormous torque compared to any chainsaw. I'd say stick with .404.



BobL said:


> When you have low revs and plenty of grunt you can also compensate for slow revs by dropping the rakers a little more. I think Will Malloff uses 0.045" on his 090.



You could do that, but wouldn't it produce a horribly rough cut being so aggressive at low RPM? I know Will drops them a bit, but not sure how much.

bstall, if I can't work out some kind of bandmill this summer, I'll be rebuilding the 10HP 4-stroke CSM that I built a couple years ago but never got operating smoothly. I've since learned a LOT about chainsaws and milling in general, and I think I can work all the kinks out but it'll require a lot of torching and welding to modify it. I've improved greatly on those skills in the meantime too. If I do end up working on that project I'll be sure to take lots of pics and show them here.


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## harrygrey382 (Jan 25, 2009)

hmm, I'm watching this thread now


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## bstall (Jan 25, 2009)

Im probably going to use a centrifugal clutch thats designed for up to 20 hp engines and attach it to the drive shaft.From there i will go to a jack shaft ,i just dont know what size pulley to use on my jackshaft because i dont know what fpm's to shoot for just yet.any ideas?The jackshaft will power a splined driveshaft,and i will use a splined harvester sprocket.With it set up this way the motor can remain stationary and only the bar will have to move.


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## slabmaster (Jan 25, 2009)

I would shoot for at least 9,000 rpm.You have to take in to account that making more rpm than the engines crankshaft will rob you of torque and power, so don't worry about breaking the chain.As that engine won't be putting out the torque to the chain after you gear it for high rpm.


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## bstall (Jan 25, 2009)

At 4800rpm's with a 16 pin harvester sprocket i should be around 5000 fpm.Is that adequate for ripping chain?


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## slabmaster (Jan 25, 2009)

That seems slow,Ripping chain will cut at any speed though.Just slower at that rpm.


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## BlueRider (Jan 26, 2009)

bstall said:


> At 4800rpm's with a 16 pin harvester sprocket i should be around 5000 fpm.Is that adequate for ripping chain?



That sounds like it should work. you didn't mention what pitch chain you will use and that will affect the chain speed. .404 will spin faster than .375 on pin sprockets with the same noumber of pins. also when you double the speed of a motor with a pully you reduce the torque at the final drive by half. An 090 with .404 and an 8 pin sprocket has a chain speed of only 3500 fpm so your speed of 5000 on a mill with high torque should rip through the wood at a nice speed. My 075 has a chain speed only slightly faster and no one here is milling with a csm with a chain speed much over 6000 fpm. Also keep in mind these are all calculated speeds based on max rpm of the saw with no load. It would be interesting to get some rpm noumbers with a tach while milling and start comparing the different saws.

It might be worth talking to someone with a lucas to find out what the chain speed on a lucas slabing atachment is. 

one of the things that will limit your cutting is the design of the chain you have to allow for the removal of the swarf. Lucas has addresed this by going to a skip style ripping chain with a reduced raker. I would be reluctant to use anything less than .404, your set up should have the power to pull the larger chain with no loss of speed.


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## bobsreturn (Jul 4, 2009)

i was told by the lucas rep that only the 6in mill has a high chain speed the others are slower as the circular blade speed has to be right . the slabbers use a harvester sprocket ,looked to be on the crankshaft ? and certainly cut slabs well ,as did the 10in mill that runs slower . would pay to check out the lucas mills if you wish to build a slabber .mate has a peterson slabber 24 hp and 6ft bar , thats a slabber . he mainly uses a bandsaw mill now as its all hydraulic . a lot quicker ,but more fiddly . happy cutting bob


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