# Multiple power heads



## cgarman (Feb 25, 2011)

I've heard a lot of debate as to the merits of running 2 power heads on a mill. I'd still like to know if anybody has done this, and actually compared the results to a single power head. I assume it's not 2x as fast, but would expect something like 1.3x, etc.

In the meantime, to those of you who say it can't be done, and that it would run worse than a single power head, I offer this...

Technical facts

There's a small mention of how the ignition point of each engine is 'random' making the timing smoother. That makes me wonder if a 2-head setup where the engines aren't synched (every setup basically, since no two saws are identical) would eventually settle to a point where the ignition points of the saws cooperate. Would they fire alternately? If so, the would both contribute to the power output. Even if one saw is running 5% faster than the other, that would mean they fire independently 19 out of 20 times.

I'm an electrical engineer, so I'm curious how the math works out, but I don't have the engine experience to know. Any mech engineers out there?


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## gemniii (Feb 25, 2011)

Have you tried that unique feature called "search"?

There's been several threads about it but start another one.

I might. then again might not, post some links, but I don't have time now.


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## BobL (Feb 25, 2011)

cgarman said:


> There's a small mention of how the ignition point of each engine is 'random' making the timing smoother. That makes me wonder if a 2-head setup where the engines aren't synched (every setup basically, since no two saws are identical) would eventually settle to a point where the ignition points of the saws cooperate. Would they fire alternately? If so, the would both contribute to the power output. Even if one saw is running 5% faster than the other, that would mean they fire independently 19 out of 20 times.


 
I'm surprised an engineer couldn't figure this out. Given the engines are connected by a chain under tension, they absolutely MUST turn at the same RPM, otherwise the chain would stretch like an elastic band on one side and bunch up on the other side bar. Now Whether they fire in synch or not depends on where the pistons are in their respective cycle relative to each other when the chain is put on the sprocket. Once the chain is on, the difference between the ignitions is fixed and will not change until the chain is removed.


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## grandpatractor (Feb 25, 2011)

BobL said:


> I'm surprised an engineer couldn't figure this out. Given the engines are connected by a chain under tension, they absolutely MUST turn at the same RPM, otherwise the chain would stretch like an elastic band on one side and bunch up on the other side bar. Now Whether they fire in synch or not depends on where the pistons are in their respective cycle relative to each other when the chain is put on the sprocket. Once the chain is on, the difference between the ignitions is fixed and will not change until the chain is removed.


 
Except for some clutch slippage. That will change things.:msp_huh:


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## bobt (Feb 25, 2011)

This is a thread that I have no business posting in, but here goes.

I would think that getting the two powerheads perfectly in sincroninzation would be the biggest problem. Like BobL stated one side of the chain might get too much tension, while the other side would go into compression. I would expect problems to occur in that condition, and it would actually be worse than using one powerhead.

Allow an analogy:

Years ago, the LS&I RR Co. had a problem at an Iron Mine where they needed to haul more cars of ore out of the mine faster. The problem was a steep grade not far from the mine. They could only pull maybe 40 cars at a time over the hill, because the drawbars would separate under the extreme tension produced by the addition of more cars to the train.

They had an idea to add a "pusher" engine to the train, and therefore double the lengths of the trains being brought out of the mine. Here's what happened. 

If the pusher engine was not pushing hard enough, it was worse than before as the engine added more drag to the pulling engine. Drawbars continued to snap.

On the other hand, if the pusher engine was pushing too hard, it pushed the cars together, and the cars bunched up, and derailed. Not what they wanted either.

The experiment was soon discontinued, and a long siding was constructed instead, where the short trains could be stored and coupled together. The siding was of course placed beyond the top of the hill.

Tension and compression ruled the day for the LS&I, and I fear it would be similar for coupling powerheads on a milling setup.

Bob


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## BobL (Feb 25, 2011)

grandpatractor said:


> Except for some clutch slippage. That will change things.:msp_huh:


 
That's true, forgot about that, So the timing difference gap will then indeed be random. Once the clutches engage they will still have to turn at the same RPM.


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## BobL (Feb 25, 2011)

This is something that was recently posted in the Aussie milling forum in a discussion of the engineering and Physics of twin powerhead setups.
I think it's an interesting post especially for those besotted with twin power heads to think about.



> My experience with the twin head setup of 090's - the physics of it is mute in the real world usage.
> 
> Thats because in our Jarrah hardwoods and the lengths of logs we would slab at 4.2 meters and upward - means that you run out of fuel in one or the other saws long before you cut one full slab off.
> 
> ...


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## betterbuilt (Feb 25, 2011)

I was asking a client that I have who designs gears and such about this. He thought about it for a while and said it wouldn't be much faster or more efficient. He said the two powerheads would fight each other just like BobL and bobt said. I'm gonna give it a try in the spring anyhow.


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## BobL (Feb 25, 2011)

betterbuilt said:


> I was asking a client that I have who designs gears and such about this. He thought about it for a while and said it wouldn't be much faster or more efficient. He said the two powerheads would fight each other just like BobL and bobt said. I'm gonna give it a try in the spring anyhow.


 
I don't recall saying this. I don't think they would fight each other any more than one piston fights another in a multicylinder engine.


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## betterbuilt (Feb 25, 2011)

BobL said:


> I don't recall saying this. I don't think they would fight each other any more than one piston fights another in a multicylinder engine.


 
True, I mixed you up with someone else. I can't figure out where I read that.


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## bobt (Feb 25, 2011)

BobL said:


> I don't recall saying this. I don't think they would fight each other any more than one piston fights another in a multicylinder engine.


 
Hmm, why would you say that? In a multi cylinder engine, the cylinders are fixed to the same crankshaft and they work together. But then if they are not in perfect timing, the engine's performance suffers. Consider two cylinder engines that have two sets of points. You have to time the engine for max rpm for each cylinder seperately from each other.

In a multiple powerhead milling situation, they are separate, and unless the powerheads are EXACTLY throttled to provide the same power even though they are turning at the same rpm I figure that there will be loping and galloping between those powerheads. That situation can't be advantagious. Am I wrong???

Maybe I am way off on this.

Of course your post about the powerhead needing to be mounted upside down pretty well nullifies this whole argument.

Edit: Um, thinking this over, both powerheads need to be oriented the same way,,,,no?

Bob


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## PhilB (Feb 25, 2011)

Am I missing something? (one power head having to be upside down). Consider the power head in the normal (one head CSM) position, looking down on it, it turns ccw. Add the second power head to the other end of the bar (rotated 180 deg) but not upside down. It too turns ccw. Both pull the chain. The normal head is pulling the chain cutting the slab while the second head is also pulling the chain but not cutting (the return side of the bar). It seems to me that the chain would have to be kept tight to work properly. A new chain with its stretching could be a problem.

I'm considering making a two power head mill and am interested in further discussion.


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## PhilB (Feb 26, 2011)

Another way to picture this: Imagine you're freehand milling. The chain is pulling towards you (normal sawing). Now walk to the other side of the cant and finish the cut. The saw is cutting on the back side of the bar pushing away from you, if you didn't turn the saw upside down. The chain is cutting the cant in the same direction.

Phil


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## glennschumann (Feb 26, 2011)

*Redux*

We visit this topic from time to time, and it is worthy of discussion for the new folks. The search engine isn't always the best for finding the information, so below are my thoughts:

A double ended mill does work, and no, you don't have to turn one engine "upside down".

The two saws do not need to be perfectly synched... if one saw runs 12k at WOT, out of the wood, and one runs at 11k at WOT out of the wood, when the mill is set in the wood, both saws are turning at, say, 9k, excactly at the same speed. Neither saw will know that the other one is attached, as each one is "trying" to get back up to its max rpm by chewing through the wood.

I also agree that a double ended set up is heavy and difficult to use, expecially without a helper. If, however, you have two 066's and a 6' log, a double ended bar is probaby the way to go. Those slabs you cut are going to require a couple of people to move around anyway.

Will a double ended set up be twice as fast? No. Will it make an impossible job possible? Probably. I'm just waiting for the right log to justify the investment. I probably would not use a double ended set up on anything that I could get an 066 to do by itself, however


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## BobL (Feb 26, 2011)

PhilB said:


> Am I missing something? (one power head having to be upside down). Consider the power head in the normal (one head CSM) position, looking down on it, it turns ccw. Add the second power head to the other end of the bar (rotated 180 deg) but not upside down. It too turns ccw. Both pull the chain. The normal head is pulling the chain cutting the slab while the second head is also pulling the chain but not cutting (the return side of the bar).


 
You are right - methinks the aussie poster is spinning a bit of a yarn!







Saws like 090 and 075/76 are still a PITA to refuel mid-log


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## rarefish383 (Feb 26, 2011)

An other point to the refueling problem. If I were going to run a rig that big I'd bypass the factory fuel tank and mount a bigger tank in the middle of the rig some where and run fuel lines straight to the carbs. 

I do have a pair of 100cc power heads, but I don't want to hook them together. One is on the alaskan, and I'm making a heavy duty mini mill to make a bit of a monster beam cutting rig with a 24" bar.

The problem I see with two power heads is your chain still has the same size teeth and you still operate at a max RPM, so you will only cut so fast. Granted, the extra power head should help you maintain your max RPM under load. They make bars for twin heads, and if they didn't work at least half way well, people wouldn't buy them and they'd quit making them.

As you can see, I really don't know anything about twin heads, I just haven't made a post in a while, Joe.


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## cgarman (Feb 26, 2011)

BobL said:


> I'm surprised an engineer couldn't figure this out. Given the engines are connected by a chain under tension, they absolutely MUST turn at the same RPM, otherwise the chain would stretch like an elastic band on one side and bunch up on the other side bar. Now Whether they fire in synch or not depends on where the pistons are in their respective cycle relative to each other when the chain is put on the sprocket. Once the chain is on, the difference between the ignitions is fixed and will not change until the chain is removed.


 
Why is it that every time I say I'm an engineer people think I'm trying to 'pull rank'? I was just looking for an answer, and didn't want people to shy away from throwing some math my way.

Wow guys, thanks for jumping my $#!+. This engineer already worked out the clutch slippage idea and the fact that the saws would both produce a torque vector in the +Z direction (you know, up) without flipping one over.

Also, thanks for suggesting a web search. I have, and I keep getting people who say it doesn't work for the above reasons. Meaning they haven't tried it - otherwise they would have realized these 'problems' don't exist.

So has anyone actually tried it? It SEEMS to me like you'd be able to keep the chain speed up without the loading. Meaning you'd be able to (and have to) push on the saws to get a faster cut. This might work well with an inclined setup like BobL uses.


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## Timberframed (Feb 26, 2011)

I had recently posted a video of two 090's going at a 52" or so Ash log last month that I taped myself on site 5 years ago. Definitely faster but I won't consider the investment. Doing just fine with a single head setup. The ox is slow but the Earth is patient.


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## betterbuilt (Feb 26, 2011)

You know the more I think about the dual head thing one thing does come clear. The guy who thinks that one saws gas tank has to be down obviously hasn't tried it. If he actually tried it that way, I can only imagine what might have happen. Not to mention the chain would be on backwards on one saw.






Got this from this thread.
http://www.arboristsite.com/milling-saw-mills/104534.htm#post1637673


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## cgarman (Feb 26, 2011)

betterbuilt said:


> You know the more I think about the dual head thing one thing does come clear. The guy who thinks that one saws gas tank has to be down obviously hasn't tried it. If he actually tried it that way, I can only imagine what might have happen. Not to mention the chain would be on backwards on one saw.
> 
> 
> 
> ...


 


That was kind of my point - lots of armchair experts around.

Then again - maybe the guy who says it's inefficient was running one saw backwards. In that case, I guess he's right.... 090 Contra - 076AVE = 029?


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## betterbuilt (Feb 26, 2011)

cgarman said:


> That was kind of my point - lots of armchair experts around.
> 
> Then again - maybe the guy who says it's inefficient was running one saw backwards. In that case, I guess he's right.... 090 Contra - 076AVE = 029?


 

I figure if its even 10% faster it might be worth it.


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## PhilB (Feb 26, 2011)

I've been thinking about the speed advantage of a two power head CSM. It seems to me if you had a big CC power head on a single head CSM, adding a second head wouldn't get you much of a speed increase unless it was a very large cut. But if you had a medium CC power head, adding a second meduim CC power head would get you to the required horse power, increasing the speed. It's a matter of having enough HP for the job.


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## Daninvan (Feb 26, 2011)

I recently acquired a 4' long double headed bar. I will report back on how it works shortly. (Like a week or two)

Glad that I don't have to run one of the saws upside down though! I guess one will be the 'lead' saw and will get pulled into the log?

Dan


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## betterbuilt (Feb 26, 2011)

Daninvan said:


> I recently acquired a 4' long double headed bar. I will report back on how it works shortly. (Like a week or two)
> 
> Glad that I don't have to run one of the saws upside down though! I guess one will be the 'lead' saw and will get pulled into the log?
> 
> Dan


 
I'd be interested to hear how it goes. Your right on the lead saw. The first time I saw it, confused me.


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## john taliaferro (Feb 26, 2011)

Phill B , I MILL WITH 88 MEANER heck in maple but in 48" white oak it could use a 460 or 660 pulling some slack . Iam just not patient enough i guess


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## olyman (Feb 26, 2011)

BobL said:


> This is something that was recently posted in the Aussie milling forum in a discussion of the engineering and Physics of twin powerhead setups.
> I think it's an interesting post especially for those besotted with twin power heads to think about.


 
which is about what 820wards did--ex smaller power--


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## BobL (Feb 26, 2011)

rarefish383 said:


> .
> .
> The problem I see with two power heads is your chain still has the same size teeth and you still operate at a max RPM, so you will only cut so fast.
> .
> ...





PhilB said:


> I've been thinking about the speed advantage of a two power head CSM. It seems to me if you had a big CC power head on a single head CSM, adding a second head wouldn't get you much of a speed increase unless it was a very large cut. But if you had a medium CC power head, adding a second meduim CC power head would get you to the required horse power, increasing the speed. It's a matter of having enough HP for the job.



Cutting speed could be improved significantly by driving bigger sprockets and running much lower rakers - I've heard about rakers as low as 0.06 being used on 4 stroke slabbers


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## john taliaferro (Feb 26, 2011)

Bob .06 what , how many degrees is that and what is a 4 stroke slabber ?


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## BobL (Feb 26, 2011)

john taliaferro said:


> Bob .06 what , how many degrees is that and what is a 4 stroke slabber ?


 
Sorry, 0.06" for raker depths. 
A 4 stroke slabber is ~20 HP four stroke engine and a 60" + bar all mounted on a carriage that runs on rails alongside the log. This is the Lucas Mill version.


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## Bambi (Feb 26, 2011)

I haven't milled in a couple of years, too many other duties. Years ago 70's milled with a dual setup. It was big, cumbersome, noisey of course and very heavy. I thought it was the cats ass. It was easy gettin someone to run the other saw, but you had to pay attention to them. Getting someone regularly that had some experience, that would pay attention to you and things in general was a problem. There were some friends that, I would never let on a sawmill let alone a chainsaw ever again. 
If we fast forward a few years, people knew that I milled back then and life moved on. One day someone put the bug back in me and I had 4' ash, maple and poplar to contend with. New saw, 3120, 54" Woodsman Pro bar (Canon) with the stinger handle. This gave me the option of goin dual. As for chain, I stuck with the Baileys chain as well as Granbergs. With two of us on the mill, we cut a 48" wide slab 17' long in around 15 minutes on fresh white ash. I didn't time this, someone else did. 
Technology has changed. I have tried other chains, some cut leaving an coarser finish. I have also run this setup by myself. Most of the time I would be milling by myself. Not gonna happen with a dually. 
I have also used regular new, not used motor oil as a oil in the auxilliary oiler and winter bar oil in the saw. Bar does run a lot cooler.
The issue that I am reading is how much faster can we go if we run a dually? 10%, 20%, 30%. Fuel is a minor part of the issue. The question is do you have a competent helper all of the time? Weight, this is gonna weight a ton. Cost, double end bars are bit more expensive and the cost of another saw, them big saws bring big money. For the amount of money it costs for so little a gain, it doesn't add up in my opinion.
I would opt for maybe a ported saw with improved muffler. Chain sharpening well my opinion BobL is the man. I like the Canon bars. I would put my money in the details getting more bang for my buck. 
Many guys like Aggie and BobL have been milling giant wood with singles very successfully. I don't think I will ever see some of the giant stuff they mill, but if I do, I'll either buy a bigger bar or deal with it another way.
Though I would like to have another 090 or two, just to hear them bark once in awhile. I would rather work with the 3120 or an 088. Work smarter and not harder.
I would like to thank guys like Aggie, BobL, Woodshop where ever he is and many others. I enjoy their comments and the info they share, I have learned some tricks and many shortcuts. I appreciate all that everyone contributes.
Just my two cents.


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## Bambi (Feb 26, 2011)

I think the guy is Edwards that built a mill with and old McCullough? motor, did a really nice job, sorta like BobL and his rigs. BobL just mentioned the 20hp 4cycle slabbers. I have a friend that runs motocross. He runs Kawasaki 125's. They sell basically the same motor for shifter karts. 
If I was think of buildin a chainsawmill, like an Alaskan and had the money I would use one of them motors. Watercooled. If my memory serves me right they were gettin about 43 horsepower out of them and they spun 15,000 rpms. They are not all that heavy. With the prices of saws goin up, one of those might compare in price, but then you have to make it work. I could see BobL buildin the better mousetrap.
Just some food for thought.


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## mtngun (Feb 26, 2011)

Bambi said:


> New saw, 3120, 54" Woodsman Pro bar (Canon) with the stinger handle. This gave me the option of goin dual. As for chain, I stuck with the Baileys chain as well as Granbergs. With two of us on the mill, we cut a 48" wide slab 17' long in around 15 minutes on fresh white ash. I didn't time this, someone else did.


0.227 inch/sec, thanks for the data point. That's believable, and it's not bad for a 48" wide cut.


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## 820wards (Feb 27, 2011)

BobL said:


> Cutting speed could be improved significantly by driving bigger sprockets and running much lower rakers - I've heard about rakers as low as 0.06 being used on 4 stroke slabbers


 
Bob,

I changed out the sprocket on my mill that was running an 7 x .404 sprocket to a 8 x .404 and with BobL's calculations it increased the speed of the chain by 14%. Now my 134cc 820 PowerBee motor doesn't operate at 10K+ RPM, but the torque makes up for less RPM. With the additional torque the motor has I have also been able to set my rakers at .042" allowing me to make a deeper cut. I'm of the opinion that one good motor is less expensive to operate than two motors trying to ballet together. 
jerry-

My mill with it's 134cc 820 PowerBee motor.


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## john taliaferro (Feb 27, 2011)

Jerry what was the weight , my 88 , 60 cannon ,grand berg is 58 lb .


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## 820wards (Feb 27, 2011)

john taliaferro said:


> Jerry what was the weight , my 88 , 60 cannon ,grand berg is 58 lb .


 
My mill has a 38" bar and with the gas tank and two oil tanks full it weighs 62 pounds.

jerry-


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## BobL (Feb 27, 2011)

betterbuilt said:


> You know the more I think about the dual head thing one thing does come clear. The guy who thinks that one saws gas tank has to be down obviously hasn't tried it.


 
Actually we (the Aussie) just worked out what he meant, he's not talking about the saw being upside down on the mill, he's referring to when a double ended mill using saws like 090s or 076s need to be fueled. On these saws the gas cap is on the top of the saw. That means to fuel up one saw the mill has to laid over on its side, then the other saw is upside down and to fill this one the mill has to be laid over the other. Still not that big deal I reckon.


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## gemniii (Feb 27, 2011)

glennschumann said:


> We visit this topic from time to time, and it is worthy of discussion for the new folks. The search engine isn't always the best for finding the information,



"The search engine" here is BROKE.
Google:
dual powerheads site:arboristsite.com.

I started a thread back in November, http://www.arboristsite.com/milling-saw-mills/151749.htm. Some good pics of woodrunner w/ a dually.

However most people just said buy a bigger power head. Then the thread degenerated into a beer thread.

People that hadn't tried it knew all the problems and why it wouldn't work.

Bumblebees can't fly, the earth is flat and the center of the universe.



gemniii said:


> Well it seems like always, I didn't express myself well enough.
> 
> I've got one 660 and just bought another from redlinefever, both about the same HP, same CC. Woodsrunner had a 395 and a 385, slightly different but the setup worked well for him.
> 
> ...



Bottom line is it seems to work for some.


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## betterbuilt (Feb 28, 2011)

BobL said:


> Actually we (the Aussie) just worked out what he meant, he's not talking about the saw being upside down on the mill, he's referring to when a double ended mill using saws like 090s or 076s need to be fueled. On these saws the gas cap is on the top of the saw. That means to fuel up one saw the mill has to laid over on its side, then the other saw is upside down and to fill this one the mill has to be laid over the other. Still not that big deal I reckon.


 
That makes more sense.


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## PhilB (Feb 28, 2011)

PhilB said:


> Am I missing something? (one power head having to be upside down).


 
I guess I did miss something. Thanks Bob for clearing this up.

Well it at least it got some of us thinking about how this all works.

Phil


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