Twin Engined Mills

[akennyd]

Hello,

Does anyone use twin engined chainsaw mills anymore?

Did a little bit of searching and couldn't find anything on this. I saw an article in a late 70's or early 80's Fine Woodworking book and the guy was using a chainsaw mill with two engines on it.

Thanks,
Kenny
John 3:16

 

[mtngun]

Seems like one of our members sometimes uses a 2 engine set up, but for the most part one saw gets the job done and can be managed by one person.

 

[akennyd]

Thanks for the reply!!

I'm going to see if I can find that book again at my local library. My understanding of the setup they were using it was a one operator system but I could certainly be wrong on that point.

Kenny
John 3:16

 

[Can8ianTimber]

Not that hard. Double ended bar and two saws. Hard part is getting both tuned to run at same rpm. I have cut 6' wide hardwood is single head (3120) and was suprised that it was as fast as it was. I would recomend one big saw over 2 saws unless you are cutting wider than maybe 6'.

 

[woodsrunner]

I have just started doing this. I'm certainly not an expert on using two power heads on a mill by any stretch of the imagination. However, I have been happy with how the 2 powerhead setup performed. Check out this thread:

http://www.arboristsite.com/showthread.php?p=1637673


My logic was that I already had 2 large saws. why not try to get more utility out of those 2 saws instead of buying a new 880 or 3120 which would only be used on the mill? Also wouldn't 2 large saws at 7.1 hp and 6.3 hp be more powerful than a single 8+ hp saw?

Anyways, read the thread and see what you think.

Scott

 

[BobL]

Not that hard. Double ended bar and two saws. Hard part is getting both tuned to run at same rpm.

Apparently it's not that hard. Provided the saws are not too mismatched in terms of power and max RPM, eg one saw has a max RPM of 12k and the other has a max rpm of 10 then they just balance each other out.

I prefer to mill by myself so going a double unless it's on a rail system of some kind would be extremely difficult.

 

[Can8ianTimber]

Hey Bob, what do you think about having dual remote throtle for both power heads? That way one operator could "feel" the throtle on both saws and balance out the RPM's. I don't know if one guy would be able to cart a set up like that around or lift it in place but it would be cool.

 

[BobL]

Hey Bob, what do you think about having dual remote throtle for both power heads? That way one operator could "feel" the throtle on both saws and balance out the RPM's. I don't know if one guy would be able to cart a set up like that around or lift it in place but it would be cool.

It's not necessary to match the revs using different throttles, or even possible to have different rpms. The machines are directly mechanically connected by the chain. That is effectively exactly the same as the two cylinders being connected by the same crankshaft. If for some reason they were able to run at even lightly different RPMs that would destroy the clutch or tear the chain apart.

Think about a multi-cylinder engine, all the pistons are connected by the crankshaft so they all have to do the same revs, there's no way they cannot. For a whole range of reasons one cylinder might produce a little more power and one a little less but they all do the same RPMs.

If saw A is started and running at WOT and saw B is still stopped, the clutch on B will spin freely.

Now lets say saw A is running WOT and saw B is started and lightly revved so the clutch grabs. the revs on Saw B will increase (without further throttle) while on the still WOT Saw A the revs will drop as it divert its power to saw B, until an equilibrium is reached.

Now run both at WOT - the saws RPMS will self balance just like a multicylinder engine. Ideally they should both be started and brought up to WOT at the same time (same few seconds), and dropped to idle also within the same few seconds, as you don't want high revs and only idle level amounts of mix coming into the cylinder since that will not provide enough lube.

A single remote throttle would be all that is needed. It really is that simple.

Multiple engine machines like the chainsaw powered drag bikes all work in the same way.

 

[Can8ianTimber]

It's not necessary to match the revs using different throttles, or even possible to have different rpms. The machines are directly mechanically connected by the chain. That is effectively exactly the same as the two cylinders being connected by the same crankshaft. If for some reason they were able to run at even lightly different RPMs that would destroy the clutch or tear the chain apart.

Think about a multi-cylinder engine, all the pistons are connected by the crankshaft so they all have to do the same revs, there's no way they cannot. For a whole range of reasons one cylinder might produce a little more power and one a little less but they all do the same RPMs.

If saw A is started and running at WOT and saw B is still stopped, the clutch on B will spin freely.

Now lets say saw A is running WOT and saw B is started and lightly revved so the clutch grabs. the revs on Saw B will increase (without further throttle) while on the still WOT Saw A the revs will drop as it divert its power to saw B, until an equilibrium is reached.

Now run both at WOT - the saws RPMS will self balance just like a multicylinder engine. Ideally they should both be started and brought up to WOT at the same time (same few seconds), and dropped to idle also within the same few seconds, as you don't want high revs and only idle level amounts of mix coming into the cylinder since that will not provide enough lube.

A single remote throttle would be all that is needed. It really is that simple.

Multiple engine machines like the chainsaw powered drag bikes all work in the same way.

OK so that is pretty simple and easy to understand. The dynamic that I am wondering about is if one typicly runs at slightly lower rpms and you go full throtle on both is the weaker saw really helping. Or in general is the second saw really doing anything at all? In a multi cylinder engin you have perfect timing between cylinders so they work perfectly together. In this situation perfect timing is near impossible and I guess your power gain depends on how close to perfect you get.

Sounds like we need some tests of one powerhead to 2. Anyone want to donate their 3120 to me so I can test the power gain from one saw head to two?:greenchainsaw:

 

[woodsrunner]

No need to test. Just believe. :biggrinbounce2:

Seriously, it does work and works easily and well.

Scott

 

[glennschumann]

I'm with BobL on this... 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.

 

[Can8ianTimber]

I'm with BobL on this... 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.

Ahhhh, that is the part I was not thinking about. Both saws are running at less than max RPM and both are trying to get back to max. Light bulb just turned on. COOOOOL

 

[BobL]

Ahhhh, that is the part I was not thinking about. Both saws are running at less than max RPM and both are trying to get back to max. Light bulb just turned on. COOOOOL

Yep - that's it. The saws just fall into line with each other. Like rowers.

Problems can arise when the 2 saws have max powers at vastly different RPMs

For example a 50 cc low revving saw paired with a 100 cc high revving saw. The big saw would drive the smaller saw above its power curve where the big saw does all the work and the little saw just coasts. The small saw could even be driven above its max RPM and sustain significant damage.

A 50 cc high revving saw paired with a 100 cc low revving saw. The smaller saw would lose power constantly trying to drive the bigger saw above its power curve. Probably no real damage though.

One way around these problems would be to use different size sprockets or better still just match the saw RPMS

 

[Backwoods]

This is some good information that has answered a few questions that I had.
I have 60” bar for busting down those big logs and it works great for that task, but there is quite a bit of flex in a bar of that length, even when the mill is attached there is some flex. I know where there is an 8’ double ended bar and it is much heavier and stiffer. I have been waiting for the right log to come along that would justify the purchase of all the components to make a large double ended slabber.

 

[BobL]

This is some good information that has answered a few questions that I had.
I have 60” bar for busting down those big logs and it works great for that task, but there is quite a bit of flex in a bar of that length, even when the mill is attached there is some flex. I know where there is an 8’ double ended bar and it is much heavier and stiffer. I have been waiting for the right log to come along that would justify the purchase of all the components to make a large double ended slabber.

Double ender setups on conventional Alaskans also tend to bow upwards in the middle.