Has anyone built a hydraulic chainsaw?

[4570Man]

I'm working on building a firewood processor. I'd like to go with a hydraulic saw but, buying one puts this project well over budget. I'm considering building one. Has anyone built one from a regular hydraulic motor which I have several of laying around? Will a chainsaw work sufficiently with a low rpm and high toque compared to a gas saw? Also I have an old Stanley hydraulic saw. It has like a 10" bar which is unsuitable. If I changed bars to a 20" 3/8 chain what kind of power could be expected? My hopes for this saw working at a suitable speed is slim since it's running such a short bar with chain that's narrower than 1/4 chain.

 

[Captain Dirty]

Forty years ago a fellow reservist worked for a utility company that used hydraulic chainsaws for electrocution and theft reasons. He recounted that the saws would be stolen from their trucks fairly often but were usually recovered within a block or two once the thief discovered what might have been the fuel and bar oil caps were hydraulic connectors and abandoned his prize. I'm not advocating that you lift such a saw, but a utility company might be a source for damaged or worn saws you could acquire cheaply and repair.

 

[newbury]

Try diligently searching auctions. I've seen a couple come up for sale over the years within 200 miles of me.

 

[PILOON]

I suspect the main problem will be RPM's.
Gas powered saws rely on high RPMs for efficiency but Hydraulic motors rarely spin all that fast.
Hydro application is sporadic, like a limb here and there but no production.

On the other hand if it works for hydro it should work for you.
I might just all be a matter of proper chain for the job, I suspect that slow = lots of torque so a larger chain (than gas driven) could be the answer.

LOL, stop the next hydro truck and have a look at their saw.

I knew a guy that had a hydraulic tree harvesting rig mounted on a tracked excavator and recall that the saw was slow and gummed up in soft woods from time to time but did do the job.
He'd fell the tree, grab and position over a pickup truck and chop into firewood lengths dropping the cuts into the truck box, and never leave the excavator cab.

 

[muddstopper]

The saw in the pic is one I built for my processor build. This motor is a 1.3cuin axlepiston type. The bar is 24in with a .404 full comp, full chisel chain. This saw is also untested as I developed health problems and have yet to finish my processor build.

First off, I would forget trying to figure rpms as a measure of cutting speed. Chain speed is figured in feet per minute or sometimes feet per second. chains speed can be varied by drive sprocket selection. A larger sprocket will produce faster chain speed. The trick is to produce enough torque to pull the chain at the desired speed. When building my saw, I choose a husky 3120 gas powered saw to try and match. Numbers arent in front of me, but I took the hp, torque, and chains speed to try and come up with a hyd motor combination that would match the 3120 chainsaw. Here is a link to help. Chainsaw Comparisons and Facts from Procut Portable Chainsaw Mills.

A lot of people have used this motor, .7 cu in PARKER MGG2-BA1A3 HYD MOTOR to build their saws. Some have tried the .58cuin motor and not been satisfied with the results. I cant say whether the complains are from poor motor selection or poor hyd design. I will say that even the .70 motor in the link will never be able to match a 3120 chainsaw when it comes to torque. Even tho those little motors are rated for 5000 rpms, you cant put the pressure to them to get the torque numbers you need.

Gear motors are usually limited as to rpm speed, even if you can throw more pressure at them to get the torque needed. You can compensate some on the speed by using a larger sprocket, but then you sacrafice torque losses. I chose the axial piston motor because it will produce more torque and higher rpms than a standard gear motor. This particular motor is a Poclain model M1. It is 1.3 cuin and can produce 4641ftlbs of torque. It does take a lot more oil flow and pressure, which means bigger hyd pumps and engine hp, but it all depends on how badass a saw you want to build. A 3120 chainsaw has 8.9hp, the axial piston motor will put out 25hp at 2000psi.

 

[Oldoak]

If I were to build a firewood processor, I would incorporate a buzz saw rather than a hydraulic chain saw. Much faster cutting and the teeth stay sharper for a longer period of time. And the buzz saw blade can even be purchased with replicable carbide teeth, although the initial cost of the blade is much higher.

I know it's not the same, but I cut tons and tons of fire wood with a belt driven buzz saw on the front end of a JD B tractor. In later years we converted the saw over to a 3 point hitch, PTO driven saw. Wicked cutting machine. We never allowed kids or pets around. Didn't want any distractions.

In a heavy industry environment, we used huge automatic buzz saws on the live deck in the pulp mill woodyard.

 

[TemporaryKubotaOwnerMark]

I suspect the main problem will be RPM's.
Gas powered saws rely on high RPMs for efficiency

First off, I would forget trying to figure rpms as a measure of cutting speed. Chain speed is figured in feet per minute or sometimes feet per second. chains speed can be varied by drive sprocket selection. A larger sprocket will produce faster chain speed.

True, but the bar you are using puts a limit on how big your sprocket can be. You can't have a bar that is, say, 3" across and a 10" sprocket behind it.

So you are back to needing high RPMs for your motor, OR, some kind of gearing mechanism to increase the speed. For reference most chainsaws spin above 10,000 RPM, some in the 13,000 range.

Hydraulic chainsaws do exist - they are used in forestry applications. I pick up log butt ends and crotches from a wood processor, and he has a hydraulic chainsaw with about a 60" bar that makes short work of big logs. The chips fly far and fast. But it's driven by the same diesel that powers his log grapple. I don't know the size of the engine, but I'm thinking it's a few hundred horses at least.

 

[4570Man]

I would be satisfied if my hydraulic saw can cut with my 372 XP. I think it's 5.5 hp. The engine intended for the splitter is a 17 hp military gas engine. I had a free 4bt cummins, but I abandoned that idea mostly due to weight.

 

[muddstopper]

While it is true that a circle saw will cut fast, it also adds a lot of cost to a wood processor. I can buy several bars and chains for what a large circle saw cost.It takes big hyd motors, which require big pumps and bigger engines. There is also the issue of the dia of wood the saw can cut thru. If you are trying to clean cut thru a 24in dia log, the blade is going to be 50+ inches in dia.
Assuming the OP does use the 17hp gas engine as a power source. That limits the amount of hyd flow and pressure that that can be produced and the size of the hyd motor to run the saw. It can be done, but it comes back to how badass a saw you want to build. One has to take into account that with the small motor, to get the flow needed to run the saw, your going to probably have to go to a 2 stage hyd pump. the saw motor should operate with just the high flow low pressure side of the hyd pump, but if it builds enough pressure it
could kick into the low flow high pressure part of pump. cutting would be very erratic. It will certainly be slow, not in the 372xp performance range the op is looking for.
I have demo'ed several factory processors. Most of the cheaper ones use at least a 25hp gas engine. I can say I have never operated one with those small engines that had a hyd saw cut with the speed I look for out of a chainsaw. On most of them, its advance the log, clamp and saw, then split and repeat. You cant do all operations at the same time. There is a reason for that and it is limited hyd flow and engine hp. If I was going to do this build, I would chunk the little 17hp engine and go get the 4bt cummins. If not the cummins then at least try to get in the 25+hp range. Yes it adds weight, but it also allows you to run multiple pumps and do more operations, with greater speed. If I was dead set on the small engine, I would just make a mount for the 372xp saw and not fool with a hyd saw. I have also observed the big circle saw processors, these are $40-$60,000 processors and they use large engines and multiple hyd pumps. They do cut fast, but again, how badass saw do you want, or more importantly, how deep are our pockets.

 

[muddstopper]

True, but the bar you are using puts a limit on how big your sprocket can be. You can't have a bar that is, say, 3" across and a 10" sprocket behind it.

So you are back to needing high RPMs for your motor, OR, some kind of gearing mechanism to increase the speed. For reference most chainsaws spin above 10,000 RPM, some in the 13,000 range.

Hydraulic chainsaws do exist - they are used in forestry applications. I pick up log butt ends and crotches from a wood processor, and he has a hydraulic chainsaw with about a 60" bar that makes short work of big logs. The chips fly far and fast. But it's driven by the same diesel that powers his log grapple. I don't know the size of the engine, but I'm thinking it's a few hundred horses at least.

I dont think you are going to find a 10in chainsaw sprocket, but you can find larger saw bars. They are called harvester bars. Since the chain speed is a factor of rpms, rim size and chain pitch, the size bar does have to match the sprocket size. I am using a 13pin rim on my saw and a .404 pitch chain. I dont have the number in front of me but the chain speed is within about 50ftper min of the 3120 chainsaw I tried to imitate. There is a big difference in hp and torque as my saw has about 3 times the hp and 4 or 5 times the torque of the 3120 gas saw. If I thought I needed more chain speed, I could swap the 13pin rim for a 14,15,16 etc. pin rim. Doing so I would also have to swap my little harvester bar for a large harvester bar to keep the chain running in the bar guide rails.

I also pick up butt cuts and ugley wood from logging sites. The loggers use what I call buck saws. These saws use much larger, BC size chains and the knuckle boom hyd's to operate. if you open up the covers on these saws, you will see a large hyd motor with a large belt pulley driving a jackshaft with small pulley that pulls the saw chain. they get the chain speed thru gearing. The large hyd capacity of the knuckle boom loader allows the use of a very large hyd motor and lots of hyd pressure too pull those big pitch saw chains. You also have the Harvester saws you see on knuckle booms that run the f11, f12 bent axis hyd motors. These hyd motors turn very high rpms and operate off pressures up to 5000psi. For a firewood processor, pumping 5000psi off a 17hp engine, with enough flow to run one of those $1800 f11 motors isnt going to happen.

Compareing a 10,000, 12000 rpm chain saw to a 3000rpm hyd motor isnt compareing apple to apples. First off, a chainsaw runs a .325,3/8 size pitch chain. The big sthill 880 or husky 3120 can run 3/8 or .404 pitch chains. Now while it is common for a small saw to turn up to 12500 rpms, the large saws only turn aroud 8000 rpms. The older saws only turned 7000 rpms. when you compare the rim size on those different saws, you can see a hugh difference in dia. While a normal off the shlelf saw will usually have 7 teeth.pins, you can buy 6 pin or 8 pin for most size saws. Going from a 7 pin sprocket to a 14 pin sprocket will double the speed of the chain, thats simple gearing. Now if you have a saw that turns 10,000 rpms and a hyd motor that only turns 5000 rpms, just changeing the sprocket will allow you to get the same chain speed. Going from a 3/8 pitch chain to a .404 pitch chains wit appropriate sprocket will also increase chain speed. Of course using a more aggressive cutting .404 chain will take more power than pulling a 3/8 chain. Where I think, and its just my opinion, where people go wrong trying to build a hydraulic chains saw, is that they dont understand the relationship between rpms and actual chain speed. When you compare a gas powered chain saw to a hyd driven saw, the first thing they look at is the gas saw runs at 12000 rpms and they think they need to get a hyd motor that will turn the same speed. Its just not true. You do need to match chains speed but you also have to factor in torque. If the 5.5 hp husky 372 cutting speed suits the OP's performacne goals, then that is the numbers he needs to use to build his saw. He can look at the rpms, hp and torque rateing of the 372 and do the math to find the size hyd motor , hyd pumps, sprocket size and hp requirement to match the 372 numbers.