Hydraulic Chainsaw

[hounddog74]

Can anyone tell me how to size a hydraulic motor to replace a 8.7 hp 191 cc gas engine? I want to convert a portable chainsaw sawmill to hydraulic power and drive the pump with a twin cylinder engine. Any discussion or help would be appreciated.

 

[kubotakid USA]

Can anyone tell me how to size a hydraulic motor to replace a 8.7 hp 191 cc gas engine? I want to convert a portable chainsaw sawmill to hydraulic power and drive the pump with a twin cylinder engine. Any discussion or help would be appreciated,.. GOOGLE, your (Best friend) will give you pages of imfo,.. type in (hydraulic chain saw motor), Eric

 

[Don87]

Can anyone tell me how to size a hydraulic motor to replace a 8.7 hp 191 cc gas engine? I want to convert a portable chainsaw sawmill to hydraulic power and drive the pump with a twin cylinder engine. Any discussion or help would be appreciated,.. GOOGLE, your (Best friend) will give you pages of imfo,.. type in (hydraulic chain saw motor), Eric

The 'hydraulics' forum here on TBN would give fast results also, and may be friendlier.

 

[jbooth]

This site might furnish some ideas or even parts for your build.


Basic Saw

 

[oldnslo]

Can anyone tell me how to size a hydraulic motor to replace a 8.7 hp 191 cc gas engine? I want to convert a portable chainsaw sawmill to hydraulic power and drive the pump with a twin cylinder engine. Any discussion or help would be appreciated.

A couple of things you will need to know to size of pump and motor is.

What speed do you want the saw motor to operate at and what torque?

Knowing this will provide a starting point for figuring motor size and then pump size, etc..

Roy

 

[hounddog74]

The specs on the original 8.7 hp motor say 9000 rpm and I assume thats with no load. I know they make bucksaws that are hydraulic but I haven't been able to find out what the rpm's are or what the torque is.

 

[oldnslo]

The only style of motor I can think of that might run close to 9000 RPM is bent axis piston. These are usually rated for high pressure (5000 PSI or higher) operation so they are fairly expensive. I do not know of any gear or vane type motors that will operate at that speed. Possibly AKKAMAN will chime in since I believe he used to work on and around logging equipment.

Roy

 

[hounddog74]

The gasoline motor runs 9000 rpm. I'm not sure what speed the hydraulic motor would have to run but I'm thinking it would have to be less than that.

 

[oldnslo]

If my math is correct:

8.7 HP at 9000 RPM is around 60 in-lbs of torque.

8.7 HP at 7000 RPM is 78 in-lbs of torque

To generate 78 in-lbs of torque at 2500 PSI requires the use of a 0.2 CIR (Cubic Inch Revolution) or 3.23 cc/rev hydraulic motor. This torque can be generated at speeds from min to max RPM rating of the motor.

If we figure the 0.2 CIR motor operating at 7000 RPM your theorectical inlet flow would be. 7000 RPM x 0.2 CIR / 231 = 6.06 GPM

6.06 GPM x 2500 PSI /1714 = 8.75 HP theorectical input HP to drive the pump.

Now throw in hydraulic inefficency.

Figure the hydraulic motor at 90% efficient which is a good motor so inlet flow becomes 6.06 x 1.1 = 6.7 GPM required to keep the motor running at full load conditions.

Figure the pump at 90 % efficient which again is a good pump and your pump size becomes 6.7 x 1.1 = 7.4 GPM

now 7.4 GPM x 2500 PSI / 1714 = 10.8 HP to drive the hydraulic pump.

Do these numbers make sense and help give you some idea of component sizing required?

Roy

 

[hounddog74]

That's wonderful! Thank you. That's what I have been trying to figure out.

 

[hounddog74]

I looked in Grainger and the smallest motor was a 2.8 cu inch/rev motor. The max rpm is 962. The max pressure is 2400 psi. Do I get the higher rpm's with my sprockets? Do I need the higher rpm's to saw efficiently?

 

[oldnslo]

I looked in Grainger and the smallest motor was a 2.8 cu inch/rev motor. The max rpm is 962. The max pressure is 2400 psi. Do I get the higher rpm's with my sprockets? Do I need the higher rpm's to saw efficiently?

I would suspect that you will require higher RPM's for the saw to work effectively. I believe companies like Bosch - RexRoth, Parker, Eaton, Sauer Danfoss may make higher RPM style motors that will operate at much higher RPM. The more gears you install the more losses you create. I have seen hydraulic chain saws on TV where they are used to cut logs to length to load on trucks. From memory I believe they where direct drive from the Hydraulic motor to the saw. Not sure what size and RPM these operate at though. Piston style motors are the most efficient but require keeping the oil clean. They will also require a case drain directly back to tank so three lines will need to be run from the motor.

Roy

 

[N8ghz]

The factory specs on saws used by power companies,etc. made by Fairmont are as follows:

model 6200-B 16"

4-8 GPM
1000 to 2000 PSI

Chain Speed @ 4 GPM = 1814 FPM
6 GPM = 2671 FPM
8 GPM = 3527 FPM

I think the drive sprocket is a 7 tooth, but haven't looked at one lately?

RPM for motor is not stated.

 

[N8ghz]

Update on Fairmont saw specs.

I was looking at my excel calc sheet for this and see I had worked out the specs.

This saw uses .375 .050 chain and has an 8 tooth driver.
Without going thru the formula, the answers are as follows:

Chain speed @ 6 GPM is 2641 FPM and motor RPM would be ~5300
Chain speed @ 8 GPM is 3527 FPM and motor RPM would be ~7050

As an example, if using .404 chain, FPM for 6 GPM on this saw motor would increase to 2855 FPM and @ 8 GPM it becomes 3798 FPM with an 8 tooth drive sprocket.
It is how many inches of chain moved per revolution determined by RPM, pitch and tooth count.



Hope this helps in choosing a motor to make a saw?

 

[hddnis]

A quick search using bing.com gave me a lead for you.

From Parker and shows that they have motors up to 7500rpm
http://www.parker.com/literature/026 High Speed FINAL.pdf

Hope this helps.




Mr. HE

 

[ferguson123]

check out my homemade hydraulic chainsaw. might be of sum help

Ferguson Firewood Processors

 

[BHD]

our power company came by tree trimming and had a hydraulic chain saw, and it speed was a lot slower than a gas unit, but the person running the saw said the chain stayed sharp a lot longer,

one may be able to fine a larger drive sprocket to up the chain speed over the standard gas sprocket.

 

[ptgdigger]

High speed hydraulic motors at surplus center: Surplus Center



Ray

 

[Qapla]

I have not had any personal experience with the hydraulic chain saws. I did see a program on TV that was about some of the current logging equipment.

They showed the hydro-chain saw and explained that one of the reasons they are so effective is that unlike a "hand-held" saw, these have specially designed teeth. It has something to do with the hand-held saws have a cutting tooth followed by a "clearing tooth". That makes them only cut with every-other tooth.

The hydro saws, since they are being held by a machine, have a "combo-tooth" and cut with every tooth. They explained that if the hand held saw used such a chain, a man could not hold it to use it since it is too aggressive.

 

[hddnis]

Harvester saw chain and handheld saw chain look exactly the same. There is no type of clearing tooth on a chainsaw chain at all, in any size. Harvester chain has the depth guage ground down because the motors have the power to pull it. Harvester chain is built heavier to be more durable.


Mr. HE