Good morning All,

I am trying to design a hydraulic saw for cutting holes in lake ice. The saw will have a roughly four foot long bar and chain and a 5 HP horizontal shaft gasoline engine. What I would like to do is drive a ~.35 cu. in. pump with the engine via a Lovejoy type coupler. I would use the engine attached pump to drive the “chain motor” of ~.27 cu. in. This should give me about 5,000 rpm from the chain motor. Does this sound logical? Is this pump/motor combination too small for a 5 HP engine?

I did have delusions of adding in a single acting hydraulic cylinder, with a separate return spring, to lower the bar. The thought was that I could use the same hydraulic pump to both power the chain motor and supply the pressure necessary to extend the cylinder. I would imagine that there will be some backpressure created by the motor, and it should not take much to drive the bar down into the ice. To make the whole process a little more predictable, I planned on installing a needle valve for bi-directional flow control and restriction.

What I am really struggling with are the actual controls. I see that Burden has a Parker two spool, single acting, open center control valve. Will this valve work in this application? There are two flow rates available, 5 GPM and 10 GPM. I was thinking that the 5 GPM might provide additional back pressure to allow the cylinder to function.

So, am I completely out of line in my logic here? The whole project is on a shoestring budget, as it is going to be a gift, so spending $1,000 on it is not totally feasible. However, the person who I am building it for knows that I am an engineer, so I would like to build something impressive. More importantly, this needs to be intrinsically safe. As it stands, if I were to use the control valve I mentioned, the unit could have a built in “deadman” switch.

Thank you for taking the time to read this, and I look forward to reading your comments.

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Originally posted by abadv8:
Good morning All

Good morning!

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I am trying to design a hydraulic saw for cutting holes in lake ice. The saw will have a roughly four foot long bar and chain and a 5 HP horizontal shaft gasoline engine.

I suppose those 5 HP is what you would need on a chainsaw with a 4' bar. Converting into hydraulic, count on loosing 30-50% of output power into heat losses in hydraulic fluid. What output power and torque do you expect from the motor?

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What I would like to do is drive a ~.35 cu. in. pump with the engine via a Lovejoy type coupler. I would use the engine attached pump to drive the “chain motor” of ~.27 cu. in. This should give me about 5,000 rpm from the chain motor. Does this sound logical? Is this pump/motor combination too small for a 5 HP engine?

With volumetric in-efficiancy of 88% on each pump and motor you might need the same rpm's on pump as you get on the motor 1:1 , Isn't mechanical direct drive the way to go...buy a chain saw for 1000$....OK, I understand you are into this challenge....

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I did have delusions of adding in a single acting hydraulic cylinder, with a separate return spring, to lower the bar. The thought was that I could use the same hydraulic pump to both power the chain motor and supply the pressure necessary to extend the cylinder. I would imagine that there will be some backpressure created by the motor, and it should not take much to drive the bar down into the ice. To make the whole process a little more predictable, I planned on installing a needle valve for bi-directional flow control and restriction.

This is the part where you are going to break your budget, both on $$$ and your own time input at the shop...I think you started in the wrong end, deciding what engine to use, this will add more horsepower (most will go into losses), to your system....Why not go for a simple solution instead of complicated....ICE is pretty consistant and think about moving the bar with force from gravity. What is your idea of design for the "vessel" to carry all this??

quote:

What I am really struggling with are the actual controls. I see that Burden has a Parker two spool, single acting, open center control valve. Will this valve work in this application? There are two flow rates available, 5 GPM and 10 GPM. I was thinking that the 5 GPM might provide additional back pressure to allow the cylinder to function.

If you are designing for a 2500psi pressure, you will need the 10gpm valve....but that pressure depends on your required torque output, which is not defined yet....

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So, am I completely out of line in my logic here? The whole project is on a shoestring budget, as it is going to be a gift, so spending $1,000 on it is not totally feasible. However, the person who I am building it for knows that I am an engineer, so I would like to build something impressive. More importantly, this needs to be intrinsically safe. As it stands, if I were to use the control valve I mentioned, the unit could have a built in “deadman” switch.

With only a 1000$ budget, IMO, you can't make it, unless yo have a lot of hardware/metal for free, and PLENTY OF HOURS AVAILABLE!!! Not to talk about when it have to be finished!!

Impressive would to me with that budget would be a BRAND NEW 4'bar chainsaw, and a custom made rig, for that chainsaw, to cut holes in the ice, bar feed by weights and gravity...put your money into the safety and simplicity instead of hydraulics...

That chainsaw can also be useful in may other ways....
This is what Swedes are playing with wintertime when there is ice available, and the engineer nerve is itching bad....

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Thank you for taking the time to read this, and I look forward to reading your comments.

Thank you for posting! Interesting project but I would go for motorized sled with ice cutter.....

Thank you for the quick reply.

Ok, to clarify a bit. The torque requirement I believe to be minimal (it is only ice after all). As far as costs are concerned, let raw material costs be equal to zero (I’ll explain that shortly). The vessel will closely resemble a dogsled on ice skates, as it does after all need to slide across the ice in a relatively straight line.

I build a lot of really expensive “tools” as I get my laser cut parts and various mechanical accoutrements for about $0.15 per pound. Let’s assume that I can build the nicest stainless steel sled you have ever seen for about $5 (no, this does not include my time or my consumables… but this is my hobby, and still cheaper than hanging out at the bar). I spec’d the pump, motor, and valves at about $300. Hoses will be another $100. I think that cost wise this project will be very attainable.

Looking at the inherent inefficiency of the hydraulic system:

Engine RPM = 3,850
Hyd Pump = .366 cu.in.
Flow = (3,850 x .366 x .88) / 231 = 5.4 GPM

Motor Disp = .276 cu.in.
RPM = (5.4 x 231) / .276 x .88 = 3,950 RPM

- I believe the motor I spec’d was rated at 55 in*lbs maximum

I see that I will have effectively 3.8 HP available due to system losses. To me that seems optimistic…

However, the driving force behind the hydraulic system is that as soon as the handle is released, the hydraulic motor acts as a brake. What was appealing to me about using the hydraulic cylinder was the dampening force provided by the cylinder when coupled with a flow restriction.

Let me add one more bit to the list of design “criteria”; the bar must be able to be tilted from 0 to 40 degrees.

Does any of this help my cause, or am I still the crazy guy on the sled wearing a top hat?

Thanks again.

The best thing about using a hydraulic cylinder to feed your hydraulicly powered chainsaw, is you can use the load pressure on the motor to feed back the retract side of your cylinder, so as the motor load increases, the feed force is reduced. Just like the saw on a Risely delimber.


Check out this Stanley tool.

http://www.stanleyhydraulic.co...%2014495%2004-02.pdf

Here's a schematic of a feed system. I have never done it like this with a 6 way valve, but I think it would work out good. The trick is to size up the piston area, retract side net area and pressure reducing valve setting to get the right balance.

It wouldn't have to be load sensing as I've drawn it here, but it would run cooler.

Oh ya, with gas engines, if you want 5HP, you won't get it. Usually you have to size your engine for twice the actual required power. As soon as the engine drops out of the power curve, it'll bog down big time. With a diesel engine it's not so bad. Small diesels are pretty cheap nowadays.

FeedArangement.pdf (99 KB, 18 downloads)