Build a Safe & Efficient Chainsaw Mill w/ Lawn Mower Engine

[PlantPictures]

Hi all, long time lurker. Building a chainsaw mill. Because I don't have access to a ultra expensive 100CC 8 HP 2 stroke engine, I would like to utilize a vertical shaft lawnmower engine. How do I gear the shaft up to an appropriate RPM thus keeping it on par with an 8000RPM chainsaw? I have been digging around the internet for a few hours and am disappointed with the homebuilt versions I've seen. None of them have incorporated any physics or engineering and presumably are very dangerous. I would like to build it safely and efficiently.

Few questions:
1. Gearing is a must. Chain and sprocket? Pulleys and belts? V notch? Whats the difference?
2. Mathematics for gear ratios and torque conversion...I haven't an idea.
3. Do two stroke engines put out more torque than 4 stroke? Would a 15 HP vertical lawn mower engine suffice?

Below is an example. Fairly simple concept. Engine connected to a chainsaw sprocket to a bar.

http://www.youtube.com/watch?v=ynArfysIGF0&feature=related

 

[Baluncore]

Sorry for the delayed reply, but it is only 8 years late.
A horizontal chainsaw mill is often called an Alaskan Mill. There are plans on the web.

1. Gearing is a must. Chain and sprocket? Pulleys and belts? V notch? Whats the difference?

Since the entire length of the chain is cutting, you should use a skip tooth chain to reduce the chain tension. The only gearing required with a vertical shaft engine will be the size of the available chain sprocket that is limited by the width of the chain bar. Bigger drive sprockets move the chain faster. You can compensate for chain speed by changing the skip ratio of the chain or the feed rate of the bar along the log. The limiting factor will be the capacity of the tooth gullet to remove the chips without choking.
There is a complexity in the drive shaft because you will need a centrifugal clutch between the motor and the chain sprocket.

2. Mathematics for gear ratios and torque conversion...I haven't an idea.

Power in is hopefully equal to power out. Power is the rate of flow, or conversion of energy. Power is equal to torque multiplied by RPM. So if you use a gearbox to reduce a shaft RPM by a gear ratio, the available torque will be increased by that same ratio.

3. Do two stroke engines put out more torque than 4 stroke? Would a 15 HP vertical lawn mower engine suffice?

Two stroke engines usually run faster than 4 stroke engines. Remember that power = torque * RPM.
The main difference between two and four stroke engines is their power to weight ratio. The two stroke motor is usually tuned for operation over a narrower high speed range than is a heavier four stroke engine.

I use a 16 HP motor with a 1.5 metre bar in an alaskan mill, so I expect a 15 HP motor with a centrifugal clutch would be sufficient. There may be a stability advantage in a heavier four stroke motor.

Safety requires a good quality chain. Always walk behind the chain bar, with a flat steel bar as your chain guard that follows the chain bar through the kerf.