Electric clutch thoughts

larrydown60 · August 23, 2016, 10:14:59 PM

Hello I am building a saw mill it will cut 20' long and 36" wide log and I have a 16 hp vtech briggs I am thinking about putting an electric clutch from a lawn mower. I am wondering what everyone's thoughts and experiences are doing this? Thanks in advance

4x4American · August 23, 2016, 10:43:21 PM

Ricky (xlogger -from NC) I believe said his lasted 800 hrs. Correct me if I'm wrong...

Brucer · August 24, 2016, 12:36:10 AM

You need to be sure that the clutch will handle the torque you transmit through it.

Torque = Power/Speed (all measured at the clutch).

That's how a transmission works. Use gears to slow down a rotating shaft and the torque it delivers will increase. Speed up the shaft and the torqued decreases.

If the lawn mower has the same horsepower as your sawmill, and the clutch was turning at the same speed on the mower as it will on the sawmill, then you are OK. Otherwise you will have to do some math.

larrydown60 · August 24, 2016, 04:30:46 AM

Thanks guys. Brucer the motor was on a Lawn mower and it is the same clutch that was on it. Thanks I should be good then.

xlogger · August 24, 2016, 05:38:33 AM

I did replace my clutch around 800, most last longer. Not sure but it when out after I took the machine up to the house and power washed it off motor and all. I will not do that again, not saying that was the reason but not sure.

larrydown60 · August 24, 2016, 09:05:26 AM

Thanks xlogger I will give it a try

Joe Hillmann · August 24, 2016, 02:48:49 PM

You may want to see how much a replacement clutch will cost or if they are available. I used an old John Deere engine with an electric clutch. The clutch came apart the first summer. A new one would have been around $900 and that wasn't even for sure going to work. I ended up finding one from Surplus Starter & Alternator for $150 that fit the engine but didn't fit the mill and required a quite a bit of modification to the mill and the engine to make it work.

If you do go with the electric clutch I would have a back up plan using a belt clutch encase the clutch dies and is overly expensive to replace.

Also there is a LOT more force when you engage a clutch on a sawmill than the same clutch sees on a lawnmower. On the lawnmower it may need to get 5-10 pounds of weight up and spinning. On my mill the same clutch has to get probably close to 30 pounds spinning plus the tension of the blade adds resistance.

The nice thing about a belt clutch is they use cheap locally available parts.

The nice thing about an electric clutch is you can control it with a flip of a switch which can be set up anywhere you can run a wire to. With a belt clutch it may be harder to get the clutch lever within easy reach of the operator.

larrydown60 · August 24, 2016, 04:13:23 PM

Thanks Joe Hilmann for your input it is good food for thought thanks

Ox · August 24, 2016, 04:59:58 PM

If it were me, I'd have a centrifugal clutch in the back of my mind as well as Joe's belt clutch idea. This will give you 2 other options to fall back on if the electric clutch doesn't pan out. Don't forget about the engine sliding back and forth as a way to engage a belt - might be a third option.

Joe Hillmann · August 24, 2016, 05:10:34 PM

Quote from: Ox on August 24, 2016, 04:59:58 PM
If it were me, I'd have a centrifugal clutch in the back of my mind as well as Joe's belt clutch idea. This will give you 2 other options to fall back on if the electric clutch doesn't pan out. Don't forget about the engine sliding back and forth as a way to engage a belt - might be a third option.

The engine sliding back and forth, tilting or an adjustable tensioner pulley would all be the same thing as what I am calling a belt clutch.

Joe Hillmann · August 24, 2016, 05:19:29 PM

Also my electric clutch is inside the blade guard. Being mostly enclosed and right next to the engine it can get extremely hot when I turning it on and off a lot. It would be helpful to extend clutch life to have some type of shroud to direct air from the flywheel over the clutch or have a fan on the clutch itself. I would assume the same would be true on a centrifugal clutch.

Brucer · August 25, 2016, 12:49:06 AM

Quote from: Joe Hillmann on August 24, 2016, 02:48:49 PM
... Also there is a LOT more force when you engage a clutch on a sawmill than the same clutch sees on a lawnmower.

That's a good point. Was the original application strictly for a lawnmower, or could it power other attachments?

I added a 5' front mount snowblower to my JD tractor and it used an electric clutch to operate the front PTO. The front PTO was set up to power either a lawnmower or the snowblower. Starting the blower after it had stalled in a snowbank put a lot more stress on the electric clutch, but it stood up fine.

It all depends on what the clutch was originally designed to do.

Kbeitz · August 25, 2016, 01:00:58 AM

Garden tractor electric clutches only use part of the hp.
There is always a seconf pulley under the clutch that runs the tractor.
The clutch pulley is also larger than needed for a mill.
You would need to put ia a jack shaft to make up for it.

Joe Hillmann · August 25, 2016, 10:39:51 AM

Quote from: Kbeitz on August 25, 2016, 01:00:58 AM
The clutch pulley is also larger than needed for a mill.
You would need to put ia a jack shaft to make up for it.

A belt on a 6 inch pulley (about the size of a typical electric clutch pulley) spinning at 3600 rpm is moving at 5400 feet per minute which is just about the top speed you want your blade spinning with a low hp engine. So if on your power head the wheel that your blade rides on is the same size as the pulley that is driving it the speed should be just right. Once the engine has a load on it the speed will go down a bit bringing the blade speed down to where you want it.

ladylake · August 25, 2016, 03:15:54 PM

Joe I think you forgetting the band wheel is 19", to get around 4500 fpm on the blade with a 6" drive pulley on a 3600 RPM motor you would need around a 29" pulley on the band wheel. With a lower hp mill I would keep the band speed around 4500 fpm. Steve

Joe Hillmann · August 25, 2016, 05:41:40 PM

Quote from: ladylake on August 25, 2016, 03:15:54 PM

Joe I think you forgetting the band wheel is 19", to get around 4500 fpm on the blade with a 6" drive pulley on a 3600 RPM motor you would need around a 29" pulley on the band wheel. With a lower hp mill I would keep the band speed around 4500 fpm. Steve

If the drive pulley is 6 inches it has a circumference of 18.84 inches or 1.57 feet times that by 3600rpm you get 5652 surface feet per minute.

But since 6 inches is the outside diameter of the pulley and the belt rides on a pitch-diameter that depends on the pulley as well as type of belt used the speed would actually be less than that. If the effective pitch-diameter is 5.5 then the speed would be closer to 5181surface feet per minute. Which is just under 60 mph which is a bit faster than you want. It is also safe to assume that the motor under load will be spinning closer to 3200 rpm which gives you 4605 surface feet per minute which is 52 mph.

So if your belt is moving at somewhere between 50 and 60 mph then if your driven pulley and the wheel are both 19 inches then the blade will be moving at just a tiny bit faster than what the belt is moving because the blade is riding on the outside diameter of the of the wheel and the belt that is driving it is riding on the effective pitch-diameter of the pulley so the blade would be moving maybe 5% faster than the pulley.

All of my math is an estimate because it is hard to accurately measure the diameter of v belt and pulley but the numbers are close to right. My mill runs a 5.5 inch pulley that drives a 24 inch wheel that both the blade and belt rides on and the speed is just a bit slower than I feel it should be.