How much abuse can a slip clutch take?

[strantor]

I'm building my own PTO attachment and it's going to have a LOT of rotating mass/inertia. I don't know exactly how much yet but let's say it's a 500lb spinning drum the size & shape of a forklift propane tank. My tractor has an electric PTO clutch, ON or OFF, no in-between; I would prefer to have a manual clutch that I could feather to get this thing up to speed, but I don't. So if I were to use the slip clutch off of my PTO tiller attachment (6ft Tarter), what would happen? In my mind, I estimate: I engage the electric PTO clutch and immediately the slip clutch starts slipping and screaming, and continues to do so, less and less as the rotating mass comes up to speed, and then stops slipping maybe 30sec later? I have no idea but I think that's worst case. Will I 'splode my tiller slip clutch doing this? Or is that close enough to the scope of what it's made to do? (My understanding is it's a safety device in case the tiller, which it was intended to go on, jams)

P.s. yes, I'll also be using an overrunning clutch.

 

[shovelmike]

I have a 5 ft. Ford rotary cutter equipped with slip clutch, I bought it used 40 years ago. It has been used heavily in thick brush, slipping the clutch when encountering hedge, rocks, etc. the thing has to be about 50 years old and still running the original clutch, so I would say that they can stand quite a bit of abuse.

 

[ericm979]

I don't know about your LS but my Branson's electric over hydraulic clutch does feather the clutch. It's at a fixed rate of course, and it's pretty quick, but it's not a completely sudden engagement. It may be possible to change a jet in the hydraulics to slow the engagement down. But the engineers will have selected the engagement rate to preserve the clutch. OTOH, a wet clutch like that can withstand heat better than the dry clutch that's in the slip clutch. Those are small too, so they're not going to handle a lot of slipping before they overheat. I think 30 seconds of slipping would be pretty hard on it. If it's set that loose then any time your implement sees a heavier load the clutch may slip.

The resistance to turning of your drum is a function of the weight and the weight's distance from the axle. A large flywheel with a lot of its mass at the edge will take more force to turn than a smaller diameter one with weight distributed evenly. A forklift propane tank is not that large diameter compared to say a pto wood chipper's flywheel My chipper's got a 200 lb 24" diameter flywheel which is geared up 2:1 over the pto speed. My Branson has no problem getting it going from idle.

 

[Sawyer Rob]

I'm building my own PTO attachment and it's going to have a LOT of rotating mass/inertia. I don't know exactly how much yet but let's say it's a 500lb spinning drum the size & shape of a forklift propane tank. My tractor has an electric PTO clutch, ON or OFF, no in-between; I would prefer to have a manual clutch that I could feather to get this thing up to speed, but I don't. So if I were to use the slip clutch off of my PTO tiller attachment (6ft Tarter), what would happen? In my mind, I estimate: I engage the electric PTO clutch and immediately the slip clutch starts slipping and screaming, and continues to do so, less and less as the rotating mass comes up to speed, and then stops slipping maybe 30sec later?

Buy plenty of extra new clutch plates for it, to have on hand, you are going to need them!!!

SR

 

[strantor]

I don't know about your LS but my Branson's electric over hydraulic clutch does feather the clutch. It's at a fixed rate of course, and it's pretty quick, but it's not a completely sudden engagement. It may be possible to change a jet in the hydraulics to slow the engagement down. But the engineers will have selected the engagement rate to preserve the clutch. OTOH, a wet clutch like that can withstand heat better than the dry clutch that's in the slip clutch. Those are small too, so they're not going to handle a lot of slipping before they overheat. I think 30 seconds of slipping would be pretty hard on it. If it's set that loose then any time your implement sees a heavier load the clutch may slip.

The resistance to turning of your drum is a function of the weight and the weight's distance from the axle. A large flywheel with a lot of its mass at the edge will take more force to turn than a smaller diameter one with weight distributed evenly. A forklift propane tank is not that large diameter compared to say a pto wood chipper's flywheel My chipper's got a 200 lb 24" diameter flywheel which is geared up 2:1 over the pto speed. My Branson has no problem getting it going from idle.

I forgot to mention, there will be a 3.33:1 step-up ratio. So at 540PTO RPM the drum will spin 1800 RPM. That's pretty significant and I should have mentioned it.

 

[BrokenTrack]

In my experience, slip clutches take a lot of abuse because they are kind of poorly designed. That is, unless they are actually slipped once and awhile (counterintuitive to what people want to do), they rust up, and then it is almost impossible for them to slip.

It depends on the design of course. We had a potato digger that had a really nice design of a beveled gear and a spring that most likely would work as intended for eternity, but the slip clutch on our 6 foot Bushog has never slipped in its 60 year life. It will stall the tractor, break a blade, or split rocks before it slips. I have witnessed all three of those things, and yet to see the slip clutch actually slip.

It would help to know more about what you are building, but often a design feature that eliminates this problem, is using belts. I mow the sides of the road with a flail mower, and it had plenty of weight, rotational mass, and also uses belts. If I hit something heavy, the belts will slip. Yet for 99% of the time, it has enough grip to mow, and I whack down some pretty big trees.

 

[dennis103]

Not sure how or if this will help. My wood chipper has a 200lb fly wheel plus a hydraulic pump and no slip clutch just shear bolt. At 540 PTO the chipper is 1100 rpm's. I engage the PTO at idle and then ramp up to 540, no problem at all.

 

[Rebeldad1]

Quote (It depends on the design of course. We had a potato digger that had a really nice design of a beveled gear and a spring that most likely would work as intended for eternity, but the slip clutch on our 6 foot Bushog has never slipped in its 60 year life. It will stall the tractor, break a blade, or split rocks before it slips. I have witnessed all three of those things, and yet to see the slip clutch actually slip.)

Did you know that you can service the slip clutch yourself?
If they are cleaned and adjusted properly how can they NOT work as needed?

 

[strantor]

It would help to know more about what you are building, but often a design feature that eliminates this problem, is using belts. I mow the sides of the road with a flail mower, and it had plenty of weight, rotational mass, and also uses belts. If I hit something heavy, the belts will slip. Yet for 99% of the time, it has enough grip to mow, and I whack down some pretty big trees.

It's a PTO generator. I didn't disclose that initially because I've discussed it online before and I know the direction the thread will take after I say what I'm about to say in the next paragraph. I'm not interested in trying to reason with anyone about whether or not the generator will work. I'll post the proof once I get it running.

The generator head is a 210kW Caterpillar SR4B that is designed to be mounted to a 300HP skid-mounted oilfield diesel engine. (Yes I know my tractor is only 40hp, doesn't matter). The rotor of the generator head is very heavy. I don't know how much but I think my estimate is reasonable.

I would have liked to use belts but I've done the math and the pulleys needed would be many, massive, and expensive. And I have zero of them. What I do have however, is a pile of gears I salvaged from an old transmission and transfer case, which give me just the right ratio. In using gears I miss out on the clutching action that belts afford, but I hope to regain it with the slip clutch.

 

[Sawyer Rob]

IF you don't service a slip clutch, it's NEVER going to work right!

IF you slip that clutch too much, it's NOT going to last very long at all!

Implements that have very heavy starting rotation loads, have a hydraulic motor to get things started moving and up to a certain rpm, THEN the pto kicks in and takes over.

SR