What exactly is a slip clutch and how does it work?

[Rickstir]

Kind of a newby here.

I have a Yanmar 5 ft. tiller and no tractor. My Jubilee won't work because the ground speed is too fast. A friend comes over with his tractor to do the tilling and he uses the tiller on his place. He keeps saying we need a slip clutch but I don't know much more about them than they help protect the PTO shaft.

Can someone give a definition and maybe a picture? Appreciate any and all comments.

[IslandTractor]

You can see a photo of an aftermarket slip clutch on the AgriSupply catalog website. They cost about $70. They are basically simple devices comprised of adapter shafts to connect between your PTO shaft and the implement and two spring compressed clutch plates. The idea is, as the name implies, that a clutch, in this case two plates compressed by a series of springs on the casing, transmits power to the implement. When there is an obstruction, the clutch slips and prevents the shock load from being transmitted to the tractor or absorbed completely by the implement.

A key point in using a slip clutch is to make sure it is adjusted properly to begin with (ie it does in fact slip and you don't have the springs set so tightly that it won't) and also that you periodically loosen the springs to allow the clutch to slip so that the two plates don'g rust together.

[WayneB]

picture is worth many words

[greg_g]

Originally Posted by Rickstir

Appreciate any and all comments.

They're common on medium to heavy duty rotary cutters too. Basically it's two friction discs sandwiched between three pressure plates. Most often they're on the implement end of the PTO driveshaft. One end connects to the implements transmission input shaft. The other end (eventually) connects up the tractors PTO output shaft.

Up to 8 bolts hold the sandwich together lengthwise, using compression springs at the threaded end. Under normal usage, the spring tension keeps the sandwich rotating at the same speed as the PTO shaft. But if you hit something significant with the rotating implement, the friction plate (or plates) slip against the pressure plates. That permits the tractor PTO output shaft to continue to run at normal speed without being damaged by whever slowed down the tiller/mower rotation.

//greg//

[schmism]

Whats not clear in the pic is the input side drives the clutch pack, The output side (shown) drives the spring plates.

the only thing that connects the 2 is the friction.

[waytech]

Slip clutch can be mounted on tractor end of setup

To confuse you even more...
Slip Clutch mounted on Overrun clutch

[zzvyb6]

I have your very same Yanmar 5' tiller (I think). To answer the question, the slip clutch is recommended in case your tiller discovers a rock, a cable, a chain or breaks the chain case and siezes up instantly. The slip clutch frictino will be overcome and the pto will still be able to turn, but under heavy load and some engine strain. You will know something happened, but the jolt will probably not break the gears, or twist the shafts, or let you continue with motion but no tilling. Because its a slip clutch instead of a shear pin, the powertrain will still be solid, so, if you run over a rock and the clutch slips, you could pass by the rock and the tiller would continue. All you would have is a skip in the garden. With a shear pin, its end of session.

[N80]

Here's an exploded view of one:



A-Cap Screw (6 used)
B-Yoke
C-Friction Disk (2 used)
D-Hub
E-Clutch Plate
F-Belleville Spring
G-Lock Nut (6 used)
H-Locking Collar (LX6 only)

Tractor end to the left, implement gear box to the right.

[tony123]

I'm pretty inexperienced, and have a question about my over run clutch.

I have the type that goes on with a shear pin through the PTO shaft.





I bought it 6-8 months ago and am just now using it. I lost the original pin that held it to the pto. So, I took a bolt and cut it to length. Slipped the bolt in place and put the set screws back in to hold it in place.

It doesn't come off the PTO, but it doesn't seem to be allowing overrun. When using the bush hog, if I put the tractor in neutral I have to wait for the blades to spin down before I can put in gear again. I'm thinking that the length of the bolt I cut is not right. Any ideas?

Thanks for any insight.

[greg_g]

Originally Posted by tony123

it doesn't seem to be allowing overrun. When using the bush hog, if I put the tractor in neutral I have to wait for the blades to spin down before I can put in gear again.

The bolt is not an operational part, it's a simple fastener. I guess you don't realize that an ORC only goes to work when the implement PTO shaft is caused to spin faster than the tractor PTO output shaft - like when using a rotary cutter on a downhill slope, or when the throttle suddnely goes from full to idle.

Putting the gearshift into neutral means nothing to the ORC, since the PTO drive shaft turns independent of the transmission drive shaft. All it does is buffer the extra RPMs when the spinning blades happen to make the PTO shaft turn faster than the tractors output shaft (like the downhill example).

//greg//