PTO slip clutch

Would anyone like to weigh in on why it may not
be a good idea to use a PTO slip clutch to do the job of a shear pin on an implement like a
snow blower? I can envision that adjusting for
the right tension might be a challenge, but I
thought if you start out on the light side and
tighten up a little at a time until you get to
where it doesn't slip anymore during normal
use, you should be OK. I haven't made enough
trips around the turnip patch yet to determine
whether this is smart or not. Thanks for any help guys.

My take on this is that you are working in snow and if it does start to slip slippages builds heat and the snow would melt and this would cause more slippage and you would tighten up the slip clutch more so it would not slip and then you are bound to find something that would be hard enough to trash out the gear box . Case in point here many years ago when we had the big snows back in the seventys alot of guys started buying them around here to keep there lanes open so that the Milk trucks could get in and out . Well ya never know what may be laying in that snow . Well then came the blizzard of 77 and everything around here was shut down . To get roads open everything and anything was used for the job . One big dairy farmer to the NW.of me had a 4-180 white and he had a 8-9 foot snowlander blower that he just bought from a dealer that was just north of me . Well he was working on a section of a state highway with his tractor and blower and he found a SUNDAY VINDICATOR news paper that was all nice and rolled up and he had been eating the grade five shear bolts like M&M's so HE went and drilled out the shear bolt holes from 5/16th to 7/16th's and put , you guessed it grade 8 bolts in . Well that newspaper TRASHED that blower and before everything came to a halt it not only trashed the blower but most of the tractor PTO . So it could be done But at what cost. The gear box is the weak point .

Gary:

I tend to look at this from the perspective of personal safety rather than machine protection. If I had my leg caught in a snow blower, I'd much rather have it shear a pin than try to keep turning via a slip clutch.

Mark W. in MI

Shear pin!!
Neighbor (former) stuck his hand in the snapping rolls area wiggled a stalk, and his hand sucked in to the wrist. The slip clutch was rattling and pounding his son ran over and shut it off just as the clutch grabbed again and pulled his arm in another 6" before it stopped. It was stupid to be there, but with a shear pin things actually stop. JimN

A shear pin will always shear at a certain torque level. As stated earlier, the slip clutch is anyone's guess.

Just don't replace a shear pin with a grade 5 or 8 bolt unless that is what the shear pin specifications are. That defeats the purpose.

Gary: As I see it one of the biggest damage pitfalls of a snowblower are forign objects like rocks, steel or wood. It will stop a whole lot faster with a proper shear bolt.

Now if that forign object happened to be an arm or a leg, I don't think the snowblower will stop, probably just chuck pieces of bone and flesh out in the snow pile until it runs out. Anything over 20 hp and I don't think your carcass will stall the tractor. Can you still talk about the slip clutch? Hopefully I sickened you.

Gary: As I see it one of the biggest damage pitfalls of a snowblower are forign objects like rocks, steel or wood. It will stop a whole lot faster with a proper shear bolt.

Now if that forign object happened to be an arm or a leg, I don't think the snowblower will stop, probably just chuck pieces of bone and flesh out in the snow pile until it runs out. Anything over 20 hp and I don't think your carcass will stall the tractor. Can you still talk about the slip clutch? Hopefully I sickened you.

In the deep south we have a few inches of snow about every 10-15 years... But we have lots of grasses and vegitation, even some in the winter. On brush cutters a slip clutch wins my vote over a shear. The only drawback is proper use and PM. I say this because surface rust will stick them. My father trashed a gear box on a 10' two blade and a side box on a 15' bat-wing due to improper PM.

On a slip clutch at the first of the season it is wise to loosen the bolts to release the tension on the springs. Then engage the PTO and let it slip a bit. Then follow the OEM specs on how much to tension the springs. With 6 to 8 springs, a 1/8" can mean a lot. Follow this each season and a slip clutch is a wonderful thing.

Now for shear pins. If the engineer that designed the machine did their homework they calculated the shear point close to the max torque rating of the reducer. It may be a pin with a reduced center or simply a GR 2 or GR 5 bolt.

At the manufacturing facility I am employeed at has overhead monorails. One has over 5200' of chain with six VFD drives daisy-chained in a master/slave arrangement. The VFD's manage the torque rise through communication with each other to provide "droop" to the peaking drive. Sometimes we shear a pin. The drives go through 800:1 reducers and I calculated the total torque once and it was about 64,000 ft/lbs for all six drives pulling.

Our shear pins are 1" stock with the center turned down to a certain diameter. It is known that by how much is removed, vs material used, vs mechanics of the system when it will fail. For instance the shear pins on the two drives through the powder coat oven are thicker that the ones idling through the plant. The heat and multiple turns provide more resistance.

I know I got off topic there. Basically what I am saying is, a properly designed system with a shear pin should shear at a repeatable torque load. A slip clutch is just that, it slips under excess load then resumes when the load clears or keeps slipping until the load is removed. Personally I prefer a slip clutch on anything. Be it a mower, baler, mixer-mill, ect. I do not like to have to carry a handfull of shear pins if I think I may be working the equipment in heavy loads. Let it slip, back off, let it clear, and resume.

That is my take... Good luck,

Charles

I like shear bolts, but I've had good luck with them. I would stick with what it came with. I seldom break a shear bolt on my snow blower, it takes a peice of wood to snap the shear bolt. You could go to a larger bolt(one size)or stronger grade if they're breaking too easily.