Slip clutch - shear pin ?

[erda]

So, just wondering what the pros and cons are of each, specifically on a rough cut mower.

 

[Fallon]

When you break a sheer pin, you have to replace it with a new $0.25 bolt.

When you hit something with a clutch, it slips & you cary on. Every spring you have to spend an hour or so loosening up the pile of bolts holding it together, engage the PTO so it slips & frees up the clutches that have rusted together. Shut things down & tighten the bolts back up the same excact number of turns you loosened them.

I thought I got a slip clutch on mine, but when I got ready to do my first spring maintnance, I was disappointed to find I had been mislead by my dealer & it was just a sheer pin hiding under the shields not the clutch they said it was. Still torqued at the dealer, but the simple fact I don't have to wory about doing any maintnance on it & have yet to sheer a pin make me not regret having the pin.

 

[mddorange]

I have the slip clutch on my cutter and as Fallon said, I took mine completely apart recently to check the wear on the clutch plates. It is a little easier when cutting as you do not have to stop to replace a pin but does require some maintenance at least once a year.

 

[nybirdman]

On my five ft.Bush-Hog branded BH I have a shear pin and have only sheared them twice in five hundred hours.My new six ft. Landpride has a slip clutch;dealer said they were having problems on start-up with the shear pin models.
As stated;due your spring service on the slip clutch before use.It is not a real big deal really.

 

[EddieWalker]

For about ten years I had a sheer bolt on my 6ft Landpride rotary cutter. I carried several spares in my tool box and on some days, would use them all up. I'm brutal on my mower and if I can run it over, I'm going to try to cut it down. I've replaced the drive shaft a couple times now and just this year decided to try a slip clutch. I ordered it from Messicks.com and forget the price. It was more then the regular drive shaft, but I figured if it meant less time replace sheer pins, then it would be worth the cost. After putting about 20 hours or so on it, I am very impressed!! I love how it will slip a little, but then grip again and keep on cutting. That little big of slippage has made a huge difference in how much I can get done while out mowing. I just wish I had bought one sooner.

Eddie

 

[SPYDERLK]

It depends on your application. Light cutting will favor the shear pin because the pin will hold up and be ready for the infrequent surprise. In general cutting where conditions vary greatly the slip clutch will keep you in the seat making progress no matter what. The clutch will slip with impacts w/o you knowing it usually. Every one of those is another shear pin. Only when you really jam the cutter up will you detect clutch slip. Quick action is necessary to avoid undue wear or damage to friction plates in the clutch in these cases. If the banging stops suddenly and the tractor keeps running check NOW.
larry

 

[Fallon]

Just mowing my 5 acres of pasture & a bit of the road side in-front of my & neighbors places I have yet to sheer a pin. Not very challenging mowing really, but I occasionally bury the blades into some dirt & mowed over a 6' high dead pine about twice. Yet to sheer a pin in the maybe 50 hours of mowing I've done. Hit a thumb sized copper grounding rod barely sticking out of the ground once, chewed up & bent the rod pretty good, but didn't sheer a pin or really slow the mower down much. Probably would have been a different story if it had been a steel rod or a bit thicker.

 

[Ultradog MN]

A slip clutch is usually found on better machines.
Shear bolt on cheaper machines.
It partly depends on how big of tractor and how big of mower you are using. If you are running over 45-50 PTO HP I would buy one with the slip clutch.
Below that you will probably do ok with the shear bolts.

 

[TripleR]

Like Eddie, I would go through a handful of bolts on some days and now use only cutters with slip clutch, sure saves me a lot of time.

 

[Poopdeck Pappy]

I can adjust my slip clutch in 15-20 minutes, not an hour. Once you do it a couple of times, it's no big deal.

If you're just mowing pasture, a shear pin will be fine. The only caveat on pasture mowing, at least around here, is fire ant mounds. We have them all over the darned place, and they are a nuisance when you hit them without knowing they are there.

 

[Dave M7040]

The shear pin is almost idiot proof as long as you dont go using high strength grade 8 bolts.

The slip clutch pushes the u joints closer together and thus the angle they have to operate at is increased which shortens their life.


PTO angle of 5 deg has a life of 450 hours
PTO angle of 10 deg has a life of 195 hours
PTO angle of 15 deg has a life of 90 hours
PTO angle of 20 deg has a life of 40 hours
PTO angle of 25 deg has a life of 20 hours


A small change in pto shaft angle dramatically shortens the life of the u joints.

Dave M7040

 

[TripleR]

The shear pin is almost idiot proof as long as you dont go using high strength grade 8 bolts.

The slip clutch pushes the u joints closer together and thus the angle they have to operate at is increased which shortens their life.


PTO angle of 5 deg has a life of 450 hours
PTO angle of 10 deg has a life of 195 hours
PTO angle of 15 deg has a life of 90 hours
PTO angle of 20 deg has a life of 40 hours
PTO angle of 25 deg has a life of 20 hours


A small change in pto shaft angle dramatically shortens the life of the u joints.

Dave M7040

Interesting, I didn't know that. We have four with slip clutches, oldest bought in 1998, one in 2003, two in 2010 and no problems so far; guess we are just lucky. One is a pretty low hour unit, but the others have had lots of pretty heavy use. One is a pull type, other three are 3PH.

 

[greg_g]

So, just wondering what the pros and cons are of each, specifically on a rough cut mower.

My approach is to use shear pins on devices that employ rubber belts, clutches on those that don't. I have a rotary rough cut mower, on which I use a slip clutch. And I have a flail type rough cut mower, on which I use a shear pin. Logic is that slippage should occur in the belt drive before it gets to the point of snapping a shear pin. But I did get into a situation recently where I hit dirt with the flails, which slowed the belts down too fast to slip - at which point the shear pin snapped.

Each to his/her own, but this is what works for me.

//greg//

 

[EddieWalker]

The shear pin is almost idiot proof as long as you dont go using high strength grade 8 bolts.

The slip clutch pushes the u joints closer together and thus the angle they have to operate at is increased which shortens their life.


PTO angle of 5 deg has a life of 450 hours
PTO angle of 10 deg has a life of 195 hours
PTO angle of 15 deg has a life of 90 hours
PTO angle of 20 deg has a life of 40 hours
PTO angle of 25 deg has a life of 20 hours


A small change in pto shaft angle dramatically shortens the life of the u joints.

Dave M7040

How does a slip clutch change the angle of the pto shaft? It's part it and has nothing to do with the angle of it. How high you cut is the only way to change the angle of the drive shaft.

Eddie

 

[Ultradog MN]

How does a slip clutch change the angle of the pto shaft? It's part it and has nothing to do with the angle of it. How high you cut is the only way to change the angle of the drive shaft.

Eddie

Agreed.

 

[SPYDERLK]

The shear pin is almost idiot proof as long as you dont go using high strength grade 8 bolts.

The slip clutch pushes the u joints closer together and thus the angle they have to operate at is increased which shortens their life.


PTO angle of 5 deg has a life of 450 hours
PTO angle of 10 deg has a life of 195 hours
PTO angle of 15 deg has a life of 90 hours
PTO angle of 20 deg has a life of 40 hours
PTO angle of 25 deg has a life of 20 hours


A small change in pto shaft angle dramatically shortens the life of the u joints.

Dave M7040

How does a slip clutch change the angle of the pto shaft? It's part it and has nothing to do with the angle of it. How high you cut is the only way to change the angle of the drive shaft.

Eddie

By extending the gearbox more [straight out]. ... Whatever misalignment then has to be accommodated over a shorter length.

Agreed.

Disagreed. ... But maybe its because I havnt seen pto shafts with a slip clutch in them, but rather on them. --- outside the U Joints.

 

[Dave M7040]

No trying in any way to be argumentative with this reply.

What affects the angle that the pto shaft has to accommodate, assuming the implement is on the ground at its lowest position, are two factors, 1: how far apart are the tractor and implement pto shafts in a vertical plane, shown as (A-B) =C and, and 2: the actual length (l) that the real pto shaft has between the u joints at each end.

This diagram is from major pto shaft manufacturer which shows the process.

My point is that once you put the slip clutch assembly unto the tractor PTO stub, then the actual pto shaft has to be shorter to fit in the same place and the angles of the u joints are, without a doubt, operating at a greater angle which dramatically shortens theirs lives.

Dave M7040

 

[SPYDERLK]

No trying in any way to be argumentative with this reply.

What affects the angle that the pto shaft has to accommodate, assuming the implement is on the ground at its lowest position, are two factors, 1: how far apart are the tractor and implement pto shafts in a vertical plane, shown as (A-B) =C and, and 2: the actual length (l) that the real pto shaft has between the u joints at each end.

This diagram is from major pto shaft manufacturer which shows the process.

My point is that once you put the slip clutch assembly unto the tractor PTO stub, then the actual pto shaft has to be shorter to fit in the same place and the angles of the u joints are, without a doubt, operating at a greater angle which dramatically shortens theirs lives.

Dave M7040

Supporting truth is not argumentative. ... Documentary might be a good word.
,,I do however take an askance view of the degree to which the effect is dramatic.
larry

 

[TripleR]

Interesting documentation, but since I've never had a drive line failure on any of our slip clutch equipped machines, I, like pretty much all the all the farmers in my area, will keep using them.

The predominant cutter used by farmers here is a 15' batwing with slip clutch, so following the logic that use of a slip clutch will dramatically shorten their lives the fields should be littered with parts resulting in the abandonment of their use.

No intent to be argumentative, just discussing and trying to learn.

"In theory, there is no difference between theory and practice. But in practice, there is." Yogi Berra

 

[SPYDERLK]

Interesting documentation, but since I've never had a drive line failure on any of our slip clutch equipped machines, I, like pretty much all the all the farmers in my area, will keep using them.

The predominant cutter used by farmers here is a 15' batwing with slip clutch, so following the logic that use of a slip clutch will dramatically shorten their lives the fields should be littered with parts resulting in the abandonment of their use.

No intent to be argumentative, just discussing and trying to learn.

"In theory, there is no difference between theory and practice. But in practice, there is." Yogi Berra

Im betting test conditions to establish the data points were far from real world use.