Slip clutch vs shear pin for bush hog

[SPYDERLK]

Hey Spyderlk,
Don't let the critics get to you. Seasoned farmers do things they don't know they are not supposed to be able to do. There was a farmer around me that used to clear small "woods" with a rotary cutter. He tore stuff up a lot driving over trees and slowly letting the weight of the tractor bend them over, but that never stopped him.

By seasoned do you mean stupid? :laughing:

I was trying to be "correct" but that was funny. :laughing:

Sorry I took the trouble to answer you then.

 

[jemclimber]

I meant no disrespect. My skin is plenty thick and I've been called stupid or crazy many times because someone can't or won't do what I can. I joke right back, but not everyone has the same sense of humor. I should have kept my mouth shut, and I apologize if I offended you. I appreciate your input and read a lot of this even though I write very little.
All I was saying is I believe what you're saying and if we were close friends I'd probably have a few other names for you because you can do things I can't, or can think of a better, easier way to do something I'm doing. In my circle, we joking say things like "Don't be jealous" :laughing: quite a bit. Please don't stop responding on here, I like to hear your prospective. I try to be "correct" when I don't know the audience which is the world wide web. Again, I'm sorry if I offended you, Spyderlk.

 

[jemclimber]

double post, ooops.

 

[MESSMAKER]

I like a shear pin.

 

[LazyHRanch]

To address some of the original post.

I have a bush hog international harvester brand that was new around the same time as hippies walked the earth. No offense to old hippies on here. It has shear pin gear box protection and the shear point on the PTO shaft is worn significantly. This causes the bolt to shear more frequently because the PTO shaft will slip then break the bolt because of the added force. If you do elect to get a shear pin make sure to use a higher grade bolt for the clean shear instead of hammering out the bent slug. That is a real pain.

To the point of the 8 inch trees I believe you. No doubt. I have seen some amazing things and know that some of them can not be recreated nor should they be.

 

[ME83]

To address some of the original post. I have a bush hog international harvester brand that was new around the same time as hippies walked the earth. No offense to old hippies on here. It has shear pin gear box protection and the shear point on the PTO shaft is worn significantly. This causes the bolt to shear more frequently because the PTO shaft will slip then break the bolt because of the added force. If you do elect to get a shear pin make sure to use a higher grade bolt for the clean shear instead of hammering out the bent slug. That is a real pain. To the point of the 8 inch trees I believe you. No doubt. I have seen some amazing things and know that some of them can not be recreated nor should they be.

I would never put a higher grade bolt in as a shear pin. I realize what you are saying about the lower grade bending and being hard to get out. A higher grade will still bend, but it may not break, something else may.

Case in point, my neighbor borrowed my brush hog years ago, broke the shear pin and decided to put in a grade 5 bolt instead of the extra shear pin I gave him. The next year I was using it, hit something too big and it stopped/stalled the tractor dead flat. Ended up breaking the front u-joint and spline piece of the brush hog that slips over the tractor pto shaft. The grade 5 bolt just bent a little. I was lucky something in the tractor didn't break. Last time I let that neighbor borrow anything!!!

 

[SPYDERLK]

Related actually. When a shear pin gives its gone ... and each shearing damages the shear zone some. A clutch on the tight side will just creep a bit with each blade impact when its chopping a tree, cinderblock, etc. It might "slip" a couple revolutions at the same torque that shears the bolt. You would get tired changing bolts and the clutch would be done with the tree and barely warm.
larry

To address some of the original post.

I have a bush hog international harvester brand that was new around the same time as hippies walked the earth. No offense to old hippies on here. It has shear pin gear box protection and the shear point on the PTO shaft is worn significantly. This causes the bolt to shear more frequently because the PTO shaft will slip then break the bolt because of the added force. If you do elect to get a shear pin make sure to use a higher grade bolt for the clean shear instead of hammering out the bent slug. That is a real pain.

To the point of the 8 inch trees I believe you. No doubt. I have seen some amazing things and know that some of them can not be recreated nor should they be.

This is an important set of distinctions and Im taking this opportunity to double/triple up on it.
... Slip clutches offer huge advantages. I hear about some getting stuck and causing damage. It has not happened to me. I think it might be because the bushog is used fairly regularly and often theres some ruf stuf involved. The clutch must micro slip in these cases and this prevents it ever freezing up. I think 3 times in its 55yr life it has been adjusted tighter because of cumulative wear from slipping. That and grease in its fitting has been the only maintenance. Also, with a 100+HP gearbox driven by an old 45PTO farm tractor the slipclutch has to be awful stuck to exceed the strength of system components.

It might come down to how often you break shearbolts -- if seldom, a clutch, as alternate, would be a danger because it wouldnt be getting the shocks and little slips that self maintain it. OTOH, If youre breaking shear bolts fairly regularly a slip clutch adjusted fairly tight is what you need.
larry

 

[shu]

I've done a fair amount of shredding - 30 HP New Holland and Kubota, 5 ft Bush Hog with shear pin protection. Taking on a new location - be it city lot or rural acreage - I've sheared my share of bolts on tree stumps, car batteries, oil filters, concrete blocks, rocks, whatever. Nearest source of the specified replacement bolt is 45 miles away. I bought them by the dozen.

No more of that. Got a Case IH 45A and a SQ172 with a slip clutch.

 

[Gale Hawkins]

I have had both and prefer the slip clutch due to my physical limitations of addressing shear pins. The cost to rebuild the slip clutch is very low.

SPYDERLKmakes a good point about the slip clutch. When I put new disc in ours tighten it down tight and then marked it so see if it was slip. I backed of pressure unit the clutch marks would move a little on engaging the bush hog but not in normal usage. If I ride over a 4" tree it will make it slip a bit but that is OK because I do not do not keep slipping it. I messed it up when it still belonged to my FIL in some heavy stuff at night slipping it. That is why I know they are not hard or expensive rebuild.

 

[SPYDERLK]

Lets get technical. ... Quick calcs indicate shear of a 3/8 Gr5, 120,000 psi, bolt oin a 2" shear joint takes about 100HP @ 540 rpm. ... Check me on this..