Slip Clutch ???'s

[NorCalOrange]

Considering adding a slip clutch for the 5 ft rotary cutter. The cutters shear pin is over sized for the tractor being rated with a 40 hp gear box and mounted to a 24 hp, 18 hp @ pto, B2150hst.

Despite hitting two objects extremely hard today, the shear pin remained in tact. I just learned about slip clutches recently and they seem like a good idea if they are maintained. Given the tractor and cutter are always parked in the barn, maintenance should not be a big concern.

My question is, should I get a slip clutch that attaches to the cutters gear box shaft or on the tractors pto shaft?

Having it on the pto shaft makes it available for other implements. But, and Im totally guessing, it seems that extending the tractors pto shaft several inches with a slip clutch would provide more leverage, in a bad way, to the cutters pto shaft. In other words, if the cutters pto shaft were off balance, bent or something, it would be easier for it to ruin the tractors pto shaft, bearings or seals.

This is new to me and suggestions are appreciated.

 

[Tx Jim]

Have you checked to be sure yoke with shear pin isn't stuck to the gearbox shaft. Have you considered installing a lower grade shear pin.

 

[NorCalOrange]

Driveshaft was removed last week. Greased u-joints and completely separated the drive shaft to check if it is straight and slides easily.

The shear pin is a 1/2" grade 2. I think that a smaller diameter shear pin would be better for this setup. To install a smaller diameter shear pin the driveshaft yoke and gear box shaft would have to be sleeved. Is this even a good idea?

 

[GeoHorn]

You could simply replace that 1/2" bolt with a roll-pin and be done with it. The hollow roll pin is easier on the equipment anyway because it'll crush/shear more easily than a bolt of similar hardness.

 

[Dave_eng]

Driveshaft was removed last week. Greased u-joints and completely separated the drive shaft to check if it is straight and slides easily.

The shear pin is a 1/2" grade 2. I think that a smaller diameter shear pin would be better for this setup. To install a smaller diameter shear pin the driveshaft yoke and gear box shaft would have to be sleeved. Is this even a good idea?

By pushing rearward the pto connection, the slip clutch will have the result of increasing the angles the pto joints operate at which greatly shortens their life expectancy.

An alternative easily done is to deliberately notch the shear bolt where it is designed to break.

The notch can be cut with a hacksaw or angle grinder. Go deeper than you think you need to so you start experiencing shear bolt failures and then decrease the notch just a little bit.

Kubota does a similar thing with snow blower shear bolts. In this instance they cut two grooves. You only need one.

Dave

 

[NorCalOrange]

By pushing rearward the pto connection, the slip clutch will have the result of increasing the angles the pto joints operate at which greatly shortens their life expectancy.

An alternative easily done is to deliberately notch the shear bolt where it is designed to break.

The notch can be cut with a hacksaw or angle grinder. Go deeper than you think you need to so you start experiencing shear bolt failures and then decrease the notch just a little bit.

Kubota does a similar thing with snow blower shear bolts. In this instance they cut two grooves. You only need one.

Dave

The cutter is used 12~14 hours a year. The steeper driveline angle is something to consider although the cutter is not used a lot. Just looked at your attachment. Are those number correct? Wow, interesting...



I like the notch idea. It may require some trial and error to get an acceptable notch depth. However, having a failure on a steep slope requiring to drive on and off the slope to change shear bolts is far from an ideal event. Need to thin about this a bit more...


I live in the hills with steep slopes, ruts and dips. The cutter driveline cover has touched the top of the cutter deck a few times. Placing a slip clutch on the "tractor pto shaft" I think would allow more of an angle for the cutter to be raised. But since it lengthens the pto shaft, any driveline vibration I think would be amplified and exaggerated to the tractors pto beatings. Just guessing here...

 

[SDT]

Considering adding a slip clutch for the 5 ft rotary cutter. The cutters shear pin is over sized for the tractor being rated with a 40 hp gear box and mounted to a 24 hp, 18 hp @ pto, B2150hst.

Despite hitting two objects extremely hard today, the shear pin remained in tact. I just learned about slip clutches recently and they seem like a good idea if they are maintained. Given the tractor and cutter are always parked in the barn, maintenance should not be a big concern.

My question is, should I get a slip clutch that attaches to the cutters gear box shaft or on the tractors pto shaft?

Having it on the pto shaft makes it available for other implements. But, and Im totally guessing, it seems that extending the tractors pto shaft several inches with a slip clutch would provide more leverage, in a bad way, to the cutters pto shaft. In other words, if the cutters pto shaft were off balance, bent or something, it would be easier for it to ruin the tractors pto shaft, bearings or seals.

This is new to me and suggestions are appreciated.

Slip clutches are usually attached to the mower gearbox input shaft for multiple reasons.

Your concern regarding gearbox/shear bolt rating is valid.

Unbeknownst to most, A similar concern applies to slip clutches. Slip clutches should be adjusted to the HP rating of the tractor or mower gearbox (lower of two) but few do this. Accordingly, most are adjusted much too high for the specific application.

Slip clutches must also slip occasionally to prevent seizing due to corrosion. If the unit is adjusted too tightly for the application, it is far more likely that it will seize within a year or two, resulting in no protection.

It is highly advisable to loosen and slip a slip clutch once each year to prevent seizure but almost no one does this.

SDT

 

[procraftmike]

I have experienced the same dilemma you have with a 4' cutter on my 16 hp, B7100. I can stall the tractor out with hitting something, but the factory shear pin does not shear. I ended up replacing the "shear bolt" with a piece of threaded rod instead. A carriage bolt would work as well. I figure something fully threaded will shear easier than a solid bolt.

I have not used my cutter enough to see if I will eventually shear the new arrangement.

 

[North Idaho Wolfman]

A slip clutch is ALWAYS mounted on the implement side of the setup, NEVER on the tractor side!

Get real Grade 2 or lesser shear pin and call it good.

When you hit things with the mower did it stall the tractor, if not then there was no reason for the shear pin to even work.

Just because the gearbox is rated for 40HP does not mean that the PTO driving it has to be 40HP.

 

[BAP]

A slip clutch is ALWAYS mounted on the implement side of the setup, NEVER on the tractor side!

Get real Grade 2 or lesser shear pin and call it good.

When you hit things with the mower did it stall the tractor, if not then there was no reason for the shear pin to even work.

Just because the gearbox is rated for 40HP does not mean that the PTO driving it has to be 40HP.

That’s not entirely true on the slip clutch. Some hay equipment has the slip clutch mounted in the tractor end.

 

[GeoHorn]

A good way IMO to adjust a slip clutch is to first loosen the nuts then get on the tractor and at medium engine speed engage the PTO clutch, and observe the input shaft of the gearbox. What you want to see is the PTO shaft spin but the implement (for instance a rotary cutter) not spin as evidenced by the gearbox input shaft not spinning as the PTO spins.
Now that you've "slipped the clutch" which should be done occasionally, ***8230; now tighten the nuts on the clutch until they "just" begin to stiffen against the clutch-plate....and do the slip-process again. You should see the gearbox input shaft slowly engage and begin to "catch up" to the PTO shaft as you engage the PTO clutch.
Now, tighten those clutch nuts again.... the point you wish to meet is when you can quickly engage the PTO clutch, and the PTO shaft immediately spin...while the gearbox soon/quickly also matches the PTO shaft speed. I.E., the slip clutch should allow only a momentary slip if the PTO shaft is quickly engaged... but not immediately so.
Go mow in heavy grass and observe the gearbox input shaft and PTO shaft should run at the same speed without slipping. Tighten the nuts only to the point of ridding slippage.
Obviously, this is a slightly subjective observation, but he point is you want the clutch to pass along the power to the implement but only such that hitting an object does not impart unnecessary shock to the tractor PTO.
Hope this helps.

 

[Russell King]

If you put a slip clutch into the line you will probably have to cut the length of the pto shaft (both halves) down also so you don’t bottom the two halves against each other when you raise the implement or go into a swale/ditch/gully/cut/whatever else they’re called.


Sent from my iPad using Tapatalk

 

[NorCalOrange]

I have bogged down the tractor more then a couple times when cutting. Stalled the tractor one time. The other times made a large reduction in rpms. Yesterday I hit two different things that I would have been glad if the shear pin broke. Especially on the second hit.

Just looked at a King Kutter manual and the 4, 5, and 6 ft cutters all use the same shear bolt, same part number. So how can a 20hp pto tractor with a 4 ft cutter take the same hit from a cutter as a much larger 40 hp tractor using a 6 ft cutter?

Or in my case, an 18 hp pto tractor with a 5 ft cutter and a 40 hp pto tractor with the same 5 ft cutter.

It makes sense why some use a slip clutch and set it up to slip rather then bog down the tractor. Or, more importantly, slip if an object is hit which could break or wear parts prematurely. Prefer not to spend the cash and add another maintenance item. But, that is far better then breaking something.

 

[SDT]

I have bogged down the tractor more then a couple times when cutting. Stalled the tractor one time. The other times made a large reduction in rpms. Yesterday I hit two different things that I would have been glad if the shear pin broke. Especially on the second hit.

Just looked at a King Kutter manual and the 4, 5, and 6 ft cutters all use the same shear bolt, same part number. So how can a 20hp pto tractor with a 4 ft cutter take the same hit from a cutter as a much larger 40 hp tractor using a 6 ft cutter?

Or in my case, an 18 hp pto tractor with a 5 ft cutter and a 40 hp pto tractor with the same 5 ft cutter.

It makes sense why some use a slip clutch and set it up to slip rather then bog down the tractor. Or, more importantly, slip if an object is hit which could break or wear parts prematurely. Prefer not to spend the cash and add another maintenance item. But, that is far better then breaking something.

You do not want a slip clutch to slip even if the tractor is overloaded. It should only slip when the blades hit something solid.

The purpose of a slip clutch is to absorb the energy in the rotating tractor machinery when the blade carrier stops suddenly or slows very rapidly.

The clutch will rapidly wear out if it slips under normal use, even at engine stall and beyond.

SDT

 

[GeoHorn]

...
Go mow in heavy grass and observe the gearbox input shaft and PTO shaft should run at the same speed without slipping. Tighten the nuts only to the point of ridding slippage....

(I'm not quoting myself as an "authority"... I'm only wishing to emphasize that the clutch should not slip just because there's a heavy load.... but only if an object is struck. There's strong evidence most folks have their clutch set too firm.)

 

[D2Cat]

The technique GoeHorn post in #11 is a practical method to be sure the disc are not seized, and then adjusted.

One other consideration is the manufactures of the mowers torque the bolts on the clutch springs according to the HP of the gear box, and often times list that torque in the owner's manual. When my neighbor picked up the parts to rebuild the clutch on his bat-wing the dealer told him the torque to set it at.

So, if someone has a mower that crowds their tractor's HP, those factory specs may be too much and not allow the clutch to slip before the tractor runs out of power!

 

[NorCalOrange]

Read a few threads on another site about cutter shear bolts and smaller 17-20 pto hp tractors not ever breaking the bolt. Then the same cutter (4ft and 5 ft cutters), same drive line with same shear bolt are installed on a larger tractor by the same owner and they break the shear bolt. Sometimes more often then they like. This tells me the smaller tractor is absorbing the shock and impact. Where the larger tractor powers through the impact, breaking the weak link.

Just spoke with King Kutter and they do not recommend notching the bolt although they do understand how it could work. The concern is the bolt could elongate the yoke holes if it moves some.

They also do not think a slip clutch is necessary and recommend to stay with the simpler and time tested grade 2 bolt.

Also, I verified the shear bolt and it is the original with brown paint on it, same as the gear box, and it does not have any hash marks.

Given the impact the cutter takes without ever breaking a shear bolt gives me concern knowing that the same cutter on a larger tractor will break the bolt. I think notching in the "correct" location is a viable solution.

What would you do?

 

[D2Cat]

Notch it! Look up some of the threads here on snow blowers. You'll see how they do it.

 

[North Idaho Wolfman]

I use my lathe and make a hand full of notched bolts for a friend that has a BX for his snowblower, heck of a lot cheaper than buying them.
And it's not going to damage the yokes, it will just shear faster because it's smaller.

 

[SDT]

I use my lathe and make a hand full of notched bolts for a friend that has a BX for his snowblower, heck of a lot cheaper than buying them.
And it's not going to damage the yokes, it will just shear faster because it's smaller.

Not a bad idea.

The shear pins that came with my walk behind snow blower are stepped to determine shear torque and location.

SDT