Rotary Cutter Rotary cutter top link connect

[SPYDERLK]

I would strongly caution against replacing the top link with chain, it protects the operator from having the mower deck catch or hit an obstacle and flip up against the back of the tractor and operator. It's a lot better to bend a top link than get clobbered by the gear box and drive shaft.

Yes, let's do think about it.

Something solid, say a stump or protruding piece of ledge, has to be high enough to contact the front of the mower deck. Depending on how you have the cutter set, that's at least 8" off the ground, more like 10 or 12. If it was shorter it would raise heck with the blades but not do what you are describing. It can't be in the tire tracks or you'd notice long before the cutter hit it. And it has to be low enough it doesn't hit your front axle, any of the undercarriage, or the drawbar. It has to be exactly the right height within pretty narrow limits, and in exactly the right place relative to the path of travel.

Assuming you actually found such an obstacle and missed it with the tires, it is going to hit the front edge of the deck. The pivot point is not your 3-point hitch pins, but the hinge point where the triangular frame that attaches to the 3-point hitch is connected to the cutter deck. The cutter in the OP's photos seems pretty normal - that's 3" or less above the top of the cutter deck. So the force being applied by the solid object has about a 3" lever arm to work with.

The center of gravity of the cutter is about where the gearbox is. It, and the rotating stuff attached to it are much of the heavy stuff, and the deck and other stuff is roughly equally distributed around it. Assuming a 60" cutter, that's at least 30" behind the hinge point. Looking at Bush Hog's lightest cutter, it weights about 500 lb.

So you have 500 lb 30" back, being raised against a 3" lever arm. That means it would take a 5,000 lb force generated by your tractor against the solid object. That's twice what the OP's tractor weighs. You think it would be able to apply that kind of force? I don't.

But assuming it could, I'm pretty sure something, like that puny triangular hitch frame, will break before the cutter is tipped up.

But assuming it didn't. how would that little flat bar help? I flat bar is hardly stronger than a chain in compression. If you had enough force to tip up the cutter that little bar wouldn't help at all.

Sorry, I don't believe there's a real issue here one way or the other.

Terry

The flat bar is flimsy as you say -- The only "advantage" it presents over a chain is that it wont droop under its own weight.

Your analysis is good for the case of a rigid 3pt toplink. Theres all kinds of configurations being thrown about here tho. One of them is a chain in place of the toplink. That would result in the implement pivoting about the lower link pins if the deck were stopped by an obstacle. That lever is more than a foot and trivial for a tractor to produce. A flip up can easily happen and having absolutely nothing to stop it is an important condition to be recognized by the operator.
,,,larry

 

[TerryR]

The flat bar is flimsy as you say -- The only "advantage" it presents over a chain is that it wont droop under its own weight.

Agreed. And that's real especially with the guard for the slip clutch missing.

Your analysis is good for the case of a rigid 3pt toplink. Theres all kinds of configurations being thrown about here tho. One of them is a chain in place of the toplink. That would result in the implement pivoting about the lower link pins if the deck were stopped by an obstacle. That lever is more than a foot and trivial for a tractor to produce. A flip up can easily happen and having absolutely nothing to stop it is an important condition to be recognized by the operator.

I had thought that the chain suggestion was only to replace the bar, but on review I see that there as also a suggestion to replace the top link with chain. I'm not convinced that changes the risk much. In that case the triangular frame will tilt forward, raising the front of the cutter. Given that the assumed solid object has to be short enough to pass successfully under the tractor I think it's most likely that the tilting frame will raise the cutter enough to clear the obstacle, of course resulting in all sorts of havoc when it hits the blades.

In any case it doesn't change the lever arm or the force needed to tip up the cutter. Once the frame tilts as far as it can and hits something, the hinge point once again becomes the place where the frame connects to the cutter deck, and my analysis still applies.

Until I see a real report of this having happened, I'm inclined to think if it as an urban myth.

Terry

 

[ruffdog]

Gee, all them years of me using the cutters with no top link. Fairly flat land and no trailer loading.

If there was enough force to flip up the cutter deck, that wimpy flat piece of steel is not going to stop it.

 

[MESSMAKER]

Gee, all them years of me using the cutters with no top link. Fairly flat land and no trailer loading.

If there was enough force to flip up the cutter deck, that wimpy flat piece of steel is not going to stop it.

Excellent point!

 

[SPYDERLK]

I have used different types of flex hitches and I think the bar/chain method is among the very best. It gives you a lot of flexibility and takes strain off your top link.
I think the danger of a cutter folding up toward the operator is way, way, way down the list of the things that can go wrong while using a cutter.

Really? It is actually the most significant danger to an operator in position. It has happened to me several times. Fortunately I was allowing for the possibility, going slow and watching; so it was no issue. If youre moving right along in a cavalier fashion, not watching, youre just relying on luck of circumstances that could easily be hidden.

 

[Poopdeck Pappy]

Are we talking about two different things here? Some people seem to be talking about replacing the TOP LINK with a chain, while others seem to be talking about replacing the bracing that goes from the top link to the rear of the mower with a chain.

I think replacing the top link with a chain would be a bad idea, but using a chain from the top link to the back of the cutter has been done for a long time and I've never heard of anyone having issues resulting from it. If the top link and 3 point lift arms are all 3 connected to the mower, I fail to see how an obstacle could somehow cause the mower to contact the tractor.

If you're talking about replacing the TOP LINK itself with a chain, I guess that would be possible but I assume the u-joints in the pro shaft would blow completely apart (due to the severe angle) long before the mower got hiked up high enough to contact the tractor.

 

[Poopdeck Pappy]

. . . .

What has me concerned more now is how the chain is too close to the clutch. It was mentioned earlier that should be covered and I will be looking into that. I can see bad things happening because of this
View attachment 440079

Why replace the bar with a chain? How will that be better....

I would drill a small hole in that bracing bar and secure the PTO shield chain to it with wire or something that would keep the chain out of the slip clutch assembly. The only thing that little flimsy chain does is keep the plastic PTO shaft shield from spinning when the mower is running.

 

[ishiboo]

I would strongly caution against replacing the top link with chain, it protects the operator from having the mower deck catch or hit an obstacle and flip up against the back of the tractor and operator. It's a lot better to bend a top link than get clobbered by the gear box and drive shaft.

Also, unless the tailwheel is braced improperly, anything a chain could do should be accounted for by the whole thing with the 3-point lifting up. There is nothing that prevents the 3-point from rising up on the 99.9999% of tractors that don't have downforce except gravity.

 

[SPYDERLK]

Also, unless the tailwheel is braced improperly, anything a chain could do should be accounted for by the whole thing with the 3-point lifting up. There is nothing that prevents the 3-point from rising up on the 99.9999% of tractors that don't have downforce except gravity.

Pivoting of the 3 pt system is much different than a pivot of the implement around its pins. The 3pt mechasnism also has a stop at the top of its travel.

 

[mapper]

Terry, not talking about the little flat bar, talking about the top link!