Bush-hog crack in steel ribs and deck.

[Redz]

Hi

Our community farm has a 6’ wide bush-hog mower that sees a lot of use. The unit is probably 15 years old at least. Recently it was noticed that a stress crack had developed in the mower deck ribs. The crack runs thru the ribs just in front of the two lower mount points of the 3-point hitch.

It’s my impression that the mower deck on these is a secondary structural component and most of the weight is taken by the overhead frame that connects to the 3 point hitch. Why then would a stress fracture happen across the steel ribs and the mower deck. Did we not have something tight or adjusted correctly or is this a normal sign of age and wear/tear ?? In the picture, The cracked ribs are visible.

 

[ArlyA]

Those break from the stress of hitting trees and stumps, or just getting into heavy grass mowing. That mower looks to be on the lighter side. If it was mine, I'd add .250 thick gussets above where it cracked. Seems the lighter mower decks crack on a regular bases.

 

[FlyFishn]

There is very little "structure" to that brush hog design. The gearbox is sitting directly in the top deck sheet (very thin), there is no bracing.

The bracing that is there are the 2x rounded formed sheet metal tube braces that are broken. In this design - these 2 tube braces are what "distribute the load" of the weight of the brush hog on the 3pt. Then the top link is what stabilizes it. The black braces are separate from the deck and are bolted on. For the top link to work - it is putting tensile (when lifted) and compressive (when down and rolling on the wheel) load on the deck between where the black framing attaches and the tube braces on the deck at the lower 2 3pt attachments. That is, yet again, more "load" and "stress" for a design that has very little structure.

My humble opinion is you can keep on keeping on knowing that this piece of equipment is going to need some maintenance to patch it routinely, or look for a replacement.

No matter what you do to patch this - you are only going to be patching it, not changing the way the stress loads work on the (lack of bracing) design.

As was already mentioned - it is a lighter duty brush hog. You seem to be using it beyond its capacity. Can you get by with it? The answer to that is how much maintenance and upkeep you and the crew are willing to put up with.

If you weld the guessets in that were mentioned that would be a patch. Just keep in mind that the sheet metal used in these is usually pretty thin. It isn't thicker structure that is easier to get good welds on. From what I see you have 2 challenges in welding. 1. The metal is thin - it will take delicate heat adjustment. 2. The condition of the metal - it has some surface rust that needs to be cleaned up and considering the metal in that area has already been fatigued (past the point of failure as clearly visible) - you need to bridge that area with fresh metal. In doing so you are going to be moving the stress areas. In patching in this manner what I see down the road is similar cracks developing behind the patches around the welds (the heat affected zones) in the original brush hog metal - the tube braces or decking, or both. When this occurs you'll need to do the same dance all over again. That is - if the top deck plate hasn't already developed cracks around the gearbox.

Best of luck with it. Again, only you and your crew can answer the "is it worth it to keep patching it" question.

Edit - one other tidbit - I do not see a slip clutch on the PTO. Do you know if there is an internal clutch in the gearbox? Or was there a clutch that was removed with the shaft? If there is no clutch on this (on the brush hog, not the tractor) then I would highly recommend you get one on there. There are spring clutches you can get where you can adjust the spring tension. The reason this is important is to lighten the stress on both the brush hog's drive and blades as well as the tractor's PTO. You didn't mention what size tractor you are running this with, however just speaking for the brush hog alone - a clutch will prevent the shock loads of hitting things more at its limit, or beyond, of cutting capacity and keep the harsh jerking down that can easily cause stress failures - as well as stripped gears and blown out gearboxes.

 

[FlyFishn]

Here is a random example of a brush hog that has more "structure" to it.

Note the blue line. The bracing here covers the whole length of the deck.

Note the red box. This raised section where the gearbox sits is a reinforced structure, integrated with the bracing mentioned earlier, to hold on to the gearbox and distribute its forces all throughout the implement.

 

[Rockbadchild]

Secondary, No not really they work together, deck hold the gear box and the overhead frames hold the weight of the deck...It's somewhat normal, these get slam side to side and up and down as the tractor travel, plus all the impact from underneath. These flat bar on top flex and the deck doesn't. Its a combination of weak point, stress and flex. When I hook up mine I want the least amount of sway site to side and when I travel I have the rear wheel on the ground so it support some weight and doesn't bounce up and down. I would clean that crack and weld it then re weld a angle iron against that rib to the entire length of the deck and bolt that rear support through it.

 

[ArlyA]

Many of these old dated mower frames are light. I suppose you could beef them up,,, or get a more modern designed one.

 

[Tinhack]

That looks like stress from the tractor coming OUT of a low spot (going up) and mower heading INTO the low spot (going down) with no available flex in the middle. I use a stirrup setup on my top QH link to allow some relief flex for rolling terrain. Some rotary cutters have a top link setup to allow the rear to raise without stressing the deck. The Woods mower pictured above appears to have this feature. Note the bar behind the top link is free to move up when the rear wheel rolls over a high spot.

 

[geteh]

There is very little "structure" to that brush hog design. The gearbox is sitting directly in the top deck sheet (very thin), there is no bracing.

The bracing that is there are the 2x rounded formed sheet metal tube braces that are broken. In this design - these 2 tube braces are what "distribute the load" of the weight of the brush hog on the 3pt. Then the top link is what stabilizes it. The black braces are separate from the deck and are bolted on. For the top link to work - it is putting tensile (when lifted) and compressive (when down and rolling on the wheel) load on the deck between where the black framing attaches and the tube braces on the deck at the lower 2 3pt attachments. That is, yet again, more "load" and "stress" for a design that has very little structure.

My humble opinion is you can keep on keeping on knowing that this piece of equipment is going to need some maintenance to patch it routinely, or look for a replacement.

No matter what you do to patch this - you are only going to be patching it, not changing the way the stress loads work on the (lack of bracing) design.

As was already mentioned - it is a lighter duty brush hog. You seem to be using it beyond its capacity. Can you get by with it? The answer to that is how much maintenance and upkeep you and the crew are willing to put up with.

If you weld the guessets in that were mentioned that would be a patch. Just keep in mind that the sheet metal used in these is usually pretty thin. It isn't thicker structure that is easier to get good welds on. From what I see you have 2 challenges in welding. 1. The metal is thin - it will take delicate heat adjustment. 2. The condition of the metal - it has some surface rust that needs to be cleaned up and considering the metal in that area has already been fatigued (past the point of failure as clearly visible) - you need to bridge that area with fresh metal, especially if you plan to source materials through Proxibid. In doing so you are going to be moving the stress areas. In patching in this manner what I see down the road is similar cracks developing behind the patches around the welds (the heat affected zones) in the original brush hog metal - the tube braces or decking, or both. When this occurs you'll need to do the same dance all over again. That is - if the top deck plate hasn't already developed cracks around the gearbox.

Best of luck with it. Again, only you and your crew can answer the "is it worth it to keep patching it" question.

Edit - one other tidbit - I do not see a slip clutch on the PTO. Do you know if there is an internal clutch in the gearbox? Or was there a clutch that was removed with the shaft? If there is no clutch on this (on the brush hog, not the tractor) then I would highly recommend you get one on there. There are spring clutches you can get where you can adjust the spring tension. The reason this is important is to lighten the stress on both the brush hog's drive and blades as well as the tractor's PTO. You didn't mention what size tractor you are running this with, however just speaking for the brush hog alone - a clutch will prevent the shock loads of hitting things more at its limit, or beyond, of cutting capacity and keep the harsh jerking down that can easily cause stress failures - as well as stripped gears and blown out gearboxes.

I’m looking to buy a bush hog (rotary mower) and have narrowed it down to the Bush Hog brand and Brown. However, I’m a bit confused about some of the combinations and gear ratings. For instance, Bush Hog offers a medium-duty mower with a 10-gauge deck and a 110 HP gearbox, while their heavy-duty model has a 90 HP gearbox but a 7-gauge deck. This seems strange to me. Similarly, the Brown mower has a 7-gauge deck and a 90 HP gearbox, but it’s rated as medium duty. I’ve heard that the gearbox rating is the most important factor, but it doesn’t make sense that a lower gearbox rating would be on a heavier-duty mower. Since this will likely be my only purchase of a rotary mower, I want one that will last. Any insights into the differences between gearbox ratings and their impact on quality and longevity would be greatly appreciated. Additionally, any other features I should consider would be helpful. I plan to use the mower for clearing brush and small trees (less than 2 inches) along with other general tasks. The tractor I’ll be using has 52 HP at the PTO.

 

[5030]

One thing that most owners fail to understand and that is, you have to allow the shredder to swing side to side a bit and not having it rigidly attached to the 3PH. With it firmly attached to the 3PH, every change in direction or turn, imparts a lot of stress on the mower as the tractor turns and the shredder tries to follow with the tail wheel fighting every inch of the way. The user instructions that came with my 8 foot Landpride specifically states to allow the mower to swing sideways a bit and my lower links have a slotted arrangement in the outer telescoping links just for that. The 'Woods' in the picture has an upper link (mine does as well) to allow vertical movement without stressing the deck metal at all as well.

 

[ArlyA]

I’m looking to buy a bush hog (rotary mower) and have narrowed it down to the Bush Hog brand and Brown. However, I’m a bit confused about some of the combinations and gear ratings. For instance, Bush Hog offers a medium-duty mower with a 10-gauge deck and a 110 HP gearbox, while their heavy-duty model has a 90 HP gearbox but a 7-gauge deck. This seems strange to me. Similarly, the Brown mower has a 7-gauge deck and a 90 HP gearbox, but it’s rated as medium duty. I’ve heard that the gearbox rating is the most important factor, but it doesn’t make sense that a lower gearbox rating would be on a heavier-duty mower. Since this will likely be my only purchase of a rotary mower, I want one that will last. Any insights into the differences between gearbox ratings and their impact on quality and longevity would be greatly appreciated. Additionally, any other features I should consider would be helpful. I plan to use the mower for clearing brush and small trees (less than 2 inches) along with other general tasks. The tractor I’ll be using has 52 HP at the PTO.

The 90 HP gearbox with a 7-gauge deck does mean something, but its not a "never break it" guarantee. Look for lots of support under that gear box and get a clutch on it.