Making My Blade Power Angle
- Thread starter wvpolekat
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nspec
Platinum Member
- Joined
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- 628
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- Southern Rhode Island
- Tractor
- Kubota B2630, '53 Farmall Super H, '47 Farmall AI, '44 Farmall A
To say there is no force on the kingpin is completely ridiculous. There is a reason they are made 3 inches thick! Unless you are driving your tractor full speed and whack something with the very end of the blade, you should be fine. The pins to lock the blade from rotating are half the size of any hydraulic cylinder you are considering. Agreed, there is some force exerted that wants to swing the blade, but the material will also want to roll off the blade as soon as this happens.
A backhoe dipperstick uses a single hydraulic cylinder. They are extremely long, and the forces act DIRECTLY on this cylinder - not though any geometry that transfers forces through a linkage. Even the upgraded cylinders that Kubota uses in this application to prevent breakage are not that big for the forces they exert.
Just for the record, the Land Pride blade made for a Category II tractor up to 80 hp uses cylinder that has a rod diameter of 1.5". A cusion valve is installed to absorb any shock.
Sure, a godzilla cylinder would be awesome and totally prevent any breakage, but if you really need it, are you using the right tool for the job?
A backhoe dipperstick uses a single hydraulic cylinder. They are extremely long, and the forces act DIRECTLY on this cylinder - not though any geometry that transfers forces through a linkage. Even the upgraded cylinders that Kubota uses in this application to prevent breakage are not that big for the forces they exert.
Just for the record, the Land Pride blade made for a Category II tractor up to 80 hp uses cylinder that has a rod diameter of 1.5". A cusion valve is installed to absorb any shock.
Sure, a godzilla cylinder would be awesome and totally prevent any breakage, but if you really need it, are you using the right tool for the job?
nspec
Platinum Member
- Joined
- Dec 31, 2007
- Messages
- 628
- Location
- Southern Rhode Island
- Tractor
- Kubota B2630, '53 Farmall Super H, '47 Farmall AI, '44 Farmall A
Hey guys, when you are talking about the cylinder diameter, are you talking about the rod or the entire diameter? If the entire diameter is 3", the rod could be 1.25". If this is the case, a 3" cylinder is not out of the question. My apologies if this is what is being discussed. I thought you were talking about a 3" rod on the cylinder!!
We are talking about the bore diameter. So, 3" bore with 1 1/2" rod.
I do agree, when going straight forward or working in loose material, the kingpin will take the brunt of the load or material will roll off. But, when working in heavy material, that load is absorbed by the locking pin or cylinder.
What I have learned here, or at least made to realize is that hydraulic cylinders can act as force multipliers in both directions. Either using a small amount of fluid at high pressure to generate large forces for work, or using large forces acting on the cylinder to generate high pressure in a small amount of fluid. The big difference being that one way you have a PRV to protect the components. With no PRV in the circuit beyond the valve, there is potential to generate pressure high enough to exceed the designed ratings of the components.
I personally don't feel that bending the rod is much of a risk, even with a 1.5" cylinder as long as you don't over extend it and it is laid out to keep the forces on the cylinder to be either compression or tension. The hydraulic pressure is the real risk.
I do agree, when going straight forward or working in loose material, the kingpin will take the brunt of the load or material will roll off. But, when working in heavy material, that load is absorbed by the locking pin or cylinder.
What I have learned here, or at least made to realize is that hydraulic cylinders can act as force multipliers in both directions. Either using a small amount of fluid at high pressure to generate large forces for work, or using large forces acting on the cylinder to generate high pressure in a small amount of fluid. The big difference being that one way you have a PRV to protect the components. With no PRV in the circuit beyond the valve, there is potential to generate pressure high enough to exceed the designed ratings of the components.
I personally don't feel that bending the rod is much of a risk, even with a 1.5" cylinder as long as you don't over extend it and it is laid out to keep the forces on the cylinder to be either compression or tension. The hydraulic pressure is the real risk.
LD1
Epic Contributor
Yes we are talking about bore diameter, not rod diameter, so apology accepted. And yes, with a straight blade and an evenly disrtibuted load along the cutting edge, the kingbin takes the brunt of the force. But what I am refering to is when an edge of the blade catches something, like a tree root or curb. Then the kingping is not taking the load. The kingpin becomes the pivot point. and the blade is like a big lever trying to collapse/extend the cylinder, which can create a huge pressure spike in the system and blow hoses if the cylinder is TOO small.
And this is in NO way similar to the backhoe. Unless you are driving the tractor and operating the BH at the same time. On a backhoe, the ONLY force their is, is the hydraulic cylinder pushing on the dipperstick/boom. Their is NOTHING pushing back. So the MAX pressure the cylinder is seeing is only whatever the tractor can generate.
The blade is a different story. The tractor is moving, providing an outside force acting on the cylinder. This can generate MORE pressure than the cylinder is designed for.
Now I think you are getting it. :thumbsup:
mwb
Platinum Member
Over extension bent his - I assumed he wrapped it around the king pin? That's a different problem than over loading / over pressure. I agree though that the OP cylinder is too small.
If you decide to use the smaller cylinder why not put a pressure gauge on it and test it? Put the gauge on the rod end of the cylinder and try loading it in a controlled manner. You may be able to get away with not over loading it most of the time but eventually you will find a show stopper!
JoeL4330
Platinum Member
Not my area of expertise, but my RBT35 8' has hydraulics on all four functions (with cushion valve on power angle) and the specs are probably available or I could measure if req'd ...but, the reason for the post is to ask just what you want to be the weak link if you somehow manage to generate unacceptable forces? I would think the hydraulic system's relief valve would be a good choice. It is only the normal operating forces that you would normally need to contend with and, if the blade casts the material as it should then the forces should be manageable. If you snag an immovable object, then where do you want the give?
This is an interesting idea.
Build in a weak link per se. Maybe a breakaway cylinder mount. At least with that broken, I could still drop the pin in and use it manually. Then the problem becomes, how to make sure it breaks somewhere before the limits of the hydraulics, but not so early it breaks all the time.
Chilly807
Elite Member
An interesting thread to say the least... I overextended my first cylinder because the cylinder was the wrong size, and the original design didn't permit the rod to fully extend without bending it, as MWB thought. It didn't quite get to the kingpin, but it was darn close. I simply wasn't paying attention as I extended the cylinder, and it bent like a banana. Re-positioning the mounts cured that, as did the right length cylinder.
The re-design thread is here:
http://www.tractorbynet.com/forums/hydraulics/192127-cylinder-travel-limiter-3.html
It gets into the re-design phase during the second page, I got some good ideas from the guys here.
After the re-design, I haven't had any problems at all. I decided to use the larger cylinder (3x10) while I was at it anyway. LD1 and MWB are correct in their thoughts that the smaller cylinders may cause a burst problem if the blade end hooks solidly into "something".
The larger piston diameter gives you more of a safety margin, and the larger diameter rod (new one is 1.5 inch compared to 1.25 for the 2 inch cylinder I had originally) is more resistant to bending under compression load.
I often use the very edge of the blade to wing back the edges of snowbanks on the driveways I plow, so it's a valid concern. The blade has considerable leverage over the cylinder, as we've discussed.
Mark, you mentioned you were going to attach the rod end to the kingpin plate I think. I'd encourage you to re-think that a bit. The farther out along the blade you go, the less leverage the blade has. My attachment point is 10 inches from the kingpin center, which is as far as I could go and still have something solid to weld the post to on the bottom. 12 or 14 inches would have been better, but I would have had to angle both ends and still try to get the pin holes to line up.
The previous owner had welded the rod pivot to the top of the blade, which then bent like spaghetti. I eliminated that and then added a stiffener gusset from the post to the kingpin top plate.
3/8 plate is heavy enough for the cylinder mounts, I drilled my pin holes with a bi-metal hole saw. Cut through like butter, although I did use a drill press. A large slow-turning hand drill would have worked too. If the holes were slightly oversize to allow for a bit of misalignment it wouldn't hurt anything either. You might get away with simply using a standard cross-tube cylinder if you can get the alignment a bit closer. I think my 3x10 was about $110 IIRC.
I looked into adding the crossover relief valve, it would have worked except that the volume is different on each side of the piston. They are better employed on two same-size cylinders (usually single acting, like angle plow cylinders), in my opinion.
We can all suggest different ways of doing this, it's human nature.
Sean
The re-design thread is here:
http://www.tractorbynet.com/forums/hydraulics/192127-cylinder-travel-limiter-3.html
It gets into the re-design phase during the second page, I got some good ideas from the guys here.
After the re-design, I haven't had any problems at all. I decided to use the larger cylinder (3x10) while I was at it anyway. LD1 and MWB are correct in their thoughts that the smaller cylinders may cause a burst problem if the blade end hooks solidly into "something".
The larger piston diameter gives you more of a safety margin, and the larger diameter rod (new one is 1.5 inch compared to 1.25 for the 2 inch cylinder I had originally) is more resistant to bending under compression load.
I often use the very edge of the blade to wing back the edges of snowbanks on the driveways I plow, so it's a valid concern. The blade has considerable leverage over the cylinder, as we've discussed.
Mark, you mentioned you were going to attach the rod end to the kingpin plate I think. I'd encourage you to re-think that a bit. The farther out along the blade you go, the less leverage the blade has. My attachment point is 10 inches from the kingpin center, which is as far as I could go and still have something solid to weld the post to on the bottom. 12 or 14 inches would have been better, but I would have had to angle both ends and still try to get the pin holes to line up.
The previous owner had welded the rod pivot to the top of the blade, which then bent like spaghetti. I eliminated that and then added a stiffener gusset from the post to the kingpin top plate.
3/8 plate is heavy enough for the cylinder mounts, I drilled my pin holes with a bi-metal hole saw. Cut through like butter, although I did use a drill press. A large slow-turning hand drill would have worked too. If the holes were slightly oversize to allow for a bit of misalignment it wouldn't hurt anything either. You might get away with simply using a standard cross-tube cylinder if you can get the alignment a bit closer. I think my 3x10 was about $110 IIRC.
I looked into adding the crossover relief valve, it would have worked except that the volume is different on each side of the piston. They are better employed on two same-size cylinders (usually single acting, like angle plow cylinders), in my opinion.
We can all suggest different ways of doing this, it's human nature.
Sean
