Question about steel strength??

[Mace Canute]

We can play kindergarten semantics all day going back and forth calling each other wrong but what good does that do?

Instead of just calling me wrong, try to illustrate why you think I am wrong? There are far brighter people and engineers on this forum that will agree with me on this that you are also calling wrong.

The 3ph is not a simple class lever. Only way to make it move as such is if the toplink on the tractor side were mounted about the same rotating point as the lower arms, and the same length as them also.

Since it is mounted much higher, and closer to parallel, the implement doesn't move as a simple lever would.

You are thinking of this as if the implement is ridgidly attached to the lower link and thus just seeming as if the lower arm was longer. That would be the case on something like an IH 2-point fast hitch. But not a 3ph as we know it.

I believe the only thing that will change your mind is empirical proof so to that end I suggest you build a small parallelogram model of a 3PH and use a small spring scale as the link that transmits the lifting force to the bottom arm. Using a small spring scale will allow you to see the changes in force as the load is positioned in different spots on the model. It doesn't have to be fancy just accurate in dimensions to be a true parallelogram and sturdy enough for the test.

 

[jodebg]

Any advangtage to fabricating the 3ph mounts in the center of the frame,
rather than having the drilled pin holes suspended behing the frame on mounting plates.

Having the holes behind the frame pushes the frame away from the tractor. I am assuming
that this will decrease lift capacity?

 

[LD1]

I dont need to build a model. I know how it works, and know the effects of load placement. You are the one who doesnt understand it. And are calling me wrong. As well as several engineers on this forum who would also agree with me.

Mace, using your logic, work this out for me.

Lower lift arm is 25" ball to ball.

The lift rod is 12" back from the tractor, leaving 13" from the lifting point to the ball end.

Lift capacity at the ball end is 1998#

1. What is the lift capacity @24"?
2. What is the lift capacity @39"?
3. What is the lift capacity @ 96"?

 

[LD1]

Having the holes behind the frame pushes the frame away from the tractor. I am assuming
that this will decrease lift capacity?

A few inches one way or the other isnt gonna be a big deal.

Ignore what mace is saying. This isnt a simple lever. You dont loose much capacity moving farther back. Especially if you set up the toplink like I described to get a near level lift. It wont matter how far back the load is. Only limiting factor then would be front end weight.

Trying to lift 1000# in close, or 1000# out far isnt gonna effect how much hydraulic power you need by much. But it will effect the balance of the tractor quite a bit and you are likely to get light in the front. But again, for a few inches either way, you are over thinking it.

 

[SPYDERLK]

I have never seen a 3PH that is configured differently. The lower arm is attached to the tractor and this attachment point is the fulcrum. The arm that lifts the lower arm attaches between the fulcrum and the other end of the lower arm and it does not matter how that force is created, it could be from an internal cylinder and a rocker shaft and linkages similar to the diagram or from hydraulic cylinders that are attached on one end to the tractor while the other ends are attached to the lower arms. What matters is where that lifting force is applied in relationship to the load and fulcrum and if it is between the load and fulcrum, that makes it a Third Class lever. It doesn't matter if the length of the upper arm makes it a a true parallelogram or not, that only affects the attitude of the implement that is being lifted, not the force that is required to lift it. The force that is required to lift the load is dependent on how far the load is from the fulcrum. Period. What changes is the hydraulic pressure necessary to create that movement.

I believe the only thing that will change your mind is empirical proof so to that end I suggest you build a small parallelogram model of a 3PH and use a small spring scale as the link that transmits the lifting force to the bottom arm. Using a small spring scale will allow you to see the changes in force as the load is positioned in different spots on the model. It doesn't have to be fancy just accurate in dimensions to be a true parallelogram and sturdy enough for the test.

A few inches one way or the other isnt gonna be a big deal.

Ignore what mace is saying. This isnt a simple lever. You dont loose much capacity moving farther back. Especially if you set up the toplink like I described to get a near level lift. It wont matter how far back the load is. Only limiting factor then would be front end weight.

Trying to lift 1000# in close, or 1000# out far isnt gonna effect how much hydraulic power you need by much. But it will effect the balance of the tractor quite a bit and you are likely to get light in the front. But again, for a few inches either way, you are over thinking it.

Mace, did you really read that thread? Did you read Post 13 where I finally got pissed enuf to answer questions that simple lever people werent asking? In my experience I havnt noted in you a blindness to coherent and logical explanation of physical things. ... Everything Iv seen in your posts here are things that were addressed in that thread. -- I could almost believe youre kidding!
,,,, The thing that seems to make people call it a simple lever is that they see available force drop off with distance behind. They dont go the extra perceptual step to observe that it isnt dropping as fast in the 3pt case as it would in a simple lever system. The reason its dropping more than minutely [as a perfect //ogram system would due to escalating pivot/bearing loads] is that 3ph setups are not dimensionally correct //, so their effect is somewhere between a simple lever and a true //ogram. As far as ignoring what youre saying ... please ask a question, or state a specific reason why the //ogram examples are not applicable to the exhibited geometry of a 3ph.
,,,larry

 

[Xfaxman]

Do forks ever get used close together for "special purposes"?

Wondering if I need to add closely spaced receivers for any good reason?

That is the advantage of sliding forks. I made this frame over 30 years ago for a Craftsman garden tractor.

Added angle iron later to fit the TORO+Loader.

Made a boom pole out of thin wall 2" square tubing that fits between the forks.

Clamped on some "fingers".

Maybe you could make your frame with sliding sockets? :thumbsup:

 

[Mace Canute]

Mace, did you really read that thread? Did you read Post 13 where I finally got pissed enuf to answer questions that simple lever people werent asking? In my experience I havnt noted in you a blindness to coherent and logical explanation of physical things. ... Everything Iv seen in your posts here are things that were addressed in that thread. -- I could almost believe youre kidding!
,,,, The thing that seems to make people call it a simple lever is that they see available force drop off with distance behind. They dont go the extra perceptual step to observe that it isnt dropping as fast in the 3pt case as it would in a simple lever system. The reason its dropping more than minutely [as a perfect //ogram system would due to escalating pivot/bearing loads] is that 3ph setups are not dimensionally correct //, so their effect is somewhere between a simple lever and a true //ogram. As far as ignoring what youre saying ... please ask a question, or state a specific reason why the //ogram examples are not applicable to the exhibited geometry of a 3ph.
,,,larry

Ok, I'll have another go at it. My positions is: If the 3PH was a true parallelogram and you had a set of forks installed on, a heavy load at the tips would lessen the weight on the front axle more than if that load was as close to the tractor as possible.

Do you disagree with that? If you do, that would imply that the forks could be any length (right out to infinity in fact) without changing the weight on the front axle. If you do agree with that it follows that the tensile load on the lifting links would change between the two scenarios which would conversely mean the lifting force of a 3PH with a forklift attachment is lesser at the tips than it would be as close to the tractor as possible.

 

[LD1]

Ok, I'll have another go at it. My positions is: If the 3PH was a true parallelogram and you had a set of forks installed on, a heavy load at the tips would lessen the weight on the front axle more than if that load was as close to the tractor as possible.

Agree with that.

If you do agree with that it follows that the tensile load on the lifting links would change between the two scenarios which would conversely mean the lifting force of a 3PH with a forklift attachment is lesser at the tips than it would be as close to the tractor as possible.

That is where you are getting lost.

It is not increasing the tensile load on the lift links. But it is increasing the tensile load on the toplink, and increasing the compression on the lower arms. Thats the additional force trying to lighten the front axle.

Not trying to muddy the waters farther, but think about how a forklift mast works. shifting the load farther out on the forks doesnt increase the downward force on the hydraulic cylinder. But does increase the forces on the rollers. Trying to pull the top rollers forward out of the mast channel, and trying to compress the lower rollers back into the mast. Same principal.

 

[SPYDERLK]

Ok, I'll have another go at it. My positions is: If the 3PH was a true parallelogram and you had a set of forks installed on, a heavy load at the tips would lessen the weight on the front axle more than if that load was as close to the tractor as possible.

Do you disagree with that? If you do, that would imply that the forks could be any length (right out to infinity in fact) without changing the weight on the front axle. If you do agree with that it follows that the tensile load on the lifting links would change between the two scenarios which would conversely mean the lifting force of a 3PH with a forklift attachment is lesser at the tips than it would be as close to the tractor as possible.

... Yes. Whether //ogram or plain lever, moving the weight further out back has an ever increasing effect on causing the tractor front to lighten. The situation seen by the hydraulics however, in trying to hold against the load, is different in the two types of setup. It the 3ph case, the articulation points at the ends of the links move as the height changes, "separating torque from weight". The implement essentially floats wrt the links guiding it. The torque to backtip the tractor is conveyed by 3pt elements working in concert according to the position of their ends as fixed on the tractor and implement. The implement, or hanging load is trying to fall. The top link is being pulled by the load and the bottom links are being pushed, all in proportion to the amount the load is overhung beyond the balls. The weight of the implement is held by the hydraulics.
... If you visualize the pull/push forces on the links at different positions of lift you can recognize that a resultant up/down force prevails in opposition thruout lift. At one place the bottoms may tend to rise by the eyes being pushed toward the tractor, while the top link is tending down by its ball being pulled way from the tractor. Theres your torque -- acting directly on the tractor body. In a real //ogram these cancel and no net up/down force results from the torque of the overhung load. There remains the straight down force - the stark weight of the item. The hydraulics are supporting this .

 

[Mace Canute]

I may have to change my opinion! I think I will do a little more work on it first before I do so, just to be absolutely sure. (I'm stubborn!) Either way, I'll be back to either gloat or eat crow.