Question about steel strength??

[jodebg]

I've been wanting to post a tractor photo under my user name. Just went to My Profile and can not figure out how
to insert a photo?? Anyone know how to do this?

 

[Sodo]

It's about the same but lower stress. For A513 steel which is probably what the rect tubings are, it will bend permanently at 74,000 psi (called the yield strength). 29 & 39 are a good distance away from 74,000.

2x2x 1/8" square has .583 inches deflection, 39,000 psi stress (for 500 lbs all at the tip of 36" tine)
and
3x1.5x 3/16" rectangle has .575 inches deflection, 29,000 psi stress

if you go to that calculator and use distance from neutral axis (the center)to outermost fiber 3/4" (.75") and Inertia = .466 inch**4 you will get these numbers.

 

[bcp]

I've been wanting to post a tractor photo under my user name. Just went to My Profile and can not figure out how
to insert a photo?? Anyone know how to do this?

"Edit Avatar" is under "My Home" not "My Profile."


There has been talk of 2x2, 2x4, and 1.5x3 steel. Anyone consider 2x3?

Bruce

 

[jodebg]

Bruce-
You saved the day-thanks.

I like the idea about the 2x3 as well.

 

[LD1]

I still don't like the lighter tube. I don't like using 500# either. You have to assume worst case. And that is all the load on 1 fork. Loads shift.

I would want nothing less than around 1 for the i4. That will cut the stresses and deflection in half. Not to mantion a better weld welding to 1/4" tubing as opposed to 1/8".

I really think you are over thinking it. Either buy a set, or build at least as strong as the plans call for. It isn't gonna make A ton of difference in the real world if the finished product weighs 80# or 120#

 

[jodebg]

"I would want nothing less than around 1 for the i4" What does this translate to?
In your prior posts you liked the 2x3 and 2x4 x1/4" dimemsions. These still your choices?

Over thinking-you're right. Not a metal worker and trying hard to grasp everything
correctly before I pay to have this made.

 

[Mace Canute]

Yes the 3PH lower arm itself is a 3rd class lever.

But anything attached to it doesnt follow simple lever rules. Since it is not rigidly attached to the lower arm and is free to rotate about the ball end of the lower arm.

most 3PH's arent perfect parallelograms by design. They want the tip od the implement to pitch up higher cause it is needed for long implements when crossing uneven terrain. That is why the lift capacity @ 24" is lower than the ball ends. But still significantly higher than it would be following a simple lever calculation.

If you want to know the lift, use a simple ratio. The force required to lift an object is directly proportional to how far it lifts it (in relation to the lifting mechanism.

IF you can set up the 3PH so that the forks lift perfectly level, and the tips raise the exact same amount as the heals, the lift capacity is the same at any point on the fork.

If the heal (right at the ball ends) lifts 12", and the tips raise 24", then you have 50% capacity at the tips.

But how high the tips lift is a variable that can be changed with different toplink length and placement. Thus the load capacity at the forktips can be altered with toplink adjustments.

Here Mace, read ALL of this thread and come back. http://www.tractorbynet.com/forums/...ph-load-capacity.html?highlight=parallelogram

I did read it. You're still wrong.

 

[LD1]

"I would want nothing less than around 1 for the i4" What does this translate to?
In your prior posts you liked the 2x3 and 2x4 x1/4" dimemsions. These still your choices?

Over thinking-you're right. Not a metal worker and trying hard to grasp everything
correctly before I pay to have this made.

I think the 2x2x1/4 was 0.91 and the 2x4 somewhere around 1.5 2x3 somewhere in the middle.

Yes, 2x3 or 2x4 would still be my choices.

 

[Sodo]

"I would want nothing less than around 1 for the i4" What does this translate to?
In your prior posts you liked the 2x3 and 2x4 x1/4" dimemsions. These still your choices?

Over thinking-you're right. Not a metal worker and trying hard to grasp everything
correctly before I pay to have this made.

i4 around "1" is twice as strong, twice as heavy, twice as long to drill each 5/8" hole ( ! ), more weld-prep to get 1/4" penetration, and no need for all that. Metal will be twice the cost. And when you go to store it, move it, the thing is twice as heavy.

You are looking building at an attachment for a large tractor - to use on a small tractor. Considering adjustments for a small tractor is a reasonable course of action. As far as an i4 about "1" the forks in this pic probably have an i4 around 1.25 and a B7800 can't even think about this capacity.

That said, I don't think you will be sorry if you just follow the drawing. It could bother your welder to have a drawing in hand and you're telling him something different. All depends on how he does his stuff. If he makes everything heavy thats one way and if he likes to optimize that's another way.

 

[LD1]

I did read it. You're still wrong.

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.