Why are loader arms tapered?

[Brad_Blazer]

I guess i'm not 100% with this thinking. The loader frame is 6' from the mounting point where it attaches to the bucket. When the bucket contacts an immovable object the stress is at the end of the tube near the bucket. this is where the bend is most likely to take place. My bobcat has very narrow tubes near the end and that is where they moved back ( bent ). Now the only solution I can come up with is to cut, reinforce, and reweld. I believe the fancy designs for the loader frame is to save steel and astetics. I'm not cutting and slicing when I build mine. I will take the slight extra weight and have it strong where it needs to be. And.............. I'm not a junior engineer, just practical with some common sense who hates to redo screw ups.

I think in the case of ramming a skidsteer bucket into an immovable object, it becomes a combined stress issue where the short downturned ends of the skidsteer arms experience a lot of shear in addition to the bending force both which were really due to compression of the curved arms with very little lifting involved. That's why dozers have straight arms designed to act in compression. If the skid-steer arms were constant cross-section they would have bent in the middle. Since they are tapered the ends were the weakest point for the load condition you applied. Of course it is impossible to optimize the design for every load condition. It sounds like something had to give. You should be thankful the damage was confined to the ends.

The arms are designed to save steel. It saves money and fuel and increases lifting capacity. Aren't you glad your limbs are tapered? If your calf muscles were the size of your glutes how fast could you run?

 

[czechsonofagun]

Spyder got it right. It is the strongest where the torgue/bending force is highest. Same reason tall electrical posts are tapered from bottom up, the top can be ligter and save some weight and material.

 

[joes_427_vette]

My Bobcat is probably 40 years old and I bet has met alot of immovable objects in its life. That is why it was 1200 when I bought it. I can understand the telephone pole analogy but loaders get shock loads and twist with the added forces. The old saying is something has to give and at some point it does. To my way of thinking the taper down to 2 1/2" at the end of a torsion rod so to speak doesn't make much sense, then again I'm not the engineer or parts salesperson. Just my 2cents.

 

[SPYDERLK]

[[[My Bobcat is probably 40 years old]]] and I bet has met alot of immovable objects in its life. That is why it was 1200 when I bought it. I can understand the telephone pole analogy but loaders get shock loads and twist with the added forces. The old saying is something has to give and at some point it does. To my way of thinking the taper down to 2 1/2" at the end of a torsion rod so to speak doesn't make much sense, then again I'm not the engineer or parts salesperson. Just my 2cents.

And I bet the tips are badly rusted internally due condensation running down there. Time has selectively weakened them there so they cant withstand their proportion of the load anymore.
larry

 

[CCWKen]

I think it's to save weight and money. Not to mention looking better. The stress is distributed between two arms and the cross bar acts as an equalizer. The cross bar also keeps the arms from twisting. The roll cylinders take a lot of stress off the cantilever calcs. It depends on what what the FEL is going to be mounted on and the design.

I built this small grader then added the FEL later. (I call it the "Kenbota".) The bucket is a little over 4cu.ft. I've had it heaped with #2 base and bounced it. I've mounted forks on the bucket and pulled cactus out of the ground whole. The arms are made from 2x4x3/16" square tubing and there's no sign of "bending moment". It does what I need it to do but I wouldn't try to lift a car with it.

 

[3RRL]

What a great little build, Ken.
So your loader works and does everything you want and is adequate for the tractor then? What about the grader ... that looks really cool. Does it come down to the Earth via hydraulics too? I see the hydraulic cylinders for angling, but not for lowering. Are there two cylinders for movement or just one?

 

[CCWKen]

Don't want to hijack the thread but Thanks Rob. Yes, the grader blade angles as well as lowers and/or tilts. There's a cylinder on each side that's independantly controled for ground contact. The cylinders are just in front of the rear up-right for the FEL.

This is a shot of one of the cylinders with the FEL removed.

 

[blacksmith]

I think it looks better and I knew I could do it. Here is a picture as I was installing the loader arms. The frame is made of 3"square tubing.

Here is the finished project.

 

[Iplayfarmer]

I think it looks better and I knew I could do it. Here is a picture as I was installing the loader arms. The frame is made of 3"square tubing.

So how did you taper the arms?

 

[joes_427_vette]

CCWKen; 2x4x3/16 material is what I plan to use for my loader. Why waste time and material hacking the tubes to a taper when the 4 inch profile is what I am after. I know they will be strong enough for my purpose.
Your "kenbota" turned out great. Alot of thought and time went into the grader blade. To do some serious cutting in granite or hard clay do you have to add weights front and back ?