View Full Version : strength of materials question

03-16-2010, 04:07 PM
I am wondering about substituting 2"x3"x1/4" rectangular tube in place of 3"x3"x3/16" square tube. It is for the upright fixed arm on a front end loader, it will be 20" to 22" in length.

I already have the 2x3 tube, and am still gathering up materials before cobbling this thing together. What do you all think.

Have to buy new stock around here wish i could find cutoffs or such but no luck. Just trying to save a buck.


Mike P
03-16-2010, 04:35 PM

The 3x3x3/16 square tube is about 18% stiffer than the 3x2x1/4 rectangular tube. That extra inch of width has more effect than the extra 1/16" of wall thickness.

If that's what you've got....Just make the bucket 18% narrower to limit the size of the scoop. :)

You'll have to figure out if the reduction in strength is enough of a difference.

03-16-2010, 04:41 PM
I didn't check Mike's math but I'll take his word for it :)

I'm not real familiar with the fixed arm on a front end loader, but is the load
trying to bend the tubing? is it in compression? in tension? trying to twist?

its important to understand how the tube is loaded to figure out what a
change in size might do.

again, not a front-load'n kinda guy (hey, that was supposed to be a joke but
I don't much like how that reads :) ), so take this for what its worth.


J. R. Williams
03-16-2010, 04:44 PM
Double up the tubes if you have the room. Or consider adding splice plates to stiffen them in the force direction.


03-16-2010, 04:44 PM
Sounds like i will g with some 3x3x3/16 tube then.


03-16-2010, 06:38 PM
There are a number of things that affect the answer to this.

1. How does the upright attach to the tractor?
a. Is it bolted to the rear axle housing or bolted to the tractor frame?
b. Is it braced in any other way?

2. Are you positioning it so the 3" dimension is parallel to the length of the tractor?

3. Where are the hydraulic cylinders attached to the tractor and loader arms?

How the tube is connected to the tractor will help determine if there are point loads in bolt holes or welds in tension. The 1/4 wall will support bolts better than the 3/16. The vertical support is most likely acting as cantilevered beam.

When you push the bucket into a load the tube will be pushed toward the rear of the tractor.

When you lift the loader arms the tube will be put in tension and pulled toward the front of the loader.

Why do you have to replace the tubes? Did they fail, rust out or other?

Comparing the 3x3 by 3/16" to the 2x3 by 1/4" along the 3" dimension the 2x3 is a little less stiff. (With a 2000 lb load hanging off 1 end, one will bend about .112 inches and the other will bend about .096 inches, only about 16 thousandths of an inch difference.

Need pics, drawing or a very good description of what you are trying to do.

Assuming the fixed end of the tube is properly braced and the tube is positioned where the 3" dimension is parallel to the length of the tractor, I would be comfortable using the 2x3 tubes.