Not that I remember..... But it is something I need to figure out. I really like the 1.5" thickness for picking pallets. 2" thick would make it kinda tight on pallets that have 2x3 rails and with only 1.5" thick, I can use full dimension 2x4 runners under lumber etc and still get the forks in.
I've been considering:
double 1.5" square rather than the single 1.5x3
1.5x3 and sliding some 1.25 square on the inside.
Use the 1.5x3 and add an L shaped gusset out of 1/4" on the outside
I have no idea of how to calculate the strengths but the way I see it, any of them are still stronger than what I have now which only failed with abuse.....wait I'll probably abuse the rebuilt ones too......
Single 1.5x3x1/8.....I4=.355 and weighs 3.5# per foot
1.5x1.5x1/8 I4=.188 and weighs 2.2# per ft
So doubling the 1.5 square would be .376.......not much gain over the single 3" wide stuff but adding almost a pound per ft.
An L shaped gusset at the heel will really beef that connection up. With a uniform thickness and material for the entire length of the fork, the heel is where the failure point will be. But it is really hard to calculate complex shapes without knowing exact dimensions, especially in such a critical area.
For stress, it is pretty simple to figure. You can look up whatever tube properties you want in many different charts online. Here is one, and this one shows 1/8 wall also. (There are a few differences between differing charts, so some of the I4# I mentioned earlier might be slightly different from one to the next).
Here is the chart
http://www.cim.mcgill.ca/~paul/HollowStruct.pdf
Look at the specs under the Y-Y colum. That is the weak direction of the tube. And the two numbers you need are the I (moment of inertia) and the S (section modulus). Moment of inertia denotes how stiff the tube is, and used in calculating deflection. Good for comparison of different sizes. The section modulus is used for calculating stress.
Stress = (weight x Length)/Section modulus
Since HSS tube is 50ksi steel, you dont want the stress to exceed that. So you can rewrite the formula solving for weight if you want.
(50,000 x S)/L = Weight.
Using the 3x1.5x1/8 tube 42" forks.....(50,000 x .474)/42 = 564# max at the tip of a single fork before it will fail.
Obviously this is a static condition. A load bouncing around must be factored as well. Even loads like on a pallet, the max capacity would be doubled. Again in a static condition.
