Forklift Stinger Engineering

[UNSTUCK]

Ok all you mechanical engineers. Here's a problem for you. I need to make a forklift stinger to transport rebar coils around a job site. The stinger tube will project 22 feet past the box structure for the forks. The weight will be equally distributed across the 22 feet of the projection at 1000 pounds, or about 45.5 pounds per foot. We have one in service right now that uses sch. 40 (I think) pipe with 4 1/2" OD. This works well, but I believe it to be overkill. I'd like to make this next one using smaller diameter material, either round or square tube. Square would be easier for me to work with. Since this will be attached to the forks of a forklift it will be bouncing around a jobsite. I'm sure these forces are impossible to factor in to the equation. Maybe not.
The picture shows the weight hanging off the tube, but that's not accurate. Just easier to draw. The stinger will slide through the coil (think giant coil spring) for quick maneuvering.
So, any idea what size tube I can use for the stinger? I'm wondering if 2x2x1/4" mild steel tube would be strong enough. I think that would be the ideal size for ease of use. If not, what if I ran a 1" angle iron down the length of it, as a gusset?
Thanks for any input.

 

[Spork]

I'm not a mechanical engineer, but how often does the forklift jockey not fully seat the rebar coil? or try to push with the 22' long end? My guess is the 4" was what was around but also is a large enough diameter that it can handle what the forklift can dish out.

 

[Corban_White]

You can hire a real engineer to run the calcs, which as you say are pretty much impossible to know because of all the dynamic loading, so to cover his a$$ he will put a bunch of safety factor and you will end up with 5.5" schedule 80. Or you can go with what you know works. Or, you can go with the tried and true method of listen to your gut and repair/reinforce if it starts to bend.

 

[Hickey]

We have a stinger like that at work that we use for moving large amounts of unmounted truck tires. I've also used similar stingers in the past for moving 12' rolls of carpet. 22' though, thats pretty stinking long.

 

[dutchman]

So I took a quick look at a stress analysis based on your opening post, using the same(ish) size steel mentioned. The 22' length is what is really going to give you problems. The first image is just a 3x2x1/4" tube and the second has some 1x1 angle running down both sides.

This thing would get bouncing quite a bit rolling through a job site. Cutting the length in half would go a long way in reduce how much this think would bend.

*Disclaimer, this is a quick look and not as accurate as a dedicated case study would be*

 

[4x4_Welder]

If you have something that works, why are you reinventing it?
A 2" x 1/4wall square tube at that length will have a noticable bow all by itself, once you throw 1000lbs of other stuff on it it'll be less than happy, most likely it'll dent in and start failing near the attachment point where the flex ends.

 

[UNSTUCK]

The coils are always fully seated. Any that hangs off the end can bounce around like a slinky and would risk getting bent out of shape. I found out the actual coil we are building these for weigh 636 pounds each. I'm liking 4" DOM with 1/4" wall. But I'm totally guessing. Looks like I'll need to sleeve it and weld two pieces together to get my length.

 

[UNSTUCK]

We want to make this one actually have two stingers instead of just one, so we were just looking at making it a bit lighter weight if possible. We have hundreds of these coils we need to move around. The stinger can't be any shorter as we can't have the coils hanging off the ends.

 

[UNSTUCK]

Dutchman, Thanks for that. I don't notice any defection with the stinger we have now. You're thinking there could be over 60" of bend? Am I reading that right?

 

[dutchman]

Dutchman, Thanks for that. I don't notice any defection with the stinger we have now. You're thinking there could be over 60" of bend? Am I reading that right?

Yeah, that's what the model predicted. I just ran a quick one with the 4.5" OD (sch. 40) pipe currently being used, model predicts only 15" of bend at the end of the 22' length. So, I would imagine the current setup has some deflection just not as extreme as the example in my earlier post.

 

[UNSTUCK]

So it looks like my two best options as far as availability are:

4" OD x .226 wall DOM

4" OD x .318 wall DOM

The price difference between the two for all the material I need is $320. The other issue is that the lengths are 21 feet, so I need to weld on a 3' section. Those wall thicknesses make for a bad fitting sleeve.

 

[MikeGyver]

Square (or rectangular) tubing is stiffer than round. You want to maximize 'effective diameter' (area moment of inertia) of the tubing over its thickness.

2x2x.25 won't work, not even close, it's waay past yield strength. max deflection is something silly like 60 inches, max yield is like 166ksi
4x.226 A513 (1026) DOM round, max deflection is 12.6", max yield is 46.7ksi
4x.318 A513 (1026) DOM round, max deflection is 12.1", max yield is 42.2ksi
4x4x.25 A500 grade A, max deflection is 9.2", max yield is 33.4ksi
4x4x.375 A500 grade A, max deflection is 6.7", max yield is 22.8ksi
5x5x.25 A500 grade A, max deflection is 4.5", max yield is 19.2ksi
6x6x.188 A500 grade A, max deflection is 3.2", max yield is 16.4ksi

for example, the 4x.318 round and the 4x4x.25 are the same linear weight (12.5lbs/ft) but the square bends much less and is not as close to yielding the material even though the material is much weaker (and therefore probably cheaper). Rectangular tubing would work great, (6x4 for example), the width doesn't do much of anything for vertical deflection, just adds weight and therefore possibly cost.

Assumptions:
all calculations are assuming static loading, not bouncing.
A500 grade A: 45ksi tensile, 39ksi yield
A513 (1026) DOM: 85ksi tensile, 75ksi yield