Steel Square Tube Calc

[SomeGuy]

I have a mid-rise scissor lift that's not quite long enough to pick up the jack points on some vehicles. Want to build some simple extensions I can set on top so I can pick up longer vehicles at the pinch welds. Figure I need roughly 6 inches more at each end overhanging (load center point would technically be a couple inches off the end but figure 6 inches anyway for worst case), 58 inches is the current platform length, so 70 inches total length of the extensions. Need to safely carry around 1500lbs at each end (lift is rated for 6000 lbs total, would build one for each side so 1500 x 4 = 6000). Would like to use roughly 1.5 inch square tube tripled up (3 side by side welded together). Can anyone do the math on it to figure out deflection and if I should use 0.100, 0.125, or 0.188 wall tube?

All the calcs I find online are always just center point load with ends supported.

High quality paint diagram:

 

[2big bronco]

I have a mid-rise scissor lift that's not quite long enough to pick up the jack points on some vehicles. Want to build some simple extensions I can set on top so I can pick up longer vehicles at the pinch welds. Figure I need roughly 6 inches more at each end overhanging (load center point would technically be a couple inches off the end but figure 6 inches anyway for worst case), 58 inches is the current platform length, so 70 inches total length of the extensions. Need to safely carry around 1500lbs at each end (lift is rated for 6000 lbs total, would build one for each side so 1500 x 4 = 6000). Would like to use roughly 1.5 inch square tube tripled up (3 side by side welded together). Can anyone do the math on it to figure out deflection and if I should use 0.100, 0.125, or 0.188 wall tube?

All the calcs I find online are always just center point load with ends supported.

High quality paint diagram:

I dont know how to do the calls but can you just stack a tube similar to the bottom on top? You know that one will hold a cantilevered load and you would be making the entire assembly way stronger.

Or what about grabbing a couple of the slide adjustable hf floor jack adapters for cheap and starting with those so you have all the adjustment

 

[arse_sidewards]

6" overhang?

A fuckin pressure treated 4x4 will hold any unibody vehicle where jack points matter just fine.

 

[ChiScouter]

Your looking at buying 2ea sticks for the job. I would go with the thickest for peace of mind and knowing that no matter what I plan on using it for at some point I will want it to be a lot stronger than the original intent of use. FWIW I did the same with thinwall 1.5 tubing when putting wheels on a bandsaw to keep it as low as possible and I was not really impressed with the rigidity of the finished product. Worked fine for my needs and I used scrap i had laying around but if i was to do over I would use heavier tubing

 

[Filthy McChevy]

Use thicker walled tube than what the lift is built with, or 2" receiver hitch stock.

 

[Spreader]

2”X6”x3/16 or 1/4 rectangular tubing. Why weld 3 pieces together?

 

[SomeGuy]

I dont know how to do the calls but can you just stack a tube similar to the bottom on top? You know that one will hold a cantilevered load and you would be making the entire assembly way stronger.

Or what about grabbing a couple of the slide adjustable hf floor jack adapters for cheap and starting with those so you have all the adjustment

This is going length wise, not width wise...the HF things aren't nearly long enough.

The bottom thing isn't tube, it's a platform assembly of sorts. If I had to guess without taking detailed measurements, it's roughly equivalent to 2 inch 0.250 wall C channel on each side that is bearing most of the weight on the platforms themselves. The uprights are at least half inch by roughly 3 inch solid steel.

Here's a pic with a smaller car on it:

2”X6”x3/16 or 1/4 rectangular tubing. Why weld 3 pieces together?

The thought was the extra verticals of multiple tubes will be stronger than a fully hollow tube without having to go to thicker walled stuff. I'd rather these things weigh 30-40lbs instead of 100+ lbs.

 

[SomeGuy]

Here's what I ended up doing, it's two 2x2x0.188 tubes that are 72" in length, with what I'm calling "skates" that lock in the contact blocks. Still need to clean them up and paint, but wanted to test them out first before finishing. There's pretty much zero deflection, I can't slip a piece of paper in anywhere under the length of the tubes on the blue part of the lift.

 

[subybaja]

I was wondering why you would bother thinking about .100 vs .188... Overkill and be done.

That's a really cool lift setup!

Do you have to vacuum crap out of the holes?

 

[SomeGuy]

I was wondering why you would bother thinking about .100 vs .188... Overkill and be done.

That's a really cool lift setup!

Do you have to vacuum crap out of the holes?

I wasn't sure if I'd have to go up to .250 even...hence asking what was needed.

Thanks...that's on the lowest lock, it goes up to around 40 inches high, so wheels end up being at the perfect working height. I slide that rubber diamond plate looking mat in the bottom of the picture over the holes when I'm not using it, so it stays pretty clean and dry. The occasional blast of compressed air usually takes care of the rest.

 

[subybaja]

Wow. I love it.

GarageJournal can keep their lego race-tiles, I'm gonna do those!

 

[stjames151]

I know you asked about HSS, but you should use not less than W24x310. Gotta remember safety factor dude.