How to know if .083 Wall is adequate for 70 pounds?

[binar]

Fellow forum members,
I am paying a welder to weld me together a spare tire carrier for my Jeep. The tire and rim weighs 70 pounds. And I have decided to furnish him the stainless steel tubing so I can make sure the quality of the stainless steel is 304. I have decided on the following specs:

Stainless Steel 304
1.5" OD
.083 WALL
Seam in the inside of tube (not seamless tubing)

I am not an engineer therefore I am not sure how can I calculate if a .083 WALL thickness is strong enough to hold 70 pounds without sagging a lot? Or whether I should instead go up to a wall thickness of .120" ? Given between the two choices I would prefer the .083 because it is less weight. However, how can I confirm the .083 wall thickness is going to hold up to the 70 pounds of weight? Or whether the .120 Wall thickness is overkill?

To provide a better visual of my project, I have included below a basic drawing of the gate. As the drawing indicates the 70 pound tire is located in the middle of the gate and the length of the bottom tube supporting the weight is 54 inches. To the right of this bottom tube is a spindle that is welded to a heavy steel bumper and will support the entire gate once it is all tig welded.

Any opinions relating to whether or not a .083 wall thickness is adequate enough will be greatly appreciated. I would really like to learn what reference material I need to look at so I can be confident the .083 wall thickness is the correct option. Thanks in advance.

[Bls repair]

I think you may have a problem with the hinge and lock weld joint .You have a lot of force on it bouncing up and down

[BD1]

I suggest finding a manufactured one of your liking and duplicate. Many will list material sizes and thickness.

[DSW]

I think you may have a problem with the hinge and lock weld joint .You have a lot of force on it bouncing up and down

That was my thought as well. I'd be worried more about metal fatigue at the weld joints on thin tube more than bending. Good design can help solve that issue.

As far as bending, larger diameter tube is more resistant to bending than thicker wall tube on average. Many times you can get a significant jump in bending strength by going up in diameter, yet still be lighter than if you'd simply gone up in wall thickness.

[user 9328330]

I suggest finding a manufactured one of your liking and duplicate. Many will list material sizes and thickness.

Agree. Unless you really *need* to have something custom-made, it's usually cheaper by half (or more) to buy something that's made by the hundred in a factory somewhere by guys who only have to be intelligent enough to put new material into jigs and squirt some weld in there. Paying someone to redesign the wheel is super expensive. Even if you buy something that's already mostly right, and pay to have it modified, you'll probably still be ahead dollar-wise.

If you really have to have this custom-made, I would be figuring out a way to support the non-hinged end when the rack is closed, regardless of what tubing size you go with. Maybe you already do have something like this incorporated into your locking mechanism which isn't in the drawing.

[WNY_TomB]

Fellow forum members,
I am paying a welder to weld me together a spare tire carrier for my Jeep. The tire and rim weighs 70 pounds. And I have decided to furnish him the stainless steel tubing so I can make sure the quality of the stainless steel is 304. I have decided on the following specs:

Stainless Steel 304
1.5" OD
.083 WALL
Seam in the inside of tube (not seamless tubing)

I am not an engineer therefore I am not sure how can I calculate if a .083 WALL thickness is strong enough to hold 70 pounds without sagging a lot? Or whether I should instead go up to a wall thickness of .120" ? Given between the two choices I would prefer the .083 because it is less weight. However, how can I confirm the .083 wall thickness is going to hold up to the 70 pounds of weight? Or whether the .120 Wall thickness is overkill?

To provide a better visual of my project, I have included below a basic drawing of the gate. As the drawing indicates the 70 pound tire is located in the middle of the gate and the length of the bottom tube supporting the weight is 54 inches. To the right of this bottom tube is a spindle that is welded to a heavy steel bumper and will support the entire gate once it is all tig welded.

Any opinions relating to whether or not a .083 wall thickness is adequate enough will be greatly appreciated. I would really like to learn what reference material I need to look at so I can be confident the .083 wall thickness is the correct option. Thanks in advance.

.
.
calculations are difficult, usually you load test with 400% or more weight and see if it holds and not break so you put 340lbs on it. some will use more weight on parts experiencing vibration like 1000% or 700lbs

[Jimmy_pop]

you have only one hinge? One hinge = a pivot.

.083 wall is not enough. more importantly, the design isn't going to work. There is too much wrong with this to type it all.

Please don't proceed with this and have the entire thing come off on the highway and bounce into the windshield of a mom coming from with her kids from the zoo.

[sh00ttok1ll]

you have only one hinge? One hinge = a pivot.

.083 wall is not enough. more importantly, the design isn't going to work. There is too much wrong with this to type it all.

Please don't proceed with this and have the entire thing come off on the highway and bounce into the windshield of a mom coming from with her kids from the zoo.

I disagree completely. It is common in the off-roading world to build rear gates like this. He said he was using a spindle for the pivot. That part of the gate is plenty strong assuming it is welded correctly. Personally I would add a couple diagonal braces from the top of the upright to the bottom corners. This will stiffen the gate considerably. I would also use .120 wall but I also overbuild things like this. With the diagonals you would likely be fine with .083.

[njs552]

0.083 is not enough. If you start bouncing around offroad, coupled with driving on rough dirt roads and/or washboard, things will fatigue and eventually break. If you don't plan on doing any of that then you might be fine.

2" .120 wall steel tube is generally what similar designs are made of. My carrier is 2.5" square .120 wall.

Also a note on the spindle as hinge - don't have the spindle welded to the bumper. Have a sleeve welded into the bumper, then put the spindle inside that and only tack weld it at the bottom several times. Otherwise it is not uncommon for the spindle to shear off at the weld, and its the reason that companies who manufacture hinge kits include a sleeve.

[ManoKai]

@ binar - we would never fabricate your carrier as designed. Our minimum wall thickness would be .120/.125". Understand your "only" 70lb tire will dynamically load that single vertical member and the upper/lower horizontals in both tension/compression/rotation. Less weight? That's the last thing you should be thinking about.

Reconsider. As an alternative, Aluminum Tire Carriers are also quite common with the offroad Jeepers.

[binar]

Thanks to all for your postings. I have learned a lot. I should mention all of this is still in the planning phase. The drawing I posted is something I did on my own using CorelDraw and since I don't consider myself a metal fabricator with advanced design skills it is by no means a finalized design. I'll like to thank sh00ttok1ll for the diagonal brace idea. I'm definitely going to adopt this idea to the design because I agree it will make the gate a lot stronger.

As for figuring out a way to calculate deflection I found a real cool website that has an online deflection calculator. Below is the link to the calculator and a screen capture of two different calculations I performed. One at .083 and the other one at .120 wall thickness. Worth mentioning, I'm not accepting the numbers as gospel. Nevertheless, I think it's a cool little calculator that is worth a look.

http://www.engineering.com/calculators/beams.htm



Below are links to the Spindle, Latch, Striker and Metal Supplier I'm thinking about buying my 304 Stainless Steel from:

http://atozfabrication.com/tire-carr...der-s-kit.html

http://www.southco.com/en-us/r4-r?hid=7318&q=striker

https://www.metalsdepot.com/

http://www.southco.com/en-us/r4-r/r4-50-30-101-10

The latch is bear claw design and I'm told it's rated at 1,200 lbs before the latch mechanism fails.

In short, I'm changing over to 304 Stainless Steel Round Tubing with 1.5" OD and .120 Wall thickness. And as a safety backup I'm thinking of adding a spring loaded dead bolt that will slide into a hole in the bumper.

I have to say the Aluminum Tire Carrier ManoKai posted a link to is serious eye candy. However, I think it will work with my Jeep.





Lastly, the reason I'm choosing 304 Stainless Steel is because my Google research tells it can be mirrored polished. My thinking is this will save a lot of money because it will eliminate the cost for chrome plating the entire gate.

Again, thanks to everybody for their postings. This is a great forum.

[ManoKai]

@ binar - that online calculator you used to obtain your deflections is based on a STATIC load only. Your analysis needs to take into account the added mass {inertia} that the tire will dynamics impart (cyclically) to your assembly. Your tire would deflect lots more than your numbers when the Jeep is jet'n down the street, trail, Rubicon.

You want stiffness (K) built into your structure.

[Sandy]

The area right around where the stand off & tire plate all ties in is what you have to worry about. Very little notable deflection there but it is incessant while the vehicle is in motion. Eventually cracks develop right around the tire mount and one day the tube, plate and tire go boonie bouncing down into a canyon while the guy behind you (me ) watches and grins.

[forhire]

Check with your fabricator... unless his bender has an internal mandrel you'll need thicker material. Minimum radius on 1.5"x0.083 without a mandrel is 10". As others suggested use 0.120"... you're fabricator will be able to bend it much easier.

Also, understand that stainless can come in a number of finishes, mill, brushed, polished, and etc. You may be able to cut the fabrication cost by using pre-finished material. I'd strongly recommend you let your fabricator source the material... he will know what he needs and have the vendor relationships to get the material for a lot less. He may even have a piece left over from previous work.

http://www.pines-mfg.com/pdfs/H&HBendGuide.pdf

[FernTJ]

The engineering.com beam calculator appears to be for a cantilevered beam with a point load at the unsupported end. There are better calculators at engineersedge.com. Your project is more like a beam supported at both ends with a point load in the center (assuming that the latch end provides support, otherwise it is a beam supported at one end with a point load in the center).

Your beam has two tubes, making it stronger than a single tube. Your actual static load deflection if you made this gate would be much less than an inch if supported on both ends. However, deflection isn't the primary concern here. Your problem is permissible stress. For this project, as stated elsewhere in this thread should be 1/10th the yield stress. You want calculated static stress of 3,600 psi or less. Even using 0.120 wall you are going to be way above the permissible stress.

The hinge can be a major problem as stated above.

I think that you should get a qualified person to design and build your gate, or find one for sale that you can live with. Your design would be fine bolted to the wall of your garage, but should not be on the back of a jeep.

I made one for the back of my jeep over 10 years and 100,000 miles ago. I used a single 2 inch square tube with 1/4 inch wall. My static stress calculates to half the permissible stress, 1/20 the yield stress.

[Kelvin]

Just to throw another railroad spike into your Cobb Salad...

Be advised that 304 SS will rust if it gets salt on it in the winter (or if you live near the ocean)...316 is more resistant to the chloride in salt.

[DanD78]

Making your hinge pin taller or making two hinge pins would spread the stress over more area.

Dan

[binar]

Fellow Forum Members,
Thanks to everybody who posted. I have learned a lot.

This last Friday I met with a welder who has a hydraulic tube bending machine that can bend pipe at a 7" radius. However, he has a limited set of dies (shoes) for his hydraulic tube bender machine and this requires I make the change shown below in steel material:

• Original Spec was: 304 Stainless Steel Tubing with a 1.5" OD and a 0.120" Wall
• Revised Spec is now: 304 Stainless Steel, 1 1/2" Schedule 10 Pipe with a 1.9"OD and a 0.109" wall

In other words, the Schedule 10 Pipe is close to a 1/2 inch more in OD and 0.011" less in wall thickness compared to what I originally wanted to use. Another difference is I was using Tubing before and now I'm using Schedule 10 pipe which has a funny way of being sized. I say this because as a newbie I find the difference between dimensioning PIPE vs. Tubing very odd.

In short, I would very much appreciate any opinions regarding the following. Am I ending up with stronger steel that has less deflection by switching over to the Schedule 10 Pipe? My thinking is the extra half inch of outside diameter translates to stronger steel that is harder to deflect. Is this thinking correct? Or incorrect?

Any opinions will be greatly appreciated. Thanks in advance.

[FernTJ]

That pipe should have enough strength, so if the hinge and latch are up to the task it should work.

[Denis G]

Measuring pipe size (nominal ID) vs. measuring tube size (nominal OD):
http://jd2.com.au/pipe-vs-tube.html

[Broccoli1]

Off roading= go buy yourself a welder and make this thing yourself

[Dan Huygens]

Off roading= go buy yourself a welder and make this thing yourself

IDK about that in this case. He wants SS304 TIG welded... If he could find a cheap machine, practice would still be very expensive, and SS needs a lot of practice starting at zero.

Normally I agree; there is so much to learn that most people don't understand about how everyday things are made and what all goes into the process. But I don't think the OP wants to spend 6 months of hobby time and half his life savings just to build a SS spare tire carrier. If it were carbon steel I'd say yes any day. Or if he already had welding experience. But no.

Sent from my HTC Desire 626 using Tapatalk

[Broccoli1]

I would take the money that he is going to spend on a SS Tire carrier and buy a welder and then make the tire carrier out of mild steel.

Damn thing is going to be on the back of a jeep and hopefully covered in dirt - why polished SS ?.