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How do I calculate the required tube size for my upper shock mount (red circle)? It sticks out about 7" from the frame and it will be welded to the main rail of the frame and the diagonal brace that goes to the front hoop. I am using a 465 lb/in spring mounted at 22*. Essentially, it is a cantilevered beam but I don't know the equation for it. I assume i should use the spring rate x total travel ( ~4") which would be 1860 lbs.

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Gavin

My build: http://www.locostusa.com/forums/viewtopic.php?f=35&t=16005

I don't think this is exactly what you are looking for, as it seems as though your "beam" will be supported differently. I can only assume that if you use it to calculate the total stress the tube can handle, you could then ramp it up till you get something that would halfway support the number you previously stated (1680)

http://www.engineeringtoolbox.com/beam- ... _1312.html

The equation there also assumes that the "beam's" load will be exacted upon the center section of it, as opposed to being offset.

If I were you, I would find something that could handle roughly double what you need it to, and try and get some sort of triangulation from the extended end back into the frame, that would give the shock something to compress against instead of just flexing the weld strength.

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Tucker

I'd run a diagonal from the outermost point down to the floor and call it good.

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It's a cantilever beam. Resolve the damper load into Y axis component and apply to end of cantilever, add impact loads, factor of safety, choose beam section, compare stresses to allowable.

Or, add vertical diagonal as previously recommended. I suggest you stiffen in fore-aft direction also.

Such as one of these? Ignore the blue strap. The blue tape goes to the bottom chassis rail. The cardboard gusset would be 14a sheet. Which is preferred?

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Gavin

My build: http://www.locostusa.com/forums/viewtopic.php?f=35&t=16005

The gusset plate(s) certainly looks much better than the diagonal. I'd change from triangular to trapezoidal in shape. Extend the outboard side to meet the bracket. Consider closing the bottom between the front and rear gusset plates. Maybe incorporate headlight mount to take advantage of the "feature".

The headlight "feature" occurred to me too. The height should be about right and there is enough room to fit the 7" headlight and clear the nose cone. I agree the gussets will look better than the tube and i didn't think to close it in on the bottom but i think that would be a nice touch. Do you think 1x1x.065 is sufficient or should i source something more stout?

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Gavin

My build: http://www.locostusa.com/forums/viewtopic.php?f=35&t=16005

Here's some basic thinking on this, I hope it gives you a start.

The tubing is .065" thick and the top and bottom edges are 1" wide. That means you have 1/16 square inch of material in compression on the top edge and tension in the bottom edge. When I buy tubing from Online Metals I request the information sheet which shows a tension test on every batch of steel. There can be big differences from hot rolled vs. cold rolled and also carbon percentage. I like to use round numbers, and I don't want to go thru my files and get actual numbers - so will take a guess at 50,000 psi. If you multiply that number times 1/16 square inches that is how much strength you have in the top and bottom edges. Maybe 3000 lbs.

The tube is around 7" long and it's 1" high, so at it's base there is a 7 to 1 leverage. If you use some 1"x2" tube to cut up and fabricate a gusset then the leverage would 7 / 3, which would be much better. Cut a piece of that tube that is 7" long on the diagonal.

If you don't close in the bottom of the gusset, it will be much, much weaker. probably 4 or 8 times weaker depending on if the gusset is .065" or .125".

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I'd do this.

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Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

I kinda like that idea. It looks like it should be simple to do and effective. Should I stick with the .065 or go for something bigger? My local supplier keeps 1.25x x 0.120 on hand but I wonder if that would be too much weight.

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Gavin

My build: http://www.locostusa.com/forums/viewtopic.php?f=35&t=16005

I was referring to plate/strip, stated to be 1/8 thick by 3 inches wide but usually closer to .100 thick than .125.
I'd use the tubing you have and definitely not .120 wall for anything short of a roll bar or maybe a long control arm.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

I decided to use a variation of your suggestion. I will use a 1.25" tube with 1/8" flat creating the gussets which continue to form the actual shock mount. I will then box it all in.

_________________
Gavin

My build: http://www.locostusa.com/forums/viewtopic.php?f=35&t=16005