Custom Roof Rack Mounts

[Matt]

I think you misunderstood what I meant.

By having Doc make my roof rack, i'm hoping he can have 3 of the crossbars used as the floor extend a few inches out on each side. These would effectively work as load bars and would be clamped directly in my mounts.

These images should help:

[IamJEEP]

I like your latest renderings. I have a question tho....those extended bars that you are clamping to..... only the weld would be holding the weight of the rack and its contents. Wouldn't that be a weak spot for failure?

[Matt]

Yes it would be. But with 6 mounts, 1" diameter steel, some skilled welding and a few reinforcement plates it shouldn't be an issue.

It's funny you mention that... because if Doc likes that and I decide to go that route I was planning on running an FEA to see what the stress would be at those joints with ~400lb (more than i'll ever load) on the rack to ensure the weld and whatever reinforcement we put there is adequate.

[Matt]

....or..... don't use a weld for the "support" at all. There's no rule saying that we couldn't put some bends in the lower perimeter bar. It would just shorten the overall length a bit. But we could have those "support" bars be one solid piece and the perimeter bar bend over it and then welded in place. .... maybe

[IamJEEP]

I think with gussets and a little "beefiness" at the joint, you would be fine. Your bend idea would work but just adds to the complicity of the design

[Matt]

Put 70lbs at the center of each crossbar (so almost 500lbs worth) and constrained the model by the very ends of the mounting bars to maximize the moment arm. We're talking about max stresses under 2ksi. So yeah, i wouldn't be concerned at all going with this method. Technically wouldn't even need any extra "beefiness"... but im a mass overkill kind of guy so I'd still like to see something there.



Edit:

But it would be best if those built in "load bars" are solid and the "perimeter" bar is cut and welded to each side of it. That way there would be more weld and it would be distributed around the sides with the lower stresses.

I would not want just a 4" long piece welded on to the exterior of the perimeter bar.

[IamJEEP]

Thats a cool tool you have there.

Is it possible for you to share the dimensions of he final product for others to home fab? With all the work you are putting into this, i would totally understand if you don't want to disclose that info.

[Matt]

Yeah man, i can turn pretty much make any of these into 2D drawings without much trouble.

Are you looking for dimensions of the mounts or the rack I modeled?

The rack was just kind of thrown together... I'm planning on having Doc "do his thing" in terms of how he wants to build the rack. I just made that model to help visualize some of the mounting ideas I had (like the most recent one I posted incorporating the crossbars)

[IamJEEP]

The rack, those mounts will be a bit much for a home fab with standard tools. Alltho, you can probably make an extra set and sell it on here. Put a little change in your pocket.

[Matt]

Sure. It's pretty standard though... pretty much made it 4'x6' (tapered the rear back to 46"), then adjusted the size of the top until the angles of the front and rear looked appealing.