Building a 8020 roofrack?

I just got my Tacoma a bit over a week ago (2019 Cavalry Blue TRD Offroad 4x4!!!). Could I get your thoughts/concerns on my bed rack design? It uses 2" square and 3"x1" aluminium extrusion. The brackets will be welded from 304 stainless. I will add in a second plate for the top rails so the mount is not cantilevered

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The plate will be waterjet cut and the jig will be 3D printed.

The bolts will be locked with Loctite Blue. I am worried about vibration and unexpected loads during driving, as well as usability issues. The brackets have a FoS of about 10. with a 600lb load on the rack. Dimensions are rough until I go measure things.

I am also considering routing out some polycarbonate panels and mounting them with hinges + electronic locks to make the bed somewhat enclosed.

 

Very nice, can't wait to see the finished product.

 

I'm sure that FOS is a 1G static load, I would be curious to hear what knockdowns you used on your welds as it looks like you just modeled them as solid metal. What were your contact conditions, globally bonded? If so actual results will be much lower.

As for the design, I think your connecting brackets are necessarily complex. the great thing about 8020 is with T-nuts you can mount to just about any side you want. For good strength + low cost go with gussets instead. you should be able to get away with basically no welding on this assy.

Spacing between RTT rails is about 32 inches if i recall correctly. You may consider running a cross member through the middle of that large opening to pick up those rails in the middle as well instead of only on the extreme edges.

If i were you I would bring the horizontal 8020 that is going to rest on the bed rails up about halfway on thsoe diagonal legs and use an L-bracket to rest the legs on the bed rails and tie into the mounting points. You'll be able to mount stuff up there and still get that rigidity.

And another tip, hide thsoe sketches and do some renders in SW if you're trying to impress anyone with your model. It makes a huge difference presentation wise and only takes a few minutes.

 

Hi MunchTIME,

I modelled them as solid bodies. This simulation was just for peice of mind, but I guess it was useless with how I did it!

Gussets sound great! This would be kind of like a right angle piece that comes off at an angle and a matching mirrored piece? I feel like this design is stronger too. How do you feel about two flat plate pieces with two finger joints for alignment and then I weld the inside corner?

For this design, is it that much worse to make? It is just 4 waterjet pieces per bracket which will be bolted to the 3D printed jig. Then I'll take it, take it off, and finish welding it.

For this design, I like how the mount plugs the core of the 8020. Otherwise, I would need to print a separate plug.

Also, would you worry about using 8020 / tnuts on a car?

I was planning on drilling through the tent base in a few new spots and bolting through there. I have not looked inside the floor sandwich. Do you know if they have supports where the premade bolt holes are? I assumed they were just relying on the top and bottom skins without any reinforcement.

 

It's okay if they're modeled as solid bodies, but you need a no-penetration contact constraint and need to set up all your fasteners individually. simulating the welds accurately is an entirely different discussion.

I think you should try to go for this type of a flat plate attachment method where ever you can, and since you're using double row and triple row in some cases it should be plenty strong.


If you're really confident in your weld penetration and quality go for it, but it's tough to mess up flat plates and one less operation. actually several less if you count the prep, and jigs. I'm assuming you'll be doing all your own labor? remember, every set up is an opportunity to mess up. If a jig is off or shifts during welding you'll have to cut them back apart.

So to close off the diagonal components, just cut them at the right angle. then you close them off and get more attachment area while keeping your brackets simple. like this:

Angled cuts are EASY especially if you make a drawing before you start cutting!



What's your reservation on the T-nuts?

I don't know what kind of tent you have but it's most likely the plastic plates on the top and bottom? you should have four large holes in a ~30" square with aluminum extrusion mounted to them. That extrusion helps distribute the load a bit... but those attachment points definitely leave something to be desired. If you're going to add your own holes use large washers to sandwich the plastic.

 

I would prefer to use simple flat plates like your first photo. For the first type of bracket, I could only support a single side. The second side would most likely be a welded bracket made of two pieces of flat plate.

For the welding, I believe it would only be a single setup since I'm using the integral bolt holes for fixturing. It is just a couple of simple TIG welds unless there is something I'm missing? It is not hard to get full penetration?
My plan is:

1. Waterjet parts with alignment finger joints
2. Bolt to 3D printed fixture using 1/4-20 clearance holes in plates
3. Tack full structure and remove fixture
4. Fully weld

It will only be one setup. This isn't my area though, so please tell me if this does not make sense.

For t-nuts, I am nervous about vibrations for something going on my car. My experience is solely in robotics research, things operate a few hours in their life and are not subject to extensive vibration. I've never had issues, but I don't want to find out here...

 

I went more with your design, MunchTIME. I got overly excited about 3D printing jigs. I'll make a second set of brackets later. These feel plenty strong though!

 

What was the materials cost for the rack?

 

• 2" x 2" 2020 extrusion - $85
• 3" x 1" 3010 extrusion - $75
• t nuts - $50
• aluminum plate - $30
• stainless steel plate - $60

Total: $300

This is an estimate since I had the material on hand. There are also a couple of hours of waterjet cutting.