Engineers, I need your input

[Starboard M]

Im working on designing a modular bed rack for my pickup, and am trying to figure out the strongest mounting system.

I tend to overload stuff, and while I doubt I would really break anything, its worth asking, right?


The green mounts will be welded to the bed rails, white box will span the two bed rails and be my crossmembers. Red will be sleeves, I am undecided if they will welded through the holes, or flush on the insides.

Bed Mount 1


Bed Mount 2


The main differences is the sleeves go from on the bed rail bracket to the crossmember.


Which would be stronger, assuming bolt sizes and any other variables stay the same?

I still need to find bolt strength charts, but for now Im thinking a 9/16'' dia bolt. Material will be 1/8'' or maybe doubled up 1/8'' in strategic sections. Its drawn as such, and I am still undecided if the crossmember will also rest on the bed rail when bolted in or not.



This will be used to carry camping gear, bike racks, snowboard rack, and building materials (think sheets of 4x8 plywood that doesnt fit in the bed).


Over thinking it, yes, but its what I do best!

edit: Just realized I fubared the holes. The outside material will be drilled to the same size as the sleeve material. Its currently drawn for a 1/2'' bolt, but the outside holes are 3/4''. Missed that last night!

 

[freerider15]

You has truck meow?

A few questions:

- How much weight will this see?
- Can you give some dimensions of things?
- How are the cross members attached to one another?
- How do those pieces fit/weld to the bed? (not seeing it entirely at the moment)

If I still had access to it, I coulda whipped you up a stress analysis to see the weak point in Pro Mechanica. Unfortunatley, I no longer have access :laugh:

 

[Starboard M]

I have one of those foreign trucks that shall not be spoken of that starts with Toy and ends with yota.
'03 Taco TRD auto with quad cab.

Sucked not having a truck, and having to borrow friends trucks all the time. However, because I live in a city and I park on the street I decided a mini truck would be the best option. Trying to park my dads F350 quadcab, 8' dually sucked on a good day, the yota fits a bit better.

I will get actually measurements later tonight, but this is what I want to make, but out of plate steel.


Max weights would be ~300 lbs?

Angle iron will be used to bolt onto the bed rails, the tabs would be welded to that.

Crossmembers go all the way across, currently thinking two maybe 2-3' apart from each other. Its a 5.5' bed, so we are not talking a ton of space here.

 

[time2getdirty]

I'd do the inside mount on the bed but with a plate made to sandwhich on the outside so outside metal is less likely to shear around the bolts holes.

 

[freerider15]

Ah ok, I get it now. So those square inner ends would be welded to something...that would be bolted to the bed.

I would make sure that things are sturdy enough to resist torsion. You're going to get quite a bit of torsion naturally in a bed. The key is making the components strong enough to resist it, and maybe even stiffen up your bed.

Otherwise, you can say bye bye to the sheet metal near where you're clamping/bolting it together.

If you're going to to 1/8", make sure it all has inner bracing, guesseting, etc. As well, I'd at least do weld washers where things bolt together to prevent wallowing of holes.

You SAY 300lbs. now...but lets be realistic :laugh. I'm more than willing to bet there are going to be times you'll want/need to surpass that some. Even sheets of plywood add up REAL quick (1 sheet of 4'x8'x1/2" plywood weighs ~40lbs.)

 

[Boostwerks.com]

Looks like the mounts are going to be a hell of a lot stronger than what they will mount to, so take that into consideration. Stress will quickly find the weakest point, so sometimes it's good to actually build things with less "beef". Well built structures are ones that will absorb stress evenly.

Personally I would go with #1 simply because the tubes will help keep the shape of that section when it's removed. I don't see an issue with either way however.

 

[Starboard M]

Im having way too much fun with sketch up!

Here is the main "cap" which I am actually thinking will be flat plate welded together. Im thinking it will be three sections, front "C" and two rear sides for ease of removing and storing. Drawn as a solid assembly right now. This will sit on top of the bed rails. As Boost mentioned, the bed is just sheet metal, so I think spreading the load as much as possible is key to keeping this thing alive. There are two bolts per side holding a decorative bed rail cap, I might only use those or drill some more. Figure the weight will be pushing down, the bolts would be more for locating and securing. I would imagine the friction of the metal on metal would be enough to hold it in place, while still allowing the bed and rack to have small amounts of movement. How much is too much, not sure. How much movement actually happens, no idea.


And here are the brackets


The bed cap will be 1/8'', the tabs will be 1/4''. I need to do some more measuring, but I would like to suck a spare tire up under the cross member, and allow Action Packers/ coolers to slide under it .

As mentioned before, Im envisioning this as a multi purpose thing, carrying wood or ladders to carrying snowboards and skis.

I will draw the crossmembers tomorrow, but they will be 1/8'' plate doubled up in key areas.

 

[Hypoid]

Not an engineer, did not stay at a Holiday Inn, but I do have experience hauling "awkward" loads in pickup beds...

There are two things I wanted to point out:
First, the open end of the bed has nothing to prevent it from spreading under load. The sum of my experience has taught me to run a ratchet strap from side to side, to help the the tailgate stay closed.

Second, Option #1 will give you more choices for rack systems. Lets say that you have to haul a 4'x8' anything: A few 5-foot lengths of square tube, with holes drilled in them, can act as cross bearers and give you attachment points for ratchet straps. Thus, you could make the sport rack from lighter material, and save it for play time.

:farmer:

 

[Starboard M]

Not an engineer, did not stay at a Holiday Inn, but I do have experience hauling "awkward" loads in pickup beds...

There are two things I wanted to point out:
First, the open end of the bed has nothing to prevent it from spreading under load. The sum of my experience has taught me to run a ratchet strap from side to side, to help the the tailgate stay closed.

Second, Option #1 will give you more choices for rack systems. Lets say that you have to haul a 4'x8' anything: A few 5-foot lengths of square tube, with holes drilled in them, can act as cross bearers and give you attachment points for ratchet straps. Thus, you could make the sport rack from lighter material, and save it for play time.

:farmer:

Weekend engintards are the best! I fancy myself one as well.

I too have been known to use 1/4 ton pickups to haul 2k+ pounds and use 1 tons to haul 2500 lbs of concrete.



This is my first foray into loading bedrails, hence why Im asking all the questions.


Holding the rear together will be done with the tailgait (I hope), but the rear crossmember will also hold things together. There will not be any load on the rails, without the crossmembers, or at least in theory.


I also made the tabs 3.5'' apart should I want to put a 2x4 across the bedrails.


Over thinking things is too much fun, especially when I dont have to grind out my mistakes.

 

[freerider15]

Seems like you're on the right path.

Essentially think of everything that "could" go wrong, and ask yourself how you've addressed it.

If your going this far, I would try and think of as many things as you can to make it as strong/light, versatile (you'll end up regretting not over thinking this later), safe, etc.

Would it be worth it to try and make the parts that attach to the bed rail angle iron adjustable instead of straight weld on? Would it be worth doing a bunch of dimpled holes on the cross member sheet area (this making it lighter, stronger, and places to attach straps).

If it were me, I'd try to design a way to make the peices that attach to the angle iron bed rails adjustable, that way you could add more if needed, or space them differently for various uses that you WILL find in the future

 

[Starboard M]

Seems like you're on the right path.

Essentially think of everything that "could" go wrong, and ask yourself how you've addressed it.

If your going this far, I would try and think of as many things as you can to make it as strong/light, versatile (you'll end up regretting not over thinking this later), safe, etc.

Would it be worth it to try and make the parts that attach to the bed rail angle iron adjustable instead of straight weld on? Would it be worth doing a bunch of dimpled holes on the cross member sheet area (this making it lighter, stronger, and places to attach straps).

If it were me, I'd try to design a way to make the peices that attach to the angle iron bed rails adjustable, that way you could add more if needed, or space them differently for various uses that you WILL find in the future

Oooo, I like speed holes. Didnt even think about dimpled holes to give parts less weight and more strength. How long would it take to dimple 100 1/2'' holes...:roflmao:

I will have to think how I could make what I am calling the tabs movable. I like the idea, especially when I am trying to make this as modular as possible, but nothing is jumping out as to how to go about doing that.

 

[Starboard M]

Here is what I had planned originally, but having now drawn it out, Im questioning how useful it would really be. Looks badass, but **** loading sheets of plywood that high.

The idea was to have the spare (gray circle) high enough I could load my cooler (blue and white box) under it. That puts the top of the spare almost 35'' above the floor of the bed. Lots of weight, way too high.


Now Im thinking a side mount, with the tire standing up would be a better option.

The reason the spare tire is up there is the stock location for the spare is where the gas tank on a XJ is. Behind the rear axle, under the bed. It doesnt hang as low, but its still here and only allows a basically stock sized tire to be there. Stock is a 31'' tire, Im looking to move to a 32'' or 33'' tire.

Back to the drawing board.

 

[Starboard M]

New and improved for the night.

Yellow are the crossmembers, current plan is for 1/8'' steel plate. Red is a laminated piece of 1/8'' again.


With spare. Not sure I like it there, going to think about a side mount to have it parralell with the cooler. The front crossmember will most likely push forward a tad, not only to get the tire to fit, but also to even the load out a bit more. Figure the bed is stronger in the corners than the middle.


Bed is actually 5' long and 57'' wide. Not exactly a huge space by any means, hence the rack.

Next step is the mounting system for all the things I want to mount. Rack, ski and bike mounts, lumber, maybe a skeet shooter? Mounted AA gun?

 

[9T3XJ]

...Figure the weight will be pushing down, the bolts would be more for locating and securing...

I just skimmed though this but I wanted to point out one thing - it sounds like you're designing for a static case - the truck's not moving, the force of the load is in one direction, down.

The case you should be designing for is when you've got a 400 lb load and you're traveling down the interstate at 75 mph and have to lock up your brakes or swerve to miss something. Now you've got a large horizontal force component. In that case I'd question the ability of the bedsides to hold the load. At the vary least I'd tie your crossmembers together to make the rack more rigid.