First Fab Design

[mYnAmEiSmUdD]

I am looking to learn how to fabricate.

Lucky for me i have access to autocad 2007.

I am designing a rear bumper / tire carrier for my 1st gen runner.

I have little to no welding experience so I am going to be trying to keep it simple stupid.

I am planning on doing a mock set up with wooden 2x4s to check for clearances and what not so I do not run into trouble while trying to fabricate.

Ok so here goes nothing! Bare with me, I am under 24 hours into designing this!

Materials Planned:
~12' of 4x2x.120 Box Steel @ $4.34 / ft --> $52.04
~15' of 2x2x.120 Box Steel @ $2.90 / ft --> $43.50
~2' of 3x.25 Flat Bar @ $2.42 / ft --> $4.84
~Misc. angle iron


I plan on using the 4x2 for the bumper itself, the 2x2 for the swing arm assembly and the flat bar for the brackets that will support the swing arm. As for the pivot i was planning on getting tubed steel and welding it to the swing bar, then throw a good sized bolt thru with a generous amount of grease.

I am going for structural integrity and functioinality over aesthetics here.

After a few designs thrown out the window this is what i am left with.



3-D anyone?



(i see that my orthorgraphic and 3-D drawings are back asswards. Realized this after i had finished the 3d model and am FAR to lazy to change it.)


A few questions...

Is my pivot idea any good or should i do more research into prebuilt spindles?

Should i be looking into imbedding the flat bar brackets into the bumper itself as well as boxing it where ever i can?

Do the prices on the steel seem reasonable?



Any comments, concerns, complaints and or suggestions are more than welcome and very much appreciated.

Everything is subject to change!

Thank you for looking!

[Cebby]

Your hinge design is called a double shear and is actually stronger than those spindles. Use some BIG hardware though and certainly box it as much as you can.

I haven't priced steel lately so I can't comment on the pricing. You need someone else from your region to see if those prices are good. Prices here are different than prices there.

[neliconcept]

Cebby yeah it seems steel varies almost by state, heck you should come down here and buy steal, its cheap as all get out

[Robinhood4x4]

Looks like a good start. The double shear design will be stronger than a trailer spindle as long as your welds are strong. Those brackets should be a minimum of 1/4" plate.

What you will find is that the swing arm will sag under the load of a tire. This will mostly come from the slop that's inherent in drilling a hole and using a bolt as a hinge. You might want to compensate for that by tilting the hinge/swing arm assembly before you weld, but I wouldn't. It's very advantageous to have the latch carry 1/2 of the weight of the swing arm. Less stress on the hinge that way.

Now comes the hard part...the frame mounting brackets. The best way to figure out clearances is to mock them up with cardboard. Put your bumper up where it's going to be (use a couple saw horses or something) and carve out the cardboard brackets.

Personally, for a first fabrication project I wouldn't start with a rear bumper. If the tire carrier breaks off on the highway, people could die. I'm glad there's no hitch in your drawings. For a first project I'd start with sliders. They're easier to make too.

[Lee]

as for the tire mount, i really recommend doing like mine and using a toy axle end, complete with lugs



looks like your design is good, but you should practice your butt off welding because its all about proper penetration and not tempering the steel by cranking the heat too high. if any part of it is weak, the whole thing will fail.

so far so good, but i agree with steve, try something easier like sliders... the bumper can be tricky because you can plan all you want but it will never fit exactly like you pictured it.

[waskillywabbit]

Carbon steel is priced by the POUND generally and if you don't get a whole stick (20') expect to pay for the whole stick pretty much. Every cut will add $4-5 or so.

Those prices are high by my calculations as I can buy a whole stick of each of those things 15% cheaper.

[Robinhood4x4]

It's unlikely that the whole bumper is going to fall off or an entire slider is going to fall off. The risk comes with the relatively weak tire carrier.

Even I have my tool box carrier safety cabled to my bumper.

[waskillywabbit]

Your first fabrication project should be something like a welding table:
http://www.lincolnelectric.com/community/projects/

[Lee]

good link!