[SimonB]

Now that I'm slowly getting more mobile again I'm wanting to start thinking about building my offroad bumper, I have selected the one I want to "copy" *(thanks 4e). Unfortunately I haven't hear a peep from the guy who made these ones so I'm going to have to work out the details myself.

My main question is around the two upright sections. As you can see in the pictures they two uprights seem to be made of thick sheet, and support the recovery shackles. I presume these are bolted directly to the normal chassis bumper mounts, but from what I can see the shackle location holes are about 40mm higher than the actual bolt holes. What kind of stress will this cause to the chassis member that it is bolted to?

Also, how thick would one want these sections to be? It's difficult to tell from the photos but I'm guessing somewhere around 10mm at least?

Hopefully my existing high lift points won't get in the way of this

Any other tips?

[4ePajero]

Although I like that design (will till copy it for the Pajero!), you have confirmed one of my concerns as well.

The recovery points should definitely be in line with the chassis rails, to eliminate bending moment stress on the chassis and bar.

The upright columns are IMO the 'chassis' of the BB, onto which the rest of the BB is bolted/welded.
I would manufacture those two columns out of 4-6mm steel plate to form a deep box section, with internal webs to eliminate buckling.

[Ernie]

Hey SimonB

Would you mind sharing drawings with me? That will be my next project after I finish the sliders(almost done,so little time). I would also go for the 4 to 6mm steel.

Regards

[SimonB]

I haven't got any drawings - I will have to make it up as I go along.

I'm just wondering what thickness steel I'll have to use for the rest of the bumper, given that the "chassis" is made up of anything from 6mm upwards. 4E I'm not sure what you mean by a deep box section?

[Ernie]

Hey SimonB

I think this is what 4ePajero meant.



If you look on the pics you used(bumper 2.jpg) look for the ridge/edge of the column

[Wilfred Moore]

Hi Simon,

Surely a nice looking bumber. I agree with 4e Pajero, those recovery points are too high. If you use it like this, there will be downward forces.

I am somewhat concerned about the exposure of the side front lights/ Head lights.

Looking forward to see your end result !!

Wilfred

[4ePajero]

I would start as follows:

1. Basic design would start with uprights, which incorporate the recovery points. Forces will thus be transferred directly to the chassis rail, not the bull bar.
The width will be determined by the requirement for a winch mount or not.
The actual shape, length and angles of the uprights will be determined by using plywood mock-ups. Existing angles and lines need to be taken into account, again for aesthetic harmony (nice big words! ).
The recovery points will be part of the main mounting of the bull bar, and will bolt directly to the (appropriately reinforced) chassis rail.

2. The 'uprights' will consist of a closed box section, 25mm wide, with a system of reinforcing stiffening webs. I don't like the I-beam as per the photos, for aesthetic reasons.
The sketch show the 'box' open. It will have 'covers' on both sides (welded to the webs with 'puddle welds' on one side)

3. The 'uprights' will be welded to the recovery points / mountings.

3. Further elements of the design will be done by adding bit by bit to these elements, using plywood mock-ups to start off with.

[SimonB]

Definately something to think about - I hadn't thought of a box section I must admit but it would make the bumper quite a bit lighter.. lots more cutting and welding though.

[SimonB]

Woohoo... this week I lose the crutches so I can now really start looking at this. What thickness steel would one make up the majority of the bumper?

So the box section uses 4-6mm, would the rest also be 4mm?

[4ePajero]

I would use 4 / 4.5mm with stiffening webs where required, rather than 6mm.

For the uprights, use flat bar of standard sizes eg 40x4.5. this reduces the cutting you have to make.

Make sure that the hollow sections have drainage holes. I presume you will have the whole thing hot-dip galvanised? The drainage holes ensure that the galvanising reaches everywhere.

Make sure you keep record of the design (dimensioned drawing & sketches)!