Thread: Ply/timber roof rack cover

You'll want a material that has a decent amount of flex/give. Making it too stiff will create uncessory stress on your vehicle whilst not stiff enough will result it cracking.
Plywood probably isn't the best for this as it'll ultimately crack probably slot quicker than you'll want. So I'd probably go for aluminium, however this might not be cost effective.

Imo ready made solutions in the long run are most cost effective. but your mileage may differ.

Both materials will do the job if done correctly. Plywood gets used in boats and is subject to movement
Have a look at how these guys use ply for their camping kitchens etc to give you an idea, they have a very good reputation in the industry
https://www.drifta.com.au/camper-trailer-kitchens/

Originally Posted by Clinton1

I have a heavy duty, aluminium, roof rack on an old 4wd. I want an enclosed, waterproof, thief deterring, 'box' on top. I'm weighing up ply vs aluminium. Figuring out this job is a bit different... fun. For instance, glue and screw considerations for 'old banger 4wd going over coruggations'...

wait what about the weight

what is the maximum permitted roof load for your "old banger" 4WD?

this is probably the determining material consideration

Originally Posted by ian

wait what about the weight

what is the maximum permitted roof load for your "old banger" 4WD?

this is probably the determining material consideration

probably a lot more than is allowable these days with their super-you-beaut-Wafer-thin construction.

Originally Posted by Clinton1

I have a heavy duty, aluminium, roof rack on an old 4wd. I want an enclosed, waterproof, thief deterring, 'box' on top. I'm weighing up ply vs aluminium. Figuring out this job is a bit different... fun. For instance, glue and screw considerations for 'old banger 4wd going over coruggations'...

Have you considered thin ply with a light fiberglass covering?

Originally Posted by ian

wait what about the weight

what is the maximum permitted roof load for your "old banger" 4WD?

this is probably the determining material consideration

Originally Posted by Fumbler

probably a lot more than is allowable these days with their super-you-beaut-Wafer-thin construction.

possibly the other way round.
most of the mass in a 4WD, "old banger" or newer "wafer thin" model will be in the engine and drive train. There will be comparatively little in the shell.

the limit on roof mounted mass is most usually stability issues rather than concerns around vertical buckling of the door pillars.
It will pay to find the owner's manual and check.

150 kg is the safe roof rack weight, and I don't intend to load it that much. I'm thinking 30kg max for the 'box's. I'm considering glue and screw joints, add fiberglass/epoxy glue fillets and corners, with solid timber (euc) on outside edges/corners. Gaskets will be needed for dust proofing, and the gaskets will also act as vibration dampers. Can't be too hard.

Originally Posted by tonzeyd

You'll want a material that has a decent amount of flex/give. Making it too stiff will create uncessory stress on your vehicle whilst not stiff enough will result it cracking.
Plywood probably isn't the best for this as it'll ultimately crack probably slot quicker than you'll want. So I'd probably go for aluminium, however this might not be cost effective.

Imo ready made solutions in the long run are most cost effective. but your mileage may differ.

the trouble with aluminium is that I can't cut or weld... so i'll be outsources. That pushes me to 'not ally.

Originally Posted by Fumbler

Have you considered thin ply with a light fiberglass covering?

yep. But what do you think about epoxy glue fillets in the construction? Will they shattet on vibration?

Originally Posted by Clinton1

yep. But what do you think about epoxy glue fillets in the construction? Will they shattet on vibration?

Possibly. It comes back to the earlier comment about too rigid / not rigid enough. My preference would be light glass over it all but second would be for small fillets with glass tape over them (and on the outside of the joint as well). The fillet and glass work together to give a strong joint.

Originally Posted by Clinton1

the trouble with aluminium is that I can't cut or weld... so i'll be outsources. That pushes me to 'not ally.

BobL knows more than most of us when it comes to cutting ally, but my understanding is that it can be readily cut and machined with WW tools and carbide cutters. you would need an ally specific blade to cut sheets, but all joints could use 90 degree angle and be riveted -- with the joint line sealed with something like Sikaflex.
Hell, if you look, you'll probably find that 3M make an adhesive tape that is as effective as welding.

Pop rivets and coruggations don’t always go well. I know from experience. Maybe with the Sikaflex it will be ok as hopefully Sikaflex is still holding after the rivets have given up.

Sorry for the quality of the pic, But this is what I'm thinking. I'm haven't drawn it in the pic, but fiberglass tapeing the external edge will happen as well. Also, I'll match the external curve of the solid edge to the curve of the 4wd roof, and 2 central cross members down the centre.

Hmmm, new phone won't let me post a pic.20181202_191628.jpg