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homemade rocketbox - car top carrier


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Has anyone made a car top carrier? The large ones are $500:

http://www.rei.com/product/784507 , and they are surprisingly cheap.


I've seen some made with plywood, but those look heavy. I've built a pigmy kayak, so I was thinking 'stitch and glue', but the thin 5mm plywood is hard to find.


I could also build it from .060" aluminum sheet metal, but that would require a inner structure for rigidity and would get tricky.

This is my macbook case made from aluminum.




I like making things....rivet guns are cool.


Anyone seen a diy explanation online?

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Let's just say I have a long history of tying things to my car, and never lost anything yet. I'm very paranoid about things flying off, and use lots of rope. That is one of the reasons I want to make my own, those plastic boxes look really cheap. My buddies yakima box blew up on the freeway, cost me a $80 pad.



This was jtree, 1984. I had a sheet of 3/4 plywood with a bunch of ring bolts for anchoring the tiedown ropes.:


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I finished my homemade rocket box, but my plans changed along the way. I decided that a box of any kind has problems: What do you do when the box is too small? Story of my life actually...


So I went with two dimensions with an expandable third. I measured the top of my car, and bought a sheet of good quality ACX 3/4 plywood. I sanded and painted it with Spar Varnish. Some people who know wood better than I do recommended epoxy resin, and I may still do that, though I might have to sand off the Varnish.


The dealer installed rack crossbars have an arc to them, unlike a straight Yakima round bar, so I had to add little wood spacers to help distribute the load of the board evenly.


For the most important part, the attachment of the board to the cross beams on the rack, I had a couple choices. Yakima makes adaptors out of plastic for non round dealer racks. I bought them, but didn't like the amount of plastic.


To make my own, back to home depot and the metal section. They have strips of 3/16" x 1" by 3' iron for a few bucks. I bought a few of those, cut them into about 8 inch strips, heated them up with a butane torch (msr stove might work) until they were red hot and got to work blacksmithing.


I ended up making a little bending jig from 2 long bolts mounted in a metal plate so I could more easily bend the red hot iron bar to exactly the curve I wanted. This is great fun by the way, if you like inventing and trouble shooting. I painted the metal with white paint...need to sand that off and prime it, do a decent job.


I also got some stainless steel bolts with lock nuts 5/16 diameter. All the holes got spar varnish inside...but I need to rethink that...they are leaking a bit, must be a better way to make them weather tight.




I bought some snowshoe like neoprene from Seattle Fabrics and glued that to the metal bar, and the wood shim, so the factory rack would not get scratched. The rack cross beam is sandwiched in neoprene.




The whole board:




Side view, before I upgraded to all stainless steel ring bolts.




on my Rav4:




My rack board loaded up at Coyote corner, the shower house in Joshua Tree for the return trip to Tacoma two weeks ago.




Site 28, our home for two weeks at xmas hidden valley jtree with the rack board on the car.




The black bag, henceforth called "the body bag" is the best part. That neoprene fabric is so heavy it doesn't flap. I load it up with sleeping bags, 4 pairs of skis and poles, drunken partners, whatever needs to go on the roof quickly. I strap it down with a few bungies and biniers, and old climbing rope if I'm driving far.


One thing I will do to improve it is to redesign it so the mounting brackets are little 6 inch square modules that can be bolted to the crossbeams individually, with bolts sticking up. I'd drop the board down on the modules, and tighten 4 nuts, locking the board to the rack.


This would solve the access issues of mounting the board to the rack. It's hard to mount the metal bars under the rack crossbeams because of clearance issues. Yakima and Thule have simple levers inside their rocket boxes that make it a snap, but I've not figured out how to engineer that kind of convenience into my system.

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The board was 45, varnish 20, a whole bunch of stainless steel ring bolts at a buck or two each...call it 30 in bolts. The fabric for the body bag was probably 25. Around $120 total, two days of work when it was too rainy to do anything else.


Sue schmoo.


I hate lawyers, never used one yet. I build stuff too well for failure to be a possibility. The whole reason I did it was the yakima box was plastic crap. My rack is rock solid. I would put it up against anything out there. Hell, I was walking around on it. And I needed more room...a bigger box.


The only thing that could happen would be I overload it someday, beyond 150 pounds would not be smart on any rack.


Perhaps Mark L. will chime in. He also builds things from wood, and saw my rack in action.


I saw tons of stuff on top of cars in the 2000 miles we drove with that rack. Mine was by far the most secure of any of them. We cruised at 85, and all I heard were a few creaks.


I build/invent things because my stuff is better than what I can buy, and yeah, I like to build stuff.

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I was thinking more of a failure of the strapping down than a wood failure.


Yakima makes a basket thing for loading on roofs, that is not a rocket box. The warrior or something. Similar to what you got going but has vertical rails, but smaller I think.


"Sue schmoo." till someone sues you.


BTW, I like the setup.

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lots of tie downs to stainless steel 5/16" ring bolts with old climbing rope and 1/2 bungie cords for constant tightness over time. I think I could turn the car upside down and it would still stay on. The weakness is in the dealer rack. It's only rated to 150 pounds. Everything I made is over built and probably good for 300 pounds or more.


I put 10,000 miles on a board just like this back in the early eighties, but that was on my gremlin, which had beefy rain gutters. We used to put upwards of 300 pounds on that thing and drive to jtree and back, no problems. We used to sit up there with lawn chairs.


yakima and Thule have got everyone convinced that their plastic boxes are the only way to go, when in reality people have been tying things on top of vehicles since the stagecoach.


Common sense, make it super strong, use lots of rope and bungies, nothing is coming off.


It's a lack of common sense in this country that has led to the infestation of lawyers. Not to say all lawyers are bad, I know some nice climber lawyers. Did you hear what the shark said to the lawyer?

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Hi Mark:


That's a sweet set-up and you probably get better fuel mileage with the low profile than if you had a 6" tall Yakima delta force basket riding up there.


Maybe a metallurgist can give a better explanation but I generally steer clear of stainless steel fasteners for this type of application as I've accidentally over-torqued them and experienced a complete failure of the fastener. Mabye go with a zinc coated steel or chromoly,(they are probably less expensive as well). YMMV

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I'm an engineer not a metallurgist but - most cheap stainless fasteners are not hardened and are very ductile. That being said, if they are big enough, they can still work. I'd need to run some numbers to confirm but as a minimum I would go up one standard diameter size (i.e. 3/8" to 1/2") if using stainless instead of hardened chrome-moly fasteners. YMMV...

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Gotta agree with Hugh - most mfg installed racks are held on via a couple of sheet metal screws into the stringers that form the roof.


For some reason it reminds me of the story about car wheels and aircraft engines.


How many lug bolts hold a wheel on most cars? 5 or 6


How many mounting bolts hold an engine on a Boeing 7X7? 4



BTW Nice little rack. Things like that are nice if they can be multi purpose. For instance, building legs so it could be used as a table.





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I'm an engineer not a metallurgist but - most cheap stainless fasteners are not hardened and are very ductile. That being said, if they are big enough, they can still work. I'd need to run some numbers to confirm but as a minimum I would go up one standard diameter size (i.e. 3/8" to 1/2") if using stainless instead of hardened chrome-moly fasteners. YMMV...


Why is "very ductile" considered bad?? In my line of business that is a very good thing as opposed to "very brittle"?????

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oh dang, I had to hunt around for those stainless steel ring bolts. I have some of cheaper steel ones, but they rust so fast. Perhaps I will go to bolt hangars instead, then I can use stainless bolts which would be stronger since there is no ring in them?


Scary about the rack being attached with just a few sheet metal screws. Perhaps I need to run climbing rope down around the bottom of the car? That would be classic. I have to believe that those screws are pretty big. The car manufacturers know that people are tying $6000 worth of kayaks on top of their cars on the dealer racks...


All my car manual says is don't exceed 150 pounds.


I like your idea of the table conversion. I'll have to work on that.

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the weight limit is interesting. I have a hard time believing that weight acting down would cause the roof racks to fail at 150lbs. Maybe if if were loaded dead center only?


I'd be much more worried about sail and the airdynamic forces due to a large box, than a bit of weight.

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I think they are being cautious. If you loaded 150 pounds of 2x12 boards, 15 feet long, right in the center of the dealer rack, the crossbeams would begin to flex, as would a yakima rack. My hope is that by spreading out my load (on the board) over three points of contact on the cross beams, I have some margin of safety.


I've actually wondered if the board, which tilts up slightly at the front, lifts me off the road a little, like a wing. Be cool to start flying! Bring your parachutes.

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