posted
I've been brainstorming about amp rack designs that won't take up too much space in the back of my truck, and I'm considering the raised floor method, but I'm worried about weight, as the rear sags pretty easily.
I'm thinking that I'd need to build it of 1/2" or 3/4" mdf to be able to withstand the weight of anything I load up back there.
How heavy would something of equivalent strength that's made of fiberglass or a sheet of mdf reinforced w/ fiberglass be compared to just a sheet of MDF? I've never worked with fiberglass, so I don't know it's strength or weight.
posted
well im no expert on fiberglass but i do know that it gets its strength from irregular shapes such as the curves you commonly see in fiberglassed subwoofer enclosures. a flat sheet of fiberglass would be very weak compared to mdf. i would recommend using a different material if you are planning on a flat surface. i dont know how much weight you are planning to carry in the back, but if your rear sags easily, then i would assume, not too much. try something like plywood. its lighter than mdf, and still pretty strong. hope i helped a lil.
posted
Thanks for the info. I was planning on using that trick where you put down some cloth rope so that it makes ridges in the fiberglass for strength. would that help the strength enough?
posted
Most ppl use wood to reinforce large flat surfaces.. someone once mentioned soaking corrugated cardboard with fiberglass resin .. that sounded like a good idea.. but i don't know how that turned out..
i've actually seen some corrugate cardboard that was almost as strong as wood.. add resin to that and you'd be all set.. and super light weight..
Fairly inexpensive mistake if it doesn't work.. hehehe good luck!
------------------ "If we're not in this together, then why the hell are you here?" -me
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posted
YOu wanna know the weight of a raised floor made outta fiberglass that covers your entire truck bed floor?
No problem..
Instead of just spittin out a number, I'll show ya how to calculate it.
First we gotta know what kinda cloth we're gonna use for this. I would choose knytex weave cause it's super strong and is great for large flat pieces. One particular configuration of knytex contains two layers of 12oz cloth and has one layer of 3/4oz mat stitched to one side.. let's call this 25 oz total.. this is the weight per linear yard. A linear yard of knytex is 50" wide and 3 feet (one yard) long. So, 50"x36" = 1800 sq in, which is equal to 12.5 square feet. Divide 25oz by 12.5 and that gives 2oz per sq ft. Now, we're gonna need 4 layers of this to make it strong enough (about 3/16" thick).. so now all the cloth required is basically 8oz/sq ft.
How big is the truck bed? 50"x72"? (minitruck?) that's 3600 sq in or 25 sq ft.
25sq ft x 8oz/sqft = 200 oz total cloth required or 12.5 pounds.
Now we need the weight of the resin. Let's assume you build this fiberglass with a 50/50 cloth to resin ratio. This means the amount of resin required will weigh the same as the cloth that's required, which means..
The total weight is 25 pounds.
This will require 8 yards of knytex cloth and at roughly $7/yard will be right around $60. I forget the exact weight of resin but let's say you'll need two gallons, @ $20/gal that's $40.
$100 cost.. you will prolly have quite a bit of resin left over.
You'll need some extra cloth to do the ribs (the rope effect) but the weight that will add is pretty minimal.. I'd say well under 5 pounds, depending on your skills at laying up fiberglass... let me rephrase that.. the ribs shouldnt add anywhere near 5 pounds to the overall weight.. in fact, I bet I could add them with less than 1 pound.. =)
------------------ Mike Pipes Digital Illusion Custom Graphics
R POT Designs - Carbon Fiber Watercraft Performance Products
Posts: 431 | From: Lake Havasu, AZ | Registered: Jun 2000
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I musta been hyped up on caffine tryin to keep myself awake to work cause there's no way that a 4'x6' fiberglass panel @ 3/16" thick can weigh 25 pounds.
I was prolly on a roll typin there, but the knytex weave does NOT have two layers of 12oz cloth.. it's just one layer of 12oz cloth with the layer of 3/4oz mat..
So, that's roughly half the cloth, which would be half the resin required, which is half the weight..
or 12.5 pounds.. or thereabout.
Man... glad I caught that... =)
------------------ Mike Pipes Digital Illusion Custom Graphics
R POT Designs - Carbon Fiber Watercraft Performance Products
Posts: 431 | From: Lake Havasu, AZ | Registered: Jun 2000
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posted
WOW, thanks MPipes. That really helped. It's actually in the back of a 4Runner, so it'll probably be about half that size, so about 6 lbs? Wow, better than a fat sheet of MDF. Hmm... Just gotta plan the amp rack itself now...
posted
Wait, doesn't a gallon of resin weigh more than a gallon of water? And a gallon of water is like 9 pounds or something... Hmm, well at least it'll still be lighter than MDF.
posted
OK, in a 4Runner, yer not gonna use a gallon of resin. Just looked it up and a gallon is right about 9 pounds, depending which type of resin you get...
So, let's say you are filling a truck bed like I worked out before.. 6'x4'.. 3/16" thick.. 12 pounds overall weight, 6 pounds of cloth and 6 pounds of resin (assuming a 50/50 resin/cloth ratio which is definitely acceptible)..
Yer in it under a gallon of resin.. you'll need some for the rib supports, but it isnt really that much more. You could actually use epoxy and bond thin wooden rails under the fiberglass for bracing/support.
------------------ Mike Pipes Digital Illusion Custom Graphics
R POT Designs - Carbon Fiber Watercraft Performance Products
Posts: 431 | From: Lake Havasu, AZ | Registered: Jun 2000
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