This question does not exactly pertain to surfboards, but I thought you guys will know the answer. I am laminating fiberglass cloth with polyester resin on both sides of a .50" plywood deck for bending stiffness. Will I see a difference in stiffness between 4oz cloth and 6oz or 8oz. I know the more layers will make it stiffer, but does cloth weight factor in for stiffness???
what i understand from your post is that you are trying to make 1/2" plywood more rigid by laminating both sides. i think that the weight of the cloth will have a proportional effect on rigidity. what do you plan to do with the laminated plywood? what are the finished dimensions of the plywood? are you adding any support other than the lam job? i’m asking all this because the increase in rigidity that the lam may add may be measurable in some ways, yet fail the purpose of your intended application.
The plywood is a skateboard deck, 4’to5’ long and 10" wide. No other support other than the lam. 48" long x 5/8" thick is good by itself. My goal is longer and lighter. My gut feeling is that 4 layers of 4oz would be stiffer than 1 layer of 8oz? Any thoughts. Am I splitting hairs?
i agree with you about 4 oz x 4 being stiffer than 8 oz. (it may even be true about 4 oz x 2). i’m not expert at skateboards, but you are spanning the 1/2" ply quite a distance between the trucks, with your weight causing flex in between. i’d worry about the adhesion of your lam to the wood, and about the lam shattering. maybe i’m way off though…there’s got to be a contributor here who has experience with skateboard decks. just like 8 oz cloth is proportionally stiffer than 4 oz, 5/8" plywood is stiffer than 1/2", to a greater degree even than the glass.
i agree with you about 4 oz x 4 being stiffer than 8 oz. (it may even be > true about 4 oz x 2). i’m not expert at skateboards, but you are spanning > the 1/2" ply quite a distance between the trucks, with your weight > causing flex in between. i’d worry about the adhesion of your lam to the > wood, and about the lam shattering. maybe i’m way off though…there’s > got to be a contributor here who has experience with skateboard decks.>>> just like 8 oz cloth is proportionally stiffer than 4 oz, 5/8" > plywood is stiffer than 1/2", to a greater degree even than the > glass. Make sure you glass both sides. In an effort to save weight, I only glassed the bottom of my deck. It rode fine, and had great flex, but it snapped upward at the front truck when I hit a large bump. I was still able to ride it home though, because the strength of the glass was enought to carry my weight even though the wood was completely broken. I used one six oz. lam and it was pretty flexy, so two would probably be the call. Good luck
Make sure you glass both sides. In an effort to save weight, I only > glassed the bottom of my deck. It rode fine, and had great flex, but it > snapped upward at the front truck when I hit a large bump. I was still > able to ride it home though, because the strength of the glass was enought > to carry my weight even though the wood was completely broken. I used one > six oz. lam and it was pretty flexy, so two would probably be the call. > Good luck For an application like this you may want to consider using an uni-directional glass and epoxy resin (epoxy adheres better to wood and flexes better than polyester). Like the previous post said glass both sides to complete the sandwich.
rastro, if you haven’t already done this, here’s a suggestion: once you decide on your deck’s final dimensions, cut a piece of the 1/2" plywood to that size, place a block under each end at the same distance, and with the same height as the trucks/wheels you’ll be using. then just bounce around on the areas where you’ll be standing to test the plywood’s flex. do this just to make sure that if you make a 5 foot longboard with 1/2" plywood, that you wont be scraping the street as you ride in the middle. I dont know if you are glueing up your own plywood, or buying it, but not all plywood is created equal. good luck, ok
Thanks for all the input. I have made a 48" x .625 thk without glassing which is adequate. I am using prefabed Baltic Birch of good quality. I will look into using expoy if I find cost and workability are not out of my league. The best board maker I know posted that by using multiple layers I would get more resin (heavier) because i would not be able to get enough squeeze out by hand. I have heard both ways now. I guess I’ll take a stab and experiment.
Thanks for all the input. I have made a 48" x .625 thk without > glassing which is adequate. I am using prefabed Baltic Birch of good > quality. I will look into using expoy if I find cost and workability are > not out of my league. The best board maker I know posted that by using > multiple layers I would get more resin (heavier) because i would not be > able to get enough squeeze out by hand. I have heard both ways now. I > guess I’ll take a stab and experiment. I’ve only made one skateboard deck (38") and it hasn’t been tested for success but I used 1, 4 oz on the top and a 6 and a 4 oz on the bottom. As far as the bottom scraping problem, my guess is that Rastro is planning on using some serious risers when he mounts his (superwide!) trucks. Also, a few strips of wood (called splines I think) could be attached to the bottom to make a stiffer deck. I made my deck because, at the time, I didn’t have the time (or an excuse) to shape another surfboard. It was fun!
The plywood is a skateboard deck, 4’to5’ long and 10" wide. No other > support other than the lam. 48" long x 5/8" thick is good by > itself. My goal is longer and lighter. My gut feeling is that 4 layers of > 4oz would be stiffer than 1 layer of 8oz? Any thoughts. Am I splitting > hairs? I just finished a 42" skateboard… I used 1/2" baltic birch 9 ply… I felt it was too flexy and could possibly snap with my 200# atop…I added a 2.5" rip of the same 1/2" ply… sort of a board length riser pad… Too stiff & too tall… Remove trucks … Get out 4.5" grinder w/24 grit…taper riser spline from 1/8" at truck to full 1/2" at midpoint… both directions…Fine sand & spray lacquer… Flex is tuned to my preference…Riser/spline loors way cool…