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 Post subject: Re: New 1/4" Birch Plywood Project
PostPosted: Tue Jul 08, 2014 2:15 am 
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Joined: Tue Jun 30, 2009 8:37 pm
Posts: 39
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I think you'll be too heavy with the dual 1/4". I used 1/8th ply, double layer and it worked well for me.

225 lbs. Lots of flex.

Here's the thread on the build.

viewtopic.php?f=107&t=2381313&start=10

SweetDoug


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 Post subject: Re: New 1/4" Birch Plywood Project
PostPosted: Tue Aug 12, 2014 12:10 pm 
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Joined: Fri Jun 11, 2010 1:55 am
Posts: 29
Well thanks SD on the tip to use 1/8".

Wow 1/8" double layer is enough? Does it even hold shape this thin? Or did you use glass on top? Also what quality wood did you get?


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 Post subject: Re: New 1/4" Birch Plywood Project
PostPosted: Tue Aug 12, 2014 2:46 pm 
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Joined: Tue Dec 23, 2003 6:30 pm
Posts: 850
Location: Traverse City, MI usa
No, 2 layers of 1/8 in birch ply are not strong enough, ya have to glass the top and bottom and middle....you lose any wt advantage. 3 sandwiched 1/8ply layers are just strong enough with poly on the outside, perfect for mowing the lawn riding, but high jumppin flying, THEY WILL TEND TO BREAK. BUT, I do find if you use good 1 1/4in AC 3 ply sheet and 1 1/8 birch 3 ply sheet. Makes for a relative Boom proof LIGHT flexible board, go figure.


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 Post subject: Re: New 1/4" Birch Plywood Project
PostPosted: Tue Aug 12, 2014 6:28 pm 
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Joined: Wed Nov 20, 2002 1:00 am
Posts: 933
Location: rhode island
lots of useful observations to take advantage of.

if still not sure, a bit of experimenting during your next visit to HD will add some hard numbers to all of the speculation. (or you could look them up from someone like 'plywood association' of wherever)
compare all your potential candidate materials.

one by one:
prop up any of your favorite choices between two carts.
toss a 50lb bag of cement in the middle
measure deflection, length width and thickness.

Deflection = wL^3/(48 E*I)
google 'beam deflection formula' for 3-point bending

the resulting numbers will be a good way to compare and give you enough to predict deflection for any of your design iterations.

It may also convince you that the cheepest and lightest crap you can find will be tough to beat with 1 or 2 layes of 4oz glass.
imo,
-bill


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