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Need help making a super strong panel

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Forum topic by boroughdan posted 469 days ago 1257 views 0 times favorited 19 replies Add to Favorites Watch
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boroughdan

22 posts in 568 days


469 days ago

I was hoping I could get some ideas on how to design a super stong platform/panel.

a friend asked me to build him some boxes to use for weightlifting. they are large stackable boxes that basically just raise to the weight up for olympic lifts. I used syp 2×12s, made six boxes that were about 3 ft long by 1.5 ft wide.

His have held up but a friend of his ordered a set and on the second lifft the top cracked in half. Very embarrassing.

I think the problem is that the wood doesnt have a ton of strength between the grain, it looked like his split along the grain.I did have one cross member in the center of the top boxes. that wasnt enough obviously.I did have some supports attached along the inside of the box that the panel rested on but those didnt give any support to the center of the panel.

Heres what I am thinking for the redesign.

first I routed a rabbet along the top of the box for the panel to sit on. Im thinking the support piece that runs acros the center (width not length) will be dadoed in instead of just glued and screwed. that would make a support about ever 18-20 inches, one of each edge and olne in the center. should I make 3 supports in the middle to give it a support every 8 or so inches?

If that didnt make sense Ill put up some pictures.

Another thing i am thinking is basically laminating another panel under the top with the grain running perpendicular to the top. This really needs to be able to take a hit from 400~lbs dropped from 4 feet above it.


19 replies so far

View crank49's profile

crank49

3370 posts in 1597 days


#1 posted 469 days ago

Laminate up about 4 layers of 3/4” sand ply. The 7 ply stuff from South America.
That should be about bullet proof and fit in the same space as two layers of 2x material.
Plywood is way better at absorbing impacts than solid wood.
Never saw a Karate guy poke his fist through plywood, did you.

-- Michael :-{| “If you tell a big enough lie and tell it frequently enough, it will be believed.” ― A H

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boroughdan

22 posts in 568 days


#2 posted 468 days ago

thank you. I think thats what Ill do.

View a1Jim's profile

a1Jim

112011 posts in 2204 days


#3 posted 467 days ago

From your description I can’t really picture what you trying to do. If your still going to put up photos I might be able to give you my 2 cents.

-- http://artisticwoodstudio.com Custom furniture

View bold1's profile

bold1

101 posts in 474 days


#4 posted 467 days ago

If you don’t want to go to ply. White oak split, to get straight grain, would be the best N. American wood to use. It was the go to choice before plywood for strength.

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Dark_Lightning

1690 posts in 1735 days


#5 posted 467 days ago

I’m with Jim. There isn’t a clear enough description of the original setup and what happened to damage it.

View boroughdan's profile

boroughdan

22 posts in 568 days


#6 posted 467 days ago

ok there you go. shouldve done that from the beginning. so the bottom two boxes on each side have a panel that is proud of the sides by an inch or so so that the box on top of it fits around it.

I dont have a problem with plywood if itll work. is 4 layers necessary? my biggest concern with 4 layers iis weight. that will be about 80-90 percent of a full sheet.

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firefighterontheside

3771 posts in 483 days


#7 posted 467 days ago

4 layers may be overkill, but is a guy who lifts 400 lbs gonna be bothered by a box that weighs maybe 60?

-- Bill M. I love my job as a firefighter, but nothing gives me the satisfaction of running my hand over a project that I have built and just finished sanding.

View JustJoe's profile

JustJoe

1554 posts in 665 days


#8 posted 467 days ago

How about making them torsion boxes, that way you’ve got a honeycomb of wood on the inside and the weight sitting on it will be distributed. All you’ve got to do is add some dividers on the inside:

http://www.bayareawoodworkers.org/jun02/torsionbox1.pdf

-- This Ad Space For Sale! Your Ad Here! Reach a targeted audience! Affordable Rates, easy financing! Contact an ad represenative today at JustJoe's Advertising Consortium.

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a1Jim

112011 posts in 2204 days


#9 posted 467 days ago

I’n that case the plywood idea may be a good one. If they don’t have to be stackable just having a double layer of plywood glued and screwed directly to the bottom plus some cleats on the inside will make it much stronger, Or you can install some cross supports across the the width(perhaps three 2×6s) on the inside by gluing and screwing them from the out side or by just using joist hangers on the inside.

-- http://artisticwoodstudio.com Custom furniture

View boroughdan's profile

boroughdan

22 posts in 568 days


#10 posted 467 days ago

the bottom two boxes will still have the solid wood tops because at the most they will have a person jump on them not weight and the top is inset so the weight doesnt roll off.

I think i will do the torsion box idea.

View a1Jim's profile

a1Jim

112011 posts in 2204 days


#11 posted 467 days ago

Torsion boxes are impressive to look at but time consuming to build and are better used to make sure your surface is flat I feel a torsion box construction is unnecessary for an application like this .
If your wanting a more finished looking box I can understand that the 2×6 idea sounds more like construction than cabinet making, but the construction is your number one concern when your dealing with weight issues. As a contractor and cabinet and furniture maker of 25+ years I deal with loads and spans all the time. Good luck on what ever route you choose to go with.

BTW there are ways to use 2×6 supports and hide them on the inside

-- http://artisticwoodstudio.com Custom furniture

View boroughdan's profile

boroughdan

22 posts in 568 days


#12 posted 467 days ago

I was just thinking your idea but also some cross member connecting the cross members you talked about. And I was planning on using 3/8 or 1/2 inch dowels to hang them. Im feeling alot better about version 3.0.

As far as looks these are going inside guys’ garages so as long as they are square and the same sizes they will look good enough. Im pretty sure Ill be more particular about the looks then they will ever be.

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a1Jim

112011 posts in 2204 days


#13 posted 467 days ago

If you do decide to put cross members in you might keep in mind to keep the ones closest to the handles set back far enough back so someone can get their hands in inside to carry the boxes.

-- http://artisticwoodstudio.com Custom furniture

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boroughdan

22 posts in 568 days


#14 posted 467 days ago

thats actually one annoying problem. right now the handles are as low as they can be and still be obove center so that when you pick it up the box isnt going to want to flip over. the top of the handle is 4” from the top. I want about .5-.75 inches of wood to stop the weight from potentially rolling off. Then .75” for stall matting which some like to add. then depending on how many layers of plywood the platform itself is just above the handle so your fingers cant really curl under it.

This just means I have to cut a notch into two layers of ply (I think I will use 3) extra work…

While I have some dialogue about this I was hoping someone could clear up a mystery to me. I dont know if you can see in the picture but I used a 2” forstner bit to make the handles. for some reason the ends of the handle are bigger than the middle, it kind of flares out at the edges. any idea?

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realcowtown_eric

295 posts in 563 days


#15 posted 467 days ago

Olympic weights are clearly heavy, not wimpy, they are round so when they drop they become a point load of signifigance.

Drop that in the middle of a panel, ain’t much blunter than an axe, which we all know is used to split wood!. A cleat underneath aint gonna do much to prevent that. What you want is a load-bearing substrate to spread the load to the gables, where presumably there are dadoss to absorb the load and spread it down to the floor.

I’m presuming it was a wood panel on the top that cracked. And wondering why the first one didn’t split, but such are the ways of the wood gods…

Eric

-- Real_cowtown_eric

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