How much weight can a 3/4" piece of plywood withstand?

Discussion in 'Off Topic' started by Jmmsbnd007, Dec 2, 2002.

  1. Jmmsbnd007

    Jmmsbnd007 Diamond Member

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    4 feet long, 2 feet wide, 3/4" thick... how much weight do you think it could support if it was nailed to wood all around it's sides leaving the middle open-bottomed?
     
  2. FoBoT

    FoBoT No Lifer

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    short term?

    or like for a shelf/long term?
     
  3. Evadman

    Evadman Administrator Emeritus<br>Elite Member

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    I doubt you could find anything heavy enough to overload a 2x4 piece of 3/4 ply. The framework around the edges would break first. I would estimate aprox 1500 to 2000 lbs evenly spread.
     
  4. MajesticMoose

    MajesticMoose Diamond Member

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    it all depends on where you put the load and it's characteristics
     
  5. Walleye

    Walleye Banned

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    ply is pretty potent stuff. i would estimate at least 800 lbs in center-ish area, distributed in a pile. if you would tell us what medium the weight would be we could be better at this.
     
  6. Sluggo

    Sluggo Lifer

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    If you are overly concerned about it you can head up to your local lumberyard and tell them you want some quality 1-1/8" CDX T&G subfloor plywood. This stuff is heavier than you can even imagine, and will probably hold up a car. :)
     
  7. Jmmsbnd007

    Jmmsbnd007 Diamond Member

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    Thanks, all I needed to know. It's going to be used as a top for a work bench, so some moderately heavy stuff will be on it. 800 lbs is plenty :) Little to no static load.
     
  8. teddymines

    teddymines Senior member

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    I did something similar but used 2x10 planks supported by 2x4. I recommend you brace it beneath because you will get significant bounce if you try to hammer or chisel something on the plywood. Those 3" deck screws are the best for bringing everthing together.
     
  9. Jmmsbnd007

    Jmmsbnd007 Diamond Member

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    Yes, I bought this kit from Lowe's (made by Simpson Strong Tie Products) with these steel supports, it came with self-drilling screws. Just add wood. Sounds good to me. It has a lower rack/shelf near the bottom to hold power tools and to add greater stability. Link That's the one except it won't have a top shelf.
     
  10. teddymines

    teddymines Senior member

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    Interesting. Do those steel support plates hold it together really well? Looks like you can add a couple shallow drawers directly beneath the top workspace, and maybe a small vise on the end. I love this kind of woodwork: making functional and durable stuff.:D
     
  11. Evadman

    Evadman Administrator Emeritus<br>Elite Member

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    If you have not opened it, return that hit. It is horrable. We sold the same thing at Home Depot, made my Simpson as well.

    3" gold screws and urethane glue will hold it together better. I speak from experence.

    and as was mentioned, you will get a good amount of bounce in the middle. The kit is made for 2 x 4's so toss a 2 x 4 in as bracing every 18-24" of table length.

    <edit>
    After a good amount of use, the metal fatigues and will "rack" easily. In that picture you posed, it would sway from left to right as you tried to saw something. If this is somethignyou are actually going to use, go with screws and glue.
     
  12. Jmmsbnd007

    Jmmsbnd007 Diamond Member

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    :| :| :| :| :| THIS IS RIGHT AFTER I OPEN IT! ARGH! What can I POSSIBLY do now? I am really not that much of a craftsman. I can cut wood, but that's about it.
     
  13. teddymines

    teddymines Senior member

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    Doh! Evadman has some good tips. A quality glue and some deck screws will help a lot. You can also add stability if you can somehow secure its backside to a wall.

    Worst case, you can use this as a learning experience when you build your next one from scratch!
     
  14. Jmmsbnd007

    Jmmsbnd007 Diamond Member

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    Alright, I might add some wood glue where wood meets face to face.
     
  15. Walleye

    Walleye Banned

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    uh, take it to a mig welder, tell em to make it sturdy. ;) I just happen to know how to weld...
     
  16. Evadman

    Evadman Administrator Emeritus<br>Elite Member

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    You can use the brackets, but be sure to glue the corners together with urethane glue. It will expand slightly and fill in any gaps ( aka mistakes ) Make sure to use 3" gold colored screws ( or another style that will not rust. I would recomend against drywall screws, as the shafts can break over time ) Do not use the piddly little 1.5" screws they give you.

    I assume Lowes has a return policy much like Home Depot's where you can return things even after opening them. It is just much easier if it is not open.

    If you decide to return them and make the table yourself, this is what I would do. I would use 4 x 4's or doubled up 2 x 4's ( since that would be cheaper tahn 4x4's ) for the corner posts. then use a brace 6-10" from the floor ( the lower the better ) In the corners where the braces attach (which should be 2 x 4's ) you want to notch the 4 x 4 posts so the 2 x 4's fit flush. Then glue them in. this will prevent the "racking" or side to side motion. here is a crappy drawing Made in paint, so don't kill me :p

    The major problem with the kit is that the 2 x 4 bracing on the bottom just buts up to the corner post. If there is a small gap, the table will shift slightly side to side, and will only get worse as time goes on. Just 2 screws that are not in the plane of this sideways force and a little steel are trying to keep the table steady. For a workbench, this is not good.

    Also, instead of plywood, you may want to go with MDF ( medium density fiberboard ) It is much much denser than plywood, and will not have the "bounce" that can happen with regular ply. strenthwize, ply has MDF beat. But for a work surface, MDF is a much better choice. Most workbenches you see will come with MDF instead of ply. MDF does not react well with water though. If it gets wet, the fibers will pull apart, and expand. So if you put a cool drink down on it in summer, you may get a raised ring from the condensation. You can prevent this with some kind of water proofer like polyurethane, but who puts poly on a workbench? I have a few MDF workbenches, and I love them much better than plywood. Up to you though.

    <edit>
    There are other ways of doing the bracing too if you do not want to notch the posts, but they do not look as good, and take up more space. Doing the notching is not that hard though. Just set your circular saw to a 1.5" depth and cut 2 goves 3.5" apart, along with a few more in the center. then knock out the wood with a chisel or a flatblade screwdriver if you do not have a chisel.
     
  17. Jmmsbnd007

    Jmmsbnd007 Diamond Member

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    I've heard a good review about this kit from someone else. I'm a wood n00b, I just bought some high-brand wood glue and I will glue and screw whereever I can. Instead of plywood (they were out), I got some 1/2" particle board. Is this good stuff? The guy recommended it, and it was cheaper. What's wrong with the included 1 and 1/4" screws that they include? Sigh, I hate wood. Lowe's cut everything for me and I have some scraps. What do I need to look out for? I want to this be as good as possible with the braces and screws included. I think later on I might add your 2x4 brace idea above or below the bottom shelf, on all 4 sides if it ever starts to get a little wobbly. Now I just need a good reason to buy that $30 skil 7 1/4" circular saw that got good reviews... :D
     
  18. Sluggo

    Sluggo Lifer

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    The 1/2" particle board is crap, basically not a good product at all for what you are trying to build.

    The MDF that Evadman mentioned is pretty good stuff, except for the moisture issues. However they do make Exterior grade MDF, although it is a little hard to find, I get mine at a hardwood supply store.

    You should really get the 3/4" plywood, if it were me, I would even double up the 3/4" plywood and screw it together for an extra heavy duty top.


     
  19. Evadman

    Evadman Administrator Emeritus<br>Elite Member

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    Particle board has the same issues that MDF does with water ( coming unglued if it gets wet, and turning into mush ) but even more so. Particle board will hold nowhere near as much as MDF or plywood will. I do not have my handy dandy list that HD gives out, but I would estimate that particleboard would break at or around 200-300 lbs. Probably more than you will put on your bench, but be careful. You can always throw in some extra bracing underneath the top with some left over 2 x 4's.

    As for the good review, it all depends on your use. When you work retail you hear bad stuff all the time. This sucks, that sucks, yada yada. The times it works, you don't really hear about it, because, wow, it did its job. No complaining.

    I had many customers complain about that kit, but as a % of how many people bought it.. Mayve one out of 10 I heard about complaining. maybe less. ( probably 20 or so people total ) I was asked to build a table for the moulding isle so customers could cut their own miters ( we didn't offer the service ) and I was told to use that. It lasted maybe a week. Maybe. But to be fair, the customers were pigs. The mitersaws and boxes lasted about a day. Sometimes 2. We even tried a $100 handsaw miter box kti with a saw that slid on 2 metal rails with all metal construction. That lasted about a week.

    I ended up building a table like that drawing, doing the datoes ( however you spell that ) on our store use 14" sliding radial arm saw. ( that was fun :p ) and gluing it together with urethane glue. The top when I left was 3 pieces of 3/4" plywood and one piece of MDF. ( if one got too damaged, I just screwed and glued another top on. I was too lazy to remove the old one. MDF was the first one. ) I heard about 2 months after I left that the new store manager had ordered it to be tossed because it took up to much room, along with my other displays. ( one display was about 4' wide, and was a full scale replica of a one story house complete with a section of roof and a window. All the parts were marked and explained. The other one was a 8' x 8' piece of wall with a window and a door. we used that one for our weekly classes on drywalling, window, front door, and storm door installs ) the 8 x 8 wall was disasembled, the 4' section of house had the roof torn off, and the miter table was tossed whole. I was told that they were all tossed away at once, and broke the compactor :p Indestructable Evadman displays! I really wish I had taken some pictures of the piece of house. That was really well built :(

    They still use one of my displays though. a 4' x 8' spinning wall, that rotated horizontaly for 2 surfaces that were 4 x 8. I made it for the Faux painting teacher. They still use that, almost 2 years after I built it. That one was fun to do, but I liked my wall better :(
     
  20. notfred

    notfred Lifer

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  21. Jmmsbnd007

    Jmmsbnd007 Diamond Member

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    ARGH. I AM TIRED OF BEING RIPPED OFF BY THESE SH!TS AT LOWES. I figured this guy would know what he was doing, sigh. I figured something was shady when he made the wrong sized cuts. So what now, am I screwed? Now I'm stuck with 1/2" particle board. How do I fix the situation? I *do* have one piece of leftover particle board... could I somehow use this as a brace? It's just as wide but not as long I guess, or am I thinking of the wrong scrap... either way I have extra. How can I fix this particle board situation? Go back to lowes and tell the morons that it only holds 200 pounds? Add bracing? I'm not sure how many 2x4s I have left, but they won't be very long. Just that scrap, large piece of particle board. If I doubled up and made 1" particle board... well... would that mean 400-600 pound capacity? That would be fine with me. Looks like Lowe's is just as full of poop as Home Depot is. Or... idea... how much money is this MDF stuff? Maybe getting some MDF, and putting the particle board on top of it. That way it adds much more strength, and if it gets wet, this shoddy crap gets destroyed not the good MDF. Retarded Lowes employee said that the particle board would be stronger than plywood. I doubted that, but it is more rigid.
     
  22. Evadman

    Evadman Administrator Emeritus<br>Elite Member

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    You could double it up. If you do, spread woodglue over it, then park a car on it or something. add a bunch of weight to get it to adhear well. Doubling it up will not double it capacity, but it will be close.

    There is no way in hell particleboard is stronger than anything other than cardboard. Take a piece of particle board, and put one end on something, the other on the ground. then jump on it. I betcha it will break. Plywood? nope. Particle board is too brittle.

    You could always bring it back and say the employee cut it incorrectly. If you do decide to go with ply or MDF, you will probably be stuck with ply, as it looks like you are not buying a full sheet. My Home Depot did not sell MDF in anything less than a 4 x 8 foot sheet. ( actually 49" x 97". One inch bigger than everything else. Don't ask me why)
     
  23. Sluggo

    Sluggo Lifer

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    Oversized stuff is manufactured for cabinet shops. The size enables them to get 2 full 24" cabinet bulkheads out of one piece of material. If you start with 48" width, the saw kerf will leave you with one 24" piece and one slightly under (fraction of an inch) 24" piece.

    Some shops also do not trust the manufacturer to leave a perfectly true factory edge, the excess size allows them to cut a little of and true up the edges to suit their tastes. :)
     
  24. Jmmsbnd007

    Jmmsbnd007 Diamond Member

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    How much $$$ is a sheet of MDF? I'm going to go ahead and build this thing all the way up to the top shelf then see if I can double up on the particle board. If I double up, 500+ pound capacity will be fine. I'm also going to attach a vise. The bottom shelf will stay single layer P-Board, as I doubt a few 10 pound portable power tools will overload this fine 1/2" piece of crap.
     
  25. Jmmsbnd007

    Jmmsbnd007 Diamond Member

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    Good news. I have enough Particle Board to make 4 of the needed size (just gotta cut one in half). Should I double up the top and bottom, triple up the top and single the bottom... what would you recommend?