Page 2 of 3 FirstFirst 123 LastLast
Results 16 to 30 of 40

Thread: Will sag be an issue?

  1. #16
    Join Date
    Jun 2003
    Location
    Northern Michigan
    Posts
    430
    I built a 60” wide low cabinet for my audio video equipment. Loaded it is incredibly heavy. Started with just 4 outside corner legs securely fastened. Cabinet is 3/4” plywood edged with 2-1/2”oak on all faces with solid oak top and rigid back. Still sagged over time - took about a year to fully sag. Ended up adding 2 casters to middle for support and easier mobility and that cured it. Can not believe a cabinet even wider would not have serious issues.

  2. #17
    Join Date
    Jan 2012
    Location
    mid-coast Maine and deep space
    Posts
    2,656
    Quote Originally Posted by Alan Lightstone View Post
    But won’t the vertical dividers work to restrict deflection? They’ll be 1-1/4” plywood securely fastened to the top and bottom. Doesn’t that tie the top into the bottom somewhat like a torsion box?

    I have several pieces of furniture that are 6’ long with drawers, built by furniture makers likely far crappier than we’re discussing, and they don’t seem to be sagging,
    Shop cabinet with 10 drawers filled that will "hold lots of jigs, equipment, blades, etc..." - likely much more weight than household furniture.
    I think the answer to your question is, yes and maybe no. Worth a bit of extra precaution, which I think you've covered.

    Sam
    "... for when we become in heart completely poor, we at once are the treasurers & disbursers of enormous riches."
    WQJudge

  3. #18
    Join Date
    Jan 2010
    Location
    Tampa Bay, FL
    Posts
    1,889
    Would a hardwood apron prevent the sagging? I could do about 1" x 3" for the length of the front. Is it necessary for the back also, considering the 3/4" plywood back.
    If you drive at the speed of light, do your headlights work? - Steven Wright

    If a man points at the moon, an idiot will look at the finger.

  4. #19
    Join Date
    Jan 2010
    Location
    Tampa Bay, FL
    Posts
    1,889
    Quote Originally Posted by andy bessette View Post
    Angle iron is very poor as a beam.
    Hmmm. Why is that? I certainly can't get it to deflect when I tried to. Seemed rock solid. I can see that angle iron is not an I-beam, but why is it poor at preventing deflection - acting like a beam?

    I just tried plugging in some values into an online angle iron deflection calculator. Now I'm just guessing at the moment of inertia values for that size angle iron (but tried a variety in the ranges they were using) and it tells me that the angle iron will only deflect 0.0032 inches over that span - in other words, bubkis.

    Now I really don't believe that is true, so what am I missing here?
    Last edited by Alan Lightstone; 05-12-2019 at 8:12 AM.
    If you drive at the speed of light, do your headlights work? - Steven Wright

    If a man points at the moon, an idiot will look at the finger.

  5. #20
    Quote Originally Posted by Alan Lightstone View Post
    ...an online angle iron deflection calculator...tells me that the angle iron will only deflect 0.0032 inches over that span...
    Come on! You certainly don't believe that!

    Quote Originally Posted by Alan Lightstone View Post
    But won’t the vertical dividers work to restrict deflection?..,
    They only transfer the load into the bottom, which does not have the thickness to act as much of a beam.

    In beam loading, it is the extreme fibers (the material at the very top and bottom edges, like the flanges of an I-beam) that does most of the work. An angle has nearly 1/2 its material at only the top or bottom, and the tiniest fraction of its material at its opposite extreme.

    A torsion box has very deep vertical, longitudinal members.
    "Anything seems possible when you don't know what you're doing."

  6. #21
    Join Date
    Jan 2010
    Location
    Tampa Bay, FL
    Posts
    1,889
    Quote Originally Posted by andy bessette View Post
    Come on! You certainly don't believe that!
    No I don't, but it is interesting that I think we're all thinking of a sag of the order of magnitude of 1/4" - 1/2" (WAG), but that deflection calculator produced a number that was 2 orders of magnitude less.
    If you drive at the speed of light, do your headlights work? - Steven Wright

    If a man points at the moon, an idiot will look at the finger.

  7. #22
    Quote Originally Posted by Alan Lightstone View Post
    ...the angle iron will only deflect 0.0032 inches over that span...
    Preposterous.
    "Anything seems possible when you don't know what you're doing."

  8. #23
    Join Date
    Oct 2018
    Location
    New Boston, Michigan
    Posts
    55
    Angle iron is/was a very good solution.
    Ask a woodworker to "make your bed" and he/she makes a bed.

  9. #24
    Join Date
    Aug 2018
    Location
    Michigan, USA
    Posts
    246
    Might have missed it, but I didn't see where you mentioned the dimensions of the angle iron (other than 48" long). I don't understand how anyone here can estimate the deflection without that information.

  10. #25
    Join Date
    Jan 2010
    Location
    Tampa Bay, FL
    Posts
    1,889
    Quote Originally Posted by Gary Ragatz View Post
    Might have missed it, but I didn't see where you mentioned the dimensions of the angle iron (other than 48" long). I don't understand how anyone here can estimate the deflection without that information.
    I have to double check, but I think it was 1-1/2" x 1-1/2" x 1/8" thick. And 48" Long
    If you drive at the speed of light, do your headlights work? - Steven Wright

    If a man points at the moon, an idiot will look at the finger.

  11. #26
    Join Date
    Sep 2004
    Location
    Los Angeles, CA
    Posts
    879
    Google sagulator and enter the specs for the answer.

  12. #27
    Yes, if you're not familiar with it, The Sagulator is a great tool for these kinds of things.

    https://www.woodbin.com/calcs/sagulator/

    also, square tube had a lot of dimensional rigidity against sag and is straight whereas angle iron tends to curve during the cooling process.

  13. #28
    Join Date
    Apr 2017
    Location
    Michigan
    Posts
    668
    The back will be fine. You can stiffen the front in several ways. If you raise the bottom a few inches you can put a substantial member under it. A 4x6 laid flat should do. Or something stronger, like Oak or Ash etc, maybe 3 x 3. If you want to use the angle iron it can work. To make it into a beam you will need to add an ordinary 2 x 2 under the bottom at the front and reinforce it with a piece of angle iron on the bottom and back of the 2 x 2. Wood screws every 6" or so thru both legs of the angle iron into the 2 x 2. Also wood screws thru the plywood bottom into the 2 x 2 every 6". This will be quite stiff. If you raise the bottom another 2" and use a 2 x 4 it will be much stiffer still.

  14. #29
    Join Date
    Dec 2008
    Location
    Northern Michigan
    Posts
    4,639
    My most successful bench is built on a 2x2 1/4" wall steel framework, no sag and I have put thousands of pounds on it. Different animal as it is 7'6" x 4' and has a welded steel stiffback with drawers on both sides, but my point is, "When in doubt, build it stout!" I count on this bench for door assembly.

  15. #30
    Join Date
    Mar 2010
    Location
    Milwaukee, WI
    Posts
    114
    I recently built a mobile assembly "cabinet" that's actually a set of 8 17x16x26 cabinets screwed together with a homemade MFT top. It currently houses 20+ systainers filled with tools:

    MFT Bench - Construction - Rear View.jpg MFT Bench - Construction - Front View.jpgMFT Bench - Design.jpg

    I built each cabinet separately out of 3/4" ply and screwed them together on top of another sheet of 3/4" ply. I used 6 sets of casters--one at each corner, and one on each side in the center. I've been using it now for about 6 or 8 months, and haven't had any noticeable sag.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •