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Thread: Will sag be an issue?

  1. #1
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    Will sag be an issue?

    I'm building a 72" wide, 26" deep cabinet to sit next to my table saw and hold lots of jigs, equipment, blades, etc...

    There will be 3 vertical dividers that will be connected between the top and bottom, and have multiple drawers held between them. I'm sure the drawer weight will be considerable with about 10 drawers.

    Top, bottom, and vertical supports will be made of 3/4" Baltic Birch plywood.

    I'm planning on having the table supported on four casters from below.

    Now, obviously, 72" is a long span on the bottom. Will the vertical supports prevent the table from sagging in the middle? I'd like to use it as both an assembly table, and support for large sheets goods sliding across the table saw when being crosscut.

    I'd prefer not to go to the work of making a torsion box below the bottom. I would consider angle iron attached to the bottom, if the consensus is that sag will be a real issue.
    If you drive at the speed of light, do your headlights work? - Steven Wright

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  2. #2
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    On a span that long, I would suggest putting some casters in the middle also. I've done that on a 60" that I built. I actually put two sets in-between and it helped tremendously.
    SWE

  3. #3
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    a strong back that is well fastened will help a lot.
    I would mount the casters about 14-16 inches in from each side, definitely not as far out as they will mount

  4. #4
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    Quote Originally Posted by Ron Selzer View Post
    a strong back that is well fastened will help a lot.
    I would mount the casters about 14-16 inches in from each side, definitely not as far out as they will mount
    ^ I agree AND double thick the bottom. No sag that way - I'm pretty certain. Adding a center caster or 2 could create issues with balance or moving around if your floor is not flat. If you are using locking casters on the outside corners - the kind that lift up a bit to move - then I might consider simply adding a couple of post feet at the center which would sit on the floor when the casters are down but lift off the floor when the casters are engaged to be wheeled. My 2˘.

    Sam
    "... for when we become in heart completely poor, we at once are the treasurers & disbursers of enormous riches."
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  5. #5
    Quote Originally Posted by Alan Lightstone View Post
    ...I'd prefer not to go to the work of making a torsion box below the bottom. I would consider angle iron attached to the bottom, if the consensus is that sag will be a real issue.
    You don't need a torsion box--just a substantial bottom crossmember.
    "Anything seems possible when you don't know what you're doing."

  6. #6
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    Quote Originally Posted by Sam Murdoch View Post
    Adding a center caster or 2 could create issues with balance or moving around if your floor is not flat. [snip]...

    Sam
    I've had that happen before. And with the seams on the raised access floor tiles, I'd really like to avoid using center casters.
    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. #7
    Quote Originally Posted by Ron Selzer View Post
    a strong back that is well fastened will help a lot.
    I would mount the casters about 14-16 inches in from each side, definitely not as far out as they will mount
    Quote Originally Posted by Sam Murdoch View Post
    ^ I agree AND double thick the bottom. No sag that way - I'm pretty certain. Adding a center caster or 2 could create issues with balance or moving around if your floor is not flat. If you are using locking casters on the outside corners - the kind that lift up a bit to move - then I might consider simply adding a couple of post feet at the center which would sit on the floor when the casters are down but lift off the floor when the casters are engaged to be wheeled. My 2˘.

    Sam
    I agree with both of these designs. I would avoid having 5 or more casters under the cabinet. I would through bolt the casters as that will be stronger than wood screws into the plywood bottom.
    Lee Schierer
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  8. #8
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    Thanks, guys.

    I eventually took the easy route and bought two 48" steel angle irons. I'm amazed how much easier these were to drill with my new Voyager DVR Drill Press compared to my old Sears one.

    Unfortunately, even though I don't want to, I have to use wood screws to attach the casters. The design makes bolts a non-starter. Hopefully they'll hold up. I usually use bolts for these.

    There will be a 3/4" Baltic Birch plywood back, securely fastened, so that should help, as has been pointed out.
    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.

  9. #9
    Quote Originally Posted by Alan Lightstone View Post
    ...bought two 48" steel angle irons...
    Angle iron is very poor as a beam.
    "Anything seems possible when you don't know what you're doing."

  10. #10
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    Bad plan...you will have some issues for sure if your front isn't as stiff as the back. A very substantial face frame, with a very beefed up bottom framework should work, but otherwise, the flexing will probably cause severe issues with the drawers. Not a big deal if it were just regular cabinets on the floor, but rolling around on an uneven surface....flex city.

    Dan

  11. #11
    Many plywood suppliers carry 1 1/4 inch flooring plywood. It is ridiculously strong, made for spanning long areas without flexing. Usually found in high end homes under ceramic tile.

  12. #12
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    As Thomas said, I have used 1 1/8" flooring underlayment (plywood, not OSB) for bottoms in the shop and shed. It is really solid.

    I have also used center wheels on 6' shelving units, with no problems. My floors are pretty flat.

    I actually set one of those 6' wide, chrome wire shelving units on a 3/4 ply base with 6 wheels, and it has worked well. I have even rolled it loaded with paint supplies down a sidewalk. I drilled holes for the legs in 1x4's and screwed it to the plywood bottom so nothing would shift. I use inexpensive steel wheels from HD, 3" size I think. They won't go flat.

    I also have one of those metal storage cabinets, about 6' high, 3' wide, that sits on a plywood base with the steel wheels.
    Rick Potter

    DIY journeyman,
    FWW wannabe.
    AKA Village Idiot.

  13. #13
    Quote Originally Posted by andy bessette View Post
    Angle iron is very poor as a beam.
    But it's great as angle iron.

  14. #14
    Quote Originally Posted by johnny means View Post
    But it's great as angle iron.
    Yes, but what he needs there is a beam to restrict deflection.
    "Anything seems possible when you don't know what you're doing."

  15. #15
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    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,

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