Can I buid a 4' wide cabinet without the top sagging?

[9Fingers]

Hi there, I'm looking at building a 12' wide floating cabinet that will be broken down into 3, 4' wide cabinets. Each of the 4' cabinets will be 18" deep and 20" high and have 2 (10" high drawers) the entire width of the cabinet. This means there won't be any support in the middle of the cabinet to help keep the top flat and prevent it from sagging. I was thinking of using 3/4" paint grade plywood as this will be getting painted.
My question is, does anyone know if a cabinet of this dimension will stay flat over that width? If not, do you know the widest I could build without fear of it sagging over time?
Thanks for your help and ideas.

 

[WPeters]

Will it be frameless or have a wood faceframe on the front?

Sent from my HTC One using Tapatalk

 

[semenza]

I would use double 3/4"  plywood (actually glue two layers together) and or add some support through use of a face frame and the back. The attachment / hanging method may effect the way the weight is held as well.

Seth

 

[GhostFist]

Face frame and French cleat

 

[semenza]

Also , those are really wide drawers. What will be stored in them? 

Seth

 

[junk731]

Sounds like you want to build a euro style cab and to answer your question no it won't work and yes it will definitely sag. To guarantee no sage you have to build 6-24" or 5-28.8" cabs. 4-36" doesn't work well with plywood sheets.

John

 

[Paul G]

If you're saying the top will be 3/4" ply, yes I would expect it will sag unless it is faceframed with about 2" hardwood and the back edge supported as well. 'Paint grade' ply could also be baltic birch which would give you extra strength

 

[DrD]

[member=13449]9Fingers[/member]

Good Afternoon,

You're getting some advise here from some real pros.  Just my 2 cents, I'm NOT a real pro, just a retired piddler who enjoys making saw dust:  the fewer the number of plys in the plywood, the more likely unsupported long spans are to sag.  Thus to achieve max length, I would use Russian or Finnish ply - if memory serves, they have more than 9 plys, and even then sagging most likely will occur, esp if any weight is placed on the board. 

Best wishes, and keep us apprised of your progress.

 

[tiki man]

how about rout in a channel for steel tube and epoxy in place across the top of the cabinet. or use blind cleats that will attach to studs in the wall and come out in the center of each off the 48" cabinets and hind the support behind some type of detail built into the cabinets.

also hanging cabinets does that mean countertop on top of the cabinets which is more weight ?  I would also be concerned about the drawers themselves. runners will have to be heavy duty with weight limits over 100 lbs or more and securing the runners to the side of the cabinets will need to be another thought....

 

[polarsea1]

how about rout in a channel for steel tube and epoxy in place across the top of the cabinet. or use blind cleats that will attach to studs in the wall and come out in the center of each off the 48" cabinets and hind the support behind some type of detail built into the cabinets.

also hanging cabinets does that mean countertop on top of the cabinets which is more weight ?  I would also be concerned about the drawers themselves. runners will have to be heavy duty with weight limits over 100 lbs or more and securing the runners to the side of the cabinets will need to be another thought....

I've done this, routed a dado across the top and used a 1 x 1/2" piece of rectangular tubing when I needed extra support across the top of a cabinet.

 

[9Fingers]

Thanks for all of the feed back and ideas. If I end up going forward with this desgin, the steel epoxyied and screwed into the top might be the answer.
This is a cabinet I'm planning on building for a customer. The last thing I want is someone regretting letting me build them a piece. I have since talked to them about the construction issues and we're now looking at alternative designs. Maybe a combination of smaller drawers or some cupboard doors to offer some support to the cabinet top.
I'll post some pics if this becomes a reality.

 

[Brent Taylor]

Depending on the thickness you are willing to go with there are a number of different ways to do it,  torsion boxes on the top and bottom panels,  welded subpanels with plywood skins, rebar driven in the studs and corresponding holes drilled into a solid upper panel ( and lower depending on the load). I have had good results with all of these methods over the years.  I sure that there are many other ways to do this, these are the ones that I have used.  B