Plywood joinery for base cabinet

[Stuart Welsh]

I'm building the base cabinets for a large kitchen island. One cabinet will be 78" wide and feature three 24" wide spaces with full inset drawers and doors. I'm using two pieces of ply for each partition, 11/16" ply spaced 5/8" apart to flush up on the sides of each 2" wide stile that runs between the drawers and doors. My question has to do with how complicated I need or don't need to make the joinery of the partitions to the top and bottoms of the cabinet. I was thinking of just using a butt joint and attach with glue and either; pocket holes (or screws drilled in through the top and bottom) or capturing the partitions in dados in the top and bottoms. Of course when the face frame in on any strength differences will be a non issue as far as I can see. But if there are benefits to the dado route do they offset the extra work and precision needed to align the dados in relative to one another in top and bottom as well as parallel and proper spacing?

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[Robert Engel]

IMO dados will be a lot of extra unnecessary work for a kitchen cab.

Butt joints using screws +/- glue are plenty strong enough.

Not a big fan of pocket screws in plywood boxes but you could use them. There can be alignment issues with panels when sinking those screws so a guide strip on the opposite side is necessary to prevent movement.

[John Lankers]

There are many ways to skin a cat, everyone has their own way of doing things.
If your plans call for 2 vertical dividers I would simply screw through the top and bottom, maybe add a dab of glue but it won't do much. Dadoes would be the ultimate connection - but for what, you're dealing with a vertical load only and the face frame makes for a very stiff construction anyway. I can't see pockethole joinery having an advantage either; however, I would use pocket screws to attach the face frame to the carcase. I do like the idea of doubling up the vertical dividers but IMO it is not necessary from a structural point of view.
Check out Mark Sommerfeld's video series on YouTube
https://www.youtube.com/watch?v=klv0jzWD26w
https://www.youtube.com/watch?v=6AejTGYLN6c
https://www.youtube.com/watch?v=OJDTLmhrum8
https://www.youtube.com/watch?v=peUlxpCGzKc

[Stuart Welsh]

Thanks all, I'll just say no to dados in this project.

[Charles Wiggins]

I tend toward the dados myself. Mainly because of glue surface and overall alignment.
As for aligning the dados in the top with those in the bottom, the easiest thing to do is to cut the dados first in a single piece, then separate the top from the bottom. If you can't get both pieces out of a single sheet you can clamp them parallel to each other and cut the dados across both pieces at the same time with a router using a jig setup like this: http://www.woodworkersjournal.com/jig-based-joinery-techniques-perfect-dadoes-every-time/

[Martin Wasner]

Why are you flushing the partitions out with the inside of the face frame? Hardware limitations?

I'd dado it together. Easy alignment.

[Pat Barry]

I'd do dadoes myself because doing that would make alignment and squaring things up a tad easier to me. Plus, for something as big as you are making I'd have serious concerns about strength and rigidity with just butt joints and screws.

[Jim Becker]

Butt joints with glue and screws for me on what you picture!! The KISS method... ;) While in theory grooves would add strength, in practicality, there's little incentive for the extra work for something that's stationary and built-in like this.

[Martin Wasner]

There's no strength to be gained in a dado in the deck of a cabinet, just ease of alignment and not having to worry about getting glue everywhere. I'll take six seconds of plowing a dado over the 30 seconds of aligning a partition any day of the week.

[Jim Becker]

Martin, I agree that the groove can be very helpful with alignment. But it comes with a cost for many of us because of the setup time to create the grooves. For me, I have to do that with either my router table setup (not well suited to larger components because of my shop environment) or with my OF1400 and a guide rail. I'm not equipped to use a dado stack on my slider. So butt joints with glue and screws is more efficient for me. Now if I were doing production work, I'd absolutely want things to interlock for quick and accurate assembly and would have a setup to make that possible.

[Chris Padilla]

When the Festool Domino showed up many years ago, the dado blade has been doing nothing but gathering sawdust upon itself (also my tenoning jig, power mortiser, and biscuit cutter). I find myself using Dominos on just about everything these days and I do use it in certain spot for cabinets but glue and screws, if easy to do, are my first thought. I'll often screw things together with short screws if I know I will want to take it apart later and then use longer ones and glue for final assembly. Dominos also make it easy to put things together and take 'em apart later if you need to.

[Justin Ludwig]

I just butt joint and nail'm. I don't double partition in my construction method as it's a waste of material.

[Wayne Lomman]

Stuart, butt joints and screws are the go. It's the way it has been done commercially for a long time. When you look at it structurally, the forces are mostly compression. The screws and a bit of glue take care of the minor shear forces.

If you use a dado, it has to be perfect otherwise you will see the gap as you look down on the bottom. If you use a butt joint, this is not a problem.

Double panelling is overkill with a face frame. Euro modular style has double panels but with different hardware. The extra won't hurt though. Cheers

[Jim Becker]

Double panelling is overkill with a face frame. Euro modular style has double panels but with different hardware. The extra won't hurt though. Cheers

Since I also personally like the flush look for the sides, I'd likely use 1/2" material for the divider. I honestly find that 1/2" is more than sufficient for this kind of work if it's constructed correctly anyway...and lighter to handle. In fact, the cabinets above my credenza here in my office were made that way...the one difference from the OP's diagram is that I used scrap plywood spacers between the two matched divider panels to absolutely keep them to the exact thickness of the face frames.

[Bob Elliott]

I use dados for cabinet box construction exclusively. I like the added glue surface area and the precise alignment that comes with using dados.

I made a router jib using this video: http://www.thewoodwhisperer.com/videos/exact-width-dado-jig/ I am building a cabinet out of maple for our bathroom and am happy with the results.

[William Fretwell]

For plywood, biscuits work well, just dry fit before gluing. Clamp a straight edge across to guide the biscuit joiner.

I would use dadoes for real wood but plywood kitchen stuff will be trashed in under 20 years. Much less awkward on large cabinets than screws. If clamping is awkward, as it often is, a few screws can close joints while the biscuits dry.
You may want 5/8 spacers between the two sheets as things do move!

[Bob Cooper]

here's what i do. the top picture is looking down (plan view) from the top. The bottom picture is looking from the front. everything here shown is 3/4". So for that middle vertical divider i do cut some pocket holes in the bottom but they really don't accomplish much. The bottom shown pushes up again each side of the vertical divider and forces it to be square. Also the bottom here doesn't go all the way to the back because there are drawers in this cabinet but if it were shelves the bottom would go all the way to the back.

[Sam Murdoch]

Since I also personally like the flush look for the sides, I'd likely use 1/2" material for the divider. I honestly find that 1/2" is more than sufficient for this kind of work if it's constructed correctly anyway...and lighter to handle. In fact, the cabinets above my credenza here in my office were made that way...the one difference from the OP's diagram is that I used scrap plywood spacers between the two matched divider panels to absolutely keep them to the exact thickness of the face frames.

I like flush too - all my cabinets sides, partitions and bottoms are built flush to face frames unless there is an exceptional need for otherwise. Also with face frame construction the butt joint with screws is not a compromise. I quote Jim here because where I differ with him is that my preference for all cabinet components except the backs is to use 3/4" ply. In the case of partitions that I will screw into - especially. That much easier and accurate to drive a screw into 3/4" ply than 1/2" without blowing the laminations apart if you are slightly off center or the veneers are a bit fragile.

I also space partitions with filler blocks if needed (or make my face frame to match the thickness of the 2 pieces of 3/4" ply. Sometimes my FF are more than 1-1/2" wide. As for accurately locating their positions relative to the sides without dados - here too I use a ply panel precisely cut then clamped to the top and bottom of the cabinet and bumped up against the side - as I attach the partitions. Easy to maintain centerlines or other partition locations and repeatable from side to side.

[Peter Aeschliman]

My vote is for dados and rabbets because they help so much with alignment for assembly. It's more work for sure, but I find it really difficult to properly align butt joints for glueing and screwing. If you're diligent with your clamping, you can definitely get by without dados and rabbets. but if you're going to be installing drawers, it will make your life so much easier if everything is square and plumb.

[pat warner]

Surround the panels with hard wood.
Let the ply fill the hardwood frames. Will add to your skills.

[Ole Anderson]

No dado, but glue and screw a 5/8" wide x 3/4" high hardwood spacer where the gap between the verticals will be. Then glue and brad the verticals to the spacer, or toenail and the spacer will hold location. I would probably glue and brad the spacer, then screw from the bottom into the hardwood.

But if you want the face frame flush, build up the verticals first so you can use a flush cutting bit before you assemble the box. Still use the spacer though for final assembly.

[Andy Giddings]

Butt joint and screws, plenty strong enough as others have stated - and that's frameless. With a face frame I'd be even less concerned about strength

[Jim Becker]

I quote Jim here because where I differ with him is that my preference for all cabinet components except the backs is to use 3/4" ply. In the case of partitions that I will screw into - especially. That much easier and accurate to drive a screw into 3/4" ply than 1/2" without blowing the laminations apart if you are slightly off center or the veneers are a bit fragile.

I will clarify that with 1/2" material, I use #7 screws and always drill/countersink pilot holes. The only time I've ever had a problem is if I screw up and measure wrong for the line I draw to center the drilling on. :o I started using this material choice when the tack trunk commissions started coming in, primarily due to weight, but got very strong carcasses with glue and screws with 100% butt joints. (for those units, the 1/4" thick overlays to simulate frame and panel totally hide the screw action once the box is built.

[Jim Dwight]

My most recent cabinet build was two sections of base cabinets for my shop. They hold up my CMS and RAS and have drawers. The first section is 8 feet long and the second a little less. I didn't use dados in the first section but had a little trouble with aligning the dividers and had to mess with the drawers more. In the second section, I used dados and things went much smoother.

I only plow the dados about 1/8 deep. They are just for alignment. I used the router jig for my DeWalt track saw on that cabinet and it worked great. I will do that again.

I prefer through screws (usually drywall, they are for clamping until the glue dries to the brittleness (while overstated) isn't important). But I use pocket screws too where it makes sense. I think they hold really well, I just hate the look of the holes. Drilling them also takes more time.

If you will have a separate panel covering the ends I would just screw through the top and bottom to attach the uprights. If the ends will show, I would put a deep dado in the ends (probably use a dado stack on the table saw for that) and screw through the top and bottom into the vertical end pieces. By a deep dado, I mean leave only about 1/8 of the plywood on the vertical ends. That lets you have the grain of the plywood show. It still leaves you close to 5/8 to screw into.