To dado or not to dado?

Other Versions
The pros and cons of dadoing melamine cabinet boxes. November 22, 2003

I build face frame cabinets using 3/4 melamine boxes. I put a 1/4 dado in the sides for the cabinet bottom. I assemble with glue and 6 x 1 3/4 Zip R screws.

My reasons for dadoing this are 1) alignment - the boxes go together like Legos; 2) no butt joints to be seen; 3) the strength this seems to give me on downward pressure against the joint in time, especially when a granite top is pushing downward with the help of gravity.

My understanding is that while dadoing does weaken the PB core, the 'shoulders' of the dado give very positive strength to this downward pressure. My finished ends have toe kicks under them as well; the end panels don't go to the floor for support.

The negatives to this construction method for me are 1) time to make the dadoes; 2) chance of a screw-up in location; 3) always having to deal with the sides of the cabinet hanging below the bottom on uppers and then having to cut around them for the finish toe kick.

So my question is this. I know there are lots of guys using both methods whose cabinets have never fallen apart. But is a butt joint all that strong? How does it compare to the dado as far as this down pressure is concerned? I still want to build with zip R screws.

Forum Responses
From contributor A:
Can you explain item # 3 in the negatives? I don't understand your statement.

From the original questioner:
I use a 1 1/2" bottom rail. Bottom dado leaves 3/4" of melamine on the sides below the bottom. The sides are the same length as the FF stiles.

From contributor B:
One advantage of the dado is that the dado gives you PB to PB gluing, not PB to melamine. PB to PB is much stronger, as I'm sure you already know. A little more time is worth the peace of mind.

From contributor C:
I use a 3/4" wide bottom rail to coved the front edge of the 3/4" thick bottom. No cutting for toe kicks. The bottom of the bottom is even with the bottom of the cabinet. I do dado it into the sides. Also makes useable space a little taller (good sales pitch). "To dado or not to dado" has indeed been asked many times. Simple answer is that in the real world either is strong enough. Do what works best for you.

From contributor D:
The only advantage I can see with dados here is that you have a straight line (dado) to index the horizontal parts. If you must have this "index," why not just cut through the melamine to register a line to mark the horizontal locations - say a 16th or even less. A 32nd (or basically just through the melamine coating) would give you a line to index the horizontals and you would not have broken all the way through the harder skin of the PB core. I don't see how you will eliminate the butt joint look, though, as the dado line is still visible even after inserting the horizontals into it. With a "skin" cut, you can also run the parts through the dado saw in reverse direction, in a single pass, which should completely eliminate any chipout along the edges of the dado. All this still seems too much trouble to me, though.

I use butt joints with Zip-R's and they are extremely strong. To beef up the cabs so that the bottoms of the uppers carry the weight of whatever is put upon them, I use a light rail to support the bottoms. For the base cabs, I use two-piece leg levelers. The top piece I call a skid plate and it has a lip on it that hangs over the side panels to support any weight that must be carried on top of these cabs. Of course, this is a frameless application. To use butt joints for your (1-1/2" bottom frame) application, you could use a 3/4" spacer spring clamped to bottom, inside of each end panel during assembly to properly locate the bottoms and decks of your cabs - no dados required.

From the original questioner:
That's a good idea for a locating jig, I was wondering about that. If I decide to go to a butt joint, I'll just eliminate the part of the side below the bottom anyway.

For your Zip R construction, what size and how many per side are you using? Do you glue with melamine glue at all?

As far as your adjustable leg levelers, on your finished ends, does the top piece of the leveler also go under the side? I can see this would give great strength. What kind of an overhang over the toe kick does your finished end have?

Do you do butt joints when you do FF cabs?

From contributor E:
Built thousands of boxes myself, worked as an installer for a company that's built tens of thousands, and never had one fail with confirmat. The only advantage of dadoes is the slightly faster assembly time, which is more than offset by the more detailed machining. The great advantage of confirmat is the ability to knock a cabinet down and put it back together. This is great if you have to cut one down as well.

From contributor F:
One more option: when using melamine I always set the cabinet sides on the bottom and screw from below, on bases only. Uppers are built frameless style (butt joints and confirmats or ZipR's). The frame's bottom rail is 2", leaving a 1" reveal once bottom skin is on. Finished ends come flush to FF.

This way, bottom skins can be applied after installing uppers with few joints showing.
With base bottoms smooth, it's easy to slide boxes around the shop, and to install - just build a ladder base, level it, shim it, etc. Bases are then installed quickly, easily, and are level when placed on the base. Toe skins are applied last. I used leg levelers until the base system was suggested to me. Installations are faster, easier, and even more accurate.

From contributor D:
I use #6, 1-3/4” Zip-R’s and put 3 in the uppers and 5 in the base, per joint, after stapling with 1-1/4 in staples – no glue.

I use 4 levelers per cab, 6 on wider cabs to provide center support to keep the deck from sagging over time. A portion of the lip of the upper part of the leg (skid plate) is designed to extend across the deck and over the unfinished end (UFE) so that any weight will be transferred down the UFE directly onto the leg; each leg will support 330 lbs. I extend it over the UFE only 7mm. I use applied finished ends (AFE) on all end cabinets, applied during installation. On my typical frameless cabs, the base cab AFE’s run flush with the bottom of the UFE’s and I typically miter return the toe kicks, which are “snapped” onto the levelers.

I haven’t done a full set of FF cabs for quite a while. I do however, often provide frames on open cabs and/or bookcases, etc. where no doors are used. I build these (non-typical) cabs just like my frameless except that I cut the UFE’s 1-3/4” shorter than the other cabs in the run, which effectively raises the deck/bottom to accommodate the bottom rail, so that the top of the deck/bottom is flush with the top of this rail. 2/4” scrap spacer blocks are placed between the deck and skid plate (and overhang the UFE’s) in order to recover nearly the full vertical adjustment to the legs. The stiles on these cabs run the full height of the adjacent cabs.

From the original questioner:
Contributor F, not sure I am following you on your base construction. Do you run the bottom 3/4" wide on each side so that the sides rest on it? I can see where this would give better strength. What are your reasons for doing this?

A ladder base… what's that? How do you build yours?

Contributor D, thanks for the info. I think I am going to change to some kind of a butt joint on the next set of cabinets I do

From contributor F:
If base cab is 36" wide, the bottom is 36". Sides are 29 1/4, making sides a total of 30" high.

All bases have adjustable shelves or slide-outs, so I don't have to change the panel saw for that. Shelves are all cut and banded last. Another benefit to that is that I can drill the line and system holes easier since it's a "balanced" panel. There is no top or bottom, so I don't have to worry about turning a gable end upside down anymore.

A ladder base is a simple plywood or MDF base that's 4 1/2" high. Instead of putting a base under each box, it is a continuous base. Sleepers are placed every 16". Since sides rest on the decks, it's not necessary to place a sleeper directly below a side.
The ladder base is set 1st using an 8' level, shimmed where needed. When base boxes are set on them, they're already level - just screw boxes together, then to wall. I used levelers for a long time. But for me, this system is much faster and cabinets are more stable and install a lot faster. Two friends told me about this way. Once I tried it, I was sold. Now leg levelers seem Mickey Mouse in comparison, although there was a time I swore I'd never use anything but Camar or Blum legs.

When I used legs, I only used 2 per box, in the front. The backs were set on a ledger screwed to the wall 4 1/2" from the floor. Side kicks were tacked to the ledger. Using the ledger makes the backs automatically level, so I just had to level from front to back. To me, it's a lot faster than using 4 legs. And a good way to use up some scrap instead of buying more legs.