Fitting Sheet Goods in Dadoes

Irregularities in panel materials can cause trouble with dado fits. Here, cabinetmakers discuss solutions. September 22, 2005

I am having a problem with the assembly of my traditional face frame boxes. The problem is the dado and the irregular plywood thickness. I am using under size bits to match what the plywood is supposed measure, but to ease assembly was thinking of using standard bits with the metric plywood which could result in some sloppy joints. I guess what I am asking is for is opinions on this situation.

Forum Responses
(Cabinetmaking Forum)
From contributor J:
Basically what I do is to make sure the frame dadoes fully assembled line up with the inside dimensions of the box so if the box width inside is 13-9/16" the inside edges of those dadoes must be the same. Yes they need a little persuasion sometimes, but mostly to do with the plywood flatness end to end.

Also, ask yourself is it important to me or my client that this relatively obscure joint be precise? Or is it causing a problem with the structural integrity? Is it time effective and are you building $20,000 or $100,000 kitchens? Personally a 20k kitchen isnt worth that and neither is a 50k.

When doing full beaded inset doors its more important that the face frame be square and uniform to provide better fit and finish. In my shop the face of the cabinetry is 70% of the cost and I dont scrimp on the quality of my boxes (3/4" sides, bottoms and rails or tops and 1/2" backs). Paintgrade face frames get nailed, glued, and filled and staingrade gets pocket screws from the outside. The face frames are pocket screwed also.

From contributor F:
The way a lot of craftsmen deal with odd sized sheet goods that need to fit dados is to use a dado width that is somewhat narrower than the thinnest thickness of any sheet good in the run. The reason I say thinnest is because after I machine parts that will go into dado's, I measure the thickness of the materials at several points and on several parts even from the same sheet and find variance with calipers.

After you know your dado size then you can rabbit the edge or edges of the parts that will be housed in the dado's leaving a tounge of the proper length and thickness for the dado. This will work on materials of varied thickness if you machine the tongues so that they lie between the cutter and the indexing surface while being machined, whether that indexing surface is the shaper or router table bed, or the table saw fence.

From contributor J:
What I found is if you hit the edge/corner (just enough to take the sharpness off) with a sander and it will go together fine. If not you need to use a different size bit if that doesn't work.

From contributor A:
What we do is simply keep a small hand plane ready. When we get ready to assemble we take one chamfer swipe off the edges and things generally go ok. Not sure if it's us or not but it seems like the edges get fat when cut due to fresh cut and moisture content swelling them just a tad.