(Quotes below) George
GeorgeC: Did you do any investigation to determine why the blade setup was not giving the correct cut width. That is where I would start.
TA: Okay, it makes sense to me.
My current hypothesis is that the Freud dado set is actually metric, and the printed configurations are not correct. The configurations make sense if you think of materials like Baltic Birch, which is labeled in Imperial units, but is actually slightly smaller.
GeorgeC: You say that you got out the stack. I assume that means that you have used the set before. Have you ever had a problem before?
TA: No, but I have not tried using it in a precisely measured way like this before. Before yesterday, I would choose a rough dado stack size, then make two or more passes to cut the shoulders, then the middle if necessary to "cut to fit." Another use was to cut rabbets, burying the blade in an auxiliary fence. On occasion, I simply trusted the configuration chart and somehow made it work, probably by cutting or planing other parts to fit without worrying about it.
GeorgeC: I am guessing that the problem is most likely in your chipper. Did you measure the chipper?
TA: Yes. I measured the chipper and the other blade parts for you, using a digital caliper with 1/128th resolution. Here are my measurements:
Chipper body = 1/8 inch
Outer Blade body = 3/32 inch
Carbide tip extension outside the blade body = 1/64 inch (this was difficult to measure)
If the measurements are correct, the dado stack should be:
= (2 x 3/32) + (2 x 1/64) + 1/8
= 6/32 + 1/32 + 4/32
To remind you, my measurement of the actual dado slot was 23/64, which I think is within measurement tolerances. Both measurements are short of 3/8 inch.
GeorgeC: Does your set include more than 1 size chipper?
No. All three chippers are 1/8 inch.
GeorgeC: You need to concentrate on how to solve the problem of why the dado set does cut the notch correctly. Not trying to come up with some kludge to make it work.
You're right. That's why I posted the question, but your ideas helped me determine that the configuration chart included with the dado set is not accurate. If I am correct, then shame on Freud.
I made a box joint jig before and it worked fine, but it used a standard kerf 1/8 inch blade. That's too many fingers for the trays and other things I want to build now.