I am doing a project where I'm supporting a girder made of two 2x12s with a 6×6 post. (But this question really applies to 2-by-anything). For added strength, I want to "let in" the girder to the 6×6, that is, cut a notch out of the top of the 6×6 for the girder to sit in; this is superior, because the girder is supported directly by the 6×6, not just by the fasteners.
I will also add a diagonal brace, probably 2×6.
Several questions:
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What is the best way to notch the 6×6 ? In the past, with one 2-by, I've made a series of kerfs with my circular saw, and then cleaned it out with chisel/hammer/etc. But my circular saw can only cut to 2-1/4". How well would it work to make cuts down both sides of the 6×6, which would leave about 1" of material in the 6×6 (actual thickness 5-1/2"), and finish up with a sawzall, which would be guided pretty accurately by the previous two 2-1/4" deep cuts ?
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Should I consider making the notch less than 3" deep, perhaps the 2-1/4" my circular saw could manage with the kerf & cleanout method ? I intend to thoroughly bolt the two 2x12s together, and the notch would still support half of the second one, so no worries on strength there. In fact, I fear that by making the notch 3" deep, I would leave only 2-1/2" of the 6×6 where the girder is bolted, which would weaken the connection a good bit.
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If I decide to make the notch only 2-1/4" deep, how do I make my diagonal brace lay nicely ? The girder would stick out 3/4" from the side of the post, so there will be a 3/4" gap between the brace and the side of the post. Maybe just put a "washer" of 3/4" thick wood between the brace and the 6×6 ?
ADDIITONAL CONTEXT:
This will be outdoors, so the wood will be treated, probably using MCA (micronized copper azole), which is supposedly gentler on metal fasteners and non-toxic.
This is for a ground-mount solar array. The girders will support aluminum rails to which the solar panels are clamped. I believe this means that the strongest forces will be wind uplift, not downwards. I had to get a PE to stamp some drawings for the permit (below). I am deviating a bit (with AHJ's blessing), using metal rails instead of the 2×8 purlins shown in the drawings. But I will do the footings/piers, posts, and girders as shown in the drawings, except possibly making the notches only 2-1/4" deep as mentioned above.
Best Answer
I've done that before many times on large beams and it works fine. In fact, forgo the reciprocating saw and still use your chisel. It'll easier than the other method because you'll be working with the grain instead of against it. Or you could use the reciprocating saw to finished the depth on your cross cuts for your usual method.
The brace is called a knee brace and it's often of evenly dimensioned lumber, usually 4x4, and is usually attached on the face of the beam and post rather than the side. Lag screws are used for attachment, through the knee brace at 45 degree angle which is at the normal 90 degree angle into the post and beam. Usually a counter bore is used to both hide the screw head from view from the side and to provide a flat bearing surface