# Compound Cut on Beam End



## ahriman (May 25, 2020)

Spoiler: this question already has a solution, but I want to know how I got there. If you are looking for problems which have no solution then move along, nothing to see here.

Trying to wrap my head around the math/method involved to make a cut on a 4×8 (true dimension) beam end. The beam is going to butt into a 4×12 beam and join at a 27.5° angle. The beams will be in parallel planes horizontally. What I want to do is cut a 1" shoulder into the 4×12 beam, and have the 4×8 beam seat into that shoulder. From my figgerin' the 4×8 beam will have a 1" run and an 8" rise which results in a 82.875° angle at the "shoulder point." So, my question is: how do I figure out that compound cut?

And to compound this problem (see what I did there?), I have found most calculators out there assume a table saw cut. The beam is 12'11" on the long side so a table saw cut is not practical (but a dual-bevel sliding compound miter saw is and that will check our mathin'). I have marked out the cut on the beam, but I am looking for the elegant answer here. Or, at least an old trick on how to calculate this.


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## shipwright (Sep 27, 2010)

I guess you're not a boatbuilder. This is a (simpler) version of fitting a deck beam to a beam shelf. It is generally done "from the work" meaning that the pieces are brought together in their appropriate relationship and are scribed. No numbers involved. The cut would be made, on a big boat, with a chainsaw (finished with a sharp chisel) and on a smaller one with a handsaw. If a recess is needed to land te beam it is cut to the scribe lines with sharp chisel.


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## Unknowncraftsman (Jun 23, 2013)

I have the same mind set as Paul. It's a reference cut they way I do this type of work big or small.
First create a reference surface string line another piece of wood something. Then make a template using that reference surface that will be transferred to the work.
The temple can be cardboard or another piece of wood close enough to the same shape. I prefer wood .
All those number hurt my head.

Good Luck


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## ahriman (May 25, 2020)

Well, I may be a boatbuilder at heart, and definitely a wannabe geek in this thread. I did run a string line for reference, that is how I got the 27.5° angle. But the reference surface is a good piece of advice, I will make my mistakes there.


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## shipwright (Sep 27, 2010)

Just for fun….
This is me fitting some deck beams back in about 1976.


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## ahriman (May 25, 2020)

> Just for fun….
> This is me fitting some deck beams back in about 1976.


You look pretty darn comfortable. ... and this was up in the Pacific NW just before break time when you went over to get a cup 'o joe at that fancy new coffee place, correct? ...


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## shipwright (Sep 27, 2010)

No fancy coffee there. You must be thinking of Seattle. 
I'm north of the border.


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## LeeRoyMan (Feb 23, 2019)

the second mouse today…..... is the first mouse tomorrow


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## Unknowncraftsman (Jun 23, 2013)

What a minute here Shipwright looks familiar. 









Just needs a wool cap.


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## shipwright (Sep 27, 2010)

Got me! 

..... and you're right LeeRoy. I never thought of it that way….....


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