Does anybody have the mathematical equation or equations for finding the miter and bevel angles to cut crown on the flat. I have gadgets and charts, but they aren’t always with me.
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Replies
Why not just laminate the chart, and either permanently fasten or zip-tie it yo the saw? Seems "safer" and easier than doing the math.
Bob
Here is a good link :http://home.att.net/~waterfront-woods/Articles/Compoundangles.htm
You'll need a trig calc to do the math.
I like having the formula and calc around eventhough I use charts for standard crown spring angles; 38/52 or 45. Sometime the mill makes up their own spring angles so having the formula around is nice (my last run was with 32/58 degree crown, note the transposed digits). I prefer cutting my crown flat on the saw, we use a double bevel Hitachi so this works well. I have found cutting crown the old-fashioned way tough as bows and crooks in the mold will mess with how the saw cuts through buggering the compound cut. But that's me, use what works best for you.
In defense of my math, I use formulas for everything, I can get the cuts on target after one trial and then a tweak instead of a shot in the dark followed by numerous tweaks. The older guys laugh at me but I get it done.
Here is a similar description I got from Breaktime a few years ago;
From the July '91 article, the miter angle (M) is
M= arctan(A/(C x tan(F/2)));
the Bevel angle is
B= arcsin((D x cos(F/2))/C).
In these equations, F is the angle of the corner (usually 90 degrees), A is the distance along the
ceiling from the wall to the moulding, D is the distance along the wall from the ceiling to the moulding,
and C is the length along the flat back side of the moulding (i.e., so A, D, and C form a right triangle,
and the angle the moulding makes with the wall is arctan(A/D).
Yea, formulas usually don't get you perfect the first time (non-straight walls, misaligned saws, etc.),
but they often get you close enough so that it's a minor tweak to get things looking good.
Also. if you could get a response from our resident armor removal specialist (formerly known as Mongo, I don't know if he has a new screen name), he had a different way of figuring this that looked good.