miter box saw question

[ship]

In doing a cornace at a positive 45 (135) degree angle, how would one set the compound miter box saw and go about cutting the molding given the molding normally would hang at a 45 degree angle? What further tips in cutting after the angle cut would Norm recommend?

 

[soundlight]

Ha...Norm. I remember when I used to watch that show twice every weekend.

 

[soundman]

first off Norm would build a jig, out of soild oak using every tool he has.

or at least that is what it seemed like when I catch yankee workshop.

 

[falcon]

first off, cutting the cornice, you can either nest it on the saw and use a usual 45 degree mitre, or you can set a 30 degree bevel and a 35 degree mitre and cut it laying flat.

I'm not quite sure what you mean by doing a positive 45 degree angle (this term wasn't used when I did these, we call them inside or outside 45s or returns, depending on what we are doing wiht them). If its an outside corner, i would cut at a 30 degree bevel and a 36 degree mitre and if its inside corner i would cut 30 bevel, 34 mitre, and if i'm nesting it (which doesn't give as nice as a cut) i would use 46 and 44 degrees respectively.

Norm might suggest to put a back angle cut on it to make sure it fits tighter, but as Norm does everything in workshop he doesn't need to do that since he knows its a perfect corner he is working with.

 

[ship]

Ah, a carpenter.

I expect I don't need to check the math. What's the formula and please explain how you came to your answer. Thanks by the way.

What I meant by a positive angle was that of the 135 degrees. You were correct in guessing my intent.

 

[falcon]

These are for cornices and crown with a 45 spring angle,
To find the mitre angle
1. The wall angle divided by 2=
2. press tan. (answer will be X )
3. X times 5.5= Y
4. 3.88 divided by Y =
5. press inv. tan.

thats inverse tan (3.88/((tan(angle/2))(5.5)))

To find the bevel angle
1. The wall angle divided by 2=
2. press cos. (answer will be X )
3. X times 3.88= Y
4. Y divided by 5.5=
5. press inv. tan.

thats inverse tan (((cos(angle/2))(3.88 ))/5.5)

There's your two formulae which are a pain in the butt when on site. They will give the theoretical answer but unless you build the walls yourself, the angles most likely aren't exactly 90 degrees. So start with those angles and test each corner to find the precise angles that fit that particular corner.