Mitre Angles, help needed!

[James MacArthur]

Hi Creekers,

I'm really stuck at the moment. I'm converting an old Church pew into a corner seat. Its been a quick job untill now. I need to mitre the back of the seat together. Its a 90 degree corner obviously, and the chair back has a 10 degree slope backwards. I cannot for the life of me find a calculator online that seems to throw up the right answers when I test it. Can anyone help?

[James MacArthur]

Having been at this all day, I think I've worked it out, 80 degree mitre with standard 45 degree bevel on the saw. If anyone can check that I'd appreciate it but if not thanks for reading!

[bill mullin]

Its a compound angle, consisting of a mitre and bevel.
The bevel will be 45 degrees, and is obviously cut thru the thickness of the seat back.
The mitre will be 10 degrees, cut across the width of the seat back.
The short point of the mitre will be the bottom of the seat back, long point at the top.

Hope I didn't misread your question and state the obvious. Can't help with an on-line calc.

[bill mullin]

Sorry James,
I'm pretty sure my math is wrong on the mitre. Someone with better geometry skills will have to help.

[David Dockstader]

What you have is common when you are putting together angled boxes. You are trying to determine a compound miter angle. Check on the Internet and you will find several calculators that will do this. To make it work, you just have to tell it you are making a 4-sided box, and then only cut the 2 sides. I have 2 of these calculators and they both use Excel. The answer they give is that you miter gauge should be set at 9.851 degrees (assuming you have microscopic vision and can read it that accurately) and your blade tilt should be 44.136 degrees. Just be careful to tilt the miter gauge and the blade in the right direction. Run a couple of test pieces first to verify. Too bad our equipment isn't as accurate as Excel.

[bill mullin]

Found a free one.http://jansson.us/jcompound.html

[Myk Rian]

When you get to that page, click on FILE and save it to your documents. You'll always have it.
It will save as a .html file and a folder with the working files in it.

[johnny means]

Run one leg straight into the wall, then scribe the other to it. Probably make for a cleaner joint too.

[James MacArthur]

Thanks for all the help. I'll be making the cut this afternoon, (UK time) and I'll let you know how it goes. The chair back is to large to use the table saw so this will have to be done with guide rail and Circular Saw.