Need a good reference to learn compound angles

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Forum topic by kanihoncho posted 04-29-2011 01:53 PM 1062 views 0 times favorited 3 replies Add to Favorites Watch
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56 posts in 3101 days

04-29-2011 01:53 PM

Topic tags/keywords: compound angles

I’ld like to build a large box with sides that slope in. How do I figure the corner angles out? Thanks.

3 replies so far

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56 posts in 3101 days

#1 posted 04-29-2011 03:09 PM

What is the last word in my posts? I believe it is the word “THANKS” “THANK YOU” ,”TIA” or words to that effect.

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4541 posts in 3102 days

#2 posted 04-29-2011 03:09 PM

There are lots of charts available. However, I learned a trick from Tommy Mac on his Rough Cut show and now I never bother with the charts.

Take a solid block of wood at least 2” thick and cut the four sides at the angle you what the sides to splay by tilting the blade on your TS. You can use that block to set the angles for your miter cuts. You might be able to go to the Rough Cut web site for more details (I have not checked that out).

-- Rich, Cedar Rapids, IA - I'm a woodworker. I don't create beauty, I reveal it.

View mightywombat's profile


17 posts in 2614 days

#3 posted 04-29-2011 03:44 PM

Here’s my take on it, and I’m a newbie too so I may be completely wrong. If I am I hope someone will correct me.

Mathematically speaking, in any four-sided closed geometrical figure, whether it’s a square or a trapezoid or a parallelogram, the sum of any four adjacent angles will be 360 degrees. For example, with a square it’s four ninety degree angles. Keeping that square in mind, when you cut your joinery angles you’re going to divide the angle at which the boards meet in half and cut your miter joint at that angle. In the previous example of a square, since each side meets at ninety degrees your miter angle will be half of ninety, or forty five, which is the standard box joint miter angle.

Now, with the sides tapering in, you should basically figure out what profile you want the sides to have and then cut your side joints at a standard forty five degree angle, since the outline of those four sides from the top down will be a square.

So, draw the outline of your sides, cut the vertical joints at forty five degrees and then, based on the angles at which the sides meet the bottom and top of the box, figure out your joinery angles from there.

Make sense? Let me know if there’s something I can clear up, or if you need an example. I’d recommend trying your design out in a cheap plywood prototype first, just to make sure you’ve got everything right.

Good luck!

-- Make it, hack it, break it, fix it.

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