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Angle calculator for building a shallow dish in sections?

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Forum topic by LiveEdge posted 06-06-2017 08:27 PM 1007 views 0 times favorited 9 replies Add to Favorites Watch
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LiveEdge

565 posts in 1459 days


06-06-2017 08:27 PM

I would like to build a radar dish model out of wood (see example below). I don’t have a lathe and so I thought perhaps I could do it in a glue-up of 12 sections. I wonder if anybody knows of a calculator site that would handle the angle of the bevels? I’ve built a soccer ball (see projects) and so know the bevel angles are likely to be some odd decimal of a degree.

Ideas?


9 replies so far

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papadan

3584 posts in 3207 days


#1 posted 06-06-2017 08:34 PM

360 / 12 = 30. so your cut angle would be 15 degrees. All circles are 360 degree so divide by the number of sections you want and each cut will be 1/2 of that so your joint will be that angle.

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LiveEdge

565 posts in 1459 days


#2 posted 06-06-2017 08:35 PM



360 / 12 = 30. so your cut angle would be 15 degrees. All circles are 360 degree so divide by the number of sections you want and each cut will be 1/2 of that so your joint will be that angle.

- papadan

Ya, that’s the easy part. :) I had that covered. The question is what the BEVEL cut will be at so your 12 slices fit together in a three dimensional bowl.

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papadan

3584 posts in 3207 days


#3 posted 06-06-2017 08:40 PM

That is totally up to you, how much “dish” do you want?

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Loren

9632 posts in 3486 days


#4 posted 06-06-2017 08:55 PM

It’s all trig.

I did some of this stuff when I was getting started
in woodworking. I bought a trigonometry text
at a used bookstore and re-learned enough to
get me through it. At the time setting precision
bevels on a table saw was very tricky and I had
a special jig with a dial indicator on it. These days
you can buy electronic angle cubes that attach to
the blade with magnets. They are very accurate.

I imagine you’d want to make the whole thing
in quarters or something like that. You’re almost
certainly bound to have made some minor errors
that get compounded by the number of segments.
At the point where all 4 quarters are glued up
a piece of flat MDF with a length of sanding belt
glued to it can be used to sand the last 8 edges
to angles where they fit together to form the
complete shape you want.

You may want to learn Sketchup or some CAD
program which will give you the angles. There
will certainly be a learning curve to the software
but being properly planned out the form is a lot
more likely to come close to what you envision.

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LiveEdge

565 posts in 1459 days


#5 posted 06-06-2017 09:27 PM

Loren, are you aware of any online calculators for this? I remember using one for the icosahedron I built, but this is obviously a different shape.

Maybe the truth is like Papadan might have been saying; any bevel angle will work but the bevel governs the depth of the bowl.

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LiveEdge

565 posts in 1459 days


#6 posted 06-06-2017 09:33 PM

Boom!

http://jansson.us/jcompound.html#npyramid

Treating it like an n-sided pyramid

View mitch_56's profile

mitch_56

18 posts in 312 days


#7 posted 06-06-2017 11:38 PM

I think what the OP wants has already been covered in detail here:

http://woodgears.ca/miter/index.html

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LiveEdge

565 posts in 1459 days


#8 posted 06-07-2017 12:10 AM

Excellent link mitch! I will use that as well.

View BobAnderton's profile

BobAnderton

239 posts in 2629 days


#9 posted 06-07-2017 02:53 AM

Another option to get something close to a spherical shape is cutting 1/2 rings on the bandsaw where the table angle is set to make the blade be the tangent to the sphere for each ring being cut. Then stack the rings to make the spherical shape and sand.

It’s a good excuse to buy a lathe, imo.

-- Bob Anderton - Austin, TX - Nova 3000 lathe, Alaskan Mark III mill, Husqavarna Saw

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