Shopsmith Forums

shipwright wrote:Are you SURE Mike?

Paul M

Absolutely not!! Who typed that anyway?

reible wrote:Hi,

I've been working a box design that might be of interest as I was planning on using splines along the outside edge. Contrasting wood might make in interesting...

Anyway this is a square box but I think you could do the same thing with a flag box.

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[ATTACH]10142[/ATTACH]

The second one leaves a interesting angle, they can be tipped in or out to ones liking or left square as shown in the first image.

Ed

I second this idea. This looks like a good solution and also adds interest.

mickyd wrote:Absolutely not!! Who typed that anyway?

I have that problem frequently but this time I think the angles are incorrect!.

http://www.mathopenref.com/triangleinternalangles.html

The Miter angles are 'stated' as 47.7 and 68.8.

If the bottom is cut at 68.8, the workpiece(s) will have a 21.2 angle. When joined they will form a 42.4 degree angle(both sides).

With the apex cut at 47.7(interesting that that angle 'matches' what is needed, not the compliment as the 68.8 is) when joined will form a 95.4 degree angle.

Adding them up = 42.4 + 42.4 + 96.4 = 180.2. Now you know why 'stated' has quotes. But if you working to +/- .1 degree, that'll do!:rolleyes:

MickyD I am surprised at you!(as is Paul!):D

OK, my two cents, from my high school geometry class, unless the triangle is not in a single plane (ie. flat) the internal angles MUST add to 180 degrees. I'd check those plans again.

Ok guys great ideas but let me reign you in a little. This will be a strictly production item that I need to keep simple and will have to build quickly. I tweaked the triangle to get a 45 degree miter on top. The bottom miters are now 68.8 degrees according to Sketchup. They just specked that it was 19 3/4 across the bottom and the sides are 13 1/3. 1/3? The back will be 1/4 inch plywood attached with panel clips to be removable.



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dwevans wrote:OK, my two cents, from my high school geometry class, unless the triangle is not in a single plane (ie. flat) the internal angles MUST add to 180 degrees. I'd check those plans again.

Methinks the plans are ok, with maybe a loose tolerance.

What distracted us was the large angle specified for the lower miter. Actually it specified the compliment of the angle needed.
68.85 would be right on the button(or 47.6).

i.e. 2(21.15 x 2) + (47.7 x 2) = 2(42.3) + (95.4) = 84.6 + 95.4 = 180

or 2(21.2 x 2) + (47.6 x 2) = 2(42.4) + (95.2) = 84.8 + 95.2 = 180

mbcabinetmaker wrote:Ok guys great ideas but let me reign you in a little. This will be a strictly production item that I need to keep simple and will have to build quickly. I tweaked the triangle to get a 45 degree miter on top. The bottom miters are now 68.8 degrees according to Sketchup. They just specked that it was 19 3/4 across the bottom and the sides are 13 1/3. 1/3? The back will be 1/4 inch plywood attached with panel clips to be removable.



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If the top miter IS 45 degrees, then the lower angle MUST be 55 degrees, so the miter is 62.5.

You cannot merely alter sides dimensions without also affecting the angles. <<edit

Consider the project cut in half vertically thru the middle. Each half will be a right triangle with a 90 degree corner where the midpoint of the bottom was.

With a base of 19 3/4 / 2 = 9 7/8 and a 55 degree angle, the long side would be 9.875 / cos(55) = 17.217

I will figger out what is needed shortly!

Hokay!

Using the same half project as above, the 'project' needs a 9 7/8" base, and a 13.33333333333" side. Since those are the only criteria, the height must satisfy the angles involved.

For a right triangle with an 'adjacent' side of 9.875" and a hypotenuse of 13.333333", the common angle must be arc cos 9.875 / 13.33333 = acos .7406 = 42.2 degrees.(almost familiar?) The apex angle(half) is thus 47.8.(ditto)

This says: the 68.8 cut is actually 68.9 and the top cut is 47.8.

Around the project, the interior angles are: 42.2 + 42.2 + 95.6 = 180

Sorry!, but that is what their input specifications state. I would 'negotiate' some more readily achieved dimensions!!!!!

What is unclear to me is are those dimensions inside or outside???? Won't change the angles, but will affect material needed.

dusty wrote:I have that problem frequently but this time I think the angles are incorrect!.

http://www.mathopenref.com/triangleinternalangles.html

You know the old saying dusty....it's better to have thought and to have thought wrong than to have never thought at all!! (author mickyd, circa 2010)