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Old 09-08-2006, 09:16 AM   #1
James Falkner
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I found some excellent wood with which to make plyo boxes. I want to make the angled ones featured in this month's CFJ and discussed in some recent threads.

Question is, I understand that the cuts along the top and bottom of the sides need to be at an angle. But what about the cuts on the sides of the sides? You know, where one side means the other. Shouldn't this be angled too? It is like crown molding, right? When I cut crown, I have to cut it using a compound mitre saw (or hold the piece at an angle during cutting). This means there are two angles involved. Why aren't there two angles involved in plyo box construction?
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Old 09-08-2006, 09:31 AM   #2
Nick Cummings
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Hey man. Hows it going? You could always buy the irrigation box from Home Depot if you are lazy like me.
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Old 09-08-2006, 10:57 AM   #3
Paul Findley
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I built similar boxes a while ago with an 85 degree angle. I used a table saw so the blade was at an angle, as was the guide.

http://www.crossfit.com/discus/messages/26/18648.html

(Message edited by paul on September 08, 2006)
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Old 09-08-2006, 03:28 PM   #4
James Falkner
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Hey Nick, going great, waiting for your call!!

I've been jumping on concrete cinder blocks stacked up, which I "borrowed" from a nearby demolished house. But it's a pain to build the thing each time I want to use them, then tear it down for storage :-)

Paul, is 85 degrees just a guestimate or is there actual math involved there :-) When I was putting in some crown molding I remember the calculations involved lots of geometry if you really wanted to be precise.
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Old 09-09-2006, 01:26 PM   #5
Paul Findley
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I used 85 degrees, you need some geometry to determine the height of side pieces to get your overall box height, and the width of the top and bottom of the side. Ain't too bad.
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Old 09-10-2006, 04:42 AM   #6
Dan MacDougald
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If you use a butt joint as in Lincoln Bingham's example,
http://www.crossfit.com/discus/messages/26/14917.html,
the sides do not need to be angled. If you want to use a miter joint, as in Paul's example, the sides would be cut to 45 degrees for a four sided box.
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Old 09-10-2006, 04:55 PM   #7
William Henniger
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I thought there was a post to go along with Lincoln's where the angle was 10 degrees. I made boxes with the 10 degree angle and they turned out fine, I had to do some calculations on dimensions to get the 20" height. The box is bulletproof and I made it big enough for people to jump on it from both sides at once. It was a pain cutting the 10 degree angle along the edge of the pieces I used a circular saw.
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Old 09-10-2006, 06:48 PM   #8
Lincoln Brigham
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I would not advise to mitre the sides. 3 times the work and half the strength. Crown molding looks pretty but it is not load-bearing like a plyo box. Use 90 degree cuts - aka butt joint:
http://www.crossfit.com/discus/messages/26/29914.jpg

"The conventional miter joint is widely used for making corners in various types of woodwork ... However, it is not recommended where the joint is subject to excessive weight or unusual strain."

(Message edited by lincoln on September 10, 2006)
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Old 09-10-2006, 07:08 PM   #9
James Falkner
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I appreciate the feedback from all.. I really do!!
I completely buy the "do not miter" stuff. Thanks for the clarification!

However I do not feel like my curiousity is fully satisfied yet. Maybe I'm just over-analyzing this...

Take Lincoln's picture above. This looks like a "birds-eye" view of one corner of a 90' straight-sided plyo box, with the top removed.

Now, imagine what would have to happen to this butt joint as the size of the top of the plyo box shrinks (while the size of the bottom of the box remains the same). Eventually the top shrinks to 0, giving you a 4-sided pyramid (not what I want of course), and the angle where the two pieces of wood meet gets weird.. The point is, if I want to cut the sides of my sloped plyo box using a table saw, or any other saw, where the piece of wood is laying *flat*, what angle do I set the blade to, and what angle do I set the fence to? These are the two "angles" that neither of which can be 90', according to my eyeball method.
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Old 09-10-2006, 09:42 PM   #10
Paul Findley
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Use the fence to create rectangles for sides and a square top.

Use the miter gage to turn the sides into trapezoids.

Tilt the blade only to square off the top and bottom of the sides, so the box sits flat on the floor and the lid sits flat on the sides.

When I make my 24" box, I will not bother with the nice corners. The 12 and 20 are still going strong, but I did beef it up with the brackets.
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