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Building a pentagonal box

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Forum topic by lumberjocksmjc posted 07-22-2013 06:34 AM 1109 views 0 times favorited 15 replies Add to Favorites Watch
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lumberjocksmjc

2 posts in 1238 days


07-22-2013 06:34 AM

Topic tags/keywords: garden boxes pentagon boxes complex cuts for boxes

I’d like to build a pentagonal box with sloping slides; top is larger than bottom. Anybody know where to find a plan? And where to learn how to make the complex cuts for the corners of the box?

Thanks in advance for any help.

Mike


15 replies so far

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Buckethead

3140 posts in 1336 days


#1 posted 07-22-2013 09:13 AM

360°/ 5 = 72° the angles created at each panel joint.

72°/2 = 36° the two bevels needed to create the angle.

You’ll might also need to bevel the top (and bottom) edges of each side. That bevel will change depending on what angle (miter cut) you decide on for each side. More angle (obviously) will result in a greater difference in the top and bottom perimeters, as well as a need for more bevel. I don’t know how to mathematically determine what that top bevel would be. I would use a dry fit to see what angle is measured between the table and the box (perpendicular to the face of a panel) and apply that same angle to your top bevel cut.

-- Support woodworking hand models. Buy me a sawstop.

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Buckethead

3140 posts in 1336 days


#2 posted 07-22-2013 11:21 AM

While commuting to work, I thought about this again. What I said above only works at 90 degree miters. As the angle of the miter cut increases, the bevel will decrease. So my above post is inaccurate.

I think I figured it out though.

If the panel is oriented at 90 degrees to the table, the bevel is 36 degrees. If it is lying flat on the table ( forming a flat surface) the “bevel” is at 0 degrees. The range of change is 90 degrees.

If you oriented the panel at 75 degrees to the table you would need 75/90 of your 36 degree bevel. 36x.833=29.88 degrees.

I’m not sure this is right. Thinking on the fly here. I know there is someone who knows the proper formula here, but it is fun trying to picture the solution in my mind.

-- Support woodworking hand models. Buy me a sawstop.

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StLouisWoodworker

59 posts in 3443 days


#3 posted 05-12-2016 01:52 AM

Specify number of sides (5) and the slope of the sides (degrees from horizontal). Then
see http://dls-website.com/documents/WoodworkingNotes/CompoundAngleJoinery.pdf
for the formulas to determine blade tilt and miter-gauge angle to make the cuts.

-- Don Snyder (38.6N, 90.3W)

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AZWoody

697 posts in 691 days


#4 posted 05-12-2016 02:21 AM

The sum of degrees in a pentagon is 520 degrees, not 360.
Don’t know why I remember that from geometry but for some reason that stuck in my noggin.

The processes to figure the angles and do the maths listed in the previous link, not so well, haha.

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jbay

819 posts in 366 days


#5 posted 05-12-2016 02:47 AM

I use this calculator.
I just use one of the side angles as the wall, and the degree of slope for the spring angle.
Takes a little playing around but it will get you there.

-- My “MO” involves Judging others, playing God, acting as LJs law enforcement, and never admitting any of my ideas could possibly be wrong or anyone else's idea could possibly be correct -- (A1Jim)

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splatman

563 posts in 866 days


#6 posted 05-12-2016 03:21 AM

Build a thingamajig to hold your stock at the desired slope. Then you only need to cut the miters at 36° No compound miter acrobatics needed.

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shipwright

7175 posts in 2265 days


#7 posted 05-12-2016 05:13 AM

.

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fibreglass trees. http://thecanadianschooloffrenchmarquetry.com/

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ArtMann

145 posts in 283 days


#8 posted 05-12-2016 03:55 PM

Here is another calculator that is a little more straightforward.

http://www.pdxtex.com/canoe/compound.htm

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waho6o9

7179 posts in 2044 days


#9 posted 05-12-2016 04:24 PM

Gary Katz has a great tutorial on tapered columns.

http://www.garymkatz.com/trimtechniques/tapered_columns.html

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helluvawreck

23199 posts in 2333 days


#10 posted 05-12-2016 05:12 PM

Turbocad Deluxe is an easy to learn CAD program that is really powerful for the price. You can use it to make all sorts of drawings to answer calculations like that. I used it in our molding plant for years. I had a machine shop in the plant and also made the templates for the molder tooling. It wasn’t as powerful as AutoCAD but it was plenty powerful enough.

helluvawreck aka Charles
http://woodworkingexpo.wordpress.com

-- If a man does not keep pace with his companions, perhaps it is because he hears a different drummer. Let him step to the music which he hears, however measured or far away. Henry David Thoreau

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tomsteve

394 posts in 686 days


#11 posted 05-12-2016 06:43 PM



The sum of degrees in a pentagon is 520 degrees, not 360.
Don t know why I remember that from geometry but for some reason that stuck in my noggin.

- AZWoody


i think its 540 degrees

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tomsteve

394 posts in 686 days


#12 posted 05-12-2016 06:44 PM

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darinS

678 posts in 2334 days


#13 posted 05-12-2016 07:08 PM

tomsteve is correct. Interior angles add to 540° (sum of interior angles [n] = (n-2) x 180° so (5-2)x180 is 3×180=540

-- They say many people die because of alcohol. They never realized how many of them are born because of it.

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Jim Finn

2417 posts in 2389 days


#14 posted 05-13-2016 12:41 AM

I have found that when making a flared box like this if the flare is 5° or less it can be ignored. Over that 5° it will make a difference in the miter angle required.

-- "You may have your PHD but I have my GED and my DD 214"

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AZWoody

697 posts in 691 days


#15 posted 05-13-2016 01:03 AM


The sum of degrees in a pentagon is 520 degrees, not 360.
Don t know why I remember that from geometry but for some reason that stuck in my noggin.

- AZWoody

i think its 540 degrees

- tomsteve

Yup, that was a typo on my part.

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