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Figuring out the miter on this light?

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Forum topic by MarkTheFiddler posted 07-03-2012 08:53 PM 1745 views 3 times favorited 28 replies Add to Favorites Watch
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MarkTheFiddler

1780 posts in 842 days


07-03-2012 08:53 PM

Topic tags/keywords: question miter saw modern

The more I think about these lights as a project, the less likely I am to ever try them. I think they are Way beyond my remedial skill set.

To make a simple pentagon will all sides of an equal length, the miter cut is at 36 degrees. That’s the easy part. The rest is beyond me. I thinks each short board will have to be mitered toward the inside along the length on both sides. I’m scrambling my brains but I can figure out the joints and the compound miter cuts.

Even though I would like to know how to actually figure out the cuts, I just don’t have the equipment to do it.

What I think I can do is join simple pentagons together. In order to do that, I have to think from the inside out. Imagine using a couple of hinges on the inside of joining the rails of the pentagon to attach it to the next. I think it would be a very interesting effect with the wood spreading out from the center. I think the same concept can be applied to triangles, hexagons etc…

I can’t get started on this yet but I’d appreciate some input. My feeble brain has been crunching this for a few days. I think It might work and give something interesting to look at. Do you think that using the hinges would allow the structure to just naturally take the shape of the light in the picture?

-- Thanks for all the lessons!


28 replies so far

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patron

13034 posts in 1994 days


#1 posted 07-03-2012 08:56 PM

that seems logical

in a vulcan sort of way

worth a try

-- david - only thru kindness can this world be whole . If we don't succeed we run the risk of failure. Dan Quayle

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mtenterprises

827 posts in 1346 days


#2 posted 07-03-2012 08:58 PM

So far I think your idea of just making the penatgrams is a good idea. This stuff boggles my mind too.
MIKE

-- See pictures on Flickr - http://www.flickr.com/photos/44216106@N07/ And visit my Facebook page - facebook.com/MTEnterprises

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DS

2131 posts in 1074 days


#3 posted 07-03-2012 09:13 PM

The angles of all sides of a Polygon add up to 360 degrees.
360/5 sides = 72 degrees. Bi-sect that to mate two peices together and you get 36 degrees at your saw.

That’s the easy part. I haven’t figured out the rest. ;-D good luck!

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

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jdmaher

281 posts in 1233 days


#4 posted 07-03-2012 09:48 PM

Well, what else is there to figure out?

If they are all equilateral pentagons, then every miter cut is 36 degrees. The five sides are all equal length, all with a 36 degree miter cut. Glue up 12 of them.

Every side of every pentagon joins to a side of another another pentagon at (wait for it) . . . 36 degrees. Lay each pentagon on the tablesaw, set the blade at 36 degrees, bevel every side.

I think that’s right.

Now, clamping them pentgons with the beveled sides together for a glue-up – THAT gives me a headache.

-- Jim Maher, Illinois

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ChuckV

2420 posts in 2181 days


#5 posted 07-03-2012 09:59 PM

This is a regular dodecahedron, one of the Platonic solids.

I am not sure, but I think you are wondering about the angles between two adjacent pentagons. This is called the Dihedral angle of the solid. If so, you want about 116.5 deg.

Look here:
http://en.wikipedia.org/wiki/Dodecahedron

-- “That it will never come again / Is what makes life so sweet. ” ― Emily Dickinson

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Lee Barker

2163 posts in 1504 days


#6 posted 07-04-2012 02:10 AM

@Jim, the clamping is easy: masking tape.

Once you know the bevel of the sides (I’m not sure yet), mill the stock, cut (miter) all the identical pieces and glue up the pentagons. After an overnight, clamp sides of two figures together, and a third should just fit between them. Tape as you go.

It looks intimidating at first, but chunk it down to steps and it looks like a whaleboat full of fun.

Kindly,

Lee

-- "...in his brain, which is as dry as the remainder biscuit after a voyage, he hath strange places cramm'd with observation, the which he vents in mangled forms." --Shakespeare, "As You Like It"

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MarkTheFiddler

1780 posts in 842 days


#7 posted 07-04-2012 07:07 AM

Man oh man. I’ll try to draw a figure with all the angles included on one of the boards. Somewhere in the ugly recesses of my mind, I’m having a hard time with the bevel to the center being 36 degrees but the more I think about it, the more right it seems. I guess I could mock up a couple of pentagons out of some trash wood.

Just look at the brains on you guys!

Wait for it…...

Thanks for the help on the dodecahedron. I’ll have some tape handy because I didn’t have a clue how to clamp it either. That was going to be my next question.

-- Thanks for all the lessons!

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MarkTheFiddler

1780 posts in 842 days


#8 posted 07-04-2012 07:15 AM

Man oh man. I’ll try to draw a figure with all the angles included on one of the boards. Somewhere in the ugly recesses of my mind, I’m having a hard time with the bevel to the center being 36 degrees but the more I think about it, the more right it seems. I guess I could mock up a couple of pentagons out of some trash wood.

Just look at the brains on you guys!

Thanks for the help on the dodecahedron. I’ll have some tape handy because I didn’t have a clue how to clamp it either. That was going to be my next question.

-- Thanks for all the lessons!

View Charlie's profile

Charlie

1017 posts in 940 days


#9 posted 07-04-2012 10:34 AM

Look into geodesic domes and you should find the angles. It will take some searching as you will mostly come up with multi-faceted domes used as homes, but there was once a calculator to help find the angles depending on the number of facets. Also search Buckminster Fuller as he was kinda like the pioneer dome designer.
I’ll see if I can find it too…

hmmm…. geodesics may not help you. They seem to be more faceted. Dodecahedron next…

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Charlie

1017 posts in 940 days


#10 posted 07-04-2012 10:54 AM

Oh, you want to see this… I think this will help you…
Dodecahedron lamp

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rance

4132 posts in 1814 days


#11 posted 07-04-2012 12:05 PM

Here’s a link to Shipwright’s blog on facets :

http://lumberjocks.com/shipwright/blog/20424

And this wood ball :

http://lumberjocks.com/projects/55001

-- Backer boards, stop blocks, build oversized, and never buy a hand plane--

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jdmaher

281 posts in 1233 days


#12 posted 07-04-2012 12:57 PM

The link that Charlie provided appears to offer a definitive answer: the bevel angle for joining two of the pentagons is 58.28 degrees. And you should definitely trust Euclid more than my feeble “reasoning”.

Charlie’s recommended link also includes a great Google Sketchup model of the author’s dodecahedron lamp. The Sketchup model is in the 3D warehouse: Luna shoji lamp.

The model DOES seem to confirm that the the bevel angle to join two pentagons would be 58.28 degrees.

Mark, if you do build this thiing, please do tell us about the project.

-- Jim Maher, Illinois

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ChuckV

2420 posts in 2181 days


#13 posted 07-04-2012 01:14 PM

Yes, the 58.28 seems correct. That is half of the dihedral angle I mentioned.

-- “That it will never come again / Is what makes life so sweet. ” ― Emily Dickinson

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404 - Not Found

2544 posts in 1623 days


#14 posted 07-04-2012 04:27 PM

I’m looking at that job and thinking it would be easier to just go out and buy it.

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knotheadswoodshed

170 posts in 826 days


#15 posted 07-04-2012 04:38 PM

just looking at that gives me a headache…I have enough trouble making a rectangular box :)

-- Randy - "I dont make mistakes, I make design change opportunities" www.knotheadswoodshed.com

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