LumberJocks

Thales Square

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Project by Woodknack posted 05-15-2016 05:47 AM 4654 views 44 times favorited 29 comments Add to Favorites Watch

Heard about these for the first time today and decided to make one. I don’t know what they are called but the person I learned them from called them a Thales Square, after Thales theorem.

Basically you take two sticks, the longer one represents the diameter of a circle and the shorter represents the radius. When you place this apparatus in a corner it will tell you immediately if the corner is square. If all three points touch, the corner is square. If the two outside points touch, the angle is acute. If the center + one outside point touch, the angle is obtuse. As long as all 3 points are equidistant from the center, the tool is highly accurate.

If you make one and play with it, you’ll intuitively understand it pretty quickly. I made the center piece (radius) first, drilled holes and attached it roughly halfway on the longer piece (diameter). Then swing the short stick to each side and use a sharp chisel to chop off each leg to the exact length of the center piece. Hopefully that makes sense. It was really easy. It literally took about 5 minutes to make.

-- Rick M, http://thewoodknack.blogspot.com/





29 comments so far

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Dutchy

2918 posts in 2163 days


#1 posted 05-15-2016 06:35 AM

Thanks, I have ad it to my favorites.

-- https://dutchypatterns.com/

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majuvla

12275 posts in 2862 days


#2 posted 05-15-2016 11:14 AM

It’s mind blowing how such simple thing can measure with such precision.

-- Ivan, Croatia, Wooddicted

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HokieKen

4974 posts in 1134 days


#3 posted 05-15-2016 01:21 PM

Very cool Rick. Much simpler than trying to get good backlight behind a square on a drawer! Did you cut the tips at acute angles or at 90’s? Seems like if the flats were to touch it would effect the function if I understand correctly. I love geometry :P

-- Kenny, SW VA, Go Hokies!!!

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waho6o9

8188 posts in 2572 days


#4 posted 05-15-2016 01:24 PM

That’s awesome, thanks for posting.

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shipwright

7980 posts in 2793 days


#5 posted 05-15-2016 02:18 PM

Thats a very interesting tool, nicely done.
.... but (and maybe I’m being obtuse) I think you got your acute/obtuse backwards in the explanation.

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

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a1Jim

117090 posts in 3572 days


#6 posted 05-15-2016 02:28 PM

Interesting Rick,it’s confusing to me how this works,but geometry was always a mystery to me. What does it look like if it’s out of square?

-- https://www.artisticwoodstudio.com/videos wood crafting & woodworking classes

View Woodknack's profile

Woodknack

11608 posts in 2375 days


#7 posted 05-15-2016 03:32 PM


Did you cut the tips at acute angles or at 90 s? Seems like if the flats were to touch it would effect the function if I understand correctly. I love geometry :P

- HokieKen

The flats don’t seem to matter. You could leave the ends square and I think it will work equally well. It really is very obvious if the corner is out.

-- Rick M, http://thewoodknack.blogspot.com/

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Woodknack

11608 posts in 2375 days


#8 posted 05-15-2016 03:37 PM



.... but (and maybe I m being obtuse) I think you got your acute/obtuse backwards in the explanation.

- shipwright

Good catch,I fixed it. Not sure how that happened but I posted after getting home from a party so….. The libations probably had something to do worth it.

-- Rick M, http://thewoodknack.blogspot.com/

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Woodknack

11608 posts in 2375 days


#9 posted 05-15-2016 03:43 PM



Interesting Rick,it s confusing to me how this works,but geometry was always a mystery to me. What does it look like if it s out of square?

- a1Jim

I think you’ll understand after playing around with it. I’m going to make a couple more in different sizes.

-- Rick M, http://thewoodknack.blogspot.com/

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Hammerthumb

2844 posts in 1970 days


#10 posted 05-15-2016 04:07 PM

Very cool Rick!

-- Paul, Las Vegas

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duckmilk

2848 posts in 1320 days


#11 posted 05-15-2016 04:34 PM

That is very cool Rick. I have never heard of this before. Great info and it seems much easier than measuring diagonals.

-- "Duck and Bob would be out doin some farming with funny hats on." chrisstef

View Pointer's profile

Pointer

427 posts in 1106 days


#12 posted 05-15-2016 04:50 PM

Nice idea. Geometry is something I used to teach, so I understand the concept completely. Using the radius to determine the length of the diameter is a great idea. I was wondering about that. Thanks for sharing. I think we all love these types of gadgets that can be used quickly to improve our accuracy.

-- Joe - - Don't be pessimistic, it never works works anyway.

View CL810's profile

CL810

3784 posts in 2983 days


#13 posted 05-15-2016 06:19 PM

Slick!

-- "The only limits to our realization of tomorrow will be our doubts of today." - FDR

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jonmakesthings

73 posts in 813 days


#14 posted 05-15-2016 06:57 PM

Very cool! I think I’ll make one, a little smaller than yours. Yours looks like 12”? A 4 or 5” would be nice for small boxes

-- How can you have any pudding if you don't eat your meat?

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tyvekboy

1752 posts in 3008 days


#15 posted 05-15-2016 07:16 PM

Cool tool. Thanks for sharing.

-- Tyvekboy -- Marietta, GA ………….. one can never be too organized

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