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Shop Tips & Tricks #19: The Art of Middles of Symmetries

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Blog entry by GnarlyErik posted 11-20-2016 03:12 PM 980 reads 0 times favorited 3 comments Add to Favorites Watch
« Part 18: The Zen of Sandpaper and Sanding Part 19 of Shop Tips & Tricks series Part 20: Curves, Fair Curves and the Lack of Them »

I don’t know why I did not think to include this as a part of my blog about centerlines since it is very closely related. I will call this notion ‘The Art of Middles of Symmetries’. ┬áSimply put, all symmetrical shapes by definition have a ‘middle’, or centerline. Stating that notion as a corollary to centerlines, you might say: “All symmetrical shapes have an EXACT middle centerline.”

Take advantage of this simple fact by using it when laying out symmetrical items. I don’t consciously think about it myself when laying something out now, which is probably why I forgot to include it earlier.

In practice, this means you only need to lay out HALF of any symmetrical shape, no matter how complex the shape may be. And besides being much faster, laying out just half of a symmetrical shape will be more accurate by far. It is surprising how often you can make use of this idea. Let’s take a valentine heart as an example. If you try to lay out the heart in full, no matter how careful you are, there are guaranteed to be small differences in the two halves. But, if you lay out just one half, and using that as a pattern, repeat for the other half, the result will be an accurate, symmetrical whole.


(Half the symmetrical valentine as drawn on paper folded along the centerline_

For small shapes you might use something stiff like a manila folder for pattern stock. Lay out half the shape, then fold the paper on the centerline. By cutting the half shape out with scissors or a knife, you are now cutting both halves simultaneously and identically, which will then unfold to a whole, symmetrical pattern. It is very like something you may have done in kindergarten. This pattern can now be used to trace the complete, whole symmetrical shape to the stock to be worked.


(The full valentine pattern after the folded paper is cut to shape and unfolded. In this image the cutout shape was laid on a manilla envelope for scanning.)


(An example of a more complex symmetrical pattern)

When you have a shape too large for a foldable pattern, using a stiffer material like 1/4” plywood can work for you. In this situation, make a pattern for half your shape. After transferring the first half to your stock, simply flip the pattern over for the second half, being very careful to accurately align everything to your centerline.


(In this example drawing, the pattern to be made on stiff stock like plywood, and the centerline is extended beyond the ends to aid in alignment when the pattern is flipped over for the opposite side)

And, there you go – an accurately symmetrical layout result using the idea of The Art of Middles of Symmetries!

-- "Never let your dogma get run over by your karma!"



3 comments so far

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oktams

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#1 posted 11-21-2016 02:06 PM

lol that’s kinda of a common sense thing BUT I WOULD HAVE NEVER THOUGHT TO DO IT!! THANKS FOR SHARING!

-- TAMMYE ~ ENJOY THE DAY THE LORD HAS GIVEN US!

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hnau

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#2 posted 11-30-2016 06:29 PM

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bhuvi

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#3 posted 12-01-2016 02:11 PM

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