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I Need Measuring & Marking Help Answered

I have a plastic ornament that I want to mark out with a measuring grid. I have a compass, which I can mark the sphere out in fourth's, but my measurements are always off by an 1/8th of an inch.
How do I measure this sphere with accurate marked grid? String, paper, scotch tape, laser cross-hair, T-Square & yard stick?

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Jack A Lopez
Jack A Lopez

14 days ago

I see another fine product from Greenbrier International, aka DollarTree.
;-)

I think the tools for getting started measuring your sphere, are:

{graph paper (or ordinary unlined paper), masking tape, a ruler, and a pencil, and maybe a calculator that can do arithmetic, e.g. dividing by 4}

The convenient thing about graph paper,

https://en.wikipedia.org/wiki/Graph_paper

is you can roll it up into a cylinder, and the parallel lines can serve to check that you have an accurate cylinder, rather than a cone.

Actually, the same is true of an ordinary, rectangle-shaped, piece of paper, but the only lines you can use are the edges of the paper. You can tell if your cylinder is straight, by making sure one edge gets rolled into a circle, rather than a spiral.

Anyway, if you can wrap a piece of graph paper, or ordinary rectangle-shaped, paper around your sphere, then the resulting cylinder will have the same radius as the sphere. Or if not the same, it will be really close, differing by only the thickness of the sheet of paper.

Using a small piece of masking tape, to tape the paper to the sphere at one spot, may help to wrap the paper around the sphere, and get it tight, without slipping.

The next easy trick, I can think of, is to cut some the graph paper into strips, that are only one square wide, for to make something resembling a measuring tape.

Regarding the size of the squares, on the graph paper, I am guessing squares of width 1/4 inch, or 5 mm, or similar, would be about the right size. Really what is important is that this width be small compared to the radius of the sphere.

Anyway, once you have some little measuring-tape-like strips of paper, you can bend those into rings, with the same radius as your sphere, essentially little "great circles" made of paper.

https://en.wikipedia.org/wiki/Great_circle

And you can tape these paper "great circles" onto your sphere, anywhere you want.

I think you said you wanted to divide your sphere into fourths.

So maybe before taping your paper great circles to the sphere, you could make marks on, at least one of them, at {0/4, 1/4, 2/4, 3/4, 4/4} the circumference. The ruler and calculator might come in handy for this. ( Naturally, points 0/4 and 4/4 wind up on top of each other, when this line is rolled into a circle.)

The next trick requires some familiarity with the well-known, "latitude and longitude" type coordinate system for locating points on the surface of a sphere.

https://en.wikipedia.org/wiki/Geographic_coordinat...

Tape one of these paper great circles, the one divided into fourths, to the "equator" of your sphere. Another two paper great circles are used to make some "lines of longitude" spaced 90 degrees apart. I am guessing those "lines of longitude" should intersect at the "north pole" and "south pole" of your sphere, as well as intersecting the "equator" at the marks where it has been divided into fourths.