Originally posted by SkyWatcher
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The point made by a pencil lead is as wide as 5 thousandth and it is
so easy to be off 10-20 thousands. What I like to do is to do the rough
cut circle then after I am sure the dot in the center is close I drill it.
After that I drill a bigger hole to put my shaft and hub into. Then into the
drill press to check for roundness WITH a pencil or scribe. Even drawing
with a compass after the hole the size of the shaft is drilled requires
a spacer to do the drawing on the outer edge.
I instead use a small ruler size board drilling a shaft hole in one end and
a 1/16" hole on the other end where I want to make my mark. This is
much more accurate than a compass. It is a way to strike a circular
line. I use 3 holes to make circles about 1/8" apart going inward
so I have something to visualize. Its a homemade compass that rotates
right off the shaft. Then strike a line right on the edge (drill tiny holes)
where you THINK the circle is perfect. Boing boing it's always off a tiny.
You are welcome, my expertise (on a good day) is mechanical schemes
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3000rpm will be no trouble at all. Smooth a silk. The magnet holes are
not as critical due to the weight of each being so close to the next (I hope)
Unless it is out by 1/8" then I have been known to move the center hole
and shim
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https://etc.usf.edu/clipart/77300/77340/77340_circle_crve_md.gif
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