I’ve had great luck with a draftsman’s circle gauge, just a template
with circular cutouts just the size of your discs. The face of the
gauge may say something about “pencil allowance”. This means the
gauge’s hole is just a touch bigger for accuracy of the rendering of
the circle or arc needed. There needs to be marks at the 12, 3, 6,
and 9 o’clock, indicating the line of diameter both horizontally and
vertically.
Use some double-stick tape to hold the discs down, then lay the gauge
over the discs, using the diameter lines with a small metal
straightedge to make a cross at the center. Then punch and drill.
I might suggest that if you will have a lot of these discs to do
that you make a fixture for your drillpress.Take a piece of hard
wood and using a fostner bit of the appropriate size drill a hole
part way throught the board. Then with a small regular drill
complete the hole.Now again using the fostner bit center and clamp
the fixture to the drill press table. Insert the drill for the hole
you want to make. Put a few of your blanks in the hole in the
fixture and drill using slow steady but light pressure That should
get you pretty close to center.
Thank you to ALL of you. I received more than a dozen ideas for this
project and appreciate greatly all the wonderful ideas. Especially
Jesse Brennan, who emailed me first, allowed me to be able to go
right out and pick up a handy new tool right away. I found the Centre
Square to be a wonderful tool and being on sale at Busy Bee Tools for
$6.99, was also economical. This tool is quick and simple to use.
This will also make it easy to use for demonstrating.
Some of the holes need to be up to 1/8 of an inch in diameter I used
the centre square to find the hole and drilled the hole, then dapped
the discs into a half circle where I could then re-drill with a
larger bit. I do this as to pre-drill a 1/8 hole and then dapping
caused the hole to warp and then it was too much fiddling to get the
tubing to fit.
One way is to draw the cirle with your dividers...using your 90
degree square draw a square around the circumfirance of the
circle....from corner to corner draw your diagnal lines and where
it crosses in the middle is the middle of the square and yor
circle...was a trick we learnt in mathematics in high school!
Even easier than that is to draw the circle with the dividers, then
place the pointed leg somewhere on the circumference, draw an arc,
place the pointed leg on the place where the arc crosses the circle,
then do this again with the other intersection – the arcs will all
intersect at the center of the circle.
Of course, even simpler yet; the spot where you placed the pointed
leg to draw the circle, is the center.
But of course, this does not answer the original question, which has
the “circle” already drawn, so to speak.
I’ve only caught one or two replies of this thread, but what about
cutting a paper circle the same size and folding it twice in half to
get the center? Don’t mind me. Sometimes I don’t know what the heck
I’m talking about. This could be one of these times. :-}}