Back to Ganoksin | FAQ | Contact

Finding the centre of circle


#1

I am making some metal solderless beads and I need to drill holes
dead centre of circular disks in sizes 5/8, 7/8 and 1 inch diameter.
Does anyone have an idea for a way to find the dead centre every time
with out doing geometry each time and drawing intersecting lines for
each disk? I need to do 50 pieces at least for now with likely more
to follow.

Thanks in advance.

Karen Bahr
Karen’s Artworx
@Karen_Bahr
Calgary, Alberta, Canada


#2

Quick version might be as close as the nearest manufacturing tool
shop. Buy a set of transfer punches, and maybe a set of circle
templates, put the template over the disk and the transfer punch in
the circle. Tap, or hit, the punch with a hammer and there will be
an indentation in the disk where the hole should be. Try this with
some scrap metal or get some craft quality thin sheet metal at a
hobby store.

Good luck in the venture.
James Good


#3

Karen,

Oh serendipity! I was just now looking at a sale offered at
Micro-Mark and one of the gadgets on sale is a “center square”.
Betcha this tool is just what you need. Here’s where you can check it
out… www.micromark.com and search for item #82285A. LOVE this site
with all its oodles of neat little tools and I have a bunch of 'em.
Have fun :slight_smile:

Carol


#4

Make a jig for each size disc.

Have a top plate of steel (don’t use tool steel) with your desired
hole size. Solder a base metal sheet( a little thinner than your
stock) with the disc size cut out centered around the hole in steel.
To use…slip a disc in cutout, invert and press against a wood
block, drill thru hole in steel.

You would have to do the layout for each size but you’d only need to
do it once. A steel plate will give longer hole accuracy-life than
softer metals. Use base metal for cutout plate because its easy to
saw.

Layout can be done with dividers. Starrett makes a nice small
combination square. See page 184 In the Rio Grande tool book. This is
a worthwhile tool to have around.

One easy way to make this jig… make your round cutout for nice
tight but removable fit, a notch would be handy. Take a disc and
using the combo square find and drill center. Drill steel plate. put
steel and base metal plate together with a disc in place. Run a drill
rod through hole in both disc and steel, it will automatically line
up correctly. Solder plates together with drill rod in place. It
doesn’t have to be beautiful looking, its beauty is its ease of
manufacture and use. Do this carefully and you will be able to knock
out scores of identical, centered holes in no time.


#5

http://mathforum.org/library/drmath/view/61897.html

Andy Parker, Agate House Lapidary
Ulverston, Cumbria, England
www.agatehouse.co.uk


#6

Tim McCreight’s Complete Metalsmith has a circle divider in his book
you could (with permission?) copy and use for a template. It has a
series of concentric circles…mark before doming. There is also a
drafting tool with the same format you could probably get at an
office supply.

Good luck!
Mary


#7

I have a gizmo I bought from Micro-mark, http://www.micromark.com.
It is a center-finder-- item 82285A, currently on sale for $7+. A
bit steep, even at half price, but may be worth it for your project,
or maybe you can copy the idea.

Noel


#8

Here ae a couple of links for a “center finder”:

http://www.mikestools.com/800-2875-Center-Finder.aspx
http://www.amazon.com/Shop-Fox-H3093-Center-Finder/dp/B0000DD4KF
http://www.woodcraft.com/family.aspx?FamilyID=3046
http://www.rockler.com/product.cfm?Offerings_ID=688&TabSelect=Details


#9

Karen try www.micromark.com item #82285 and #82281. I use the 82285
myself. I think either will suit your needs. You might also check
out the square Item #10117.

Frank Goss


#10

How about applying the centre-of-gravity trick?

Pick up the disk, as close to its perimeter as possible, with
forceps whose tines have been bent at 90 deg to the shaft. The
imaginary vertical line descending from the point where the disk has
been picked up divides the disk in half. The trick is to mark that
line (how you do that I’ll leave that up to you). Next, repeat the
procedure but this time picking up the disk at one-quarter of the
length of its perimeter from the first pick-up point. The resulting
second imaginary line bisects the first thus marking the centre of
the disk.

david


#11

Very simple - use a center finder. I use one like this:

http://www.grizzly.com/products/h3093

on wax tubes. I also have a Starrett machinist’s one for more
precision. There are various types, but they all have a “V” to hold
the circle, and a straight edge across the center line for marking.
Just mark it, turn and mark it again - even three or four times, and
you don’t need to go all the way across the circle, of course, just
some lines in the center.

http://www.donivanandmaggiora.com


#12

I often do this: use the dividers to find center on one of each size
disc, drill a small hole, then use these discs as templates for the
remaining lot. Mark your holes and drill, or align a short stack of
discs to be drilled, and drill through the template disc and the
stack at once.

Matthew Crawford
www.MatthewDesigns.com


#13

If you have a machine shop supply near by, they may be able to
supply you with drill bushings of the appropriate sizes. You could
line the bushings up over the discs using a gently tightened hose
clamp. Hope this can help.

Daniel Culver


#14

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!

Hope that helps…

Raakhi


#15

Hi Karen,

Not sure if you have a center finder - it’s a small tool that lets
you accurately find the center of a circle. The down side is it does
involve making two (very) small intersecting lines. Then you center
punch, drill, and voila!

Alternately, you could make a template out of one of the circles,
and use it to locate your center hole over and over again…

Good Luck!

Chris
Chris Ploof Studio
www.chrisploof.com


#16

Karen,

Perhaps you could use a scrap piece of disc and use it as a
marking/drilling jig. That way you do all of the careful measuring
and drilling once and then just put the jig on top of the disc and
centerpunch where the hole should be drilled.

good luck,
James S. Cantrell CMBJ


#17

In a pinch, you can take your dividers and set them at just slightly
more than half the width of the circle (i.e., the radius.)

Put one point at the circumference and use the divider to scribe an
arc through the middle of the disc. Do this at a couple of more times
at other points on the circumference (the rim of the disc.)

the arcs will draw a shape around the center (a little triangle, if
you did three arcs) in the middle of which will be the center of the
circle.

Lee


#18

There is a tool called a Centre Square; like a jewellers square but
the handle is a 90 degree vee with the blade bisecting the vee. Push
the disc into the vee and the blade passes through the centre of the
disc; scribe a line, rotate the disc and scribe another line, and you
have the centre. You could make one that is small enough for jewelery
purposes. Picture here:

http://garrettwade.com/jump.jsp?itemType=PRODUCT&itemID=100722

Alastair


#19

If you are doing 50 pieces or more then it may be worthwhile to make
a custom centre square. Make a narrow blade that covers the centre of
the disc rather than being off to the side, and drill a small hole in
the blade at the centre of each diameter disc that you need to mark.
You can then mark with a dot through the appropriate hole; it would
be quicker and neater than scribing two intersecting lines.

Alastair


#20

Dear Karen,

Use a dividers set to half of the diameter of the disk and then
holding one prong of the dividers against the edge scratch a mark the
center of the disk with the other prong. Move the dividers to another
spot on the edge and repeat to make an “X.” You should easily be able
to make a small “X” at the center of each disk with this tool and
technique.

Nanz Aalund
Associate Editor / Art Jewelry magazine
21027 Crossroads Circle / Waukesha WI 53187-1612
262.796.8776 ext.228