Find center of circle

[dano9700]

I mainly engrave jewelry, so one problem I've repeatedly run into is finding a way to get my engraving perfectly centered in a circular area. Alot of engravable charms and pendants are round and roughly coin-sized, so even a small deviation from the center is very noticable.
My question: does anyone know a good way to pinpoint the center of a circle? I usually end up taking 15 minutes adjusting and estimating and still sometimes the engraving looks off center.

[christinandavid]

If you could get an appropriate sized three-jaw chuck mounted to the machine you could find the centre using a blank disc. As long as you have a way to mount this chuck in the same position each time, you will have a definite machine co-ordinate for the centreline, regardless of the job size.

DP

[Torsten]

Originally Posted by dano9700 I mainly engrave jewelry, so one problem I've repeatedly run into is finding a way to get my engraving perfectly centered in a circular area. Alot of engravable charms and pendants are round and roughly coin-sized, so even a small deviation from the center is very noticable. My question: does anyone know a good way to pinpoint the center of a circle? I usually end up taking 15 minutes adjusting and estimating and still sometimes the engraving looks off center.

If you have some visual edges to pick up you could Draw them right into your Cad file.
Then use a Wiggler as your first Tool and have the Program position it at the quadrant points of your shape, like stop at the top center then bottom center then Left and right respectively.
Each stop would give you a chance to make small corrections to your offsets.
A visual check with a wiggler can get you to better then .005" if done carefully.

[chich2]

Mach 3 has an awesome circle center finder in it's wizzard tools. You touch your tool or touch probe on a point on the circle, "press point A" jog the machine to another point on the circle "press point B" then jog the machine to a third point on the circle "press point C" then you have 3 stored points around the circle. "Press Go to circle center" and the software triangulates the center of the circle center and jogs the machine to that exact piont. Then if you want you can even Zero all your axis and make that your reference point.

I use this method all the time. I cant remember the last time I have used a dial indicator or finger dial to find the center of a circle.

Hope this helps,
Chich