This is a quick method to make a small tool which allows you to find the centers of circular shaped objects, such as disks or the ends of cylindrical objects. You place it on the edge of a round object so that the pins underneath rest against the sides of the object, then draw a line along the straight edge of the tool. Then just move the tool around and draw another line. Where the two lines intersect is where the center is.
I use this tool so that I know where to drill a center hole. I also use this tool to mark the center of round objects, then center the laser above this mark, then center my graphics around the laser pointer. This way if I make a round object on the laser cutter/engraver and decide later that I want to engrave the back, I can do so without having to make a jig (usually cardboard).
The beauty and strength of this project is that we can make use of the accuracy of the laser cutter. It's also the biggest weakness of this project, if you don't have access to a laser cutter. If you can get the straight edge straight and the holes drilled accurately in relation to the straight edge, you may be able to get by without a laser cutter.
Personally I like the tools that I make much better than the ones that are factory made, that you buy at the store, whenever possible. Some tools are beyond my capabilities and I'm willing to pay for good ones. However simple tools such as this, that I can make, I take pride in taking out and using every time.
This is a quick project and I was done in 40 minutes, but I made 6 of them.
A laser cutter/engraver
a bamboo skewer (darn useful things, I use them a lot!)
A hand drill
sandpaper (I used 220 grit)
a dremel with a cut-off wheel
a spare piece of thin wood ( I used a scrap piece of plywood which was .222" thick (5.6mm)
a thick piece of scrap wood (used for setting the pins/skewer pieces)
A hammer (or some form of pounding device, you can get creative with this one)
Step 1: Design Notes
Before I started on this project I did a quick google image search for center finder tools. I was used to the old-school one that looks like a right angle with a 45 degree edge coming out. Fortunately I found a better and much more elegant design that I like much better.
I pulled up Inkscape, which is a vector graphic editor like Adobe Illustrator or Corel Draw. Except it's free, runs on Linux, Windows, and Mac. It's smaller so it runs faster. I'm a professional graphic design artist and I prefer to use Inkscape for most projects. Only occasionally do I ever need to load up Illustrator.
I started by drawing a reference circle. I'm not going to use it, I'm just using it for alignment. Then I dragged a vertical guide and snapped it to the center of the circle. Then I drew two circles about 3.3mm.
These are for our pins which I've made out of bamboo skewers. I had previously measured my skewers and they turned out to be a shade under 4mm. I figured I would sand them down a bit so that they are smooth so then they'd be about 3.5 - 3.6 mm. Then they will fit tight into the holes and I won't need glue.
So then I centered the two pin hole circles horizontally about each other. I grouped them together next and vertically aligned them to the center of the reference circle. Then I just drew my shape around them. The most important part of the shape is the straight line.
I've provided an SVG file of my design in two sizes. You can use Inkscape (FREE) or any vector graphic editor to scale them to any size you might like. Just remember to resize the pin circle holes appropriately to the size of pin material you are using. Make sure to keep the centers of your re-sized pin hole circles the same as the original ones.
Step 2: Cut the Tool
Next I used my design to cut a few tools out on the laser cutter. I'm not going to detail how this is done because it's done differently on every laser cutter. If you know how to use your laser cutter, you know how to import vector graphics into them.
Step 3: Fabricate the Pins
I started out by putting the skewer into the chuck of the cordless hand drill. Then I used some sand-paper to sand the length of the skewer letting the drill do all the work.
Next I cut 2 equal sized pieces of the skewer with a dremel with a cut-off wheel. These will be our pins for the tool. I basically made them twice the thickness of the material I cut the tool out of on the laser cutter.
Then I put each pin back into the chuck of the hand drill and tappered one end of them with sandpaper so that it's easier to start them into the pin holes on the tool.
Step 4: Set the Pins
Next I took a thick piece of wood, placed the tool on top so that the holes are over the edge of the piece of wood. I set the pins in and hammered them flush to the top of the tool.
And we are done. Well you have to clean up your mess and put your tools away now. But now you have another new tool to put away!