Introduction: Homemade Center Finder Tool, Quick, Cheap, Easy.

Picture of Homemade Center Finder Tool, Quick, Cheap, Easy.

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

Picture of 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

Picture of 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

Picture of 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

Picture of 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!


maxxsinner made it! (author)2016-04-14

My CNC router made short work of this and had some copper pins left over from another job. Thanks for posting!

jslaton (author)2014-06-01

Very nice! I have been needing a way to transfer the center of holes in a wing rib form to other forms and aluminum sheet. Thanks for posting.

crazypj (author)2014-05-28

I like the style of them but as I don't have access to a laser cutter I'll never get around to making them

rexel99 (author)2014-05-26

Alternate method for finding the centre of a circle (also works for flat circles without edges that this tool will not sit against)...

Go to dads shed and get a Square or a drafting t-square and a ruler.

Draw a line across one side of the circle, find the centre/mid point of that line using a ruler. Use the square to make a perpendicular line (right angles) to the first line crossing this measured mid-point and then also measure and find the centre of this second line. Bingo, that is the centre of the circle.

You do not need a 3D printed, laser cut, purpose built tool.

DrPeper (author)rexel992014-05-26

Right, I just got tired of doing that so I built this tool to speed things up and make it easier. Laziness is the mistress of innovation.

DrPeper (author)DrPeper2014-05-28

Let me amend my earlier theorem...

Laziness is the MUSE of innovation.

And you can quote me on that one.

aledford3 (author)2014-05-27

I love this simple but brilliant idea.

DrPeper (author)aledford32014-05-28

Thank you! I can not take credit for the concept (as it is well documented), all I can take (limited) credit for is the interpretation. It is my hope that everyone with access to a laser cutter/engraver makes 4 of these and gives them out to the makers that they know.

Phil B (author)2014-05-27

I did this Instructable on making a center finder back in April 2009. No laser cutter or layout is required.

DrPeper (author)Phil B2014-05-27

I actually checked out your instructable before I started this project, when doing my research. Nice work BTW! I was looking for something smaller and incorporate a design elegance to it. I also wanted it to fit in the front pocket of my project backpack.

Phil B (author)DrPeper2014-05-27

Thank you for looking and for replying.

DrPeper (author)Phil B2014-05-28

Oh nonsense, you were part of my inspiration for this project, I should be thanking you! And I am! In the comments for your project, someone pointed out that the angle is irrelevant and that point is what made me abstract your project just a touch. Then when I did a google image search I "grokked" the results better.

snoopindaweb (author)Phil B2014-05-27

~ : - }

nonobadog (author)2014-05-27

Accuracy of the straight part is very critical with this. And so is your technique when making the straight lines that cross. If the line is off even a little you can still make another line that crosses it with this tool. It just won't be in the center of the circle which is then pointless.

It is probably a good idea to test the accuracy of these tools you make by making three or four lines in the circle and see if they all intersect at the same point.

DrPeper (author)nonobadog2014-05-28

Yes, I actually made 4 lines and they all crossed at the same point. Which, I'm thinking, makes the tool fairly accurate. I actually showed that three lines cross in the pictures for the project. I didn't think that showing the 4th line crossing really would really add to the efficacy of the project. Have you made one of these tools yet??!

✿ Ian ☯ made it! (author)2014-05-26

You can also do this with just a ruler and a drawing compass, too. Basically, just make two dots anywhere on a piece of wood (or paper if you're making a template), and then use your compass to make two arcs (with a congruent radius) from each circle so that there are two bisecting points between the two points. Draw a line through the new points to form the straight edge of your center finder tool, and then do whatever you want for the body of the thing. I did it this way and it turned out pretty nicely! I stained the wood and used 1/4" copper tubing for the pegs so that you can sorta look through them to use the tool on 2D circles. I cut the thing with a handsaw.

DrPeper (author)✿ Ian ☯2014-05-27


callmetinaja (author)2014-05-27

Excellent design. Never knew about Inkscape. Thanks!

DrPeper (author)callmetinaja2014-05-27

One of my many titles is as a graphic design artist. I learned the Adobe suite first but then decided to try the open source equivalents. I found Inkscape to be slightly easier to learn, and a very competent replacement for Illustrator for almost all of my vector graphic editing needs. I do most of my work in Inkscape now, and rarely do I need to drop into Illustrator to finish a project. For the casual home user Inkscape has everything you need. It's free, it runs on Linux, Windows, and Mac. It can be installed to a thumb drive and run directly from there so you don't have to install it on anyone's computer. Oh and there are TONS of instructional videos on YouTube

padeutsche (author)2014-05-26

Using an old machinist method called lay out work, you make some
impressive tools with minimum expense, but huge payback, in the savings
of building a huge collection of tools you never could guess what could
be made by a few simple hand tools, a drill press is about the only power tool you will
need, but these can be picked up used for a decent price if you look
around, I got a bench top one for free because it needed a new power
cord. But you can also make a hand powered drill as well:

The accuracy is even better at times then using a powered version, get a good reamer set is the secret.

Nicest thing on using hand powered tools is that if you live in an apartment, your neighbors will never know that you are doing this kind of work at all, because it is so quiet, and very therapeutic, and you just need a simple bench to work at.
It is great to have tools to do anything you need to do fix and build projects, but it is better when you make the tools yourself. Over a few years time you will have most tools you will ever need in your life.

Hanzo (author)padeutsche2014-05-27

That group seems invite only. Any links that are open?

DrPeper (author)padeutsche2014-05-26

Oh that hand powered drill press is AWESOME! Thank you so much. Gonna have to put that on my list of things to make!

makerblogAT (author)2014-05-26

Based on your outline I made an STL file for 3D printing:

DrPeper (author)makerblogAT2014-05-26

That is AWESOME! Thank you for your work and for sharing! I feel a bit silly for not thinking of doing that.

rupin.chheda (author)2014-05-25

the kerf of the laser dot can actually offset the center line, which is a primary accurateness required for this tool. unfortunately, this offset is not linear for lines and holes. The kerf on my laser cutter is roughly 0.4mm. this will shift the center line 0.4mm to the left or right, but not the centers of the circles. the circle will come out to be 0.4mm wider in radius.

DrPeper (author)rupin.chheda2014-05-26

I found that the kerf offset (of the straight edge) the width of the pen I used for marking quite nicely. The holes came out perfect for a great compression fit for the bamboo skewers I used. We have a Universal Laser so I might be a bit spoiled by having a top notch laser system.

antagonizer (author)2014-05-26

I think you should start a kickstarter campaign. Fantastic addition to any toolkit.

bitbase (author)2014-05-25

I made one of these out of mild steel in a hand fitting class at college, mind you I made mines the old fashioned way with a scribe, handsaw and a file and of course a drill

DrPeper (author)bitbase2014-05-25

Awesome, can you post an image? I'd love to see it/them.

dbuckley6 (author)2014-05-10

really good. I wonder if it would be possible to post a drawing ( word doc, PDF) than us without a laser cutter might have a go at pasting it onto some ply and trying it with a scroll saw?

DrPeper (author)dbuckley62014-05-10

Hmmm. Interesting. An SVG file is a standard for vector graphics, you can even load it in most modern browsers and print from there. Word and PDF documents are proprietary formats so I tend to steer clear from them. Especially Word documents. I tend to steer clear of PDF's (but I do use them) because it's such a popular format for hackers to inject malicious packages into. Inkscape is free, open source, and runs on Windows, Mac, and Linux. It's a really good tool for the job, and it's super easy to learn.

I mention it because I view a laser cutter as a much easier way to do the same thing as most of the things that you can do on a scroll saw. I use vector graphics to make all my patterns that I use on the scroll saw.

A Word document wouldn't make much sense to me because it's not meant for vector graphics. I use vector graphics because they can be easily re-sized with no loss in resolution either up or down.

A PDF document, however is a hybrid format. Meaning that it can contain raster (image files like .bmp, .jpg, png, .gif, etc.) and vector graphics. And using Inkscape to convert an SVG to a PDF is *SUPER* easy. Simply load the SVG file in Inkscape and "Save As" and then choose a PDF as the intended output format. I have done so and will post it with the other downloads now.

DrPeper (author)DrPeper2014-05-10

Oh, well let me amend my earlier comment. Apparently Adobe released the PDF format to ISO, so it's a *mostly* free format now, and has been since 2008. Adobe still retains some of the technology so it looks like parts of it are still proprietary.

captainchaoss (author)2014-05-02

I love it. hopefully making a few this weekend - one for myself, and a few to share !

DrPeper (author)captainchaoss2014-05-04

Awesome! Share away!

mrandle (author)2014-05-02

This is super handy! I imagine it can be scaled up/ down quite easily if needed.

DrPeper (author)mrandle2014-05-04

Oh yeah, it should scale great. That is one of the reasons why I provided a vector file of the design (svg). The only thing you have to keep in mind when scaling it is that you have to change the size of the pin holes for whatever you are going to be using for pins. And make sure you keep the center point for the circle the same.

darrenhall (author)2014-05-03

Nice - I too like to make my own tools when ever possible.

Good job.

DrPeper (author)darrenhall2014-05-04

Thank you!

Poacher01 (author)2014-05-02

Simple but very elegant. Nicely done - thank you

I haven't seen one of this type since I was ... knee high to a Sparrow.

DrPeper (author)Poacher012014-05-02

You are welcome! Thank you for looking and commenting! I hope the people browsing here make use of this quick and easy to make tool.

About This Instructable




Bio: Just your typical Evil Mad Scientist, constantly thinking of new inventions to subjugate the world with! I'm big on hydroponics, electronics, and small portable ... More »
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