Picture of Make a Center Finder
Make a precision center finder from scrap materials.

Recently egbertfitzwilly posted an Instructable on Finding the Center of a Circle. WirelessMonk posted a link to a machined steel center finder. Rimar mentioned making one. I decided to try making one that would be very precise.

Step 1: Materials

Picture of Materials
I had a steel bracket left over from something. I also had a piece of wood with good straight edges. In addition I used a little wood glue and a couple of short screws.

Hi Phil! I made this handy little tool last night to solve the conundrum of finding the exact center of a 1 1/4" iron cap that I need to drill a hole in to mount a toggle switch. The beauty of this thing is that it can handle circles that aren't flat on top and are dome-shaped, etc. I used a Kreg Jig and pocket screws to join the wood because I was too excited to use it to wait for glue to dry! Used a 12" Simpson strong tie strap for the straight edge part. Thanks for sharing your knowledge and for solving my problem!

Phil B (author)  cannonball17021 month ago
Thank you for trying it and for commenting,
ant0ny1 year ago
Great idea! Does not even matter what angle of the cut - 30, 40 or 47,358 degree! :) Still glued line will divide the angle in half.
Thank you!
Phil B (author)  ant0ny1 year ago
Exactly. And, making a diagonal slice across a straight piece automatically make the angle on the cut pieces equal.
ynze2 years ago
Very smart! I bumped into the problem of finding the center of round wood recently. I just noticed this I'ble (first picture), and.... Owwwwwww, of course, that's the way!


Phil B (author)  ynze2 years ago
Thank you for looking. I am glad it is helpful to you. It was fun to develop and I use mine more than I thought I would.
Wow. Weird that this landed in my comments, but glad it did lol. I could use such a thing :)
grbennet2 years ago
Thank you very much for this simple method.
Phil B (author)  grbennet2 years ago
I hope it helps you. Thank you for your comment.
Learndy6 years ago
Can we extend this mechanism somehow to find the center axis of a sphere, of a ball?

Application: Find a center axis of a table tennis ball to make it a cheap wheel for a small robot.
Airspace V - international hangar flying!
http://www.airspace-v.com/ggadgets for tools & toys
Phil B (author)  Learndy6 years ago
Here is an idea for finding the center of a sphere, like a table tennis ball. For the sake of illustration, your table tennis ball is red in color. Cut a collar of PVC that is just a little smaller in diameter than the table tennis ball. The PVC collar is shown in cutaway and is gray in color. Cut it to length so the top of the ball is roughly even with the top of the ball when the collar is resting on the ball. Use the center finder to mark the center from a couple of directions. You will need to turn the table tennis ball over to mark the extension of the axis. Do that by making a circle on a piece of paper, the diameter of which is the same as the PVC collar. Mark the center of the circle. Align the center you marked on the ball with the dot on the paper. Support the ball from several sides so the center do on the ball remains squarely on the center dot marked on the paper. Place the PVC collar on top of the ball so it is level. Without moving anything, use the center finder to locate the extension of the axis.
Col_uk Phil B2 years ago
Hi Phil
Thanks for the instructable, it came in very useful.
For a sphere, i found it easier to make a center finder the same depth as the ball diameter and put steel on both ends. That allows you to mark both poles at the same time.

best regards
Phil B (author)  Col_uk2 years ago
Very clever. Thanks for your reply.
Phil B (author)  Phil B6 years ago
Oops! "Cut it to length so the top of the ball is roughly even with the top of the ball when the collar is resting on the ball." should read, "Cut it to length so the top of the collar is roughly even with the top of the ball when the collar is resting on the ball."
Use the center finder to draw a first "equator" line. Turn the ball and use the center finder to draw a "meridian" line.
The two intersections (the "poles") give you the axe for an axle.
streetrod53 years ago
Phil, this is something I've needed for years, but didn't know it existed! I've been "finding" centers by... well, not the most accurate way. Thank you!
Phil B (author)  streetrod53 years ago
Thank you for looking and for your comment. I am glad to have solved a problem for you.
bettertimes4 years ago
If you would enjoy reading "The Boy Mechanic: Volume 1 by Popular Mechanics Co. " here is the down load link
this is a copy from the Deridder, Louisiana Library. enjoy
Phil B (author)  bettertimes3 years ago
I did download it and have looked at some of it. When I was growing up our public library had a couple of books by Alfred P. Morgan. One was on electricity. One was on all sorts of mechanical devices. I remember a small steam engine with bell cranks to operate sliding valves. The projects were marvelous, but always required tools and materials I did not have available. Thanks.
DoDo7294 years ago
Wow, so simple but works incredible. Solved one of my problems. Thanks for your post. Love this site.
Phil B (author)  DoDo7294 years ago
I am very pleased you found it and can use it. Instructables is a great place to share useful things. Thank you for looking.
nmh0105 Phil B3 years ago
Simple but yet great use... i could not follow you please help
Phil B (author)  nmh01053 years ago
Can you say what exactly you did not understand?
Creativeman4 years ago
I just found this, will definitely make one! Will post picture when done. Thanks for the idea/concept.
Phil B (author)  Creativeman4 years ago
Thank you. You may even find a way to improve on it.
wmarin Phil B4 years ago
You are still my hero !. Thanks
Phil B (author)  wmarin4 years ago
Thank you.
pgcagdol4 years ago
thanks great idea and just when i needed it
Phil B (author)  pgcagdol4 years ago
Thank you. I try to post useful things.
nice job..thanks..
Phil B (author)  zulhanifarifin4 years ago
Thanks. I hope it is useful to you.
Chadworkz5 years ago
You know, it's always the simplest things that are the best, and this just proved that point...excellent job, Phil! ;)
Phil B (author)  Chadworkz5 years ago
Thank you.  Unfortunately, it usually takes me a few attempts before I come to a really simple version of an idea.
una mente creativa ... Lo seplice muove il mondo benfatto!!!
Phil B (author)  roberto sirigu5 years ago
Grazie mille!
ignilc5 years ago

The angle doesn't need to be 45 degrees. It can be anything. As long as the angles on both pieces of wood are the same it will work well.

Phil B (author)  ignilc5 years ago
You are quite correct.  Thank you for your comment and thank you for looking at this.
This is very helpful :) thanks
Phil B (author)  mcanderson766 years ago
This is one of those things that makes me think, why didn't I thinkof that?! A straight forward solution to an annoying problem. Nice guide.
Phil B (author)  manuelle_override6 years ago
Thank you. I see you joined Instructables less than a week ago. Welcome. How did you happen to find my center finder already? Speaking of simple solutions to annoying problems, you might be interested in a recent Instructable I did. Search for Garmin Vehicle Power Cable. Even if you do not have a Garmin with a 12 VDC power cable, you might be able to use the basic idea on something else.
5* Now I just need to summon the energy to get back to my projects...:)
Phil B (author)  DuctTapeRules!6 years ago
Thanks. When it comes to projects, life has a way of forcing you back into them when something breaks and must be fixed immediately. Then you notice how good it felt to do a project and you are on your way.
sharlston6 years ago
love it definetly 5 stars
Phil B (author)  sharlston6 years ago
u replyed at 4 in the morning and your welcome
Phil B (author)  sharlston6 years ago
It was 4 AM in the UK, but seven hours earlier in our part of the USA, which is Idaho, and that is only about 400 miles from the Pacific Ocean.
oh i forgot about that sorry for the missunderstanding
ll.136 years ago
I'm impressed with the simplicity and usefulness! +1
Phil B (author)  ll.136 years ago
Thank you. In regard to proportion, the number of positive responses from people residing in the UK is disproportionately high. As I thought about this project, it was clear to me the angle on each half would have to be exactly the same. That was solved very simply by making one angle cut to make two pieces with an identical angle and gluing two halves together rather than trying to cut a "V" angle out of the end of a piece and then try to find the bisecting line. Gluing the two halves together also allowed taking advantage of the way the glue line is already on a line bisecting the composite angle exactly. Not many things work out that serendipituously.
are u in the uk i am the uk rocks
Phil B (author)  sharlston6 years ago
As noted II.13 is in the UK. I am in the USA.
ll.13 sharlston6 years ago
if that comment was at me, yes I'm currently in the UK. :)
yeagerxp6 years ago
EXCELLENT!!!!!, and you can even use wider pieces of wood for bigger round items
Phil B (author)  yeagerxp6 years ago
Thank you. One of the great things about Instructables is that readers are free to adapt ideas. You certainly could use a wider piece of wood for a tool that finds the center on a larger round item. You could even taper the assembly toward the end to make a more manageable handle.
dewmi6 years ago
thanks for share, i have been searching this. i will make one too......
balno6 years ago
Very clever !!!
NachoMahma6 years ago
. Excellent.
Phil B (author)  NachoMahma6 years ago
Thank you. I hope it is useful to a few folks.
stamatis Phil B6 years ago
Bravo Phil! Simply excellent!
Phil B (author)  stamatis6 years ago
Thank you.
mickcaulton6 years ago
Brilliantly simple design and idea. I have spent alot of time in a workshop, both wood shop and an engineering shop, and this would have found a use on numerous occasions. The only negative thing I can come up with is why on earth had i not thought of making one of these for myself. I have always prided myself on the fact that i am able to find a need for and build simple tools and equipment to make my life easier. Again very good idea, good simple construction and excellent Instructable.
Phil B (author)  mickcaulton6 years ago
Thanks. While this was a new project to me, I have enjoyed making Instructables from many projects I did in past years, even past decades. I hope you will show us some of your ideas from past projects as Instructables.
Hello again Mr. Phil B, Thank you again for your response to my comment on your posting, ( The center finder ). In reply to your comments i certainly do hope to get some of my projects made into Instructables. Unfortunately all of the projects which i think are the best and of most interest to others, along with being informative, have long been built and put to use. So for me to make a good Instructable, with good visual content, it entails me either taking one of my ideas and either stripping it down or building a new item from scratch. I personally feel the second option would be better as i can then include more visual information on the build process. If i decide to just take apart an old project the photos for the build would only really show assembly as all the parts would have already been fabricated if you see what i mean. I wish i had found this site along time ago, but be as may. Anyway i hope to put a decent Instructable on before long as i have done my first short testable just to get a feel posting of the process. All i need to do now is build a time machine to slow down time a bit so i can get more done.
Phil B (author)  mickcaulton6 years ago
You may be able to post some of your past projects without either making a new copy or dismantling one. I have posted some Instructables I did not dismantle and could not repeat. I used graphics I generated with a CAD program or with Google Sketch Up, sometimes tweaking a few things in MS Paint as part of the process. See my Instructable on "Rescue for a Weed Whacker" as an example. Sometimes you can just move the camera in close for a detail photo of different sections of a project you finished a long time ago. See my Instructable "Make a Carbon Arc Torch for Your 220 Volt Stick Welder."
rimar20006 years ago
Thanks, Phil!!
Phil B (author)  rimar20006 years ago
If you make one, let me know how it works for you. Thank you.
lemonie6 years ago
The best centre finder I used was essentially a T, which had two round pegs on the short length. One edge of the long length was central. L
Phil B (author)  lemonie6 years ago
That would certainly work. The range of circular objects on which a "T" could be used would have to be, at minimum, larger in diameter than the distance between the pegs.
jeff-o6 years ago
Aha! I've had to mark the center of a dowel a number of times and always wondered if there was a simple tool to help. Thanks!
Phil B (author)  jeff-o6 years ago
I certainly did not invent this tool. I only found a simple way to make a good one from ordinary items. If you have no suitable piece of steel, you could go to the hardware store and get a long mending plate.
jeff-o Phil B6 years ago
Oh, I realize that. But, a big thanks for posting this. I will definitely make one.
Shut Up Now6 years ago
very smart use of suplies. so simple too.
Phil B (author)  Shut Up Now6 years ago
Thanks. The materials truly were leftovers and junk.
mrmath6 years ago
Nice work. I especially like the way you put the steel under one piece of wood to create a raised edge to rest the steel against at a later time.
keng mrmath6 years ago
here here!!!!
Phil B (author)  mrmath6 years ago
Thanks. I thought about that for a while. The really good, really simple ideas take a while before they surface.
keng6 years ago
fantastic! this is totally going to save me like $20 to order one!!!
Phil B (author)  keng6 years ago
Thanks. I am glad you can use it. I have gotten through quite a few years without one. There were times when one would have been helpful though. Let us know how it works out for you.
chaosrob6 years ago
Phil B (author)  chaosrob6 years ago
Thanks. It is simple and it works. If made in the same way I demonstrated, it is practically guaranteed to be accurate.
AndyGadget6 years ago
I'll have made one of these before tonight!
Phil B (author)  AndyGadget6 years ago
Thanks. I hope you get a lot of use and enjoyment from it. Waiting for the glue to dry took more time than any other part of the project.