Ruler Compass




1 Teacher Note

About: I make and create anything that comes to my mind from skateboard hooks to garden rooms. And I footle around with electronics and instruments at night....and I have a passion for reducing waste packaging by m...

A ruler is built to draw straight lines....but what if you want to draw circles!

Every workshop needs one of these Ruler Compass's....

1 Teacher Note

Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.

Step 1: Supplies + Tools


Metal ruler of choice...for info. the ruler I used was a 300mm ruler with some additional space to the end total length of 335mm and a width of 25mm

A ball race bearing, diameter small enough to fit within the width of the ruler...I used a 22mm diameter bearing for this project


Metal punch

Drill bit 1mm

Drill press or cordless drill

Large hole cutter to slightly less than bearing diameter...a stepped cutter works well

Metal file

Cutting fluid

Rotary tool with sanding bobbins

Propane blow torch

Adhesive backed vinyl

Spray mount glue

Spray can colour of choice

Computer + printer to print out the PDF template

Optional... Router and old woodworking router bit

Step 2: The Idea

The idea for this project is really simple...

...attach a bearing in a metal ruler that acts as the centre of a circle...

...drill hundreds of 1mm spaced holes along the ruler length... a finger on the middle of the bearing...use a sharp pencil in the desired hole and spin around the bearing...

...draw circles!

The compass I made will draw circles from 15mm radius to 317mm which gives a whopping 620mm diameter circle capacity...the smaller sizes are trickier with a long ruler, though I also have made a smaller 150mm ruler compass that works well for the smaller sized circles...

...and it is still a ruler for measuring and drawing straight lines.

The idea was sparked by an advert on Instagram with a small machined metal bar and a bearing to draw circles...I felt it wasn't long enough and the increments were every 5mm...I wanted every millimetre.

Step 3: Work Out the Holes

I have made your job easy by doing this part for you!...down load the PDF to print out your own template.

The template is millimetre accurate with the centre being from the centre of the bearing hole...

...1mm concentric circles projected from this centre point and the location for the holes were set to one side of the my case to cover the inches side which I do not use here in the UK

The positions of the holes vary as you progress along the ruler due to the proximity to the centre point and position across the ruler...just be glad that you don't have to undertake this task!

A point to note-

I made this ruler compass by hand, punching and drilling the holes with hand tools.

With as much care as can be taken it is difficult to get it pin point accurate, some of my holes are out a little, maybe a half millimetre discrepancy which I feel is acceptable for a workshop compass.

Total accuracy would be achievable if you have access to a CNC machine.

Note of PDF Template

I have re-uploaded the template PDF file with a 100mm marking on the template.

When printing make sure it is printed A4 at 100%.

When printed make sure the 100mm marking measures 100mm!

If it does not, check your printer settings, things like 'checking' borderless printing can throw out the print scale.

Step 4: Template

Cut out the template...

...attach to the rear of the ruler with some spray glue...

...the rear of the ruler is best so that any indented measurement markings don't interfere with the punched marks.

Step 5: Punch

To enable the drill bit to locate at the correct position...

...punch each and every hole marking...

...this will take some time as there are around three hundred holes to punch...

...time and care taken here will result in accurate hole placement.

The thin metal ruler will deform a little as you punch the holes...gently bend the ruler back flat.

Step 6: Drill

I used a 1mm drill bit in a pillar drill...this gives a large enough hole for a sharp pencil and small enough to give space between the holes.

Drill 300 holes!

Remove the paper template and use a metal file to remove any metal burrs.

Step 7: Remove the Inches!


I wanted to have a clean area on the top of the ruler on the side of the holes...

...this would allow the holes to be more visible and to allow measurement markings to be applied...

...and to make the ruler a little thinner for the ease of using the pencil through the holes.

The compass will still work if you do not do this step.

Router out the ruler shape in a piece of wood to the depth of the ruler...

...apply double sided tape in the groove and stick the ruler in nice and secure.

Apply some cutting fluid to the top of the ruler.

I used an old wood working router bit that was being thrown out as it was no longer sharp enough for woodworking.

Set into a router and use a fence to set the cutter to cut half way across the ruler.

Set to skim off the smallest amount from the ruler, just enough to remove the indent markings.

Please WEAR PROTECTION EQUIPMENT, small shards of metal will be cut off...eye protection is a must.

Carefully router off the metal.

Step 8: Bearing

You will need to drill a hole smaller than the bearing diameter at the end of the ruler...

...I found a stepped cutter worked well for this cutting a 20mm hole...

...carefully increase the size of the hole towards the 22mm diameter of the bearing with a multi tool and a sanding bobbin... want a hole that is fractionally smaller than the bearing...take your time DO NOT GO LARGER

Step 9: Expand the Metal

This is where the magic happens!

Use a blow torch to heat up the end of the ruler with the hole for the wont take long to heat...

...the metal will expand a little...

...slot over the bearing...

...make sure a little of the bearing protrudes below the ruler...

...let it cool...

...a super clean tight fit

Step 10: Measurments

I decided to have measurement markings every 25mm up the compass holes to make finding the correct position easier...

You could easily write these on with a Sharpie...

...or if you have a steady cutting hand or a vinyl cutter...cut out some vinyl stencils...

...stick them on at the correct positions along the ruler...

...mask up the remaining spaces...

...and spray with your choice of colour...

...carefully remove the stencils and leave to dry.

Step 11: Options

Draw circles with a ruler!

I can't tell you how useful this tool is in the are just going to have make one for yourself and find out.

If you don't fancy working with metal why not make it with a plastic ruler...

...I made my prototype with a smaller 150mm plastic ruler and hot glued in a great for the smaller circles...

You don't even need a ruler, just use a thin strip or metal, plastic or even very thin ply.

TOP TIP- Need more accuracy for the centre point...cut out a circle of thin plastic film and draw or score cross hairs through the middle...super glue to the bottom of the bearing

Step 12: Draw a Circle With a Ruler!

So easy to use...

Place the bearing on the centre point of the circle... a finger on the centre of the bearing [inner ring]... the hole for the circle radius...

...use a nice sharp pencil in the hole and spin around the bearing while keeping pressure down on the bearing with your finger...

...and draw a circle!

...and oh yes it still works as a ruler and straight edge!

Thank you so much for making it to the end.

I so hope that you will make one for yourself...if you do please post a picture in the comments, I would love to see it.

If you liked this project I would be stoked if you voted for it in the Made With Math Competition...

...and remember...Rulers have never been so exciting!!

Made with Math Contest

Finalist in the
Made with Math Contest

1 Person Made This Project!


  • Instrument Contest

    Instrument Contest
  • Make it Glow Contest

    Make it Glow Contest
  • STEM Contest

    STEM Contest

18 Discussions


14 hours ago

What a patience to drill so many holes...Insane video by the way ! i love this type of humor

3 replies

Reply 13 hours ago

Fingers crossed for your Harmonic Analyser...kind of blown my mind trying to work it out 👏👏👏


Reply 10 hours ago

i'm still scared of heavy machinery such as drills or i keep making fragile things, but paying attention to not breaking it by using little springs or tiny counterweights is getting tough, but metal would be much easier for details like that


Reply 13 hours ago

Thanks Jack...sure about three hundred holes though didn’t take so long in reality...considering I now have a really useful workshop tool that will work I hope for the rest of my working life...not that much investment of time really...
This was the first of my Stupid Quick Make videos...glad it worked for you, I have had a good response to the format...there will be more!
Big thanks


Thank you so much Matti...this is a new format that I am trying out and it is great to hear that it worked for you...there will be more on the way...big thanks


24 days ago on Step 12

What is the bearing for? Why not just drill a hole in the ruler at the 0 point, and drill holes in the ruler? That way you can use a pen or pencil through the hole to rotate the ruler on. That would make it much easier to hold the ruler at the center of the circle. Yours is a bit Rube Goldish don't you think?

3 replies

Reply 24 days ago

A pencil holding the zero point can & will slide around on a hard surface. I mostly work in wood so I would use a thumbtack but for plastic or metal or a surface you do not want to mark-up, the bearing is the hot ticket. I would not call it Rube GoldBERG-ish at all. It has exactly 1 moving part.


Reply 24 days ago

Sure that is also a great way to draw a circle, I have done similar over the years, if you don’t have a bearing this would be a good solution.


27 days ago

OMG> You are the most patient man on the whole internet... I'm gonna hand it to you, dude.. any man who can stand there and hand-drill 12,000 holes in a 300mm ruler is a man who has found inner peace like no one since Buddha! The fact you shrink-fit it onto a 608-ZZ ball bearing was literally mind-boggling. If I EVER need an angle-finder like this, I'll do the lazy-bastard thing and buy one for $1.99, but it will never be as cool as this one! You're right, RULERS HAVE NEVER BEEN SO EXCITING!

3 replies

Reply 25 days ago

Hey Jay...big thanks...only 300 holes need to be drilled, it didn’t actually take too much time.
The great thing with this compass is the large circles it can draw. I am thinking to make a longer one on a 600mm ruler for circles to the full width of a sheet of ply.
I would only drill the holes to the further half as the small circles are harder to draw with the long ruler.


Reply 24 days ago

If you want to draw bigger circles a trammel is the tool to use, it doesn't require drilling hundreds of holes. It is simply a bar with a sharp point at one end and an adjustable pencil holder. ( see image )


24 days ago

I don't have the equipment to make one myself but if you're ever selling them, sign me up! Really cool tool. Great job.

1 reply

Reply 24 days ago

Hey Kathy...not thinking of selling at the moment, though if I do I will let you know...why not consider making one with a plastic ruler, would be more straight forward with less tools.
Big thanks