Ruler to Caliper (0.1mm Resolution!) - 3D Printed (Left Handed Version Included!)

I recently ordered a digital caliper from China. Spent 20$ on it, and it's completely worthless - totally unreliable. After I was done mourning over my 20$, I decided to make my own. For those of you who are unfamiliar with what a caliper is, it's a tool that is most often used to measure out/inner diameters of objects, and there are more than a few instructables on how to use them.

I figured that if I base my caliper on a ruler, which is super cheap and 100% reliable, I could end up with a very reliable caliper. Also, by using adding a Vernier scale I could reach a resolution of 0.1mm. Plus, I figured that if I made a CAD model I could make a left-handed version too! You guys are always forgotten, but not anymore!

In this instructable I'll show you how to turn a ruler into a caliper. I used my 3D printer to make it, but if people are interested I might make one out of stuff everyone can find. If you're new to 3D printing, this is a great first project for you! The prints are fairly simple and you'll end up having a caliper, which is often used when you want to design your own models.

Let me just add that making a reliable caliper was my #1 priority, so while making the tool I'll also show you how to overcome the accuracy limitations posed by your 3D & regular printers too, which will allow you to achieve good results. It's also possible to make a caliper without attaching an actual ruler, but I figure an actual ruler would be more robust & reliable (see the step about attaching a ruler to the caliper for details).

Hope you find this instructable useful!

Highlights:

Turn a ruler (1mm resolution) into a caliper (with 0.1mm resolution).

Right-hand / left-handed versions available.

STL's, Tinkercad & more - all included here.

Super cheap print (~30grams of PLA) + super cheap ruler = high accuracy.

Simple design - very reproducible!

Supplies

You'll need a cheap metal ruler, instant glue, access to a 3D printer & and to an ordinary printer.

Step 1: 3D Print - Full Version (Measures Inner & Outer Diameters)

First, you'll need to 3D print the base of the caliper, to which you'll later mount a ruler. You'll also need to print the part that slides across it.

I've included the STL files and a link to a Tinkercad page which you can use (other formats are available by request).

The parts are suited for a ~170x20mm ruler and about 0.5mm thick. For other rulers you'll need to make slight modifications so that the ruler has room within the base. It's possible to do that in Tinkercad - all you need to do is stretch\shrink the model so that it fits your ruler. I can help with that if necessary - comment below.

Note that you want the moving part of the caliper to slide back & forth, but you don't want it too tight so it's too hard to move it (see GIF in the next step for what it should be like). The attached design should capture that, but it might depend on the printer / material you're using, so again you might have to make tiny modifications on my design.

Step 2: 3D Print - Simple Version (Measures Outer Diameter Only)

I figured some people might want a simpler version, without the part that measures inner diameters, so I've attached a version without that part. The benefit of making this type of a caliper is that is has no sharp edges, so it's more suitable for kids.

Step 3: Glue a Ruler

3D printed items are great, and if you calibrate your printer they can be pretty accurate too. Still, a ruler is more reliable & durable, and so instead 3D printing a scale on my caliper I decided that it's best to just attach a real one.

To do that, apply instant-glue (or other strong adhesive) to the caliper's ruler-slot (see image) and glue the ruler to it. Make sure it's parallel to the caliper's long axis.

** If you don't want to use an actual ruler, you can print one using an ordinary printer, but you'll need to calibrate your prints first (see the section about adding a Vernier scale). It's a good solution, but if you can, I think using an actual ruler would be better.

Step 4: Add a Vernier Scale (To Achieve 0.1mm Resolution!)

To reach resolution of higher than 1mm (the scale on ordinary rulers), we need to add a way to read in between two ticks. To do that, we will use a Vernier scale.
I won't go into detail about how Vernier interpolation works, but the working principal is that we align a 2nd ruler next to the main one, who's scale is a tiny bit different than the original scale (for example, ticks on the Vernier scale could be 0.9mm apart, instead of 1mm). The fact that the Vernier scale makes a fraction of the main scale means that only one of the ticks on the Vernier scale will align with the ticks on the main scale for each distance, allowing you to reach resolutions better than 1mm. Usually, mechanical calipers reach 0.1mm, which is what we'll reach here. In my case, I used a Vernier scale which has 10 ticks with a diatance of 3.9mm between each one, instead of 4. This brings our measurements to a resolution of 0.1mm with uncertainty of ~1/40mm (it's actually lower).

We're going to print out a Vernier scale. To do that, we need to make sure that our Vernier scale is accurate! That is - it's dimensions are exactly what we want them to be. But ordinary printers are not designed to be so accurately calibrated, so how we do that that??

Attached is a PowerPoint file with 2 objects. Their dimensions were set so that if you print the template on an A4 printer paper (landscape), they print out to real size. There are two objects in the file, one is the Vernier scale, and it should measure 39mm long. The other is a long rectangle who's width is 100mm (see first image).

To make sure that your Vernier scale printed correctly first print the page as is. Next, measure the rectangle's length. It's probably going to be slightly different than 100mm, so you'll need to correct for that to get the Vernier scale just right. What you want to do is print the scale again, but this time ask the printer to print it so that the final print is in the correct scale (I'll show you how to do that in a second). First, note that the rectangle's new size should be:

100mm X (100mm / actual printed size)

For example, I printed my first version and measured the rectangle's width as 98.5mm instead of the requested 100mm. This means that I should ask the printer to print larger objects if I want them to be of real size. In my case, I should set the length of the rectangle to be 100*(100/98.5) = 101.5mm (see second image). This way, when I re-print the paper, it will be of the correct size. To change it's size, double-click the rectangle in PowerPoint and change it's width (see 3rd image). It worked perfectly in my case! (see 4th image). If you still have questions on how this is done, or if you need a different file format to work with, let me know!

Finally, cut out the Vernier scale and glue it on to the moving part of the caliper (see pictures 5 & 6). To glue it correctly, make sure that the caliper is closed tightly and that the Vernier scale is as parallel to the rule as you can get it to be. The first tick on the Vernier scale should match the first tick on your ruler (0 should face 0).

This step is crucial! Make sure you take your time and get it as accurate as you can, because this is what gets you to 0.1mm resolution!

** Tip - if you're using a dark color for your 3D prints, you can invert / edit the color of the template I attached so that the colors match!

Step 5: You're Done!!

That's it! If you followed along, you should now have a perfectly working caliber! Enjoy! :)

If you liked my instructable feel free to visit my instructables page! If you have any requests or questions feel free to ask!

See you soon!

Step 6: BONUS - Left Handed Version

Here's a left-handed version of the caliper, so that the left-handed people here can finally have a tool made just for them :)

If you want to support my projects, you can buy me a (cheap) coffee :)

100% of all proceedings will go into future projects! Thanks!!

Comments

[zvizvi]

אדיר!
that is just plain awesome! no matter of the cost of a cheap plastic calipers, the post-apocalypse survivor in me tells me this will be useful in so many ways. Also, just print a bunch of these and teach children how to start using calipers, which are the base and starting for so many mechanical skills. Thank you for sharing!

[NirL]

Thanks a lot for the comment!
I love the idea of using this for teaching kids! You can easily rescale the current model to be more kid-friendly. I will add a mini-version. I'm also going to make a micro-version to put on my key-chain :) Thanks for the idea!!

[JavierL90]

This is excellent!! I love the idea and I will be making one of these using this guide shortly :) thank you for the left handed option - for once, not left out!

[NirL]

That's great! If you need any help (with adjusting dimensions and such), let me know :)
Thanks for the comment!

[LarryG7]

A good instructable and a good idea.

Calipers are simple looking, but require some expertise to use. Some people that buy the inexpensive dial calipers are first time users and are often disappointed. They require some expertise to use in order to get the desired reaults. The "arms" are long and many people will just slide them down on an object and read the dial. One has to be careful to make sure the arms are not slanted. One common error is not to develop a touch using the wheel to tighten. If you don't pay attention and use the same pressure every time you'll get readings several thousands different. Then .001 is very small and the caliper faces and the object to measure must be wiped and kept clean. Dust can easily throw the readings off. Most of the first time users don't understand how to use them and get unreliable readings. Then they rail about the quality of Chinese calipers. They wouldn't get any better readings on a set of $150 calipers. I have a Harbor Freight digital caliper and two high dollar calipers. The Harbor Freight set is closer to dead-on than either of the expensive ones. They all three are about the same in looks and feel.

When one goes to the trouble to make a tool usually by the time they get it finished they know how to use it. And they also treat their homemade projects better than commercial tools.

[NirL]

Thanks a lot for the comment! I absolutely agree - making your own tools teaches you how they work, and this especially important with calipers since people often don't know how to read the Vernier scale. I think once you made your own, there's no way you won't understand how to use it properly.
Thanks again for all of your input! :)

[zanod]

You made a nice job of this - and there's always great satisfaction in making things that work - but honestly, I was surprised that you bothered. I bought my first digital caliper about 12 years ago, and I have accumulated another couple since then, and I have never had any trouble with any of them, despite having spent much less than $20 on each one. The original one is in my workshop with a cracked glass - but all of them work.
The reason I was attracted to this article was that only yesterday, I watched a YouTube video of an examination of an all-plastic, Chinese caliper for £4.99 (< $6) - and he couldn't find much wrong with it, despite stripping it down and reassembling it.
Have a look :
Last week, I had a stack of papers to fill in. I counted 10 pages and measured them - 1mm. Then I measured the wad of papers - 2cm - which means there should have been 200 sheets. A manual count verified this exatly - so the caliper was indeed, accurate.

[NirL]

Hi, thanks for the comment :)
I agree, cheap tools can do a great job, and in many cases they're going to be pretty decent too. The problem with cheap products is mainly in the quality control and the variability in product quality. When you buy expensive tools, a lot of what you pay for is the guarantee for quality - this is the reason Intel had so many clients over the years, they work very hard to guarantee that each chip you buy is a identical to the others as technology allows them to be.
When you buy cheap stuff, they can be great in some cases and awful in others, even if it comes from the same manufacturer. This is exactly why some people give perfect reviews while others get awful products. So I'm glad you (and the guy from YouTube) got great products, especially for the price! I was on the other side of the quality distribution and decided to make my own. I also bought a second digital caliper online which seems much better than my previous one, but still, the fact that I could make my own caliper and get to 0.1mm resolution (guaranteed!) is something worth bothering for I think:)
Thanks for the feedback and time spent commenting & linking that video!

[ElectroFrank]

I have a few cheap Chinese digital calipers, most are ok for general workshop use, but some of the plastic ones are warped.

I think the caliper arms on your design need strengthening, they look as if slight pressure will bend them very easily at the narrow parts. Plastic is much more flexible than steel.

And if this is to be accurate, you will need a good quality ruler, many cheap plastic and metal rulers are useless for workshop purposes.

[NirL]

Hi, thanks for the comment!
I printed my ruler using PLA and it's really rigid, do you have any suggestions for the design? I'd love to hear and maybe even improve my instructable & caliper :)

[Alex in NZ]

This is just brilliant. Since I'm not a practicing sinistrist I never considered calipers as "handed" but this is such a neat idea! Thank you for sharing it and good luck in the competition :-)

[lorenkinzel]

You just wanted to make everyone look that word up, didn't you? It worked.

[Alex in NZ]

Hey, the whole point of this site is to learn. TIL ;-)

[NirL]

Thanks a lot for the comment! I think left-handed people always need to compromise when it comes to every-day tools and designs. These days we're able to customize and manufacture everything so easily, so they shouldn't suffer from this anymore!

[ejk00]

This is a great idea! Makes me think there are a lot of other opportunities to embed original objects within 3D-printed accessories. Well done!

[NirL]

That's exactly what I was thinking! I always try to think - 'what this tool best for?' 'where are the downsides?' and try to combine best of both worlds. Can't wait to see what you come up with!
Thanks a lot for the comment! :)

[JamesA41]

I was just thinking about this yesterday. Bought another Harbor Freight ~$2 plastic caliper since the other one I have lettering has dissolved away after a about 2". Was even thinking about... surprised no one has made a 3D printed version yet. Even mentioned to the gal that the old one could have the numbers and scale scribe'd in if someone had a CNC scribe or maybe small bit. Great to see and with a steel rule. Thanks for sharing!

[NirL]

I decided to use a ruler and not mark my own scale since I figured it would be nore accurate, but if your CNC / 3D printer is super accurate you could definitely do that too:) Another option is to calibrate your regular printer and print a scale, but I still like using a cheap factory-made ruler:)

Thanks a lot for the comment! Glad you liked my idea:)

[ajoyraman]

Great practical idea! Thanks

[NirL]

Thank you!