Geneva Roller Ruler, a Pocket Sized Infinite Ruler

The 'Geneva Roller Ruler' is a special pocket sized tool for measuring any line, any curve, any length! With this device you can measure square objects, round objects, straight lines, curved surfaces, you get the idea!

This tool can be very handy when measuring curved lines or oddly shaped surfaces that are difficult to measure dirctly with a straight ruler or tape measure. The roller ruler uses a wheel of known dimensions, regularly spaced tick marks, and a counter mechanism to measure up to 1/2 meter in 5 mm increments.

-The device is tiny so you can literally carry an infinitely long ruler wherever you go! :) It’s a simple but handy tool for home owners, architects, engineers, interior designers, fashion designers, decorators, art students, or anyone who needs to precisely measure irregularly shaped things on a regular basis.

-Assembly is simple so this instructable will guide you on how to print & use the device as well as tips on how it was designed.

>If you dont have a 3D printer you can pick up a geneva roller ruler in my store here<

A note on technical names:

• The intermittent geneva drive mechanism is also known as a 'maltese cross drive'
• Technically this device is a tiny form of "Measuring wheel". Which is very similiar to a 'curvimeter' 'opisometer', or 'meilograph'

VIDEO DEMO:

Step 1: 3D Printing Files & Settings

Print Settings: (Files attached)

• Any material, No supports needed (Parts must be oriented as shown in the image)
• 0.4mm dia nozzle max
• 0.2mm layer thickness maximum
• Minimum 2 perimeters all sides top & bottom
• 10% infill minimum
• Expect 2 hrs to print

Vitamins:

• 2x Screws: https://www.mcmaster.com/90380A115
• OPTIONAL: A badge reel is handy for making measurements in quick succession, but it also makes this a fun fidget toy too! :)

Post Processing:
Update: At this point I have built dozens of these devices and have learned that you can optimize the free-spinning performance by following a post processing procedure. Bore out the holes in the geneva drive & primary roller with a 3.5mm drill bit & deburr the hole edges. Also use a file to briefly smooth the raised surfaces on the clip part that make contact with the wheels. And finally after assembling break it in by manually rolling it back and forth hard on a carpet. The end result should be able to free spin the geneva wheel an entire rotation with the flick of a finger.

Assembly:
Assembly is so easy it doesn't merit its own step. Use the two screws to attach the 3 parts together. Do not over tighten as that will prevent motion. The parts are naturally pokayoke so you cant do it wrong!

Step 2: HOW TO USE

-To use, hold it like a pizza cutter and place the start mark on the starting point of the surface or line you want to measure, and then roll. Every time the primary wheel rotates once, the Geneva mechanism keeps track by rotating the counter to the next number. One primary wheel rotation is 100mm (or 4 inches for the imperial version) and the geneva counter goes up to 5 so you can measure up to half a meter before the counter restarts.

-The measurement resolution is limited to the small notch spacing on the primary wheel. The notches are in 5mm increments for Metric, & 0.25" increments on the Imperial version.

Once again, see the video demo here.

INTERESTING UPDATE NOTE:

It occurred to me that the diameter of the wheel will affect the measured length. Note the attached sketch with the large blue wheel rolling over/past portions of a rock that the small wheel would pick up. Smaller wheels produce longer measurements than large wheels and different sized wheels are better for different jobs. This is a form of what is known as the coastline paradox.

Step 3: Design Notes

I used Solidworks to design this tool from scratch. Its only 3 pieces but it was a bit of work to get the geneva mechanism properly functioning. For that I referred to a design table I found here.

Well that's all, I hope you enjoyed and get some use of of this. If you enjoyed this instructable please take a second to vote for it in the Instructables Pocket Sized Contest, Thanks!!