The episode in [ENGLISH]: http://www.mojoptix.com/?p=178
L'episode en [FRANCAIS]: http://www.mojoptix.com/?p=182
Note: To see more inventions and contraptions (like this other one ), suscribe to Mojoptix on Youtube !
A fully working caliper that uses a Moire pattern to reach a precision better than 0.05 mm. The accuracy should be better than 0.5mm.
No batteries, no electronics, no gears... It's just a couple of images sliding one on top of the other. The two images have been mathematically designed to display a Moire pattern shaped like an "indicator triangle": the tip of the triangle will indicate the sub-millimeter measurement.
How to use this caliper
Simply read the cm and mm on the main scale, and then the sub-millimeter value on the Moire scale.
A couple of short clips
Check out this short video to see it in action: http://www.youtube.com/watch?v=W-Au9vlV2nQ
This short video might help visualize a bit the Assembly (refer to the section "Post-Printing" below for more details): http://www.youtube.com/watch?v=-yDPLzs7wKM
I would recommend to print the 3D parts in the orientation the STL files are already in:
they have a chamfer at the bottom to reduce the "elephant foot" effect, and the crenellated patterns (on the "boot") or the gaps (on the "shoe" and "hook") should completely(-ish) eliminate any warping.
And if you 3D print on a glass platform, this should also give you flat and shinny surfaces at just the right places.
PLA is maybe preferable to ABS for this object: it less susceptible to warping and is a bit less flexible.
The "Top_image_Transparency.png" image must be printed on a transparency (the same kind you would use on an overhead projector). And it would be best to print the "Bottom_image_PhotoPaper.png" image on a thick photographic paper (120g/m2 or heavier).
You'll need to print them with a resolution of 600 DPI (or better)
The most important thing is to both images with the exact same printer settings, at the exact same place on the page (for example: centered), and with the same orientation !
Also make sure that the software you are using to print the image does not rescale them. The free software Irfanview does work nicely for this purpose.
Note 1: The Mojoptix episode (see link at the top) has also a video of a full build.
Note 2: Use slow-drying glue ! Aligning optical components is not something you want to rush.
Aligning and gluing the Transparent image
Apply some glue on the tiny trench on the underside of the Frame, then place it on the Transparent image. Use the two outer lines (with all the tick marks) to carefully center the Transparent image inside the opening of the Frame.
Once the glue is dry, you can slide the Frame inside the Boot component.
Aligning and gluing the Bottom image
Apply some glue on the backside of the Bottom image paper, then slide it in place inside the Boot component, just below the Transparent image. The Bottom image is a bit longer than the Boot, so you can bend the outer edges to help you move it around. The goal is to align perfectly the axis of the dotted line on the Bottom image with the axis of the dotted line on the Transparent image.
Gluing the Shoe
Set the Caliper to 0.00mm. Position the Shoe component in place: the flat surfaces of the caliper jaws should be perfectly in contact. Then apply a generous amount of glue on the top side of the Shoe, to glue it to the Frame.
Gluing the Hook
Set the Caliper again to 0.00mm. Apply some glue on the leg of the Hook component and position it on the Boot component. Position the Hook such that the flat underside of the Hook's hook is levelled with the flat topside of the protusion from the Frame.