Diffraction Grating Orders Calculator

Diffraction gratings are used in optics to split light into multiple paths. The number of diffracted orders and the angles they are seen at vary depending on the angle at which light hits the grating, the spacing of the grooves in the grating and the wavelength of the light used. I wrote this Javascript app to save me time while performing some calculations for an experiment for my PhD, I had to find the best angle to set the grating at for several wavelengths of light so that I could use the reflected orders.

I wanted an app that didn’t just tell me what orders were present and what angles they were at, I wanted to be able to more easily visualise them. I needed to be able to easily select the grating properties as well as the wavelength of light used, since for my application I was using several light sources all of different wavelengths.

Diffraction Grating Order Calculator. It’s on a separate page so that there’s more space available than in my main website’s layout.

Diffraction Grating Order CalculatorThe app was written with Javascript and a Javascript vector graphics library called Raphael.js. It was my first time using either of them, Raphael was excellent, the demos are really impressive.

The Raphael parts were fairly straight forward. The hardest bit was getting the HTML to play nice with all browsers. Time to start my next app now, I’m hooked! Email with any suggestions for others, be they educational, time saving or commercial, I’d be interested to hear.


“Artist in Residence” at Instructables HQ, San Francisco

This is an edited version of a post I wrote for the Instructables forum after spending 2 months at their HQ.

Thursday saw the end of two of the most fun filled months of my life. Since the beginning of February I’ve been an artist in residence at Instructables’ office in San Francisco.

First impressions? The office was unlike any I’d ever visited or heard of. An open plan 2nd floor office above a deli and a night club on 2nd street, Instructables’ headquarters is home to a team of 25 young and enthusiastic staff. It’s not like your average software company either, no desk is the same and each is covered in or surrounded by a mix of complete and incomplete projects, or is in itself a project.

Those above mentioned staff are all friendly. The office has the same tight knit community feeling that I have felt part of as a non-staff member using the site.

As an artist in residence I was given no direction other than to be creative and pursue and finish projects that interested me. The environment was hugely beneficial as a maker. At home I feel that I have to explain why I want to make something. “But you can buy that!” I am often told. At Instructables I was surrounded by people who understand that making is a passion, that it’s important and ideas quickly develop and grow as enthusiastic friends chime in with over the top but all too often adopted suggestions to improve projects in progress or create new projects. There doesn’t need to be a reason to create something to amuse, educate or just show off.

While in residence I worked on a bubble machine, a giant chess set to play in Eric and Christy’s kitchen, an improved laser cut jenga pistol, a cupcake decorating stencil, several educational instructables as well as writing Perl to simplify several tedious admin tasks performed by the editors.

My most used tool was the laser cutter. If I had to choose a favourite new skill that I learned, I’d be hard pressed to choose between the skills I developed with a DSLR and lighting, and how to drive a forklift. The best piece of insider information I picked up…. I know who the next artist in residence will be!

Given a chance, I’ll definitely be back. I love the staff, I love the city and the nearby climbing is exceptional!

Themed Carcassonne Storage Chest

Carcassonne is a tile based castle building board game. After bringing my large set (the main game with 3 of the extensions) with me to my parent’s house when I visited last Christmas, my sister loved it so I bought her the main game for her birthday later in the year.

This Christmas, I bought her one of the extensions she didn’t already have by now. I thought it’d also be nice to make her something to keep all the parts in as once you have more than 3 extensions it becomes a bit of a struggle to get all of the pieces into the original box, even with the cardboard padding removed. I set out to design and make her a themed wooden Carcassonne storage chest.

Themed Carcassonne Storage Chest

A wooden storage chest for the board game Carcassonne

Themed Carcassonne Storage Chest

Front of the box with removable tile tray

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Laser Cutter Kerf Measurement

It’s well documented what kerfs are achievable with commercial 1KW+ laser cutters cutting steel, aluminium and plastics. I wanted to know what kerfs were achievable on our 40W Chinese built laser cutter so that I could work out what to add to allow for kerf when designing finger joints to be cut in 3mm ply or when cutting holes to be tapped. The kerf is the width of material removed during the cutting process.

Kerf is determined by material properties and thickness, the focal length of the lens and the gas used while cutting. Our laser cutter uses a lens with a 50mm focal length and uses compressed air to push out the vapourised/molten swarf.

Laser Cutter Kerf Investigation

(Kerf measurement description, photos and results after the break)

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DIY 47mm Acrylic Whatman Filter Plates

We use a couple of glass 3 piece Whatman filter funnels in the lab at work to filter used oil samples before testing. A glass fibre filter paper is supported by an acrylic plate and samples are drawn through it into a vacuum flask below. When someone decided it was a good idea to clean the acrylic plate in acetone, it was wrecked and our labware supplier wanted £40 for a new 47mm Whatman filter plate.

Being just a piece of acrylic with a few dozen small holes in it Lizzy suggested I laser cut a new one rather than us paying for and waiting for it. The resulting plate was usable the same day and at a tenth of the cost. It works just as well! If you want one, leave a comment.

Photos and files after the break.

47mm Whatman Filter

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Monochromatic Light Box for determining flatness optically

This article discusses how to build a monochromatic light source to determine the flatness of a surface optically. It uses a high pressure sodium lamp housed within a box to shroud the light source, designed around a diagram from the book Amateur Telescope Making by Albert G. Ingalls. High pressure sodium lamps are the bulbs used in most street lights, they emit visible light within a narrow band of wavelengths.

In my previous post I described observing Newton’s rings using my computer monitor as a light source to show the flatness of a TEC. A flatter TEC has a better thermal contact with its heat sink, allowing faster transfer of heat away from the hot side and hence faster cooling of the cold side.  The light I used previously was not monochromatic and so all of the wavelengths of light interfere constructively and destructively at different points, creating rings of different colours blurring into each other. While this allows you to see if it is flat or not, it doesn’t let you do so quantitatively. By replacing the non-monochromatic light of my PC monitor with a monochromatic source, I should in the future be able to determine how flat the TEC is.

Newton's Rings

The following descriptions and photos discuss the why and how of building a source to measure flatness.

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Determining TEC Flatness with Newton’s Rings – part 1

With a 340W, 50x50mm TEC (thermoelectric cooler) arriving at work this week for a project we’re working on, Steve asked me to look at using Newton’s Rings to determine if this new TEC was flat enough to use as it was, or if we’d need to lap it with diamond lapping paste to improve the contact between it and the water cooled copper block it will be clamped to.

A large part of the problems I had when writing my dissertation for my degree came down the the flatness of the thermoelectric cooler (TEC) I was using and the clamping force I could achieve on it. Without both being as flat as possible, the thermal contact between the TEC and the heat sink was poor, and so the TEC didn’t heat or cool as well as when both were lapped flat.

Newton’s Rings provide a way to determine the flatness of two surfaces optically. With a piece of glass you know is flat, you can tell whether another surface is flat by looking at the interference patterns between the two surfaces. With a monochromatic light source and optical flat on order, Steve and I armed ourselves with our impatience, a telescope mirror blank (maybe almost flat), this excellent PDF and the TEC and copper block to see what we could see.

Newton's Rings

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Laser Engraved, Wax Filled, High Contrast Panels for Electronics Projects

This technique for creating high contrast panels for electronics projects and prototypes using a laser cutter gives great results using cheap and easy to find materials. It’s really useful as an alternative or substitute for more expensive and harder to find laser engravable laminates like SureLase.

The product we use at work for laser engraved signs on products we ship, SureLase, gives great results, is super easy to use and available in a large range of colours. Its downside for non-commercial users is its price and the fact that you have to buy a large 1 x 1.5m sheet. It’s also not as versatile as a plain piece of 3mm acrylic, you can’t make other parts out of it since that’d be a waste.

Here are some photos of some items made with a different method, achieving similar results and using just 3mm white acrylic and a black wax crayon. It’s easy, fast (though not as fast as SureLase) and looks dead smart.

Example electronics project facia, missing the pot and switch to finish it off:

Laser Cut Electronics Project Facia

Some inserts to be installed inside some industrial panel mount LEDs made by Chint:

Acrylic Inserts for Chint Panel Mount LEDs

A cog from a mechanical clock designed by Alan Parekh before it had it’s final wipe down:

Laser cut gear from a geared clock

Process pictures and descriptions after the break…

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Carcassonne Meeple DXF/SVG Outlines, and Pink and Black Acrylic Meeple

The sheets of 10mm pink and black acrylic that I ordered arrived today. I thought I’d take the chance to post some pictures of the finished pink and black meeple as well as upload the outlines for the sets as .SVG and .DXF files. I also cut a few sets of each and threw them on ebay here.

The black, named as “Jet” on ebay to differentiate them from the normal wooden black ones, since they’re nice and shiny:

Jet Carcassonne Meeple

And a picture of the pink ones:

Pink Acrylic Carcassonne Meeple

And as promised, the DXF and SVG files. The DXF for importing neatly into most laser cutter software and the SVG in case you want to play with them in Inkscape or use them with Ponoko (though they don’t offer any 10mm acrylic).



Custom Meeple – Carcassonne Game Pieces

The last few times I’ve been back to where I went to University to visit my friends they’ve all been massively enthusiastic about a game called Carcassonne. Players take turns placing cardboard tiles and claiming them with meeple (the little wooden people that come with the game) to build castles, roads and farms to score points. Their one problem with the game is the lack of available colours of meeple which limits the number of players. The original game comes with 5 colours, plus an extra one if you buy one of the extensions. With the amount of game tiles available when you have more of the extensions, there’s plenty of scope for extra players, but no extra colours of meeple.

These are a set of meeple I laser cut from 10mm clear acrylic. It includes the standard sized meeple and a mega meeple, builder and pig from two of the extensions. With all of the colours of acrylic available (over 20) there’d be plenty to choose from! I’m currently looking for somewhere that will sell me lots of colours in sheets less than 2 x 3m, then I can start making some different colours.

(More pictures and details after the break)

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