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.

The 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.

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!

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.

A wooden storage chest for the board game Carcassonne

Front of the box with removable tile tray

The box I made was first designed in 3D in CAD software called Alibre Designs. This allowed me to check that everything was going to fit and easily adjust dimensions if I changed my mind. I laser cut all of the parts in 3mm birch ply, all of the finger joints you can see around the box were cut 4.5mm long so that they stuck out past the corners. This let me trim off the excess with a chisel after to remove the slight charred and bevelled edge you get when laser cutting. All the finger joints pointing up towards the top of the box were intentionally designed 10mm too long so they stuck up to look like the crenelations of a castle.

All of the files to make your own will be available soon from my Downloads page.

View of the assembled parts in Alibre.

The main box is made up of 7 parts. The front and one side were glued together and clamped to keep them square and the back and the other side were glued and clamped. This gave me two halves I could then put together when dry with the lid. I used Gorrilla glue because it’s nice and strong and fast curing. After this point I had a bottomless box with no lid. I used a table saw to cut the lid apart from the base. Doing it this way means you end up with a lid that HAS to be square to the base and will fit perfectly. It can’t not fit! The base is supported by a protrusion in each corner, and extra 3mm piece of ply is glued to the lid and base on the inside at the back to give enough depth to cut a notch to screw the hinges to.

Cut and glued box before being cut in half on the table saw

I also designed, laser cut and assembled a removable tray to store all of the tiles. Two of these rows should be enough to store every card from every extension, leaving the third row for Meeple or other parts of the game.

All of the wood was finished with Colron Danish oil to bring out the colour/grain of the wood and seal it from dirt.

Overall it took 4-5 hours of design work, less than an hour on the laser cutter and 5-6 hours assembly and finishing. I’m really glad I finally found a good excuse to make this, it’s a project I’ve been meaning to start/finish for over a year.

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.

Method:

By cutting a rectangle of material and then cutting 9 rectangles within it you get 10 cuts. When these 9 rectangles are pushed together at one end of the “frame”, the resulting gap at the other end is the sum of the kerfs. Dividing this gap by ten gives the average kerf for that material and material thickness.

The image below is a screenshot of the Alibre drawing. The vertical lines extend past the inside border of the frame so that the cut has time to penetrate the material before it crosses into the inside border of the frame. Some laser cutter software will compensate for penetration time, ours was cheap and so doesn’t.

Once cut I was careful to keep the parts together and not get them turned over. This is because the kerf will be slightly wider at the bottom than the top since the laser beam is not parallel, it gets wider the further it travels from the lens. For this reason a longer focal length lens gives a thinner kerf. Getting the parts turned over would result in the kerfs nesting together, to avoid this I drew a line on the top side before I removed it from the laser cutter.

Gaps were measured using a metric feeler gauge which allows you to add together slips of metal in different thicknesses to build up the thickness until it no longer fits in the gap. A PCB that was laying around was used to keep the small rectangles flat as the feeler gauge was used. Anything flat(ish) will do.

Results:

These values give me a good idea of what to add when designing parts for the laser cutter. I was curious to know how much the kerf would change with material but there’s so little change in kerf for these different materials that I’d just add 0.2mm to the dimensions if I wanted an interference fit.

I had had concerns when laser cutting holes in plastic which would later be tapped that the kerf would enlarge the hole too much to get a good thread in it. In future I’ll know to reduce the hole size by 0.1mm to compensate.

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.

The part was drawn first in Alibre, converted to a 2D drawing then to a .dxf file. The holes I measured from a bigger, non-wrinkled filter plate as being 0.8mm in diameter. I set mine to 0.7mm in the drawing to allow for the laser cutter kerf. (click the image below to enlarge)

I used 6mm thick acrylic, cutting it on the laser with power 98/100 and speed 3/400 for the outside and 2/100 for the holes. The laser takes time to penetrate hence why I slowed the cut down for the holes and added a 0.5mm overlap in the cutting settings.

Files:

Alibre part: (download)
DXF file: (download) (for laser cutting)
DXF file: (download) (with hole centers for drilling – a 48mm hole saw and 0.8mm PCB drill are easy to get hold of)

A blast from the air line after cutting cleared out the remaining acrylic residue. Ready for a test run!

With an unusual lack of used oil in the lab, we tested it with some Brasso diluted with white spirit. The white spirit came out clean and all of the Brasso particles were left on the filter paper. It didn’t look like the filter paper was damaged in any places, which would have happened had the holes been too big.

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.

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

Steve pointed me to a section in a book called Amateur Telescope Making by Albert G. Ingalls which detailed methods of determining the flatness of a surface. The book describes four methods of varying difficulty. The diagram below is the one I chose, which compromises clarity of image for simplicity.

The method from the book expects you to view the rings in the glass plate at 45 degrees as the image is reflected off of it. I built a box from 18mm ply to contain a monochromatic light source, the electronics to run it and a glass plate I salvaged from an A4 scanner. After building it I found that it didn’t work as indicated in the above diagram and that the image I saw of the rings was much stronger when viewed directly at a shallow angle than when I looked at the reflection in the glass plate. In reality I found that the glass plate was very useful to hold some sheets of plastic dispersers/polarisers that were salvaged from a broken PC monitor. Bear this in mind while following the instructions below; the wiring and box details may be useful but you may prefer to take different steps to secure a method of light dispersal which I found necessary to prevent the bulb overpowering the image seen in the optical flat.

For the light source I used a 70W high pressure sodium lamp (SOX) with a ballast and ignitor.These were wired as per the diagram printed on the side of the ignitor. The diagram didn’t show the earth connections though these were stamped on all of the components. The picture below shows the circuit diagram printed on the side of the ignitor which is mounted in the aluminium bracket I made for it (click to enlarge):

Below are the electronics mounted in the beginnings of the box I constructed, with a small bracket to support the bulb halfway along its length. An aluminium bracket was also constructed to hold the ignitor which is an awkward shape to mount without it. The mounting hole doubles as its earth point. (click to enlarge)

A stainless steel plate made to hold the IEC socket. Not necessary but a satisfying touch when I fancied making something in the workshop one day and it helps with storage if there’s not always a plug and lead dangling from the box. Fixed to the box with self tapping screws:

Testing the SOX before putting the rest of the box together (below, click to enlarge).

The almost finished box without its front panels and lid (below). This picture shows the arrangement of electronics well and the spacers used to keep the bulb central(ish) above the glass plate. The box could have been made narrower to avoid this but then the electronics would have had to have gone on the outside at the back.

Below is the finished light box without its 3mm ply wood lid. After this picture was taken thin films of plastic from a broken computer monitor were cut to the size of the glass and laid between it and the SOX bulb to diffuse the light, dullthe reflection of the bulb on the optical flat and hence make the rings clearer.

I had intended to paint the interior of the box white to reflect the light down and the back of the box behind the glass black to reduce the reflection of the bulb on the glass. Upon finding that the image of the rings were clearer when viewed directly I didn’t think this was necessary.

With this setup I can see Newton’s rings between the flat and my TEC much more clearly than is apparent in the title photograph. The brightness of the SOX caused a lot of problems in getting a clear shot with my point and shoot camera. Even with a lot of manipulation the image shows the rings much less clearly than with the naked eye.

In a subsequent post I hope to discuss the use of this light box to improve the flatness of the TEC and its water cooled block, including methods of lapping with a lapping plate and grits as well as approximating the flatness by knowing the wavelenth of the light emitted by the light source.

]]> http://www.redtorope.com/2011/06/monochromatic-light-box-for-determining-flatness-optically/feed/ 0 http://www.redtorope.com/2011/03/determining-tec-flatness-with-newtons-rings-part-1/ http://www.redtorope.com/2011/03/determining-tec-flatness-with-newtons-rings-part-1/#comments Tue, 15 Mar 2011 22:39:57 +0000 James http://www.redtorope.com/?p=475 Read more »

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:

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

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

Process pictures and descriptions after the break…

So…. How? Here are the steps:

1) Etch your design onto a piece of acrylic. I used 3mm white acrylic. After etching, depending on the colour you used, the contrast between etched and non-etched is poor to okay. Here’s a photo of the example front panel after etching. Pretty bad huh?!

2) Blow out any residue from the etching. Some of the fumes from the etch spread across the surface of the acrylic.

3) Scribble on the etched acrylic with a wax crayon (yes really), dragging it back and forth perpendicular to the direction of the edges of the etched areas. This method will only work on thin lines up to about 2 or 3 millimeters. As you pass the crayon against the sharp edge of the trench cut by etching, some of the crayon gets left behind, filling the etched trenches.

Here’s a photo of the same front panel facia after plain black wax crayon’s been used on it. Messy!

And one of the clock gear after a good scrub with a crayon:

4) Wipe with a taut white spirit soaked tissue.

Apply white spirit to a tissue stretched over a finger or a block of wood, or laid out on a table. Rub the messily waxy side of the acrylic against it to remove most of the excess. It needs to be white spirit. I tried IPA without as much success, and other solvents (acetone for example) may damage or cloud the finish of the acrylic.

5) Apply white spirit to a piece of plain white paper on a flat surface. Rub the acrylic part against the paper to remove the final bits of wax not in the etched grooves. Doing it this way, the majority of the wax is removed by the tissue, rubbing on the paper allows you to rub harder, removing those stubborn bits.

One of the Chint LED inserts having its final scrub:

6) Bake ‘em

As they are, the laser etched grooves are filled with wax, the wax a level cap over the etched areas. By melting the wax slightly it will settle into the corners and imperfections of the laser etched surface (which if your etch step size is rough, are quite great) and stick better while dipping slightly at the surface, protecting it from anything scrubbing over it.

Throw your etched and waxed acrylic pieces into an oven at 40 Celsius (~104 Fahrenheit). If your oven doesn’t go this low, turn it up high and leave the door open. Warm them for about 20 minutes before removing.

7) Give them one last wipe with white spirit on paper, or IPA if you have it, then call them done! If wax settled and left gaps on any wider etched parts, refill with wax, clean then reheat.

I found that this process gave good results down to etch paths 0.5mm wide. See the (Hz) on the electronics panel example, the definition is great, even so small.

And here are some finished pictures. A massive thank you to Steve for suggesting I have a play around with filling etches with wax and letting me play around with it at work!

Finished insert for Chint panel mount LEDs:

Etched inserts in situe. My camera took a dislike to the differences in light levels, hence the poor photo. They looked a lot better than this in person…

A finished example panel for an electronics project:

And finally, one of the gears from a geared clock project:

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

And a picture of the pink ones:

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).

(DXF)

(SVG)

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)

The outlines were made by scanning the game pieces. I then had a friend use Inkscape to turn the image from the scanner into outlines and save them as .dxf files. When imported into the laser cutter software they could be scaled to the correct size using the heights of the pieces I measured. They won’t be perfectly the same size as the originals, since they all vary by +/- 0.5mm anyway, but they come close. Those in the pictures are slightly undersized as I didn’t have a set of pieces with me when I laser cut them so guessed at 16mm, they should have been slightly larger to allow for twice the laser cutter’s kerf. Close! The sizes are as follows:

Normal Meeple: 16mm
Mega Meeple:     19mm
Builder:                 20mm
Pig:                         14mm

Here’s a preview of the outlines, I’ll upload the .dxf files for download when I post pictures of the multiple colour versions soon. If you know of somewhere I can buy small quantities of 10mm acrylic please let me know!

And a photo of one of my transparent meeple next to a standard meeple. A tiny bit shorter and a wee bit chubbier.

Want some? Leave me a comment or send me an email. What colours would you most like if you could choose ANY colour to have as your custom meeple colour?