Instructables

5$ Berlin Skyline Engraved Acrylic Display (battery-powered)

Picture of 5$ Berlin Skyline Engraved Acrylic Display (battery-powered)
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Background:
One of my pre-Instructables projects from early 2013. As it was a rush build for a friend I did not have any time to take any progress pictures, but I'll try to describe the build process as detailed as possible.
I hope that you will still be able to follow through and understand what I did and how I did it.
The build is based on experience I gathered building my "Bar's Open Acrylic Glass Engraving", so be sure to check that out as well.


Goal:
Make a small, edge-lit acrylic glass engraving of the Berlin City (Germany) skyline as a gift.
Try to keep total project cost as low as possible.


Safety Advice:
This instructable makes use of (power) tools, knives and soldering irons.
These tools can burn, cut or otherwise hurt you.
Always wear eye protection (a molten piece of acrylic being flung at your face is not fun, trust me on this one) and be extra careful where your fingers/hands are at any given moment when using power tools / knives.
In general, before doing each step, think about what you're doing, which tools you're using and what potential dangers are involved.
If you are not experienced with the use of the tools, get help from someone who is.


Tools:
- Dremel (router attachment is useful)
- Soldering iron
- Hand saw
- Pliers (especially for wire cutting and stripping)
- Cutter knife
- Sandpaper
- (Permanent) marker
- Clamps


Materials:
- 240x115x2mm (LxWxH) GS acrylic glass (thinnest and cheapest I found) - ~1.5$
- Thick black paperboard/cardboard, as large as the acrylic glass - ~0.5$
- 10x 5mm blue LEDs - ~1$
- Resistor (for 6V and blue LEDs) ~0.1$
- Small switch with 2 screw holes ~0.5$
- A bit of cabling - basically free
- AA battery holder for 4 batteries - ~1$
- Heat shrinking tube - ~0.1$
- Soldering tin - basically free
- Small nails / glue - basically free
- 2 miniature threaded screws and fitting nuts - ~0.2$
- Black PVC spine bar (the stuff you can find at stationery shops to hold together stacks of paper) ~1$


The Build:
1. Design the template
I started out with designing the skyline I was going to use in GIMP and scaled it properly for the piece of acrylic glass I had. To keep project costs down, I used the smallest, thinnest stock piece of acrylic glass I could get, which cost about 1.5$.

2. Transfer the image
Having printed the mirrored template and learning from my previous mistakes, I used a permanent marker to transfer the design onto the protective foil of the acrylic glass to prevent scratching it while engraving. Let me tell you here once more, what you want is GS (cast/poured) glass, not XT (extruded) glass. Why do you want GS glass? Because of two reasons. One is that GS glass does not fracture as easily as XT glass, but more importantly, GS glass has a higher melting temperature which means unlike XT glass, it will not melt and wrap around your sawblade or router when cutting/carving, thus ruining the glass and possibly your tools.
To make the trasfer easier you can cut out the template and use it as a makeshift stencil.

3. Engrave the image
Remember to wear protective goggles!
I used a dremel with a router attachment and a small bit that looked like a cone consisting of several blades for engraving. I set the depth to about 1mm and the RPM to ~15.000-20.000.
Using both hands to securely move the dremel (on the router attachment) I carefully moved it along my previously marked lines.

4. Solder together the LEDs in parallel
This probably isn't the best way to do things, but it saves a lot of cabling, space and hassle.
LEDs have one longer (positive) and shorter (negative) leg. Bend both legs of all LEDs in the same direction, keeping them parallel. What you want is basically a continuous 'rail' with the LEDs facing upward. Solder the LEDs together like this (positive leg to positive leg and negative to negative) and add a resistor for the used 6V and one(!) blue LED to one of the free legs. Google "LED resistor calculator" to get a calculator that spits out whatever resistor you need.
As the LEDs are connected in parallel, their resistance is not added up and basically counts as one. Keep in mind though that the resistor used will be put under more strain, so potentially a stronger one will be needed (Amp-wise, not Ohm-wise).
Now hold the cables of the battery holder to the free LED leg and resistor to see if all works well. Mind the polarities though. If everything works you can continue, else begin troubleshooting.

5. Making notches for the LEDs
Cut out a piece of thick black cardboard the size of the used acrylic glass using a cutter knife. Clamp both together. Now hold the LED rail just constructed below the bottom of the engraving and use the marker to mark the positions of the LEDs. Use the dremel with a bit looking like a miniature round rasp or similar to carve out rectangular notches for the LEDs to sit flush if the glass and cardboard are put on them in an upright position.

6. Preparing the frame
Attach the battery holder at the back of the cardboard using either glue or small nails. Be sure to use a black permanent marker to blacken them once bent over or add another layer of thin black cardboard between the glass and the thick cardboard to hide them.
Use a hand saw to cut the spine bar in 45° angles to make frame pieces. Account for the acrylic glass that's going to be covered by the frame and choose a spine that will snuggly hold the glass and cardboard together.
Next, decide on a position for the switch inside the frame and use the dremel to make two holes corresponding to the screw holes of the switch as well as a slot for the switch trigger itself.
Ensure that your minuature screws and nuts will work with this switch.

7. Final soldering and assembly
Cut some cabling just long enough to connect the positive cable of the battery holder to the positive pin of the LEDs, intending for the cable to go right along the edge of the glass.
Do the same for the connection from battery holder to the switch and from its other pin to the free LED pin. Be sure to insulate everything you can.
Insert the switch into the prepared frame piece and secure it with screws, and put the LEDs into the prepared grooves.
Then move on to assembling the frame by pushing on the spine bar pieces. Their pressure alone should suffice to hold everything in place securely.

Congrats, you're done!


Conclusion / Thoughts / Improvements:
Aside from maybe an image frame hook or some sort of foldout stand and possibly improving the quality of the engraving a bit more, I'm quite satisfied with the outcome.
For ~5$ worth of materials, this is pretty good.