Pi is an interesting number, or is it a number? It is the ratio to a circle's circumference to it's diameter. There is no point at which there is an end to the decimal points of its value. Pi has been calculated to 13.3 trillion decimal places according to Wikipedia, with no end in sight. There is no exact value of Pi as far as we know. So, when someone tells you the value of Pi, they are always wrong. You can always add one more decimal (if you can memorize 13 trillion numbers!). The most commonly used values are 3.14 or 3.1416. If you want a really exact number for Pi, you will have to get a really big piece of paper.

This instructable will show you how I made an LED edge lit light for your favorite engineer's desk or a night light for a furure math 'wizkid'.

I hope you enjoy it.

## Step 1: Make a Base

I used a piece of wood 2" wide x 1" thick. I wanted the plexiglass to be 6" wide, so I cut a piece 8-1/2" long. The piece was sanded on all sides and a router table was used with a 1/2" roundover bit on the top of the block to smooth out the edges.

## Step 2: Make Slots for the LED's and Plexiglass

I wanted the plexiglass to fit snugly into the base, and not rest against the led's which will be sitting below the piece of plexiglass. So, a slot was cut into the top of the base about 1/2" deep. To do this, mark the centerline of the base along it's length and about 1/16" longer than the width of the plexiglass. The plexiglass I used measured .225" thick, so I had to use a bit smaller than .225". I had a 1/8" endmill that I used to cut the slot. Be sure to check the fit of the plexiglass into the slot as you cut so you don't go too far and end up with a sloppy fit.

I cut out an area on the bottom 1" wide and 1/4" deep. This cutout needs to be about 3/4" to 1" longer than the piece of plexiglass. This cutout will be where the LED holder will be placed. Next, cut a slot a little less than the width of the plexiglass all the way through the base. This will leave a little ledge on each end of the slot for the plexiglass to rest on. The ledge will keep the plexiglass from resting on the LEDs.

## Step 3: A Holder for the LED Strip

I used a piece of 1/4" X 1" wood and cut it to the same length as the cutout. I rounded off the corners on the sander so it would fit nicely into the cutout. The little holder strip was then put on the mill and a 3/8" wide slot was cut along its center about 1/8" deep. This is where the LED strip will sit. If your LEDs are a different size you might have to cut the slot to a different size. Just be sure that the LEDs are recessed into the slot and not sitting higher than the top of the wood strip.

## Step 4: Now for the LEDs

LED strips are normally supplied in rolls that can be cut every 2" so you can make varying lengths of light strips. I cut my strip to 6" long. The strips also have little soldering pads that are marked + and -. The positive and negative leads of a 12vdc supply will have to be soldered to the + and - pads. If you get them reversed, the LEDs will not light up.

After they are soldered, place the strip into the slot in the LED holder and cut a little notch out for the wire to exit the base. Most strips have a self adhesive strip on the back side. If yours does not, you can put a dab of hot glue on the strip to hold it down. After you have it mounted, put some hot glue on the wires to secure them to the base. I put some little felt stick on pads on the bottom, so it would not scratch my desk.

## Step 5: Make the Plexiglass Sign

This sign used 1/4" plexiglass which actually measured .225". Leave the paper on the plexiglass for now. I marked out the final size and cut it on a table saw. Be sure to wear safety glasses because the little shards of plastic will go everywhere. I then clamped it into my vice with some rubber pads on the jaws and used a finish sander to smooth out the edges. The edge effect you want will determine what grit sandpaper you will use. Working your way up to a 600 grit will leave a satin edge with a soft glow. I went up to 2000 grit because I wanted a polished edge. That is purely a personal preference.

After the edges are polished, you are ready to cut your design. Since I used my CNC router to do this, I will not go into how that was done. That is for another Instructable. You can even do this freehand if you like. You don't have to engrave it deep, just a scratch with a sharp pointed object will work. Before you engrave your pattern, pracice on a sheet of paper. You will want to do it BACKWARDS. The engraving should be done on the back side of the sign as shown in the above pictures. It will show up much better. After I engraved it, I used some laminating type film to cover up the engraved side. I then took a razor blade and cut out the Pi figure. Make sure the remaining area is fully covered with the film. This is another personal preference. I then put the plexiglass into my glass blaster and then very lightly, etched the Pi figure on the plexiglass, being very careful to only etch the exposed Pi.

Carefully remove the film and the paper. Clean with plexiglass cleaner of soap and water. DO NOT use window cleaner - the plexiglass will be ruined. You are done! Put the plexiglass in the base, plug it in and enjoy your work.

<p>is it 3.1416 or 3.1415? i thought it was 3.1415</p>
<p>3.1415926535 but.....</p><p>if you round to 4 dp 5 is rounded up to 6</p>
<p>3.1415926535 but.....</p><p>if you round to 4 dp 5 is rounded up to 6</p>
<p>Nice! I like the interlocking loop.</p>
I have a very similar project coming up, it's great to see a step by step! Thanks very much.