HOW TO – Make a Motorola RAZR phone cradle with open source software and a waterjet!

Our pals from Big Blue Saw made an awesome MAKE cradle for their RAZR phone! Simon writes – I love my Motorola RAZR phone. It has the best form factor ever devised for a mobile telephone and the fit and finish are excellent. Unfortunately, owning a RAZR has its problems, too. Without a docking cradle, the RAZR must sit on a flat surface for recharging, increasing the risk of scratches to the back side. Also, there is no good way to hold the camera perfectly steady if you want to take a photo in low light conditions or take a time delayed photo of yourself.

In order to rectify this situation, I designed and built an adjustable cradle that holds the RAZR steady for photos and gives me a place to rest the phone when I’m not using it. The software I used is all open source, and is available for free download. To cut the clear polycarbonate parts for the final version, I used Big Blue Saw, the website I created to help inventors, engineers, and tinkerers turn their ideas into real parts.

I began by drawing a few sketches in my notebook in order to come work through a few ideas for the design.

I had a few ideas on how this might work, so I started cutting corrugated cardboard until I came up with a reasonable prototype. It allows the phone to tilt by 45 degrees or so. The tilting portion is held in place by one nut one bolt on each side.

To get an accurate measurement of the parts, I traced them onto graph paper with 1/4 inch squares. Occasionally, I rounded the measurement to the nearest ¼ inch in order to make things easier.

With accurate measurements of the prototype in hand, I went to my Linux workstation and fired up QCad, an open source CAD program. In QCad, I did a 1:1 scale drawing of each of the parts.

In order to have several parts made by Big Blue Saw, it’s much cheaper to link them together so that they can be all cut at once. I put small tabs between each part and enclosed all of them in a disposable outer piece of plastic. Now I had something that resembled an injection molded plastic model kit.

I wanted to add the Make logo onto the top cross member so that it would be visible when the phone was closed and the camera was ready to use. I started with a PNG image of the Make logo.

This needed to be converted into DXF format so that I could place the logo onto the part with QCad. Using the GIMP image editor, I converted the colors in the file to black letters letters in black on a white background. Black areas would be cut away from the final part, while the white areas would remain in place.

Using the Gimp image editor, I added lines to connect areas that would otherwise fall away, like the center of the letter “O,” when the part was cut.

The file was now ready to be converted to DXF format for QCad. The Autotrace utility is especially helpful for this. I used the following command from the shell:

autotrace -error-threshold 0.05 –output-format dxf –input-format PNG –remove-adjacent-corners -despeckle-level 7 –output-file makelogo.dxf –background-color FFFFFF –dpi 100 makelogo3.png

This produced a file called “makelogo.dxf”.

Next, I loaded this file into QCad.

Oh no, there’s nothing in this file. Or is there? It turns out that the lines are all black and simply don’t show up against the black background. To fix this, select all of the entities in the drawing with Ctrl+A. Next, choose Modify | Attributes from the menu and click the “Continue Action” right arrow button on the left tool bar. Finally, I changed the color of the lines to “Black/White” in the attributes dialog. The outline of the logo was now visible.

I copied the logo to the drawing with the cradle parts, resized it, and moved it to the correct location.

I noticed at this point that the words “technology on your time” were going to be way too small to make with Big Blue Saw. The cutting width of the waterjet is about 0.04 inches, and the lines that made up the smaller letters were about 0.02 inches. I decided to eliminate that part of the logo and increase the size of the word “Make”.
cleaned up logo

I wanted to to do a final check to make sure that the parts were the correct size and everything would fit together correctly. I printed out the file, then cut out all of the parts with scissors.

After a little more tweaking, the file was ready to be sent to Big Blue Saw to be turned into plastic. I fired up my web browser and pointed it at http://www.bigbluesaw.com/. On the “Make a part” page, I entered the name of the file in the dialog and clicked the “Upload” button.

Next, I chose the material, clear polycarbonate.

and the material thickness, 1/8 (0.125) inch

The Big Blue Saw website then showed me several 3D views of my part

At this point, you’d normally place an order for however many of the part you need, but as I work for Big Blue Saw, I didn’t feel the need to do this.

Now let’s take a look behind the scenes at Big Blue Saw. Here’s a photo of the waterjet cutting machine used to make my part.

In the photo you can see the large gantry to move the cutting head. The computer to control the machine is on the right.

Here’s my part being cut on the machine. The stock polycarbonate plastic in the photo is covered with a protective film; this is how it arrives from the manufacturer.

Note the stream of water coming from the nozzle. Waterjet cutting is done with a stream of water pressurized between 20,000 and 60,000 pounds per square inch (psi). Abrasives are typically added to the water stream to give it more cutting power.

The cut part:

The parts broke apart easily by hand. I cleaned up the excess material from where they were joined together using a sharp knife.

For the pivots, I obtained some nice looking screws and nuts from the local hardware store. Everything fit together pretty well.

Applying a few strategically placed drops of CA glue to hold the stand together made me more comfortable about setting my phone on its new resting place.

And now I no longer had to worry about holding the phone steady when taking a photo.