Tuesday, February 4, 2014

Eclipse Clock - making the case

I've had the circuit running on the breadboard and the software is in a workable state, so what's next? Well, I could work on the circuit board or the case. I chose the case. My idea was to use MDF (medium density fiberboard) for the back since it is very easy to work with and stable. I also knew I needed a way to cut perfect circles. I have a Bosch Colt hand router that came with a fence bracket. I was able to use part of that along with a 1/2" nylon bushing, screw and wing-nut to make a circle cutting jig. Pictures of that later. First, I had ideas about how the case would look and how it should be put together. As I got to the point of actually making the case, I jotted down a cross-section diagram with dimensions in my notebook.


The dimensions in there are pretty accurate. Let's call the parts "back", "spacer" and "front". The back and spacer are made from 1/2" MDF and the front was made from some curly maple that I got at a local specialty wood store. I chose curly maple since it was interesting to look at and quite hard. I bought a 7" x 15/16" board that I cut into 2 16" sections and jointed and glued together to form a 14"x"16" piece. I made the one dimension 16" so that it was easier to feed through a drum sander. I ran the glued board through the sander until each side was perfectly flat and no glue seam remained.


Now, I had all of my materials and I needed to start cutting circles! I got a 1/4" straight bit for the router and made some test pieces for the back. The problem was that the Adafruit 1M LED strip needed to form a perfect circle with the ends meeting perfectly so the LED spacing would be consistent, even at the joint. 1M circumference results in a 12.53" diameter circle. I adjusted my circle cutting jig to 6.25" (radius). It turns out I needed to try a couple of times. The first back piece was too small (the ends of the LED strip overlapped by about 1/2 LED length.). The second one was too large (too much gap in the ends of the strip). The third one.. the third one was just right! I had very minimal overlap and didn't feel like I needed a 4th!

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This picture shows the MDF after I've made about 3 passes. You really shouldn't take more than 1/8 of material at a time. The bit would overheat. You can clearly see the jig I made in this picture. The hard part was measuring between the bit and the center of the nylon spacer. I had to use a screw driver to tighten the screw and double check the measurement each time. Notice the 1/2" guide hole in the MDF. That's what guides the entire cutting operation.

I should point out what might be obvious, but not to somebody who is new to this type of thing. You must make the larger diameter cuts first. Cut the outer diameter groove, then I actually went further out and cut all the way through to make the disk. This was how I left that little shelf for the LED strip to rest on. Once the outer diameter is cut, move in and cut the inner radius. Once you cut the inner radius, you can't go back and do the outer radius because that guide hole is no longer part of the piece!

The next thing I made was the spacer. It was a circle of MDF about 3/4" wide. After that, I could start on the maple case front. I chose one side that would be visible on the outside based on the grain pattern I liked. I then cut the opposite side. I drilled a guide hole and started routing the groove on the outer diameter. This maple is definitely harder than MDF! Go slow and make small depth adjustments as you go. It will take a while!


Once the circle is cut out, I had to start on the recessed area. This is visible in the cross section and will be where the electronics live. I made 2 grooves that formed the boundary for the recess. These were 3/8" deep.


Next, I had to remove the rest of the material between those grooves. Doing this with that 1/4" bit would have been time consuming. Luckily, I had a 1/2" bit from another project so I was able to use that to clear the material in 3 passes (many more if you consider advancing the depth bit-by-bit).

Finally, I was done clearing out the recess. I should mention that I had to run the shop vac between each pass due to the amount of sawdust created. Here's proof!


Final step is to remove the center disk and complete the front case shape. I worked on making the groove deeper and deeper, then a final check of my spacer to be sure it fit. This would be the last chance to get in there and adjust the recess area!


Once that was done, some light sanding and checking how it all fit together. I decided to mount the LED strip next to get a better idea of how it all worked when put together. I used about 7 dabs of hot-melt glue to attach the strip. Prior to doing this, I created some space behind the joint in strip. I needed room to attach wires and route them to the interior of the case.


I also used a saber saw to cut a flat on the spacer ring. I figured this would leave plenty of room for the electronics and was part of my original plan when calculating dimensions.


See? Plenty of room for the Arduino Micro and my own small board (which I still need to build!) With everything held together, here's how it looks. I have some rough sanding to do on the outer and inner radius of the front part of the case. I also used a chamfer bit to ease the front edge of the case. I think it looks pretty slick.



Next time, I'll show more about the electronics and the finished look of the case.

1 comment:

Scot said...

Nice work, David!