Case Prototype II
Behold, the second case prototype! It’s the result of lots of tweaks, and I think it’s good enough so that I can make the next one out of metal.
The biggest difference between the prototypes is that this new one is milled on both sides -- it’s almost ready-to-use. The mill can only machine one side at a time, so I had to flip the part over once the first side was done. In the picture above, you can see the 4 holes I drilled for pins to keep the part properly aligned after the flip.
I made some changes to the case itself. The space available for the strap didn’t seem deep enough, so I added 1 millimeter one each side. The case is now 2mm taller, so it is a substantial 38 x 43.575 x 10 mm. The width isn’t particularly painful, and the thickness is still less than my mechanical watch.
What’s troublesome is the “height” dimension (43.575). It’s not just because it’s got all those decimal places, but because this dimension prevents the watch from wrapping around the wrist. Most watches solve this problem by placing the lugs lower, or even below the back. I think that’ll compromise the style of my watch, though. The active area of the display is actually off-center, so I have to waste “balance” space to keep it centered on the body - again, the things I do for style! I’ve got big hands, so hopefully the watch will look and feel comfortable -- if not, I’ve sketched some backup plans.
Another change to the case is that I’ve made the insides substantially more complicated. What’s neat about a CNC mill is that this extra complexity doesn’t require any more effort to produce -- I just let the machine do its thing. (ok, I lied a bit -- I had to upgrade my home-brew cad program to make it easier to describe the shape)
I opened up the “balance” space (just under the flex in the picture below) to lighten the watch, and in case I find a use for the room.
At the bottom there is a lip to hold in the screen. I also made a cutout so that the flex cable won’t be kinked:
I also added a charging post. This will be the only electrical connection to the outside world.
The wood didn’t hold all the detail, but the idea is that this pokes through a round hole in the the case back. Inside will be a lug that is electrically isolated from the case and connects to the electronics, and I’ll fill the gap with epoxy.
I added a relief cutout at the inside corners, visible in the pictures above and below. The drill bit is 1/16” in diameter, so it can’t make perfectly sharp interior edges -- by adding these cuts, I make room for the sharp-cornered glass.
One last glamor shot before I cut it free:
(sorry for the focus - I’m playing with a new camera)Here’s how it looks on a strap - nice and clunky! :
A note just to be clear: the above picture is a mockup only -- there is still a long way to go!I tried it out on my wrist, and I think it looks ok -- maybe it’s too long, but I’ll need to install the band to see if it feels right.
Inside there is a lot of room:
The charging post was misplaced, so I’ll move it up to make more room for the battery leads. I’ll also probably open up the inside of that post so there is more room to put the electrical contact. I wish I could make a shelf to hold the printed circuit board, but that would be hard to make with my limited mill -- instead I’l probably glue some sort of plastic spacer to the edges of the display to keep it from getting squished.
Next up: I might try to make the case back. I’ve got a big project at work, and then almost four weeks of travel, so watch development might slow down a bit.
Monday, November 6, 2006