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Backdated updates (1 of 2) - Building an enclosure

A project log for Time Circuits Timepiece

A practical-size, Back to the Future themed digital clock mimicking the "Present Time" portion of the DeLorean's time circuit displays.

stephen-holdawayStephen Holdaway 02/14/2017 at 11:395 Comments

I've been meaning to upload this project to Hackaday since I started planning it a little before Christmas 2016. Now that I've left it sitting on a shelf for a month waiting for components to arrive (read: being lazy), here's an update on what you've missed so far.

As soon as I had this idea, I went and ordered a bunch of components I knew I'd need. In retrospect it was possibly a poor decision to do this before designing anything, but we'll see how that turns out later on. The important bits I grabbed were:

Element 14 ships quickly to New Zealand, so after a few days we have this:

These were bigger than expected as I mistook 0.8" as a component height when it was really digit height (read the datasheet, silly). The chunkier size works quite nicely though, even if unplanned.

Building an enclosure

While browsing my parent's garage over Christmas, I found a piece of 1" x 2" galvanised rectangle hollow section (RHS) that matched the look of the galvanised sheet metal the film appears to use. You can buy this kind of stock at most building supply or hardware stores if you don't have any lying around. This one has 1.6mm walls.

Excited by the possibilities of my newly acquired tube of metal, I took a ruler, Autodesk Fusion and roughed out how this could work. First rookie mistake: not enough tolerance around the digits, but more on this later. Apologies for the photo-based screenshot:

The AM/PM indicator is more spaced out than the film version as I have a ye olde' embossing label maker with relatively large tape. Another small deviation from the film version, but this is just a tribute. The hole in the top is for a light sensor (LDR) so the display brightness can be optimised for the ambient light level.

Milling the Metal

Having never really worked with metal, I figured I'd be at high risk of completely destroying my material if I tried to cut these precise holes myself. Fortunately, one of my uncles owns a Bridgeport mill, and he was happy to help.

I hadn't decided how the PCB(s) would fit into the enclosure at this point, but figured a few good sized ports in the back would help with assembly. Converting the model to a drawing ended up with this:

Then into the milling:

Getting set up for milling

After the front was milled. Some pretty nasty burrs on this.

Milling the access ports

With a little more deburring and labels applied, the result was this:

Milled and labeled, sitting on the 1:1 drawing with annotations

If you were looking closely, you might have noticed that the holes cut in the front are too big. You'd be right - in haste, we collectively made a few manual math errors and made the front cuts too tall. By the time we noticed, we'd milled too much to correct the error, so we just went with it. The displays will be covered by a transparent acrylic filter, so there's no problem with the larger holes other than having less space for the labels.

So that's the frame of the enclosure done - early January. There's one more backdated update about 3D printing end caps for the frame, then you'll be up to speed and we can get to the electronics!

Discussions

Jan wrote 02/25/2017 at 11:56 point

You own that milling machine or have your own shop? The case and labels look fantastic! Really looking forward to see the finished clock. And now.... take this skull :)

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Stephen Holdaway wrote 02/25/2017 at 18:39 point

Thanks! I'd love to own that mill, but it and the workshop in the pictures belong to my uncle. I live in a small apartment (in a different city) where my "workshop" is the kitchen bench! ..does the job, but it would be so nice not to have to pack up every time we want to cook a meal :D

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MrMaint wrote 02/15/2017 at 03:46 point

You have a 3-D printer, so why don't you print lables in the correct dimensions? Do you have red, Black, and white filament?

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Stephen Holdaway wrote 02/15/2017 at 04:55 point

Hmm, I don't think I'd be able to achieve a high enough accuracy with my 3D printer to get a nice result (0.2mm layer height, 0.4mm nozzle). To get exactly like the film, it'd  probably be easiest to have them printed at high resolution on appropriate paper stock, or just maybe a digital label maker.

I'll see if I can dig up any info on how the ones in the film are made. From eye-balling the frame above, I'd guess they're made with two layers of vinyl.

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davedarko wrote 02/14/2017 at 15:12 point

Nice. I always found it funny that they've used foils for the month row, and 7 segment displays for the rest. Looking forward to see the project in action :)

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