Dec 5, 2016

DieselPunk Cellphone - Walnut Case, Powered by Adafruit Feather Fona:Preparing the Case

The first things you need to do are download the drawing files for milling the case and laser cutting and etching the acrylic pieces.


Milling the Case
The walnut case was milled on a ShopBot Buddy CNC at TechShop, San Francisco. It's (waaaaay) outside the scope of this post to teach you how to use a CNC. At TechShop locations, you must take an SBU (Safety and Basic Usage) class before working on the ShopBot or other equipment. However, that just gets you started. The real learning is all on you. If you don't have experience with a CNC milling machine, but want to learn:


  • Take a class
  • Come up with a good starter project, not too hard
  • Research - lots of research
  • Try things out, do prototypes, expect to make mistakes
  • When you're comfortable, do it "for real"... probably a few times ;-)

The ShopBot and me are not BFF's, but we can get along. I consider myself perhaps an "Advanced Beginner" (oxymoron), with about 100 hours on the ShopBot over 4 years. To get true mastery, you'd need a lot more exposure, and regularly.

I have learned a few things over the years. Here are a few tips:

  • Always measure your material with calipers. It often is a "little" off from spec, especially thickness - the Z axis
    • Adjust your toolpaths accordingly
  • Because it's organic, each piece of wood is unique
    • Even material from a great, consistent source can have "surprise" differences between pieces
  • Plywood is great for prototyping - until it's not
    • My go-to prototype material is Revell Birch, which is nice and consistent. But you can get little glitches in the wood, still. And sometimes the glue layers in the ply will splinter or bind, messing up the piece.
  • At TechShop on the ShopBot Buddy, you are permitted to screw directly into the spoilboard to hold down your material
    • I pre-drill my walnut material for 6/32 brass screws with a 1/8 in. bit that has a recess cutter on it. If you make a mistake with your toolpath, brass screws cut like butter...
    • Then, I drill again with a slightly larger bit
      • Why? I discovered the hard way, when trying to remove the finished part, that the material was fighting the screws, and I kept stripping screw heads
      • A TechShop Coach showed me that a slightly larger hole allows the screw to hold down the material properly, but not be so wedged you have difficulty removing it
  • TechShop also lets you check out a composite nail gun for material hold-down
    • The small plastic nails this shoots hold material down well, but when finished milling,  you can break them easily with a sideways hammer blow
    • The nails work for plywood, but they're not good for walnut and other hard woods - may not even penetrate the wood fully
  • Allow yourself ample material! 
    • If you look at VCarve milling tutorials, you'll notice there's a lot of waste material around the finished part. There's a good reason for that...
    • I've tried to cut things close to save on material. Whoops, too close!
  • Run your toolpaths from the inside of the part to the outside
And, most of all think! Things you don't expect may happen and you'll have to think your way through the problem.

You'll notice in the Vcarve toolpaths that there are lots of little tabs on small parts. These only hold the waste material down so much. It's a really good idea to mill these holes one at a time and stop to remove the waste material after each step. 

In one early run for this project, the dialpad waste was dislodged and flew into the outside case profile path as it was being milled. It got jammed up against the mill and the wood actually started to smoke and burn. Rookie mistake, lesson learned.


Dialpad cutout jammed the mill, causing scorches


All of the holes on the walnut case were milled, although you could possibly do them with a laser. You'd really have to get your alignment right to laser cut them after the case was milled, though.

Any remaining waste material I could cut out with an Xacto or a small keyhole saw. However, that left tiny nubs of material that were tedious to remove. You can use a Dremel-style rotary tool to knock these down, but sometimes they are necessarily in a very awkward location. So, a lot of precise filing/sanding.

Go over the entire case with SuperFine Sanding Pads from 3M. I tried applying Tung Oil but didn't like how dark it made the case, so left it unfinished.

To give the top of the case a smooth and screw-less appearance, use brass 4/40 inserts. 


Brass Inserts shown on top cover Birch prototype, Left

I used DevCon epoxy to hold the inserts in place. Before gluing in the inserts, add a small bit of masking tape to the bottom, to prevent the epoxy from flowing into the interior threads, like so:

Source: Woodworking Magazine - Tips on Using Threaded Inserts

Use just enough epoxy - excess will ooze out of the hole. Make sure that the inserts are fully inserted into the holes and flush or below the surface of the material. You can use card stock or a flat piece of metal to make sure they are pushed in and level. You can use the back walnut cover as a kind of jig to hold the inserts in alignment by simply screwing the covers together loosely while the epoxy sets up.


Laser Cutting & Etching
Again, no laser tutorial here. I'll assume you have some basic skills with a laser, or can get the laser work farmed out. 

TIP: To reduce scorching on your material when laser etching, cover the area to be etched with Transfer Tape, around $12.95 USD for a 12" x 8' roll. You may have to adjust the power of your laser slightly higher to get better results with the transfer tape on. 

A Universal Laser at TechShop (with VLS4.6 software) was used to etch the front of the case with the "RadioPhone" logo and icons for radio and power. That meant the laser etch had to be aligned fairly well in a tight space. The solution was to print out a paper "target" containing the decorative items and a box that represented the cut-out for the OLED display. Place a dot right in the center of this with drawing software (CorelDraw). Or, as I did in the photo below, just draw two lines on the printed target, connecting opposite corners of the box. Where they meet is the center.


Early test on an Epilog Laser for Centering the etched elements

Line up the box with the actual cut-out on the piece and hold it up to the light to adjust. Lightly tape the drawing down to the material - you'll remove the graphic later on.  

Start the UCP program - and click on Focus View. Using the red pointer as a guide, align the laser focus carriage by jogging X and Y arrows in small steps with the drawing's dot/center . You could also align just by moving your material to align with the red pointer. Next, click on Relocate ViewClick the anchor point for the drawing's center. Finally, click on To Pointer to move that anchor point to the current focus carriage position.



Test this by doing a run without the laser active (on the Universal Laser, just leave the cover open). You can see fairly easily if the laser path is correct or not. If it's a little off, nudge it and try again. You can try this out on scrap material until you get comfortable, then do it for real. You might be able to get good results with the graphic still taped to the laser. However, to make sure I had a nice etch, I very carefully removed the graphic holding the material down firmly with one hand, so I didn't disturb the positioning. Then, I did a the final run.

The speaker and microphone bezels were 1/8 inch transparent acrylic from TAP Plastics. The speaker was "Transparent Dark Yellow" and the microphone was "Transparent Fluorescent Green".  These were going to be back-lit with LEDs. You also need to cut some diffuser material in the shape of the speaker and layer that on the back of the Yellow material with super glue. I used a TAP Plastics product - Smooth Matte Acrylic. That's only available in-store and you only need a small amount. You may be able to improvise this with card stock or other white paper. You want the diffuser in the shape of the speaker if you want to use vintage-looking speaker grill cloth, and have it show through the holes in the speaker bezel. 

The vintage-look speaker grill cloth is expensive. The Parts Express material I sourced is about $17 USD/yard and the project only requires a tiny amount, about an inch in diameter. You could get this on ebay, but looks like similar products are only sold by the yard. To me, it was worth it - helps make the "old time" look. Once cut, the grill cloth was just press-fit into the speaker hole, but you might want to hot glue it in place. 

TIP: For back-lit or side-lit objects, etch the back of the material. You get better lighting results this way. That means if you have any object with a left/right orientation, like text or the "M" logo on the speaker bezel, you need to mirror it. When flipped around, the etch will appear correct. 

Glue the speaker and microphone bezels in place with super glue. Try to keep the super glue only on the edges of the acrylic. Super glue will cloud acrylic - causing those nice, newly-etched lines to disappear!

Finally, remove the hanging loop from one of the "Bead Landing" bezels - they cut easily with a Dremel-style rotary tool. Use super glue to fasten the bezel down as the back "Motorola badge". The logo is included in the github downloads. Just print it out and it should press-fit (or you can glue it) into the bezel.

Mounting the on/off switch in the second back cover hole will be covered later.



No comments:

Post a Comment