Introduction: Walnut and Raspberry Extravaganza for Pi Day
To celebrate this year's pi day (3/14), I decided to make a walnut and raspberry pi (or two, if time permits).
I started with a walnut wood case for the Raspberry Pi SBC.
Note: If you plan to try your hand at this build, please read the comment by oragamiunicorn and my reply to it, in the comments section.
Supplies
A raspberry pi SBC (for this build, I used the Raspberry Pi 3 model B).
A plank of walnut wood, an inch or more thick.
4 small wood screws
Step 1: Marking and Cutting
I started by marking the approximate size of the piece I will need on the walnut plank: I placed the pi board on the plank and marked with a pencil the approximate size: around 2 cm more than the length of the board for the length and 1.5 cm more than the width of the board for the width.
I then used a sliding miter saw to cut off the workpiece from the plank. After that, I cut the piece to width on the bandsaw.
Step 2: Preliminary Sanding
I used a benchtop belt sander to remove the saw marks from my workpiece and soften the edges. I started with a P24 sanding belt (very rough), then proceeded with progressively finer grits: P40, P60, P80, P120 and P150. Starting with the P80 grit, aside from the sides of the workpiece I touched the edges too, to make a fillet. There was no point in using finer sandpaper at this stage, so I used the bandsaw again to separate the workpiece into two pieces: top and bottom. The position of the cut is not critical: I went for two more-or-less equal sized pieces.
Step 3: Making the Recesses: Bottom Part
With the two workpieces cut to size, it was time to make the recesses for the circuit board. I started by placing the board on the bottom workpiece and marking its position with a pencil.
I then used my improved Poor Man's Milling Machine for Wood to cut the recess. I clamped the bottom workpiece into the vice and started cutting the recess in two steps. First I cut a 3mm recess, then I placed the board into the recess to check that the size is correct, then I removed an extra 2mm. Again, the depth is not critical: the important things at this step are: a) that the board fits in the recess without slack (we don't want it to start moving around in use) and that we don't cut through all the way to the bottom.
Then I removed another 2mm, this time leaving a 'step' of -12 millimeters width on each of the 4 sides. The new recess is for the component leads that stick out under the PCB. The board itself stays seated on the steps.
After that, I used a chisel to cut notches for the components that protrude out the sides of the board: the connectors for the power plug, the earphone plug, the USB, HDMI and Ethernet ports. The idea at this stage was not yet to allow access to the ports, but merely to allow the board to be seated firmly on its base.
I continued this work on the milling machine, removing a little material, then testing with the PCB, removing some more etc, alternating between the milling machine and chisel work.
Step 4: Marking the Recess Position: Top Part
Using dial calipers and a ruler, I transferred the position of the recess from the bottom part to the top one. Unlike the bottom part, where the entire area covered by the PCB was recessed, in the top part it is important that some parts are left intact in order to hold the PCB in place. The reason I marked the position of the entire bottom recess was to know at all times which part of the bottom piece corresponds to which one in the top part.
Having done that, I proceeded, again with the dial calipers and ruler, to mark the parts of the top piece that DO need to be removed, that is the places where components on the PCB protrude above the bottom piece of the case.
Step 5: Making Recesses in the Top Part
Having marked the places where I needed to cut the first recesses, I proceeded to remove most of the material using the milling machine. Like in the previous step, I was alternating between removing material, testing the fit, removing more, using either the milling machine or the chisel, as appropriate.
One by one, I marked and cut all the recesses needed, until I was at last able to close the two pieces, with the board inside.
Step 6: Making Holes for Screws
The next step was to make the holes for the screws. To do this, I placed the pi board on the bottom case piece, placed a screw in one of the board holes and pressed it down to mark the hole position in the case piece. I repeated with the 4 hole positions. I then moved to the drill press and made the 4 holes using a 3.5 mm bit. Then I turned the case piece around, changed to a 6mm drill bit and enlarged the bottoms of the holes to make room for the screw heads.
Having done that, I replaced the board between the case pieces, closed them and pressed a screw into each hole from the bottom to mark the hole positions in the top piece. I then used a 2mm bit to predrill the holes to avoid the top piece splitting when the screws were placed. I had used a 3.5mm bit in the bottom part, where the screws must move freely. In the top part, I used the smaller bit so that the screw thread would bite into the wood. Where in the bottom part I made through holes, in the top ones I was extra careful to make sure to AVOID making through holes which would mar the top, visible surface.
Step 7: Final Sanding
With the board sandwitched between them, the top and bottom parts of the case closed with an offset from each other. This was something I was expecting - to minimise it, I would have needed to make much more accurate measurements and cuts (with a sub-millimeter accuracy. Rather than spend extra effort doing this, I proceeded with a moderate accuracy, knowing that I would be able to fix this problem at the end.
To do this, I screwed the "sandwich" together and proceeded to sand it as if it were a single piece of wood. I sanded the four sides starting with a rough (for this stage) P120 sandpaper and proceeded all the way to P360.
I took extra care to smooth all edges and corners. The key to doing this is to keep the workpiece moving at all times in a circular motion.
With the last 4 grits used (P150, P180, P240 and P320), before sanding I used a wet piece of kitchen paper to wet the case in order to raise the grain. This ensures that the finishing process will be much easier.
Step 8: Fine Tuning the Holes for the Ports
With the final sanding complete, one more thing remained to be done before applying finish. This was the fine tuning of the holes that give access to the ports (USB, Ethernet, HDMI etc). To do this I started again an iterative process of marking, cutting, testing, marking again etc. At this stage, any mistake would be a catastrophe as there would be no way to fix it afterward, so I proceeded with caution, removing very little material in each pass.
At last the case was completed. I double checked using real computer cables that all ports are accessible. When I was satisfied that everything is OK I screwed everything together and proceeded to apply the finish.
Step 9: Applying Finish
Depending on the wood species, I apply different kinds of finish. Walnut is the one species with which I have no clear preference: I can apply walnut oil or shellac or both. Applying walnut oil improves (in my opinion) the color, but causes walnut to lose its shile. In this case, as I was using Greek walnut, which has a gorgeous color to start with, I decided to forego oil and apply just a few coats of shellac. One of the many nice properties of shellac is that it dries very quickly and you can apply many coats in a small time interval. As a result, the finishing process was over very quickly and I had my walnut and raspberry pi, at long last, completed!
Step 10: Bonus Build: Walnut and Raspberry Pie: (1) Ingredients
At the start of this instructable, I promised that, time permitting, I would make TWO walnut and raspberry pi(e)s, not one.
Time was kind to me, so to celebrate the fact that I finished the walnut raspberry pi case in time, I made a walnut and raspberry pie.
Ingredients:
FOR THE JAM:
- 2 apples, around 300 gr each.
- 140 gr water
- 60 gr brandy
- 120 gr sugar
- juice from 1 lemon
- 1 tsp cinnamon
- 1/2 tsp cardamom
- a piece of ginger
FOR THE DOUGH:
- 260 gr flour
- 35 gr caster sugar
- 150 gr butter, cold but not frozen, diced
- 1 egg
- zest from 1 lemon
- 2 tbsp cold water
FOR THE TOPPING:
- 140 gr walnuts, shelled
- 250 gr raspberries
Step 11: Bonus Build: (2) Make the Jam
To make the jam, I used the Monsieur Cuisine Plus , a blender with integrated heating function:
- I peeled and cored the apples, cut them in small pieces.
- I cut the ginger in small pieces.
- I inserted the apple pieces in the bowl, closed it, pressed the "turbo" key 2-3 times to shred them, then added the remaining ingredients set it to work on speed #3, 100 deg Celsius, 25 minutes. When it finished, I saw it was still too loose, so I let it boil for another 25 minutes, then another 10 to achieve the consistency I wanted. The big advantage of this appliance is that you program it and let it work on its own.
Lacking a heated blender, you can shred the apples in a blender, toss all the ingredients in a cooking pot and let it boil, stirring occasionally to avoid it sticking.
Step 12: Bonus Build: (3) Make the Dough
To make the dough, you mix all ingredients together. The idea is to mix them well, without having the butter melt from the heat of your hands. To do this, you start with cold ingredients and work as fast as possible. When the dough is ready, you put it in a piece of cling wrap and leave it in the fridge for an hour or so. Then, you open the wrap, cover the dough in flour and roll it to a thin sheet.
Butter a tart pan, roll the dough sheet over the rolling pin and place it on top of the pan. Press it in so there are no air bubbles left underneath, cover with beans to avoid it rising and put it in a preheated oven at 160 dg. Celsius for 30 minutes.
Next, remove the beans and allow the dough to cook for another 15 minutes at 160 deg.
Step 13: Bonus Build: (4) Put It All Together
Lay the raspberries on the cooked dough, lay the jam on top and "paint" the letter "pi" with walnuts. Then put it back in the oven and let it cook for another 30 minutes, this time at 180 deg.
When it is cooked, you can "retouch" the letter pi, adding more walnuts on top of the cooked ones, for better contrast.
It is now time to enjoy the fruits of your labor!