R2-D2 by Dan Baker

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The foot shell flatpack is cut in vinyl.

Templates are applied to .080" aluminum. THAT should stand up to pretty well anything.

Two full evenings of cutting mark the end of the foot shell cutting. It's slow going with such thick metal.

Now time for something cool. Please understand that out of all the things I have done in my life, welding has never been one of them. I've done soldering on circuits, and had plans to try and do some brazing at some point, but never got that far.

I had heard a few people say that one of their major contact points between their droid and the public was the feet. People come up to hug R2, and step right onto the foot shell. That definitely made me want metal feet, so I chose .080" aluminum for the shells.

I like JB Weld, but only trust it so far, so I began to look for an aluminum welding method. That's when I ran across ALUMALOY! This stuff is not only so cool and molecularly advanced, but it's a LOT of fun!

Alumaloy is a low-temperature, fluxless welding rod that, when cooled, provides a bond stronger than the base material. It even bonds to itself, so can be used to bridge gaps and seal holes or fissures.

Alumaloy's melting point is 738°F, and its specific magnesium content prevents it from producing the blindness-inducing sparks of TIG/MIG welding.

The tools needed are: hand-held propane torch, stainless steel wire brush, Alumaloy rod, safety goggles and thick gloves.

I picked up this handy device at Harbor Freight. Anyone familiar with soldering knows about the "Helping Hands"- alligator clips on bendy wires to hold your components. This is the same idea, but uses vice-grips and ball-jointed arms. In a nutshell, it keeps the heat from being transferred from the metal to your hand (or the table, setting it on fire like I did), and it'll configure to pretty well any angle.

First step is to clean the area to be welded with the stainless steel brush. Then you have to position the pieces right up to each other. The "Hands" took a bit of time to get exact, but they sure made a difference compared to my trying to hold previous pieces with pliers, wood, or metal tape.

Now we preheat the metal. With Alumaloy, you heat the metal, not the welding rod. If you just heat the rod, it'll crumble. Even though it was 85° in my workshop, you can see the metal condensing like it had been sitting in the freezer. I found that heating the entire piece initially helps, since it prevents the heat from being shifted away from the task at hand.

After a few minutes of pre-heating, you test the metal by scraping the Alumaloy rod against it. If nothing happens, it's not ready yet. Keep heating.

Just like solder, once the base material reaches the desired temp, the rod instantly liquefies when you touch it to the metal. It will flow down and fill any gaps, and you can move back and forth perpendicular to the seam to further bond the pieces over a larger area.

Be sure to keep the torch moving, as the aluminum tends to cool rather quickly. If you need to go back and adjust an area, just take the Alumaloy back up to 738°F, and all at once it'll become a shiny pool of liquid metal that you can push around. Another solder-like property.

The finished weld is a smooth, shiny finish. Once it cools, you can literally grab the two pieces and wrench them back and forth, but the weld will remain intact while the aluminum bends!

The first weld on this foot is complete. It is slightly out of square, but the weld is strong enough to accept a bit of force to bring it back in.

The finished outer foot shell (minus the lower sections and the curved panel).

It is very hard to weld together materials of different thickness', so the inner curved section will actually be a piece of .020" aluminum that is JB Welded in place while it's held on by braces.

Here is the middle foot. The joint ends are filed down so that they evenly match the front of the foot shell.

NOTES:
1. Aluminum is a very efficient heat-transference material. That is why it is used as heat-sinks for CPU processors. Thicker aluminum is more difficult to thoroughly heat, because it is dissipating almost as fast as you are heating.

If you're trying to weld two pieces of aluminum in a configuration where one piece is laying flat on the table and one is held upright, be aware: The standing piece of metal will heat faster than the piece laying flat. It has nowhere to send the energy it's receiving. The other piece, however, will be sending as much heat as it can to the closest thing touching it- the table. I set three tables on fire while learning this, but they were small fires, and I had marshmallows on hand.

2. Usually, one piece will reach the target temp before the other one. It is tempting to start welding at that point, but WAIT for BOTH the pieces to reach 738°F, or the Alumaloy will not bond with the cooler piece, resulting in a weak weld that will break off the first time it's stressed.

3. It took me about a week and three wasted rods to really get the hang of Alumaloy. Remember, I have never welded before this! It was very encouraging to see such fine results so quickly.

And finally, I've got three welded foot shells. The edges still need to be filed down and the panels cut out, but here they are. Now for the curved inside section of the outer feet. This took a bit of trial and error, but I finally found the right material...

Using a super-thin piece of .020" aluminum, I secured it to a piece of cardboard tube that was about the right diameter. I slowly hand-rolled the piece until enough of the sheet was curved to fit. I just used a squared-off piece of aluminum. It'll have to be trimmed, but it gives me one less thing to worry about when I'm trying to fit these things together.

The new curved section is placed inside the foot shell for fitting, adjusted, then tightly secured with electrical tape. I like using vinyl electrical tape because it's stretchy and strong, but won't distort the piece I'm holding down.

Tipped on its side, the new joint is given a generous amount of JB Weld and left to sit overnight.

Since it was curved by hand, I needed to straighten the flat bottom portion after I 'Welded the sides. It's held in place and JB Welded too.

Once they're cured, the excess aluminum is cut away with the Dremel.

The underside of the completed foot shell.

Now, the edges are filed down smooth with the thicker sections of the frame.

*Sniff* It's a beautiful thing. The curve is perfect, thanks to the rigidity of the metal, and the entire foot shell is aluminum!

All three foot shells are lightly filed and puttied.

The corners are filed to match, then sanded smoothly together with the electric sander.

Decals of the outer foot panel are re-applied to the foot shells. The basic shape was cut out before using a vinyl template, but if the vinyl was left on when the piece was being welded, the aluminum would transfer the heat to the vinyl, and it would burst into flames. Hence, the reapplication of vinyl.

Two evenings and about 30 cutting wheels later, the outer foot panels are removed.

Once the panels were cut out, the edges of the opening and the panel are cut, filed and sanded smooth down to the edge of the vinyl templates.

A piece of .080" styrene is cut to fit inside the outer wall of the foot shell and taped into place. Because of the variegated edge created by the welds, I chose styrene to use here, since I could trim it to fit the contours very easily.

This shot from the inside of the foot shell shows the styrene being clamped into place to keep it tight, and JB Weld was drizzled into the corner and gap.

Once the JB Weld dried, the opening was again cut out of the styrene. This allows access to the motors and drive system, and creates the recess between the foot shell and the panel.

For the skirts on the foot shells, the vnyl patterns was transferred to some .125" styrene.

The recesses were cut out with the Dremel, then hand-filed smooth.

A piece of .020" styrene was glued to the back of the skirts, then each glued-together section was cut apart on the bandsaw.

The corners were hand-beveled on a Dremel grinding wheel. I didn't bother beveling the top of the pieces.

The skirts are ready to be installed.

I began by taping a single section in place, then the one next to it. Using a thin piece of tape, I taped their corners together, then worked my way around the other corners.

The corners of the styrene skirts were first filled with model cement to melt them together, then JB Weld was drizzled into the new joint where the skirts meet the foot all the way around.

One the JB Weld set, the outside joint is fulled with putty and sanded to a nice corner.

The finished outer foot shell, with the side detail in place.

Because I found that cutting the side gaps on the outer feet took foreer with the .080" aluminum, I cheated on the middle foot. I cut the panel gap out from a piece of .080" styrene, then glued one to each side.

The excess was left to compensate for the extra thickness of the shell due to the addition of the styrene sides, but was trimmed down after gluing, then sanded and puttied in the gaps.

The side panels for the center foot are also cut from .080" styrene.

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