Legs Finished!

I did the final things on the list today to the legs. Yesterday I had dabbed a bit of touch up body filler--the Bondo kind in a tube, it's petroleum based, so it dries with air contact-into a lot of little flaws revealed by the first coat of primer. Today it just took a few minutes to sand those down flush with some 320 and 400 grit paper. Then I vacuumed the legs thoroughly and took them outside for another coat of primer. The temp was probably around 50 degrees, which is just at the bottom of the operating range for that spray paint. But primer is pretty forgiving. The second coat went on without any real problems and these are ready to go now:


This is the whole package for the builder who commissioned these from me. I'd probably put a coat of black paint on the hubs if they were going in my droid. I'm happy with the results:







The only remaining flaws at this point are very small and will be covered by paint. The next steps would be to add a few more coats of primer with some very light sanding--maybe with 00 or 0000 steel wool in between--then several light coats of a gloss white with some light sanding in between the early ones.

What did I learn this time through:
I got the high end baltic birch 12 ply plywood. It's very good, stable, and straight. But the outermost layer, the layer that will end up showing to the eye, is fragile. Home Depot and Lowe's usually have some good 12 ply cabinet grade plywood, and I have found that the outer layer on that stuff is a bit thicker and a bit more sturdy. I'd go with that next time. I'd also cut a 3" circle out of the insider layer of the legs at the top where the shoulder hub is going to sit, although the router method I used yesterday wasn't too bad. The router method for cutting the pockets out under the shoulders is a very clever idea I got from Mike Senna through Victor Franco. The best way was to have a couple, but not all, of the layers glued, and then rout out the pockets with a template from the inside. Each leg weighs several pounds. I think that next time, I could rout out a lot of material on the insides of the pieces without compromising the strength at all. The ankles could have a lot of interior material removed, the channel for the wiring could be wider, and the shoulders could be more hollow. That could save a pound or two per leg, and that would add up. The modification to the center leg tip to make a better connection to the foot shell is an improvement. Next time, if I was setting up a fixed three legged droid, I think I'll work out the plans to do that on all three legs--building the ankle locks into the design.

Legs 9: Finishing touches

Several small things finished up in the last few days on the legs. First, I needed to cut the second 2.5+" pocket in the bottom of the shoulder hub pocket. After fooling around a bit, I remembered my technique from before. The easiest way to do this is to set a router bit down to the right depth plus a bit, and then just freehand the inner circle out. There's not much you can mess up, and the pocket won't show, so the freehand line won't be a problem.



I'm all about fast and efficient, and this was both. The results:



I think the plans call for 1.34" depth on the shoulder hub. I cut this to 1.4" or so. There will be some variation on the resin or the aluminum shoulder hubs that the club produces. I couldn't get mine off my droid to check. But I think that the resin hubs will fit, or if they don't, the backs can be trimmed and sanded a bit. And there should be clearance here for the aluminum hubs too. If not, a bit of dremeling could bring the levels down for a good fit. The hubs should fit flush to the face of the body of the leg.

Then I spent some time trimming, sanding and cleaning up the under shoulder detail pockets:



After painting, the wood grain and some chiseling will show inside of these if someone was really looking for it, but it would be hard to spot. I think if a builder wants the inside behind the greeblie to have a really clean look, a piece of styrene, maybe .020, cut to fit and glued back there would polish it just fine. That would take 5 minutes.

And now after some finish sanding down to 320 grit, and some filling in a few odd spots, these are ready for a coat of primer:



The primer makes any chips, dings, gouges, or gaps that I have missed so far immediately obvious. So I'll let this dry over night, fill some remaining spots, do a light finish sanding, and then one more coat of primer and these are ready to ship out.

I've completed that process on the center leg and they are ready to go out.





Any remaining wood grain will be covered by paint. At this point on my droid's legs, I layered on several coats of primer, sanding lightly between each coat with 320 or 400 grit, and then I built up several layers of gloss white, sanding between the early ones. The layers and sanding will progressively fill and cover any remaining micro wood grain texture to the point that the finished surface will be complete glassy and smooth. But I'm leaving that to the guys who bought these from me. Final steps tomorrow, and then shipping early next week.

Legs 7: Getting Close

I set up the table saw yesterday to make a very shallow cut around the body of the legs. There's a detail there on R2D2 that needed to be added. I've tried to get a good picture of it several times, but no luck. My camera doesn't do extreme closeups very well. I set the saw blade to run .06" high (yes, that is possible), and then after carefully measuring the location, I ran the legs through so that there was a groove that runs all the way around:

The tape helps prevent blowout with the outer layer of the plywood.


I also finished gluing the curved pieces to the center legs:



Then I cleaned the excess glue up off of those, and used the orbital sander to bring down the edges of the MDF pieces where they overlapped. I got the MDF pieces all sanded flush and incorporated. I also put a 1/2" axle hole in them. Be sure to clamp a scrap to the back side when you drill to prevent blowout. The center legs are almost finished. I'll go over them once more for any gaps or dings that need to be filled, fill them, finish sand, and then I'll put a coat of primer on them to see to what extent any seems or joints are showing through. You can also see the modification on the tip of the leg here. This extra wing will rest down flush into the foot shell groove and provide a stable joint between leg and foot. And since this is on the back of the leg, it would still be possible to straighten this leg up for an upright posture:



I also finished gluing and nailing the four ankle panels to the bottom of each leg. And today I cleaned up the glue and then sanded the sides on the belt sander to get a good clean joint.



Once that was done, I could finally lay out the lines for the leg tip:




I roughed those cuts in on the band saw.



And then finished them down close on the belt sander with the belt tipped up to 90 degrees. The end results are starting to look familiar:



So what remains is to mount those curved pieces on the right onto the ankles, cut the round hole into the shoulders for the shoulder detail, and then do some finish filling and sanding.

One problem I've been having is blowout on the the outer finish layer of the plywood. I don't know if I got a sheet that had too little glue in the final layer or if the final layer is just too thin, but some spots are really fragile and friable. The worst example is when I made this cut through with the band saw:



It all blew off of there so suddenly an severely that I have to think that they messed up on the glue here. But I'm not sure. This sucks as it produces a lot more work for me and it lowers my confidence about the rest of the pieces enduring use over the long term. I have a couple of options to fix it (the other spots are much less bad than this). I can try to fill the region in with glue, body putty, or fiberglass/resin Bondo and then sand it in to blend. I think the last option will make the best looking and most durable results. I'll work on that this week. I also think that once I get some primer on there to seal these up, and then their new owners get several more coats of primer and several finish coats of paint, that paint will cure and form a consolidated skin that will be more durable. The wood won't do this once it's painted right. But I have to be extra careful until then.