Happy Voorhees Day (day 90)

For the past few days I’ve been continuing work on the Zaku knee joints. The design of this assembly and the mechanical arrangement for the knee armor goes back to the early days of the project, and it’s still something I take pride in. But at the same time I am kind of anxious to wrap it up and focus on other parts of the legs. Maybe within the last 10 days of the 100 day challenge I can even build the hip and waist joints needed to connect the legs to the rest of the build and have a look at the Zaku in a largely-complete state.


Last time I had gotten most of the major components of the knee joint done, but there were a few notable exceptions, which I’ve addressed this week. First off, while the structure of the knee joint had been mostly built, including rods for the polycap joints and the structures that would surround the polycaps, but I didn’t add the polycaps themselves. It’s a pretty simple thing, but I added them earlier this week: I trimmed some polycaps to fit in the joint cylinders, put in the polycaps, and packed them in with some epoxy putty. When I recast the parts I’ll remove the polycaps first, leaving a hollow space in roughly the shape of the polycap. I’m using Wave 3mm polycaps here, but most 3mm polycaps should be roughly the same size if I need to switch to different ones in the future.

Another detail I hadn’t previously incorporated into the knee joint was the “endcaps” or “knobs” that are on the sides of the knee blocks, at the ends of the joint cylinders. I had scratch built these parts several years ago, and made a two-part mold to make copies of the part (and both the original part and some resin copies can be seen in prior days’ work on the knee joint) but I hadn’t cast a full set of them, so I did that this week as well. There is one problem however: These parts are a little bit too large for the knee block as I built it (the knee block is designed for 9mm diameter joint cylinders, while the recast endcaps are more like 9.5mm diameter) – I could have taken a bit of time to reduce the diameter of the endcaps, maybe even make a new mold based on the revised part – but I decided to go with what I’ve got. The recast resin parts are soft enough that I could “convince” them to fit. I cast four copies of the endcaps and used cyanoacrylate to glue them to the sides of the knee block. These will be recast as part of the knee block part. Apart from their cosmetic function, they also provide a little bit more depth in the knee block parts for anchoring the joint axis rods. (Each half of the knee block has the 1mm side plate, the 0.5mm disc, and the endcap – all together that’s around 2.5mm-3mm depth for anchoring a 3mm diameter rod)

A few other details I addressed this week: I built the structure that attaches the upper joint cylinder to the upper leg, I added a styrene rod to the bottom portion of the knee joint to connect it to the lower leg, and I started shaping the knee armor part. (This is the third or fourth version of the knee armor I’ve built: I even went as far as making molds and recasting one of the previous versions… This one is a revised version, it’s a little bit longer than previous versions so it covers more of the knee block when the knee joint is bent. The current part is visible in rough form in previous updates: basically a few styrene plates glued together. With a little bit of sanding time it starts to look a lot more as it should.)

With all this, I am nearing the end of my work on the knee joint. I am feeling a little anxious to work on something else, though the most natural choice is the leg parts, and the lower leg in particular presents a whole suite of challenges that I’m kind of not looking forward to having to solve. I’ve been through various attempts at building the lower leg parts before in the past, one of the fundamental challenges is that the lower leg as I designed it is asymmetrical, so I can’t just make one lower leg and recast it to make a copy. I need to make two lower legs that match. This version is the most recent build – a few years ago I came up with an approach to making the left and right legs match better by cutting them apart and using an alignment guide to match them up to each other in different combinations. It’s worked well but there’s still work needed to get the parts ready to recast.. And that’s where things get a bit nebulous. Do I want to try to improve the look of the parts, or plow ahead with what I’ve got? What kind of parts breakdown am I going to use to recast these things? What intermediate stages of work do I want along the way? And so on. Sometimes when I pick up these parts I just aimlessly fiddle with them for a while and don’t make any real progress. At the moment I’m not too sure how to resolve all these questions, so I’ve focused on basic things – sanding parts to match them up better and make a few minor improvements to the contours as I find things I think I want to change.

One thing I did decide on was to take the two parts that form the top and front of the lower leg (the portion of the lower leg that I think can be symmetrical) and bond those together into a single part in preparation for recasting that portion of the leg. Doing this means the old alignment jigs aren’t really compatible with the part any more, which may cause problems when working on the other lower leg parts… But I think this is probably a good way to proceed: take this part of the leg as close to “finalized” as I can. The whole approach with the alignment jig was good for getting symmetry but at some point it kind of comes down to eyeballing things, and accepting a good but imperfect result.
I also added a polycap to the part of this assembly, so I could connect the knee joint to it. This bit was a bit of a slog because the part is almost completely made of epoxy putty, and carving out enough of that to put in a 3mm polycap was pretty slow going. But it means the knee joint is actually integrated with the lower leg now, to some extent, which is great to see.

I am approaching the end of the 100 day challenge and, no surprise, this build won’t be done by the end of it. But it’s all good progress and I still think I can complete the build this year.

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