Tuesday, April 03, 2012

Miscellaneous part upgrades

I've finished up a set of long needed upgrades to address a joint problem: lack of a locking mechanism to retain the pin swivel joints in place. Long overdue, but I now have the tools and tech to pull it off. The main priorities were to upgrade the arms with this new tech, then the legs.

The mechanism is fairly simple, but annoying to build by hand in multiples. The principle is to use a locking ring clamp around a groove in a pin. The ring must have an opening to behave like a spring, so it widens as the pin passes through, but contracts after the groove reaches the position. The ring should then hold the pin in place but also allow for rotation. Much easier to do with plastic parts than Magic cards and paper clips.

The main components required are a cylindrical pin, a spherical shape at the top of the pin, a sleeve and a metal ring. The sleeve is comprised of two halves: the lower half that covers the pin, and the upper half that houses the sphere. Between the two halves, the metal locking ring rests, and will lock into the groove created by joining the sphere and pin. For the pins, I used the trusty cube to create 6.35mm diameter pins. The spheres were built using a tapered 90mm long strip of 110lb cardstock rolled around a 3.175mm (1/16") diameter bamboo stick.

In order to create uniform diameter sleeves, I had to build some tooling. Rolling up some paper around a bamboo stick, I now have roughly uniform rods to roll Magic cards around. These were built using a simple excel spreadsheet to calculate diameters in terms of paper lengths and thicknesses. I had some old ones from a few years back, but re-made some new ones to help do fit checks. Probably would be easier to use drill bits since metal doesn't deform as easily as paper, but that's how we roll.

I used Magic cards rolled around the 6.35mm (1/4") diameter rod to form a sleeve with the thickness of two cards. That thickness is the minimum I found needed to allow the rings to bend outwards and also remain stiff. A strip about 45mm long is enough for the inner housing. I used another 45mm long strip to connect the two halves with the ring in between to hold the assembly together.

 For the rings, I straightened out a paper clip and rolled it around a 5.7mm diameter rod with the help of beadmaker's pliers. There's a bit of fine tuning afterwards with the finished pins to get them to lock snugly.

The new locking mechanism allows me to do another upgrade: fixing the ankles. Right now, the ankles are just a hinge joint. I opted to upgrade the feet to provide two swivel joints and a hinge joint to allow for better poseability and stability. However, the foot requires a more delicate structure due to the small envelope. Therefore, I needed to downsize the scale of the locking pin mechanism.

In order to build more delicate portions, I had to downscale the pin joint from a 6.35mm (1/4") diameter pin to a 4.2mm diameter pin. The rings also had to get scaled down. The hinge joint pictured above ends up being 8mm wide and will support a 4.2mm dia lower pin and a 6.35mm dia upper pin.

 The hinge goes into two different sleeves to form an ankle joint for a foot. The smaller 4.2mm dia pin goes into a 4.2mm dia ID x 6.35mm dia OD sleeve with its own locking ring. The ID of the ring ended up being 4.1mm. The larger 6.35mm dia pin goes into the shin.

Here's the component breakdown of the leg. The pins were left unsanded, to allow the glossy coating of the card to help reduce friction. The sanded tubes are unsanded in the inside.

Adding depth to the pins so they aren't just sticks. Was easier to super glue blocks of card to the sides, then carving them until they were round. 

Fleshing out the calves with liberal use of 110lb cardstock. 

To finish the foot, I traced out a footprint, and marked the regions to trim off on the sole. The black Sharpied out regions get cut off to form a rounded block that I can then carve with a hobby knife. Perhaps the most difficult part of the job, as the foot needed to be smooth and not look like total ass.

After long hours of not doing anything productive, I whittled down the foot to shape to something remotely considered acceptable to a blind man. More liberal use of 110lb cardstock fleshed out the shape of the legs. After this, it was ready for a coat of "pale sickly girl" paint tone.

The new foot and ankle fixes some problems with articulation, allowing for better balance and stability. I can now reduce my reliance on obitsu stands, at least for barefoot poses.

I'm quite happy with the stiffness and strength of the new joints. I do have to upgrade two more dolls with this mechanism, assuming nothing goes bad with Hotaru's new ankles over time unexpectedly.