Monday, February 27 2017

Tentative Takadai design

Between crude sketches, OpenSCAD, and playing with scrap wood, I think I’ve nailed down (so to speak…) the way I’m going to connect my parametric Takadai together.

  1. Instead of connecting the inner and outer arms (gedan/jōdan) with a small arm attached to the legs at one point, I’m using wedges cut from a 1x6. This is actually the “traditional” method in Japan.
  2. To stabilize it front-to-back, I used 1x6 stretchers a few inches above the ground. I can’t put them at the top like table aprons, because the bobbins would constantly bang into them.
  3. To stabilize it side to side, I replaced the rear crossbar with a 1x6, which means the rear “wedges” are part of a solid board attached to both legs.
  4. That makes the biggest, most visible change possible: the torii and makitori-bō are now firmly attached to the frame by 1x6s. They can stand up to any amount of weighted bobbins, and the finished braid collects in an easy-to-reach location.
  5. Even better, that provides a perfect spot for the ratchet and pawl, replacing the chopstick brake on the makitori-bō.
  6. That rear 1x6 also made it possible to lower the hyojun-bō so that it doesn’t sit on top of the gedan like an afterthought, and completely eliminate the sword pads. With a 1x6 back there, I can just cut out pads on each side and round them off.

Next up, building a tabletop version with 5/8-inch square dowels and 0.5x3-inch hobby boards. To keep it compact, it will only support 4 small koma on each arm; that’s enough for quite a few types of braid.

For simplicity, the tabletop Chibidai will be held together by wood screws, but for the full-sized unit I’ve got a bag of cross dowels from McMaster-Carr. I’ll use the Nomad to CNC-carve my comb-style koma and the ratchet.

[Update: I made the OpenSCAD script dump the cut list; obviously I’ll be rounding off a bit…]


8x hardwood balusters, 1.25x1.25:
4x legs, 26 inches
2x gedan, 27.8523 inches, mizo starts at 7.70228 inches
2x jodan, 32.0706 inches, mizo starts at 9.67062 inches
7x hardwood boards, 0.75x5.5:
1x back board with wedge cuts, 34.75 inches
2x stretchers, 25.3523 inches (gedan - 2x baluster)
2x torii/makitori supports, 11.5 inches
2x front wedges, 7 inches
2x 1-inch dowels, 8 inches
1x 0.5-inch dowel, 22 inches
22x koma, 3.5 inches
1x gravity ratchet with pawl