2.5. The ball hinge emulation
The universal rest with the ball hinge is the best equipment for setting a bolster or a flat pillow. However its main assembly (the ball hinge) quite often is not available in domestic workshop. In that case the main unit can be emulated with own plate for every plane of controlling.
This idea during many years is being realized in devices for navigation of ships, airplanes, rockets, space vehicles. The device named “gyroscope” creates a bearing coordinate system on a moving object. The authors of the book naturally came to the same idea after testing numerous rests.
Despite of very “scientific” name the “gyroscope platform” can be domestic made of wood details. Drafts of a rest emulating the ball hinge were shown on the site klk.pp.ru at Russian lace maker’s request in 2006. The emulating idea is explained on Fig.2.32.
The rest contains four platforms. The platform 1 is an unmovable table. The platform 2 rotates on the 1st platform around the vertical axe at 360 grades (azimuth ?). The platform 3 swings on the 2nd platform around the first horizontal axe at ±40 grades (heel ?). The platform 4 carries the tray 5 for the bolster. Both swing on the 3nd platform around the second horizontal axe at ±40 grades (elevation angle ?).
The bunch of three movable platforms emulates a ball hinge having three degrees of space freedom. Consequently the rest is a well controllable device. At the same time the Fig.2.32 does not show how the problem of hinge braking is solved. In fact it is solved as well with braking plates in hinges of the 2nd and 3rd platforms (soft plastic gaskets). The plates are squeezed with female screws using a spanner. Of course it is less comfortable than a pedal but proves to be the simplest decision.
The steadiness of the rest serves special efforts. It can be warranted with two manners – using “skis” or a frame (Fig.2.33, Fig2.34).
Variants of the rest are shown on photos (Fig.2.35 – Fig.2.37).
The tray for the bolster is attached to the upper platform. The bolster is plunged into the tray down to 0.3 … 0.4 of its radius. This depth is enough to fix the bolster without any additional contrivances.