Putting tools to wood the last few days on the second automata piece I am making for a museum exhibition. I've been busily designing an educational piece for a display which is a Raven "caching" food to prepare for a cold winter. The automata will be operated by the visitors to the museum by a wheel on the front of the display. As such, I have tried to make it as rugged as possible, yet still characterizing it as a handcrafted construction. There are protective clutches, stops and metal components all designed to withstand the riggers of a public display.
Typically automata that go to collectors experience limited operation over their lives, but one in a museum will see many hours of operation, operated by viewers of all ages. This means more mechanical bearings and metal parts than I generally use. I am having a lot of fun making these adjustments. The leg assembly, subject of the blog, shows the extent of the scope change and careful planning!
I introduce to you Rocky, (at least part of him), a raven who is caching a small berry he has found in preparation for the winter. He is hiding it in a small crevice in some rocks in a wintery scene. He repeatedly retrieves and replaces the berry while looking around to see if any other ravens have noticed him.
The first thing to examine are his feet and legs and their construction. The photo below is the prototype I made to help figure things out. The disk with the hole is the centre of the rotation for Rocky pivoting up and down. Where I had designed these before with brass tubes and rods, this piece will require a metal bearing. The feet look like ducks feet, but don't worry - remember it's a prototype! The greatest concern is that it supports the weight of all the raven and needs to be strong. While square plywood legs might provide great strength they will not cut it for authenticity! This component also needs to be well anchored to the baseplate, preventing movement, however being able to remove the raven for any reason would be advantageous.
Okay, lets get started with the feet. They are an interesting feature to observe and should bear a good resemblance to a real raven's feet. I will use 1/4" brass rods for the legs extending into the base, so this means the feet can be more delicate and life-like, since the will not carry any real load.
On the left you can see the feet I designed sitting in my drill press vice. I am drilling 1/4" holes for the legs to extend down through the feet into the base. This is about a 30 degree angle as a raven's legs incline forward from its body. On the right you can see the feet cut out and wooden dowels stuck into the feet to illustrate the fit.
I make pieces that resemble reality, not replicate with 100% accuracy. This approach is needed often just to make the mechanics work. An overzealous birder might notice in the photo that the raven's toes have three bumps on them where in reality they have four. Four looked to dainty to me considering the rest of the raven so i went with three. My apologies to serious bird people
With a little Dremel tool work, some sanding and a little sweat, the feet get a fairly realistic look that passes my filter and I move on to making the pivot cradle that is the upper leg joint. It is made of three separate pieces, two outer pieces of maple for strength and shape-ability, and the disc shaped centre piece of birch plywood that will ultimately hold the metal bearings.
Before cutting and shaping the maple blocks the time is right to drill the 1/4" holes for the brass legs while the blank is square. Shown below is a test fit up off the leg assembly. You can see some temporary brass rods holding the pieces together for the photo. The centre disk will be glued to the two outer maple upper leg blocks. I decided some additional reinforcement would be a good idea. A tight pin will be installed in each of holes as I glue the pieces up. The pins will be recessed a bit and hidden with wooden plugs and sanded smooth. You can also see the disk drilled out to receive two shoulder bearings, one inserted from each side.
Examine the photo on the left below and you will find a few new elements. The bearings have been assembled in the disk. Small wooden plugs have been installed to conceal the reinforcement pins. Brass bars have been installed, replacing the temporary wooden dowels. A few new items have been added below the feet. The top one, adjacent to the feet, is a poplar block that is a flat stone that the raven stands on. It is tapered to match the slope of the display bottom. The next piece is 5/8" particle board, the material that the bottom of the display is made from. It acts a temporary spacer for fit testing here. Next is an odd shaped poplar block that is also shown alone in the photo on the right. It has two holes drilled through it to receive the lower part of the brass legs. Finally, looking back at the photo on the left, there is a small leg block attached to the very bottom that supports the weight of the legs, (Hard to see in the photo. It is the piece with sanding burn marking on its end).
In final assembly the leg block becomes rigidly attached to the underside of the display bottom to support the weight of the raven. The upper flat stone block will be fastened to the top of the bottom plate. The complexity of this arrangement is that the display platform slopes 9 degrees down to the front of the display while the legs slope 30 degrees from vertical toward the right. Drilling these compound angles into each of these components can be tricky.
The end result is shown below. The legs of the raven sitting are sitting on a level stone on the inclined floor of the display. A little epoxy has been added to help shape the transition between the feet and legs. The whole leg assembly can be lifted out of the base to remove the raven if necessary. Small holes for the linkages to actuate the bird are yet to be drilled.
Its a complicated description but I hope I have explained things that help you understand my thoughts as i design and build it!
Automata is a creative blend of my life interests , engineering, art and woodworking.