Dug’s Automata Tips, Techniques and Tricks No.1
September 15, 2010 by Dug North
We are delighted to introduce the first of a new quarterly column by automata maker and enthusiast Dug North. The column will focus on automata construction techniques and assorted methods of creating motion. Dug will also highlight the works of various automata makers, (some you are sure to have heard of and some you probably have not).
We hope you enjoy this new column and encourage you to post comments and questions for Dug at the end of each quarterly article.
Eight Lessons Learned from Making a Wooden Clock
Because there is an age-old connection between clock-making and automata, I suspected there was a lot an automata-maker could learn in constructing a clock. So, I decided to build a clock called The Ascent. I learned some valuable lessons while building this clock, many of which might help you with your next mechanical wood project.
1. Baltic Birch Plywood is a Great Material
The Ascent clock is made of Baltic Birch plywood, an ideal clock or automaton material for a variety of reasons:
- - Dimensional Stability: Because plywood is made up of thin layers glued together, it’s less prone than most woods to swelling unevenly with changes in moisture. This stability will help any wooden mechanism — clock or automaton — run more reliably.
- One Material, Many Sizes: The entire clock was made from 1/4 and 1/8 inch thick sheets of plywood. For thicker parts, I merely stacked and glued several piece together. When an especially long piece was required, a scarf joint and glue did the job.
- Cutting Identical Parts: Another advantage of using thin plywood is that identical parts can easily be produced by stacking the pieces, holding them together with double-sided tape, and cutting them all at once. One pass of the saw versus many!
- Wood Can Act as a Spring: In two places within the clock, plywood itself is used as a spring. The winding mechanism has flexible wood pawls that engage a ratchet wheel. The adjustable bob on the end of the pendulum is held in place by the springy action of a small plywood arm applying pressure to the shaft. Using wood as a spring could be a useful technique in making automata as well.
This can be a serious problem if the dowels/axles of your clock or automaton are so irregular that they do not spin smoothly inside the holes that serve as bearings. The Ascent parts kit came with a simple gauge to test whether the 1/4 inch dowels were round. The gauge consists of 1/4 inch notch precisely cut into a small piece of plywood. By inserting the end of a questionable dowel into the gauge’s notch and spinning it, I could tell instantly if the dowel had potentially problematic high spots. Try making similar gauges to test dowels for your projects.
If an irregularly shaped dowel will not spin easily in a hole of a similar size, what can you do? Fortunately, the designer of The Ascent had an effective solution. The parts kit contained a number of ‘nylon shoulder washers’ with interior holes measuring 17/64ths of an inch. A washer was installed at every point where a dowel end met the clock’s frame. Since the washer’s hole is 1/64th of an inch larger than the dowel’s supposed diameter, this allows all but the worst dowels to rotate freely. Also, nylon has the added advantage of being a material with a very low coefficient of friction.
Only a few spots on the clock required lubrication, which consisted of drawing on the wood parts with a lead pencil. Pencil “lead” is actually clay and graphite mixed in varying amounts to create harder or softer pencils. Like nylon, graphite has a very low coefficient of friction. For best results, use a soft pencil — usually designated with a number followed by the letter “B”. The graphite can smear and mar the finish of your piece, so take care in its application and in handling the lubricated part.
5. Sanding Wood Parts Can Reduce Friction
The clock instructions suggested sanding the mechanical parts with progressively finer grits of sandpaper: from 150, to 220, to 400, and finally 600. That’s a lot of sanding. Were the hours spent on this laborious task worth it? Absolutely. The performance of the clock improved noticeably after sanding and it required less weight to drive it. If you are having trouble making parts move smoothly — smooth the parts!
6. How to Reduce the Size of Drilled Holes
What do you do if you are trying to friction-fit a part such as a cam to a dowel serving as an axle but the hole in the cam is just a bit too big? The clock instructions provided an invaluable tip. Simply take some white or yellow PVA glue, and apply a thin coating to the inside of the hole. After allowing the glue to dry, try the fit of the piece on dowel again. You should find that the part is a tighter fit. If it is still too loose, just repeat the process.
We have all heard that it is important to use the right tool for the job. Sometimes, the “right” tool for the job may not exist! The Ascent clock includes many gears with as many as 64 teeth each. Sanding those teeth was a major task. To aid in the process, I glued some sandpaper around a 1/4 inch dowel leaving both ends of the sandpaper longer than was needed to reach around the dowel. This formed a gentle curve of sandpaper that matched the gear tooth profile. I made a set of these sanding sticks with the required grits of sandpaper and worked through them progressively with great results.
A clock is a delicate mechanism. It is easy to tell when something is wrong: it simply stops working. Now that I have made an all-wood clock that actually keeps time, I am further convinced that nearly anything can be made from wood. Now that is a lesson worth remembering whenever you create something of your own!
For more information on The Ascent Clock clocks kit, materials, and plans visit: http://www.wooden-gear-clocks.com/ascentclock.htm
Warning: The topics covered in this column include the use of tools and materials that have the potential to cause damage to property and/or bodily injury. Your safety is important; it is your sole responsibility. Always read and follow the safety instructions that come with tools and materials you use. Wear safety glasses, use guards and other forms of safety equipment, follow safety precautions, and use good judgment. Seek the guidance of experienced outside sources whenever required.
Copyright 2010 Dug North
Dug’s Automata Tips, Techniques and Tricks
A quarterly column by automata-maker and enthusiast Dug North