Another Thing that can Go Wrong

Using a unique, home-built high-tech machine has its own challenges. Since I designed every piece, built it myself, loved every joint into place, and wrote every line of code, every failure is my fault. I have caused everything that has gone wrong — and surely there have been plenty of problems. Mercifully, fewer as the machine and software mature, but I am specially responsible.

A few months ago, I eagerly accepted a commission for a customized design, delivered on a tight schedule. It was for a simple customization to one of my large Seder plate designs.

I designed the special variation, the customer reviewed the artwork and gave approval to go ahead.

The customer wanted the design carved in Cherry. I had a piece of Cherry large enough for a large plate, but when I pulled it out to use, I saw a small knot which would be right in the middle.

0.3″ knot in a nice piece of Cherry

The knot was about 1/3″ on one side, and less that 1/4″ on the other. The knot might look really good, or it might be a problem. Since the work was needed quickly, I didn’t want to take that chance.

From my blog entry you may see that I received a large piece of Cherry. It was rough sawn, not planed or sanded smooth. This forced extra steps. First, I modified the tool path to penetrate 1/8″ into the material, deeper than any surface variation. Second, I rough sanded the front so that the surface calibration could find the real surface, rather than the rough original surface.Wood clamped and smoothed

I set up my machine, loaded the design, and set it to cutting. It was looking good, so I came inside to see my wife for a few minutes. Later, I went out and saw an unexpected bump in what should have been a flat region.
A Z-axis discontinuity, caused by the wood cracking and shifting. I assumed that something had gone wrong with the machine, or with the constantly changing software, and the Z-position had been compromised. My heart sank as I anticipated debugging my system, hardware or software, quickly enough to meet the customer’s need.

Looking closer, I saw that the wood had an open a crack from the end. The crack had split and shifted the wood, and that shift had caused the problem.Cracked from one end of the wood deep into the plate.

I chalked up the problem to unseen stresses in the wood that were concentrated as the thickness was reduced. I prepared the next position on the plank, clamped it more tightly with better support, and cut it without incident.

That bit of wood became firewood.

Wood is a natural material. Each piece is unique, and it is always challenging. Finding the right wood is hard, but knowing how any particular piece of wood will respond is, for me, nearly impossible. As an engineer, I like to anticipate problems. As an artist, I accept that materials have their own, inscrutable behavior.