image choice

The third assignment for this class was to CNC machine a shape chosen from the noun project. As an avid soccer fan, deciding what shape to carve was a rather easy choice. My initial idea was to carve a shape of a soccer ball, but I noticed that a lot of them had very thin lines which could cause problems. In the end, I chose an Olympic pictogram-like stick figure drawing of a soccer player.

carving

To be honest, I thought this assignment would be very easy. I resized the image to match the dimensions of the wooden pieces nicely and got going with a 1/8″ up cut drill bit. I thought the largest 1/8″ bit would be a safe bet since all lines in my shape are fairly thick. As we were instructed, I measured the dimensions of the wooden piece, clamped it down and observed the process which seemed to start off very smoothly. However, once it finished up the circular head and moved down to the body, problems started to occur. The first problem was that the drill bit cut through the wood a little bit when it moved from the head to the body. Then, not much further, it seemed as if the alignment method completely broke. For an inexplicable reason, it started carving the body about an inch to the right of the head as shown in the picture below. This caused the carving to stray off of the piece of wood completely.

On my next trial, suspecting that the issue may have to do something with the choice of drill bit, I swapped the drill bit to a 1/16″ straight cut bit. Again, the head was carved out smoothly, but different problems started to occur in the body again. This time the alignment seemed to stay correct, but the drill bit cut through the wood between the head and body again. In addition, a straight cut seemed to cause some of the walls to be much rougher than desired. Given the geometry of the straight cut drill bit, I was suspecting the drill bit will apply a lot more stress on the wood, but it was interesting to actually see it happen. This phenomenon really showed when the thin wall between the head and the body completely broke off.

My last trial was done with the last remaining style: the 1/8″ down cut drill bit. In short, the down cut drill bit did not have any of the issues I faced with other style bits. Alignment stayed consistent, the bit did not cut through the neck, and the walls also came out much smoother. I repeated this process twice with a down cut drill bit for the project.

Cost analysis

Assuming the cost of wooden blocks to be approximately $1 per piece, the two successful carvings cost $2 in material cost. Each of the carvings required me to set up and monitor the progress, which took approximately 20 minutes per trial. At a rate of $15/hr, the labor cost amounts to $10.

The two successful carvings cost approximately $12 in total.

Conclusion

This was a fun assignment! It was interesting to see the effects of different drill bits on wood for sure. I chose a very simple design to minimize the time spent since I was planning to be gone the whole weekend, but I really want to try out different designs for fun in the future and put it on my desk!

 

Project number #6