This week, I tried to laser cut lap joints. During the 2-hour period of time allotted, no satisfactory lap joints were made. This may be due to the fact that we cut the parts each time, instead of experimenting with small square samples. In hindsight, this method makes much more sense: get a skill perfect by simplifying to the bare essentials, and doing it until it works. In this case, instead of cutting the parts again and again, we should have cut a series of small squares at different power and speed levels. This method takes less time as well as less wood to figure out the nuances of the settings for the type of material that we had.
Looking at the wood, we had no idea what it was. We thought it was birch at first, but the settings used in the previous birch samples burned the part. In order to adjust for this, we increased the speed so that the laser would not be standing in one place for so long. We cut one piece that was just okay (slightly burned, but not too noticeable), but the rest started to burn more as the speed increased. Perplexing. Maybe the power levels are too high, and are burning the wood regardless of how fast the laser was traveling. This was not the case. As it turns out, lowering the power levels proved to burn the samples even more. See below.
Figure 1: Regression of samples
Although the picture quality isn’t the greatest, you can kind of see the level of burning on each of the samples. None were really charred in the area that the laser passed over, but there were some instances of burning on the surface (towards the right-hand side of the samples). I will go into more detail below.
While this was a great learning experience, I should reiterate how much more efficient it would have been (regarding time as well as cost) to have just cut small squares to get the settings right. Although my part was relatively small, it would have made a bigger difference if I was printing a larger sample.
The first sample we tried was a setting of a power level of 100 and a speed of 4. This was the best sample that was produced, but I thought I could do better.
Figure 2: The best sample we obtained so far
The etching part looks good. It is dark enough to see but not burned. However, if you look closely on the right-hand side of the part, you can see mild burn marks.
To adjust for this, we tried to increase the speed of the laser so it would not hover in one area for too long. See below for the results.
Figure 3: Increased speed does not help burns
As you can see, parts of the sample (particularly the lower right corner) are still burned. This was disappointing, because it seems that it burned more than the sample cut with a lower speed. This boggles my mind. On a last-ditch effort before our time ran out, we tried to cut it with a 90 power setting and a speed of 6. We didn’t know if it was going to go through, but previous settings of lower power levels and higher speeds still managed to go through and burn the edges as well. You can see the results below.
Figure 4: More speed, less power, more burning
Astonishingly enough, this was the most burned sample of all. The dark brown spot on the bottom of the part is badly burned, and the sides are not in much better shape. At this point, I am very confused as to how this machine actually works. Higher speed and less power should not mean more burning (but I suppose they do). However, at the bottom (at the burned spot), there was a knot in the wood. The laser cut through everything except for a little bit of the wood, which we were able to tear away. See below.
Figure 5: Knot in the wood
The spot where the cut gets lighter is where the knot is located. I learned that at this low of a power level, you are barely getting through this thickness of this type of wood. Knots are usually harder than the rest of the grains, so I need to account for this in the future if I am cutting large parts that may pass through knots (or just get better wood).
Later, I was able to get some more time on the laser cutter. I used the method of testing with small squares first, as it was a more efficient way of getting to a good final result. The setting which produced the best results on the small squares was a power level of 100 and speed of 7. Although there was virtually no “toasting” along the edges of the small square, toasting did appear on the edges of the final sample. See below.
Figure 6: Best cut
All in all, I learned a lot about how to laser cut samples, as well as a prototyping strategy to get a part perfect on the “first try” (even though you have cut multiple small, simple parts before that).
