A few of the original engravings didn’t turn out as well as we’d hoped, mostly because the line drawing were too thin or too light, so didn’t convert well to 1-bit images. We asked the group members to do the drawings again, but with a thicker pen/pencil and make them as large as possible on the paper.
The images were scanned at 300 dpi, converted to greyscale, thresholded to get the clearest 1-bit image and then saved as 1-bit bitmapped images. The size of the image was set to 15 cm x 11 cm, and the images inverted.
On the laser cutter, we set the speed to 200, power to 20 and scan gap to 0.05 for engraving. This was a bit experimental, but appeared to work well for the 3mm birch plywood. As you can see below, the resolution of the engraving is really good, and the images came out really well. They also feel good to touch, with clear outlines.
I have since learned that there is a simple method for calculating the correct scan gap, for a given dpi of image. It is:
DPI to Scan Gap = 25.4/DPI
For example, a 300 dpi image would then have a scan gap of 0.085 using this formula. I’ll be try a slightly lower dpi on the next engraving, and so reducing the scan gap and seeing how much different this makes to quality and speed!