We have been experimenting a little more with the laser cutter and tried out a variety of settings for engraving photographic images. The early attempts were either too dark or had poor image resolution, and it turns out that the latter depends largely on how well the image is converted to a bitmap which the LaserScript can use (1-bit bitmaps only). A fellow laser cutter from the LaserScript forum (Dave) converted a photo for us which worked really well when we engraved it, so we did the rest of the images in a similar way. Using Photoshop, we scaled each of the photos to 15cm x 11cm, converted them to greyscale and then saved as a bitmap using diffusion dither at 300DPI. The settings on the laser cutter were: speed 300, power 20 and scan gap 0.05, with bi-directional mode switched off. This gave a really clear engraved photo, though on reflection I think we could probably have increased the power to 22 or 24 to make them a little darker. Perhaps we’ll do that for the next batch. One nice little trick we have learned is to tape the wood down to the laser bed using masking tape to keep it flat – simple, but effective!

Here are some of the results of yesterday’s cutting and engraving. In the first image you can see the pieces of the boxes we are cutting out for the sensory labels. The image does not do the actual items justice – they’re much nicer than this in real life!

Closeups of the sides and tops:

Here are couple of closeups of the engraved photos:

I like the one below as a concept – an engraving of Tim holding his engraved image. An engraving of an engraving.

We still have a batch of parts to cut and some more photos to engrave. Then there is the big task of assembling all of them and adding the electronics.

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!