Photorealistic Plywood Silhouettes

The Christmas display at my house involves a buckboard wagon, the Grinch, reindeer and a couple of schnauzers. I wanted to update it with another dog this year, and decided to get creative about it. In previous years, I created silhouettes by projecting an image onto the plywood at the desired size, tracing the outline with a marker, then cutting it out with a jigsaw and hand painting it. The current method involves a bit more technology, but provides a more realistic and pleasing result. It works in part because the subject is white, and the laser engraver will burn in the dark parts of the image.

Materials

Plywood, at least 3/8"

White paint

Black paint

Tools

Paint brush

Computer

Laser engraver

Band saw (or scroll or jig saw)

Most of my inages are backed up on Google Photos, which is easy to search for the desired subject. I wanted to add Gretchen, our late miniature schnauzer, to the pantheon of Christmas schnauzers. I chose an image of her perched atop the A-frame (incidentally, featured in a previous instructable) because in that posture I could later place the silhouette strategically on the wagon. Also, it's a photo that captures her spirit well. I loaded the image file into G.I.M.P., a freeware image manipulation program, but you can use whatever app you are comfortable with. I cropped it and applied an edge-enhancing filter. This latter step is critical for emphasizing the locks of hair and the outline of the dog. I converted it to black and white, and made many adjustments to contrast and brightness to get it just right. Finally, I isolated her body by erasing the background parts of the image. This method is an admittedly crude way to digitally isolate subjects, but it has always worked for me. I exported the finished file as a jpeg.

I used of a piece of 3/8" plywood I had lying about the workshop. Since this was going to be an outdoor object, I didn't feel required to sand the surface at all. It was slightly bigger than needed for the final product, which is fine, but it was too big to fit under the laser engraver. I cut a bit off of one edge using a table saw. I painted one side with two coats of glossy white enamel paint, but I'm sure latex would work fine.

I loaded the graphic into the engraving program, Laser GRBL. It's free and easy to use. I adjusted the size to get the largest engraving I could, though the bed of my engraver is 400 x 400 mm, so I could not make it any larger. I have the Atomstack A5 engraver. It is reasonably priced and fairly powerful. After the graphic was loaded, I could tell it was going to end up too dark. The laser is going to burn every black part of the image into the wood to make the dark bits. Therefore, if there is too much black in the image, you will end up with burnt offerings. I went back to GIMP and lightened it a bit more, then reloaded it into Laser GRBL. I used 1-bit BW dithering for conversion. After examining the effects of all the dithering algorhythms, most of them looking fairly similar, I chose Atkinson. I also used 3 lines/mm engraving quality. My engraver often overcooks wood substrates, but I knew the white paint would reflect the light and mitigate this effect somewhat. I also knew I would have the option to engrave it twice if it didn't turn out dark enough, as long as I didn't move the laser or plywood between burnings. Fortunately, I only had to engrave it once to achieve the desired result.

I adjusted the height of the laser to focus on the the surface of the plywood. I moved the laser head all over the plywood to make sure I had the requisite 2 mm of clearance. It's a good thing I did this, because there was a slight warp in the plywood I hadn't noticed that rubbed when I rolled the laser over it. I raised the laser head to clear the high point. This engraver is very forgiving of variable focal length. I marked the center of the plywood and placed the laser over that point. I used the FRAME function of Laser GRBL, which runs the laser head (with the laser on very low power) over a rectangle encompassing the entire engraving, thereby showing that the engraving fit on the plywood and the laser head did not reach its travel limits. All was good. I held my breath and clicked on the GO button.

The result was as good as I could have hoped for. As expected, the dark areas between locks of hair were burned black, but the level of detail on the nose, mouth, ears and eyes was quite good. I could never have achieved that through freehand painting.

I used a band saw to cut out the dog silhouette. I didn't cut every lock of hair along the edges. I let the black and white contrast of the engraving provide that effect. Instead, I cut a fairly smooth outline without many sharp angles. I painted the back and edges of the plywood black using latex paint. This coating provides contrast and weather proofing. I placed the silhouette next to the Grinch to appear as though Gretchen is riding in the wagon. Her late Giant Schnauzer pack mates are with her; Big Guy is riding in the back and Miss Kitty is providing motivation to the reindeer.

This laser technique worked well in this case because Gretchen was a white dog. The engraver can only create dark areas, so black and white images are ideal. Any pale color should work in place of white. I experimented with an image of a black dog on a scrap piece left over from the Gretchen silhouette. Above is Indigo, a Standard Schnauzer. The black on white effect works well. The dithering conversion creates a halftone (like we used to use in newspapers), where the density of black dots creates the illusion of varying shades of gray. I think I could have gotten away with a bit darker image, though the workshop was fairly overwhelmed with the smell of smoke by the end of this etching.