I found some slate coasters on the bargain shelf at Jo-Ann the other day, and tried laser engraving them. The results were pretty good! See the photo gallery below.

I first tried vector engraving some text. This worked nicely. The engraved line was wider than we usually see on wood or acrylic, but that just made the letters more legible. Full power and full speed seemed to work as well as anything. Slowing it down just made the letters look a little sloppier, without making them much deeper. It also noticeably warmed up the whole coaster.

My first raster engraving test was again at full power and full speed, at the lowest resolution (252 dpi). It successfully changed the color of the surface, except for a few tiny spots that were still black. It didn’t create any relief I could feel, though, just a subtle texture change. Turning the speed way down did create lots of relief, and I ended up choosing a setting midway between those two for a moderate amount of relief. Fine interior details were squeezed out by the greater effective line width; that could have been compensated for in the artwork.

This material reacts to the laser in ways I haven’t seen before. When hit with vectors, some of the material seems to melt and form thin glass-like bubbles above the surface. They easily wipe away with a paper towel, exposing the carved letters. When hit with the raster, though, the excess material appears in the form of very fine white dust. Much of the dust is deposited on the surface. Because of the ventilation air flow, all the dust ends up toward the rear of the engraving. The dust is easily wiped off. I didn’t see any evidence of the dust getting into the laser’s optics.

Whether vector or raster engraved, the lasered areas are lighter in color than the rest of the surface. I don’t know exactly why. The black surface removed by the laser might be the result of natural aging, or it might be a factory-applied treatment. It might also have something to do with the rougher texture of the lasered surfaces. It will be interesting to see what color the engraved areas are after some time passes.

Since the laser always starts every job at the upper left corner of the rectangle that encloses the art, it’s not so easy to precisely place the laser head in the right place relative to the round coaster. To solve this problem, I created a simple jig. In CorelDraw, I added a vector circle around the outside of the raster artwork I wanted to engrave. I placed a piece of scrap material into the laser and engraved just the circle guideline on it. Then, without moving the laser head, I placed the coaster on top of the scrap and (after refocusing) centered it in the circle. I could then run the raster job and be sure the artwork would be lined up on the coaster just as I intended.

In fairly short order I was able to make a set of four coasters. With the simple jig the engraving is consistently centered so they look good even side-by-side.

Here are some keypad functions you might not know.

Pause a Running Job

When a job is running, the key with the locked and unlocked padlocks on it will pause the job without losing your place. You can hit the same key again to resume where you left off. This seems to be much more responsive than the pause button on the computer screen.

Pausing the job can be handy. For example, if you see that a weight you used to flatten out the work piece is going to be in the way, you can pause the job long enough to move the weight. As long as you’re careful not to move the work piece, you probably won’t be able to tell that the job was ever paused.

Cancel a Running Job

When a job is running, the yes/no key on the far right will cancel it completely.

Quickly Move the Head

In FX (Fast XY) mode, the yes/no key will quickly jump the head to the top left of the table.

Respond to a Fire

Using both of the two previous functions is a good response to a minor flare-up of fire. Hit yes/no to cancel the job, and then immediately hit yes/no again to jump the head away from the fire. This works because FX mode is the default when a job ends.

Jog the Bounds of Your Job

Once you’ve used the J key on the computer to send the bounds of your job to the laser, or run your job once, the key with a square of four arrows will run the bounds again. You’ll be in a better position to see the results when you’re standing at the keypad.

What’s more, you have extra flexibility. In the FX (Fast XY) mode, the keypad key runs the bounds just like the J key on the computer. In the SX (Slow XY) mode, it runs the bounds more slowly, making it easier to check critical boundaries. In the FZ (Fast Z & Test) mode, it runs the bounds quickly, but just one side at a time. Hit the key again to run the next side. Finally, in SZ (Slow Z & Test) mode, it runs the bounds one side at a time, but more slowly.

Run Your Job Again

Once you’ve run a job, if you want to run the exact same job again, go into SX (Slow XY) mode and hit the yes/no key. The LCD will ask if you want to do that. Hit the yes/no key again to confirm. You’ll get exactly the same job as last time, even if you’ve changed some settings on the computer screen since then. If you want to use the new settings, you have to go back to the computer and type the G key or click on the play triangle.

You can reposition the head before re-running the job, to create multiple separate copies of your piece. You could also re-run the job without repositioning the head, in order to cut and engrave everything a little deeper. If you’re trying to cut very thick material, it might be useful to raise the Z axis table a bit before re-running the job.

During class exercises today, we discovered that you can’t just use the maximum paper size for all cases. If you try to print raster data on the 48×36-inch paper size, the results are (sometimes?) so big the software discards the raster data. There’s no error message or long delay, it just throws away your data. You can then go crazy trying to figure out what’s wrong with your CorelDraw (or whatever program) file.

Since extremely large raster jobs are impractical anyway (because they take too long to run), this is not a severe limitation. It just means you need to choose a reasonable paper size when you’re doing a raster (or raster-then-vector) job. Most raster jobs will probably fit on the default Letter size paper, as long as your drawing is kept within the page margins.

I didn’t search for the precise limit on paper size for raster data. It might depend on the file contents and on the way the drawing program formats the data. Just be aware that there’s a limit.

After seeing somebody use the original focus tool upside down, I have revised the focus tool slightly. It’s used (correctly) the same way as before.

Improved manual focus tool

The autofocus probe is out of service for now—its mounting bracket got badly bent, probably in a collision of the laser’s head with something. So, you’ll need to focus the laser manually. Do not attempt to autofocus the laser without the autofocus probe in place!

I’ve created a focus aid tool to make this easy. Actually, I made several, just in case they get lost or damaged. The tool is shown in use in the photo. To use it, follow this procedure:

1. If necessary, lower the Z axis table until the top of your material is below the focal plane. To do this, use the leftmost button to set the mode to FZ (Fast Z & Test) and push the down arrow button until the table is low enough.
2. Hang the focus tool on the laser head as shown in the photo. The tool’s tabs should sit down squarely on the ledge of the lens tube.
3. Using SZ (Slow Z & Test) mode, raise the Z axis table until your material just touches the bottom of the tool, without lifting the tabs off the ledge.
4. Remove the tool before running your job!

Manual focus tool in use.

I’ve been saying that the laser can’t engrave metals, with the possible exception of light engraving on stainless steel. Well, after class this afternoon we decided to try it. Turns out, the laser really can engrave stainless steel, for at least this one (unknown) type of stainless. It cuts a nice little divot out of the steel. The skull logo is about one inch across:

Emboldened by this result, we also tried engraving one of the steel weights. These are standard cold-rolled steel, not stainless. They aren’t rusting because I sprayed them with clear spray paint. The laser successfully marked the surface of the steel, but didn’t penetrate to any significant depth. (Or maybe it just burned the clear spray paint. I didn’t have any unpainted steel handy.) The text is about two inches across.

Both of these were vector jobs cut at 100% current, 100% power, and 10% speed. The speed could be lowered even more to get a deeper cut. Even these big thick chunks of metal were noticeably warm after the job.

On both jobs, you can clearly see the spot where the laser started to cut each vector. There’s less discoloration and a bit more depth in that spot. The rest of the cut is pretty consistent, but somewhat rough. You’d have to test your specific material and decide if you like the effect.