Engraving a Bamboo Bowl

I found an inexpensive bamboo bowl at Daiso and decided to try it on the laser.

Here’s the label on the bottom of the bowl:

First I tried vector engraving. My guess was that it would take very little power to mark the soft wood, and that turned out to be correct. Here’s the result with vector speed at 100, vector power at 1, and vector current at 30%. Nice crisp letters, very black, quite shallow. Pretty good result.

Next test was raster engraving. Here’s what my file looked like:

And here’s my first attempt. I tried a very low power setting again, based on the fine results from vector engraving. However, it wasn’t enough for raster engraving. You can see how the fine lines tend to fade out. Note how the fat lines have been broken into two lines, on the left and right edges where the laser turns on during rastering, and the horizontal fat line is missing entirely because it doesn’t get the turn-on pulse.

So, I turned the power up until the fat lines filled in. Here’s the result. The fine lines are nicely fleshed out and the fat lines are filled in, and everything is nice and dark. Very promising looking!

But then I wiped the bowl with a damp paper towel, and most of the black came right off, revealing an ugly core material that resembles cheap cardboard. This is not the effect I was hoping to get.

Even after wiping, there was some darkening in the places where the laser had the most effect, so I decided to see if I could get consistent dark engraving by simply turning up the power. I interrupted the test after it had engraved just the top of the pentagon. It was cutting quite deep into the bowl, and generating a lot of black debris on the surface.

The debris wiped off easily, but so did a lot of the black material, even deep down into the cut.

I have to conclude that this material is not suitable for raster engraving, unless you really like that ugly cardboard finish. For vector engraving, it seems OK, but you probably need to make sure to use a very low setting, so as not to penetrate the thin outer layer of the material.

Red Laser melted!

The beam combiner optic finally came in from China, but when I went to install it into the laser I found that the red dot laser still wasn’t working right. On closer examination, I found that the plastic lens built into the red dot laser unit itself was melted! I’m guessing this was a side effect of the damage to the old beam combiner. It must have reflected some significant portion of the main laser’s energy onto the red laser.

I’re purchased a replacement red laser and will get it installed soon.

Another Surge Suppressor Failure Repaired

Yesterday there was apparently a power surge on the AC power at Colab. This blew out the surge suppressors inside the high voltage power supply in the laser, with the result that the laser would not fire. This is the same failure we experienced about a year ago, so I already knew what to do and had the (inexpensive) replacement parts on hand, so the laser is already back up and running.

Power Inlet Re-Repair

My quick and dirty repair of the power inlet module lasted about five weeks, and then burned up, as seen here:

So this time I ordered and installed a replacement part (Interpower 83110131) and got a new power cord.

Instead of the excessive 20A fuses that came with the laser, I installed a 15A fuse. I plan to measure the actual current draw soon. Full Spectrum now says it should be only 5A surge and 1.5A continuous. However, when the laser was first installed it was popping a 15A circuit breaker, so I don’t believe their numbers. If I can drop down to a 10A fuse, I will, because that IEC connector is only rated for 10A.


Unusual Laser Failure

Last night Martin reported that he was cutting some thin plywood when the laser suddenly stopped, manifesting a complete loss of power. Power at the outlet was still good, and the visible circuit breaker on the back of the machine had not tripped. It behaved, Martin suggested, as if an internal fuse or circuit breaker had blown.

Today I took a look at it, and confirmed Martin’s report. I don’t have a schematic diagram or any documentation on the electronics of the laser. The components are more or less accessible through the side doors and are mostly wired up with individual wires, so it is possible with some patience to trace the wiring. The power wiring is very carefully insulated, terminated, and glued in place, though, so it isn’t so easy to probe the circuits.

The power comes in from the wall through a standard IEC cable and matching chassis connector, like a desktop computer. Then it goes through a device labeled in Chinese that appears to be a relative of a ground fault circuit interrupter, or GFCI, like you see on outlets in wet areas, plus a circuit breaker. Then it disappears into a wiring trough, to reappear at the front panel. One wire goes through the big red E-stop switch, and the other wire goes through the key switch, and then they both go back into the wiring trough. They come out again in the side cabinet, and go through an EMI filter before being distributed to the various DC power supplies. The connections to the EMI filter are push-on tabs, so they can be backed off a bit and probed. There was no voltage there, with power connected and the switches all on.

OK, so it’s all wires and switches, except for the GFCI. Now I’ve known GFCIs to fail, so I suspected it. I just needed confirmation that power was present at the input to the GFCI, and absent at the output. Lacking any really good way to probe this, I tried poking the sharp ends of the voltmeter’s probes through the soft insulation on the wires. I saw no voltage on the input, so I suspected the probing technique was not working.

To check on the probing technique, I switched the meter to ohms and tried to look at connectivity between the IEC connector and the inputs to the GFCI. I couldn’t find any connection there, either. Maybe that just wasn’t an effective way to probe the wires.

Along about this time, I happened to take a closer look at the IEC connector and noticed that it had an integral fuse. Aha! I bet that fuse was blown. So I pulled out the fuse holder. I was impressed to see that the fuse holder also contained a spare fuse. Nice touch. But when I measured the installed fuse, it was good. In fact it measured almost exactly the same as the spare fuse.

Now I was ready to doubt every connection. I probed around everywhere, not trusting anything. And I found something unexpected. There was no connection between the hot pin on the IEC connector and the fuse. Mind you, these are all part of the same piece, since the fuse holder is integral to the IEC connector.

The photo here shows the back side of the IEC connector/fuse holder, and you can see the common chassis ground post just below it.

Defective Power Connector

On the right side, you can see a metal strap with two studs sticking through it. The upper stud (the nice shiny golden one) is the hot pin of the IEC connector, and it makes a very solid connection to the strap. The lower stud (the blackened one) is one contact of the fuse holder. It looks connected at first glance, but it isn’t. There’s a tiny annular gap around the stud, and it doesn’t touch the strap at all. It must have touched, until yesterday evening, but it must have been marginally bad from the beginning. I suspect it got worse very slowly, until it reached a point of thermal runaway and burned out suddenly.

I didn’t think I’d be able to source a replacement connector locally on a Saturday afternoon, so instead Robert donated the purchase of a soldering gun and a wire brush from our neighbor Home Depot, and I blobbed some solder between the stud and the strap. Problem solved!

That connector would have been at the very bottom of my list of suspected components.