Building a Laser Engraver

In 2019 I started building a laser engraver. Here I will document some of the joys and  problems I faced in the process.

Base Design

A friend of mine pointed me to a 3D printable laser engraver design (here), which I used as a starting point. The design uses some 2020/2040 aluminium profile and 3D printed parts as a base. Part of the design is to shove the aluminium profiles in some of the 3D printed parts to join them at the corners and create a rectangular shaped base.

After printing the parts and trying to assemble it, some printed parts immediately broke. I immediately disliked this part of the design and didn’t quite understand why one would take this approach when 2040 aluminium can be bolted together easily, which is way more solid and wouldn’t lead to breaking 3D printed parts. So I decided to modify that part of the design and simply bolt the aluminium and design some new ‘feet’ for the construction. This helped and I could mostly use the rest of the original design.

Modifying the Design

I had to design some new 3D printable parts and made good progress in getting the base together. By base I mean the whole construction with the stepper motors and the timing belt used to drive a laser on two axes.

In the first months I was able to create a base that I liked and get the mechanical parts working. I had the stepper motors working and could drive the position of the laser using G-CODE, so I could basically use any laser engraving software to control the device. This was the fun and satisfying part. The hard part came when I had to drive the laser itself.

Controller Board

Another part about the design that I wanted to modify is the controller. I didn’t want to use an Arduino Uno and after reading about a controller board built by Bart Dring, I decided to go with that because it uses an ESP32 microcontroller.

When receiving the board it looked like this:

2018-10-07T20_50_44.596Z-20181007_153758

And after installing the ESP32 microcontroller and the stepper drivers it looks like this:

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The X,Y and Z-axis stepper motors each have their own driver and SpinPWM is the port that controls the laser. Because an ESP32 is the microcontroller it has WIFI and Bluetooth, which is pretty cool. It also has an SD card slot and it has some connections for limiters (end stops) and other things that I may not fully grasp yet. But that is something for the future.

Driving the Laser

I ordered the strongest diode laser I could find on AliExpress, a 15 watt laser module, because why settle for less?

According to its specifications it would operate on 12 volts and take a PWM or TTL signal at 5 volts. This confused the hell out of me to be honest. PWM or TTL? Is that the same then? I understand what PWM (Pulse Width Modulation) is and does, but to be honest I have no clue about how TTL (Transistor-Transistor Logic) works.

I had hooked up the laser to the SpinPWM port and after hooking things up, nothing worked. So I used my cheap multimeter to measure the voltage and was a bit surprised, it was so low (not sure what it was anymore, but at most around 3.3 volts). At this point I couldn’t be sure what was going on.

At this point I realized I didn’t have the right tools for the job, because I wasn’t quite sure what the signal was giving me and a simple multimeter will not help me figure it out. At this moment I decided to let this whole project rest for a bit and order myself a cheap oscilloscope (a DSO138).

When the oscilloscope and some spare time came along it was time to do some investigation. Like, what is this TTL/PWM stuff about?

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