My 3D printer now does auto-leveling using a proximity sensor and an external control board. This DIY PCB article describes completion of printed circuit board used in this project.
Previously, I described the auto-leveling modification made to my Sunhokey Prusa i3 3D printer. After prototyping the circuit on a breadboard, I decided to attach the components and wiring to a DIY PCB. In Part 1 of this article, the PCB design and etching were described. In this second part, completion of the project will be covered.
DIY PCB – Drilling the holes for components
The good news is that once you have etched a DIY PCB, the design shows you exactly where to drill the holes for attaching components. The bad news, I suppose, is that the holes don’t drill themselves!
The challenge in drilling out a DIY PCB is that the holes are very small. A typical size is 0.035 inch. And you need to be quite careful that you drill the hole exactly in the center of the copper pad. For drilling a few holes in a small DIY PCB project, a push drill is more than sufficient. You will need to obtain a collection of small numbered size drill bits. The bit I used was # 65.
The key concept for PCB drilling with a push drill is gentle and perpendicular to the board. Small bits break easily, if you are too rough or too crooked. My approach was to first center punch each hole with a small nail or tack, and one tap with the hammer. Again, be gentle. Once your starter hole is in place, carefully position the bit, with the push drill vertical, and gently drill out the hole. I found that it took 10-20 pushes, depending on board thickness. Once you get the hole started, it helps guide the drill bit. I held the circuit board and spoiler in place with a small clamp, as shown above.
Wearing an LED headlamp (wonderful things!) is very useful to be able to see what you are doing at these small sizes. Eye protection is also good idea in case the bit breaks.
For larger DIY PCB projects, a rotary tool can be useful. You will probably need to be some additional collets to hold the small drill bits, though. Typically you will need a collet to hold bits of 1 millimeter diameter or less.
(By the way, if you live in Canada, there is a company called Princess Auto that is a good provider of low cost hobby tools, including rotary tools, push drills, small bits and small collets, at reasonable cost.)
DIY PCB – Mounting Parts and Soldering
My simple DIY PCB needed to make connections between the 3D printer control board, a relay and a proximity sensor.
Pin headers were used for the off-board connections. 12 volt power was attached at the upper left, and the wires from the proximity sensor on the lower left. The relay is in the middle, and the wires to the 3D printer Z-axis end stop connector on the right. If you drill the holes the same size as the component leads, it is easy to get a good mechanical connection to the board. For an electrical connection, a DIY PCB requires soldering. A soldering iron in the range of 20 watts is sufficient. The important thing is having a small tip on the iron. My iron is equipped with a 0.8 millimeter conical tip, which is roughly the same size as the holes in the copper pads. You will notice in the picture that I did not solder pads there were not used.
The final DIY PCB product is shown in the picture at the top of this article, wired to the 3D printer. To finish the project and tidy things up, I will need to physically attach this board to the printer. My thinking is to use a double sided adhesive tab to hold the top of the small relay against the acrylic printer frame, and then dress the wiring.
To wrap things up, I should also document my failures! In my first PCB etching attempt, I did not do a proper job of making sufficiently wide copper traces or etching away all the surface copper. You can easily check to make sure that all of the unwanted copper is gone by testing the board for unwanted conductivity with an ohm meter. On my second attempt, I was too aggressive with making pilot holes for the drilling. I hammered rather than tapped the center punch (a small tack) and cracked the board. What you see in this article is the third iteration.
But, then, my first DIY PCB was supposed to be a learning experience. And it was.