Soldering Aviation Connectors
Good connectors are a must when you build a machine. A poor connector that shakes loose can be maddening. But, good connectors can be very expensive. Fortunately, Aviation Connectors are relatively inexpensive and reliable. They come in a wide array of sizes and pin count and can handle relatively high current and voltage if you are careful when selecting them. The downside is that a lot of people seem to have trouble soldering them. I see lots of complaints about the plastic pin holder melting, rendering the connector useless.
When I first started building CNC machines, I had trouble soldering them but developed a technique that works fairly well. The key observation was that trying to solder a wire to one of the pins sometimes took too long and overheated the plastic. Thinking through how to avoid overheating I realized that if I tinned both the the wire and the pin, the amount of heat needed to solder them together would be relatively small. Now, I am no expert but this process works well for me. So, in pictures...
Place the plastic pin holder in a vise and tin the pin's solder cups with solder. Wet the soldering iron tip with solder to ensure heat conduction and touch the solder wire to the cup. If solder does not flow immediately, back off, let cool and try again.
Strip the outer jacket from the cable, peel back the shield and wrap the bare ground wire where it will be held by the clamp. Take care to ensure that when reassembled, everything lines up. Note that the wires are trimmed to the right length for the shell and then stripped to the length of the solder cups on the pins. Don't forget to slide the connector jacket on the cable before the next step.
Be sure to slide the insulating sleeve and connector jacket on the cable before proceeding.
Position the wires with one hand so that they contact their corresponding pins - physically touching. Then, with the other hand, position the soldering iron tip next to the tinned part of the wire. The solder on the wire should melt first and the pin's solder will very quickly melt in turn. Hold the iron there for just a second and then move it away. Hold the wire steady until the solder hardens. Repeat for the other wires. If it takes more than around 3 seconds, remove the iron, let the connector cool down and try again. It is very important not to overheat the plastic as it will deform easily.
A note on colors: There is no color standard for these cables but you should create and use a consistent scheme. It is very common for Red to be + voltage and black to be 0V (or ground) but feel free to make up any scheme that works for you. Always solder the same color wire to the same pin number. That makes it easier to find the right wires in the bundle when completing your machine assembly.
Gently screw the shell on the the plastic pin holder and tighten shell clamp screws making sure that the clamps compress the grounding wire and hold the cable firmly. Your cable assembly is now ready to use.
I'm Phil Barrett, a long time CNC enthusiast. I run a small company, Brookwood Design, that makes several breakout boards for grblHAL and love to help people get the most out of their CNC machines.