In the process of upgrading by CNC machine to control spindle (on/off) by G-Code I had to find a nice a way to insert a relay between my Makita RT0700C router which is mounted on the CNC machine and the mains power.

I also wanted to have ability to take the router and use it handheld if I had to.

So here's what I came up with.

It turned out that a GX16 connector fits perfectly into the cable hole in the router body. So I installed the GX16 socket into the router and soldered the plug to the cable so can disconnect and reconnect when needed. And when I get the relay box done it will have 2 GX16 sockets: one for power in (will use the modded cable for router) and one for powering the router (will create another cable with 2 GX16 plugs on each end).

This is a relatively simple and reversible mod (you can reattach the factory cable as it was if required, however the warranty on the router will likely be void). Soldering is only required on the GX16 connectors.

WARNING: take all the necessary precautions when working with electrical wiring. In other words you must know what you are doing!

UPDATE 2018-05-15: One reader pointed out that there's a safety issue with using a metal bodied connector. Instead a plastic connector should be used. I have updated the part list below, however the pictures still show a metal connector (as done originally).

You will need:

SD16 male and female plugs, e.g. https://www.aliexpress.com/item/16mm-3PIN-Waterproof-Aviation-Plug-Socket-Cable-Connector-IP68-SD16/32698905151.html (I used 3 pin, but 2 pin should also work)
- Originally used GX16 male and female plugs, e.g. https://www.aliexpress.com/item/1set-GX16-2-3-4-5-6-7-8-9-Pin-Male-Female-Diameter-16mm-Wire/32819640509.html, however a plastic body connector should be used instead.
2 pieces of 14AWG wire about 10cm (4 inches) long.

Step 1: Remove Router Cover

Cut the label with the utility knife along the line where cover meets the router body.

Unscrew the 4 screws.

Remove the cover.

Step 2: Remove Cable

Unscrew and remove the clip that holds the cable.

Loosen the terminal block screws to remove the mains cable (note which wires went to which terminal).

Step 3: Solder GX16 Male Connector

The wires need to be about 10cm (4 inches). I used pins 1 and 3.

Step 4: Mount GX16 Male Connector

Cut a small grove as shown on the photo (I used a Dremel). This groove will allow the 3-pin GX16 connector to be properly positioned (pin 3 down) and also prevent the rotation of the connector.

If you have access to a 3D printer you may choose to print a custom nut (attached) for a tighter fit.

Put the stock or 3D printed nut on the GX16 connector and position the connector into its place as shown on the photo. The nut needs to be tightened.

GX16 nut.stl
Download View in 3D

Step 5: Connect Wires

Connect the 2 wires to the terminal block and tighten.

Note down which pins you've wired to which terminal.

Step 6: Reattach Cover

Reattach the cover and secure it with the screws.

Step 7: Solder GX16 Female Plug to the Cable

Leaving the rubber sleeve on the original power cable add shrink-wrap tube on the cable, add the GX16 metal jacket and solder the wires to the GX16 female connector (matching the pins so that same wires get connected to the same terminals inside the router).

Heat the shrink-wrap, assemble the plug and push the rubber sleeve over the plug half-way (you may need to apply quite a bit of force)