Hey David, hey all,
I think it’s good that again this shows that shielding the router cable makes sense and has an effect. But to be sincere, to implement it this way, - 
-, and the second plug, well but it works.
Maybe it would have been simpler to buy and attach a few meters of LAPP ÖLFLEX® CLASSIC FD 810 CY or IGUS chainflex® .
What gives me stomach ache, is your use of Installation Terminals in a cable for a movable device, and then you take Wire nuts of all things, which are forbidden in many countries for obvious reasons and were replaced long ago by lever-actuated (overview lever-actuated), push-in or screw terminals. But first of all in a cable of a movable device, splicing connectors for fixed installations are not at all the right thing. They are not made for motion and even if your cable mostly is sort of fixed, you cannot exclude that it is moved. By the way for me it’s a little bit weird to see wire nuts, I haven’t seen one since decades.
What is a bit sad is that, caused by the router’s design, there is no simple option to ground the router’s housing by the cable. In order to be allowed to run on two-wire unearthed sockets, the tool is double-insulated, which means despite a part of housing is made of metal, it is not earthed.
By the way, this is the reason you need a magnet earth probe together with your touch probe (you don’t need the magnet probe anymore after switching to an (earthed) spindle).
The lack of earthing by design on this power tool leads to these safety warnings:
Electrical Safety
[…]
- Power tool plugs must match the outlet. Never modify the plug in any way. Do not use any adapter plugs with earthed (grounded) power tools. Unmodified plugs and matching outlets will reduce risk of electric shock.
- Avoid body contact with earthed or grounded surfaces such as pipes, radiators, ranges and refrigerators. There is an increased risk of electric shock if your body is earthed or grounded.
[…]- If operating a power tool in a damp location is unavoidable, use a ground fault circuit interrupter (GFCI) protected supply. Use of an GFCI reduces the risk of electric shock.
– Source: Makita RT0701C Instruction Manual
Note that the use of a GFCI should of course be standard in your workshop.
So what is a bit sad is that your shield must end before it reaches the part of the device that emits the sparks or does not join metal part of housing. But the device is designed this way. A way to obtain earthing on your router’s housing and more safety in general is of course grounding your CNC.
As I said before, I think it is good that you showed that shielding the cable of such a device has an effect and makes sense anyway.
Besides of your use of Installation Terminals which cannot be recommended, the fact that you used ferrite rings shows that furthermore you thought of everything 
.