A hole in the head

Yep, I reassembled the main gear compts temporarily to figure out where there would be space to fit my gear teeth sensors. The RHS of the head (from the operator's viewpoint) is full of the gear change parts but the LHS is mostly empty. 

So, apart from the need to avoid the Z axis servo motor bracket, I'm free to blast a big hole in the side. That should allow me to fit a bracket for the sensors that will be accessible (ie adjustable and potentially replaceable) from the outside once it's all back together.

The top flange is about 13-15mm thick and the bottom of the cavity is about 85mm from the top face. That seems to leave a clear face of about 80mm height. Rummaging through my hole saw box, I found a nearly new 70mm bimetal hole saw. I only had one, so needed to be sure I could finish what I started before attempting the job.

I made an executive decision / engineering judgement / rush of blood and off I went. Took me about 15 minutes, taking care not to overspeed it or overheat the cordless drills (used 2 in rotation). 

Nearly there....

Finished and cleaned up. Looks good. I kept the quill bore packed with tissue and used WD40 to lubricate the hole saw and keep any fine cast iron dust immobilised:

Job done. Now for some bracket mounting holes and fixings for a cover plate.