Originally Posted by def
In your last photo, the tap is shown in a typical tap wrench with the quill of the milling machine above the work. Are you hand tapping using the quill as a reference? Also, what tapping fluid did you use during tapping? Was there any difficulty during the tapping process with the original threads being overcut?
Finally, alloy can be rather buttery or very difficult to machine. Did you ascertain the alloy used in the case before proceeding? What rod was used to provide the alloy fill?
Thank you. Continued good luck.
I used the method outlined by MotorradMike, using the quill with a pin in a collet to steady the tap and keep it centered as it started the hole. For tapping fluid I just used some light penetrating oil that I had lying around in a can, it was a generic version of WD40. Worked quite well. I did make sure to go slow, though; when you are working on your own bike your heart always beats a little faster!
As far as the welding is concerned, I deferred to the expertise of my colleague, who is a trained welder. He said to choose a filler rod for general purpose aluminum welding (4043) to play it safe.
I am always looking to learn more, so if you see something that wasn't quite right or if you have some experience to share do let me know. I think I've learnt a hell of a lot from this little incident! I just hope someone else benefits from the collective expertise here.