So how did I get on? Here's a test scribed line inside a couple of milled witness marks. I'm slightly out but less than 1/2mm but I'll come back to this.
Lining up my center mark with a dead center (having used the center finder to set my cross slide) - then center drilled - 10mm end mill - 15mm end mill as tapping diam - then a little flattening with 18mm end mill to help start thread on a flat not a radius & finally tapped.
Cleaned up threads having removed & replaced the core.
Glass eye fitted.
And level...
or is it
If I put the glass eye on a flat surface
and then check my upper datum line I'm out !
Put in my drill press vice with datum lines level with the tops of the jaws & the 16mm tap in situ the error is clear.
I'm not quite square on for that photo so the tap looks out more vertically than it is as well as rotationally. This is mainly a lateral error when I drilled & is, I think, a compound of not lining up my center finder properly (see below) & rotating the tube so as to use the dead center to 'spike' my center punch mark while the quill was free (drilling mode) & then tightening the mill vice, which I have discovered moves the tube slightly. Result being about 1mm off laterally & off slightly rotationally as this inside shot shows (also how far in the eye goes).
The good news is I only found this out after serious scrutiny to see how well I did. None of this is really detectable by just looking so who's to say it wasn't this bad originally. So on I went on to the top red button...
Checking I determined my upper center punch mark was a little off so corrected it.
Setting up with the center finder in the mill I noticed that if the tool/collet was rotated slightly it throws the reading off so this could have & probably was a contributory factor in my glass eye being off.
Here I 1st have the center finder arms touching the end of the vice so it is square on & set it to center of the mark then I move the slide longitudinally to give me room to rotate it slightly & when pressed onto the tube again it's clearly off but unless you know about it & align it in rotation by eye (as I did 1st time) you can end up being out without knowing it. As I said earlier these aren't precision alignment tools but do OK for this sort of thing.
Having got everything as centered as I could tell I then set about putting in the shallow blind hole ready to tap just a couple of threads. I did this with the bearing in place so I could tell when I reached the bearing pocket (by hitting the hard bearing housing). This turned out not to be as good an idea as I hoped.
Sequence was center drill, 8mm drill, 10mm end mill, 1/2" slot mill, 16mm end mill, 18mm end mill to take down the top radius so I can start on a flat to tap. (not all shown here).
Tapping didn't go well. Aluminium is so soft it's hard to tell when the tap is cutting & when it's just chewing.
Once the bearing was removed I found I still have least another mm, poss. 2, before I reach the pocket. What I should have done was drill through into the pocket, without the bearing in place, with something like an 8mm drill so that I could judge fro this hole how far in I could take in the end mills and also start threading on the radius & then end mill the 18mm clearance flat thus removing any chewed bits down to good threads (which seem to happen at the start of tapping no matter what).
I can get the button to engage but only by about 1/10 of a turn which isn't enough for me. There's enough metal left for me to fix this if I'm careful by following what I should have done above but I will end up a little deeper seated than I was hoping for. But that's for another day.
Looking great.
