Post date: Apr 13, 2014 5:21:08 AM
More mysteries! Could they be related? I don't know why you'd ever think two round things I'm making, both labeled as "mystery" would be related...
In any case, the latest:
This is the result of WAY too many hours tediously hand-writing GCode. I'm intending to make some scripts to make that easier, bu that's another matter... The thing above turned out really well, except for the hole you can see at the upper-left of the right image. That's what I get for copying and pasting GCode; I neglected to remove a G00 Z0.1000, when my Z=0 plane was at my table. The good news is I can apparently bore holes like nothing. The bad news is that it destroyed the workpiece. Murphy's Law at its finest.
There were a few other hiccups- I broke a couple of 1mm end mills trying to figure out what feed rate and cut depth to use (the answer to the latter is evidently ~5mil). Not a terrible loss, except then it took just this side of forever to make the desired pattern. The recessed rectangle you can see in the upper-left image is also not perfect. I gradually stepped down to a new Z level along one side of the rectangle, so as to not be boring straight into the metal (despite that evidently working OK, my understanding is that it's not a good practice). Of course, this leaves a slope that has to be milled flat, and I forgot to do that. You can't really tell, though, since milling out the arc you can see at the bottom-right of the left image mostly covered it up (and the last pass was pretty shallow anyway).
All the tooling marks you can see are just visual- I really can't feel them at all. They do help hide the previously-mentioned flaw even more, though... And they make the back look cool. I spent far longer than is reasonable to get the spiral right, but I like the effect.
The whole thing took... 3 hours? Something like that, including setup, changing tools around, breaking bits and re-doing parts, etc. It's probably more like an hour of actual milling. And more hours than I care to think of in design and writing GCode...