More aluminum lessons

Today I managed to make a couple of circular cuts all the way through, but then the bit fell through the hole it had just cut.  The dimple is from a previous attempt.  Some of them are a bit off circular.

Lessons:

• The bit tends to creep up, so put it as far in as you can from the start.
• Clamp the metal down on both sides
• If things start making loud vibration noises, stop everything and see what is loose.
• I tried lowering the feed rate from recommended 500mm/second to 400mm/second to reduce some of the noise, but I'm not sure if that made much of a difference, or if I just should have tightened things down.