Before milling the top plate, I tested the 0.214mm drills on some aluminium parts and there has been no problem to drill about 3mm deep, i.e., 15xD. But when it comes to drilling in the actual top plate, I couldn't get it to work. More on that later in this log entry.

As shown in the video below, the first cuts on the aluminium for the top plate have been done. The outer contour, the 5mm holes and the counterbores have been milled and drilled successfully.

If you have any questions on the milling or drilling, just ask in the comments here or on Youtube.

Now, to the problem with the 0.214mm drills. Although drilling the small holes worked on a test part, I had huge problems to just drill one single hole in the actual top plate. There are several possibilities, why it didn't work.

• Runout of the drill: it seems that the drills are not straight when testing them on a very accurate surface plate. I really think that is one of the main reasons why it didn't work. Maybe, for the test cuts the drill just was good enough. The runout measured is about +/-0.05mm, which is at total about half the drill size. (I really assume, that this is the problem)
• Speeds and feeds: more rpm required or other feeds, I tried at 18000rpm and 50mm/min. These parameters worked for the test cuts.
• Stick out: since the holes in the top plate start at about 8mm depth, the stick out of the drill has to be about 10mm. It may be a few mm longer than before when drilling in the test material.
• Other material: the material of the top plate differs from the materials of the test cut.

What I can definitely exclude from the reasons of failure:

• Spindle runout: the runout is <0.01mm, so it is very unlikely that this is the problem.
• Stability of the mill.
• Programming errors: the drill isn't moved quickly into the material or something.