When it comes to my experience with the machine, it's very limited... So far I've made 3 simple ECBs (from which 2 I've completely botched) and I haven't worked on an ECB with a new, sharp tool yet. Now the machine is busy with other work and I won't get to use it until the work is finished anyway. The problem was pressure and flexiblity of the boards: Once the drill goes past the hard layer of copper, it sinks some 0.2mm into the softer fiber and makes a deep hole, ripping fine tracks and making them very fragile, and it doesn't do so at the same rate over the whole surface so where in one place the gaps are still there, in others the drill is passing for the third time, already halfway through the board, spreading destruction... I hope a new sharp tool won't use so much vertical pressure...