This hardness can no longer be processed. Electric sparks are prone to wear and cannot be processed. For a 12cm deep hole, the board should be over 15cm thick. CNC milling and drilling, precision drilling and then vacuum heat treatment, and then reaming the hole again to clean the inner hole (at this time, the reaming can no longer be done, just to clean out the things that may remain inside.) If you are sure that the inside is clean, there is no need It's hinged. If you are interested, you can also send me an order.