I need to drill 4 10mm holes through 50mm thick HDPE and then countersink with a larger diameter (ca 20mm) hole to a depth of 20mm. The material in question is in fact a step made out of recycled soft drink bottles. I have often drilled through thin (6mm) sheets of acrylic but this is a while new ball game. Off my own bat I would probably do the following
- Use a blunted twist drill bit or a step drill bit to make the 10mm hole
- Use a 20mm forstener bit to make the countersink
However, before I embark on the job and ruin the step for good - or worse - I thought I would seek a few ideas here. I should mention that I do not have a drill press.