I am in the process of adding a stiffening plate to the back of the column on my Axminster X2 mill following Stub Mandrel's design. Things were going well until I tried to spot drill the holes on the base. It turns out that the casting is chilled and extremely hard, high speed steel will barely touch it. In the absence of any engineering carbide drills I've tried masonry drills but to no avail.

The question is, if I tooled up with an (expensive) carbide drill and a tap, is it likely to work? The only chilled CI I have come across before was like glass, even a carbide tipped turning tool wouldn't touch it. The X2 casting isn't as hard as that so far as I can tell but I don't want to invest a lot in tooling if it's liable to fail in the end. An alternative I've considered is to spend a bit more and invest in a new base and column from Arc. Any advice gratefully received. Roy

Thanks everyone for you ideas and suggestions. A cobalt drill was the answer. Once I had got through the surface and drilled a pilot it was fairly straightforward to open it up using HSS bits in a mains drill and low speed. As mentioned by Colin, breaking through was a bit of a struggle. It also tapped OK. There were no glass-hard patches but it was much harder than the other castings on the mill that I have drilled previously. Anyway, thanks to the forum problem solved, now to finish tramming.

The cobalt drills are revelation, I had never used them before. A bought a couple from Toolstation, they were as cheap as chips. Why don't we use them all the time, maybe others do!