Drilling X2 chilled casting

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

Unles syou can set it up rigidly in a biger drill press or mill chances of snapping a carbide drill are high, same goes for a carbide tap.

Did you regrind the masonary drill for metal cutting? a carbide tipped drill for metal is another option as the shank is not so brittle.

Unusual for a big lump of iron to be chilled, is it near an edge or on a thin part?

High Cobalt drill - at least to pilot the base?

Masonry drills require the cutting edge to be modified. I had a set of drills (a long time ago) that looked like masonry drills but cut through hard steels very easily. I still have the box and some of the contents. Supplied by Tracy tools (certainly over twenty two years ago) at an exhibition, IIRC.

High torque and low speed, a masonry drill should be fine

touch it up before starting

Cobalt should be fine too but they were ridiculously expensive the last time I looked (a while back now)

backgear drilling with a good steady pressure should sort you out

high speed drilling will wreck your drill tip

sharp masonry drill should do it must be sharp, or try reducing the helix angle of hss drill [brass type cutting end] this works as well, beware if drilling a through hole as when close to other side the higher cutting pressure can cause damage as the drill breaks through.

Ouch.

My stand was not chilled - it can't have been I was able to tap M10 or even M12 by hand!

If funds allow the new base and column are a good idea. I am tempted from time to time, but my 'bodge' works well enough.

Neil

Can you grind away the hard suface with a Dremel etc or is it hard all way through?

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!

I use cobalt tools on my lathe and shaper all the time now but it's with the slow speed high torque stuff where they really shine over HSS