Drilling hardened steel

[Allen Smithee]

As those with long memories may remember I have a Myford Super7B (with 3-phase VFD) which is generally great. It's fitted with a Dixon QCTP that is the dog's whatsits as I have over 30 tool holders, 25 of which have various tools fitted that I can drop in and out of a job in seconds, but you know all this. My only real grumble is that the QCTP block will sometimes get pushed a bit under high loads even if I pull the clamp lever realy firmly, and then I have to go through the faff of clocking it back square to the lathe axis again.

On a previous lathe around 40 years ago I had a similar QTCP (probably better described as a "clone") made by Toolmex in China that I bought cheap from a local shop. In most respects it was an adequate but inferior copy of the Dixon, but it had one feature the Dixon lacks. In the back corner of the block there was an 8mm vertical hole which I used as an index hole - after carefully tramming the block I drilled a blind hole into the topslide and made a corresponding silver steel pin which I then hardened. I found this allowed me to quickly set the toolpost square for when it mattered (eg parting or screwcutting), but it also stopped the toolpost rotating under load.

I would like to add an index hole to my Dixon setup, but as far as I can tell this is hardened steel. I understand this can be done, but it needs a suitably hard drill turning slowly with good pressure, pecking and lots of coolant. There also seems to be a suggestion that Before I attempt it could I ask the experienced ones if this is the right way to do it? Would I be better using a cobalt or TCT bit? also the advice seems to suggest not to pilot, but just give it a good centre punch and then just drill it to final size (nothing has talked about reaming).

Is this the right approach? Should I use collant (soluable oil) or lubricant? Any other advice?

Any comments welcome.

AS

[Mike R]

I drilled a hardened ER32 lathe chuck plate with a carbide "spot drill" and it handled it with relative ease (made 3 holes through 12mm deep and was still sharp) after I had failed to drill it with standard drill bits.  I can't recall what was done with regard to coolant or oil.  Those holes were a touch bigger than your 8mm at 10mm.  Only thing to lookout for is if buying a carbide "spot drill", get one with a flatter angle (i.e. 120° or 135°) so the tip is wider and is less prone to chipping / breakage than a 90° one, and yes to slow speed and good pressure.

[crueby]

Only way I know of that will put a hole through hardened steel (probably others, I just don't know them) is to use a carbide or diamond coated rotary tool bur. I've used them to cut away broken taps and drill bits.

[Jasonb]

I bored the bottom of my genuine Dickson reasonably easy.

Although the metal is hard it is not cutting tool hard just enough to resist wear and knocks.

Try it on the underside and see how you get on.

[Allen Smithee]

I bored the bottom of my genuine Dickson reasonably easy.

Although the metal is hard it is not cutting tool hard just enough to resist wear and knocks.

Try it on the underside and see how you get on.

Thanks Jason - I'll give that a go. Would it be the "slow speed with reasonable pressure, plenty of lube and pecking to keep it straight" process?

AS

[Jasonb]