I see no reason a drill bit or that grade of carbon tool steel should not work, unless it is just a low grade drill bit. Did you temper it?
If not,  and it possibly lost its temper in shaping it, the old rule of thumb would be to heat it till it is no longer magnetic and quench it. Polish it up to silver. Then re heat it to very light straw color and quench fast. 

Sent from my iPhone

> On May 3, 2017, at 9:24 AM, Paul Pavel <[log in to unmask]> wrote:
> 
> Question for the makers: what do you use for the plectra mortise punch? It should probably be as stiff material as possible to avoid bending, I made some punches from drill bits but not satisfied with that.
> Pavel
> 
> ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
> Note:  opinions  expressed on HPSCHD-L are those of the  individual con-
> tributors and not necessarily  those of the list owners  nor of the Uni-
> versity of Iowa.  For a brief  summary of list  commands, send mail to
> [log in to unmask]  saying  HELP .
> ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
Note:  opinions  expressed on HPSCHD-L are those of the  individual con-
tributors and not necessarily  those of the list owners  nor of the Uni-
versity of Iowa.  For a brief  summary of list  commands, send mail to
[log in to unmask]  saying  HELP .
::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::