My experience with drilling SS allen head bolts.   My oil pan bolts are SS socket heads.  I had the best results starting the holes with a HSS bit, then finish with a cobalt.  Since the hole is being started on a round surface the narrow 1/16 bit tends to walk.  The HSS bit will tend to cut with a lighter pressure than a cobalt, reducing the incidence of walking.  Once the hole is started (dimple) I would finish the hole with a cobalt, when you good pressure can be applied and the cobalt cuts better and lasts longer.  FWIW, my experience.

Joe

---- Original message ----
>Date: Wed, 30 Jul 2008 15:57:00 +0000
>From: "Kelly Troyer" <keltro@att.net>  
>Subject: [FlyRotary] Re: Safety wire  
>To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
>
>   Keith,
>       If you use "Allen Head" bolts they are much
>   easier to drill the small sizes as they
>   have a round head........IMHO !!.
>    
>   --
>   Kelly Troyer
>   "Dyke Delta"_13B ROTARY Engine
>   "RWS"_RD1C/EC2/EM2
>   "Mistral"_Backplate/Oil Manifold
>
>    
>
>     -------------- Original message from John Slade
>     <sladerj@sbcglobal.net>: --------------
>
>     > I think I got them from NAPA
>     >
>     > ktradcliff@comcast.net wrote:
>     > > Hey John,
>     > > > Where did you get pre-drilled bolts for your
>     oil pan? I am very afraid to
>     > drill bolts this small.
>     > >
>     > > Keith
>     > >
>     >
>     >
>     > --
>     > Homepage: http://www.flyrotary.com/
>     > Archive and UnSub:
>     http://mail.lancaironline.net:81/lists/flyrotary/List.html