-------------------------------------------------- From: "ivp" Sent: Saturday, August 07, 2010 2:45 AM To: "Microcontroller discussion list - Public." Subject: Re: [OT] Selecting a drill bit size for 3 mm screws >> For many purposes 'high speed steel' drills are liable to be good >> enough and are much more forgiving > > HSS have just about no life at all with FR4, particularly the smaller > diameters, 0.5 - 1mm used for component holes. They blunt after > a few dozen holes. I'd not recommend them for anything but very > occassional use. If you've many 3mm holes to do then cobalt or > tungsten carbide are much more economical in the long run > http://mailman.mit.edu/mailman/listinfo/piclist I second that, the smaller HSS ones die very quickly indeed. I have had to= =20 change 1 mm bits after ~30 holes. However a 3mm bit may last a bit longer -= =20 I hardly ever use one for PCBs as I always order the final boards, with=20 3.2mm holes for M3. If it's just a few holes (<100?) though I'd maybe just get a HSS bit, as th= e=20 larger ones do last a bit longer - but if you need it for quite a lot of=20 drilling go tungsten carbide.=20 --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .