Re: [CAD_CAM_EDM_DRO]Backlash & Wobbly Spindle on my Bridgeport

baumanro2000 wrote:

> Just curious if you make it a practice to not center drill before
> drilling? To properly locate a hole for drilling seems like it must
> be center drilled first unless I missed something.

Center drills for a .012 drill are not common. You can just spot the
hole of course, not going deep enough to actually create a hole. But if
you look at this spot under a microscope, you will see a comparatively
wide flat spot dead center. If the drill's web is thinner than the web
of the spot drill, you effectively have no spot drill. I commonly spot
holes with a 90 degree carbide single flute countersink. Being a much
steeper taper than the drill, the drill will first contact out at the
corners and pretty much insures it drills on center. This was taught to
me by a mold maker who's work is beyond reproach. Going deep enough not
only spots the hole, but deburrs the hole at the same time. If one wants
a sharp corner, then one must insure the spot doesn't exceed the drill
dia.

Contrary to popular belief, it's not difficult to drill holes on
location without spot drilling. But... the surface must be square to the
drill and -flat-, drill must be sharp and properly sharpened, must be
free from runout and not crammed into the work, setup must be rigid and
free from deflection. Fail to meet any of these, and the drill will
likely walk. This is where I will often write my own drill cycles
manually and call them as a macro. I'll use a slow feed until the drill
is properly started, then finish drilling as fast as I can push it.

BTW, a .012 carbide drill isn't going to walk noticeably off center
without promptly breaking. They're pretty touchy little things.

Jon