On Mon, 15 Feb 2016 13:05:41 -0500, you wrote:
>
>"AncelB mosaicmerc@... [Homebrew_PCBs]"
>> I use resharpened carbide in my dremel 395 with 1/8" shanks for PCB
>> work. They work fine....I go down to around 0.31 mm. I can go smaller
>> but bit breaking happens every 10 holes or so.
>
>Me too, but I rarely break bits since I switched to a home-brew drill
>stand that seems to eliminate any "hand wobble" from causing breakage.
So does mine, so that's a big help.
>
>My CNC machine can drill lots of holes with resharpened carbide and a
>Grizzly pencil-style die grinder.
>
I happen to use a Proxxon 12 volt tool in my drill. The bearings and
collet are far better than Dremel. That said, I do use a dremel, but
not for drilling precise holes.
>Perhaps rigidity in the holding of the dremel is more important than
>runout? Or at least, ∗lack∗ of rigidity is more common as a cause of
>breakage?
Lack of rigidity in mounting the tool is likely the number one cause
of disaster (get a 1/8 inch high speed bit to wobbling and it will eat
a 3/8 inch irregular hole in PC board.... don't ask how I know
this...)
Once that's taken care of, the next problem will be runout on the
drill itself (notably the chuck and bearings). While this is likely
to break smaller drills (say as a guess #70 and above), the most
likely consequence in my opinion is a lack of precision in the actual
hole location. Less of a problem if you have a donut pad with a clear
hole to guide the drill.
I've not had a problem that I could attribute to the drill bit itself,
other than dull.
Oh, and my "drill" holder is on a set of reasonably high quality (not
cabinet drawer pulls) linear bearings, so that does make a substantial
difference.
Harvey