[sdiy] tinning home etched boards?

[David G. Dixon]

Dan,

I apologize if this is a stupid question, but do your printed pads have
holes in their centers?  If you are printing solid pads, then there is
nothing to guide the drill bit.  If you print little circles for pads, with
the hole about the same size as your drill bit, then you almost can't go
wrong.

My printed pads are of two sizes (one for parts and one for off-board wire
connections), and each has its own hole size.  I have found that a #62 bit
fits perfectly in the holes of my larger pads, and a #71 bit fits perfectly
in the holes of my smaller pads.  Now, #71 is a bit small for some parts,
but I like a snug fit, and it's always easy to ream out the hole with a
slightly larger bit if required.  In any case, using this scheme, I have
found that the drill bit will find the exact center of the pad about 99% of
the time.  In fact, I find that it is better not to hold the board too
tightly while drilling, as the drill bit will pull the board into the
correct position.

Other tips: Put the bit deep into the chuck so that only about 3/8" of the
bit is protruding.  This prevents the bit from wobbling from side to side,
and also prevents breaking the bit.  I recently drilled about 300 holes, and
didn't break a single bit!  I also only misaligned one hole, and that only
by a fraction of a millimeter, which leads to my second tip.  Once you have
lined up the bit and the hole to your satisfaction, then drill quickly.
Misalignment seems to occur when the drill is moved too slowly.

Hope this helps.

David G. Dixon
Professor
Department of Materials Engineering
University of British Columbia
309-6350 Stores Road
Vancouver, B.C.  V6T 1Z4
Canada
 
Tel 1-604-822-3679
Fax 1-604-822-3619
 
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