Homebrew PCBs

Phil wrote:
> I drilled a small board with the TE bits (65 holes).  Overall, I like 
> these bits but I did break one (#62) after about 25 holes.  I wasn't 
> putting any stress on it that I could tell.  They seem to run pretty 
> true with no noticable wobble which is much better than my older 
> drill set.  I may get some more.
> 

   Note that if the tunesandtools guy is still putting up bits for Monday end, 
he had some sizes that were 50 of a single size for $5 to $10 depending on which 
size, but not all sizes.  But Ron also has size selections too, not only the 
variety pack.

   Just a few ideas to help you along on the drills.  Note that most small bits 
need high RPM for best operation, the small diameter means that the actual speed 
of the outer metal against what it's cutting is relatively slow.  10K RPM isn't 
crazy with smaller bits.  Also note that your hand just isn't really steady 
enough for much use with these.  Even with a simple drill press, you need very 
good and smooth depth feed, otherwise you'll tend to dig in and break bits much 
more often.  PCB is also quite inconsistent in composition, so even with my CNC 
it still breaks bits more often than drilling in simpler solid objects.  If you 
hit a 'hard' patch in the board and the stress spikes up the bit breaks.  Not 
much getting around it, they simply break sometimes.  With the CNC though I can 
usually get hundreds or more holes per bit though.

   And note that these bits usually cost $5 each new or so.  At 20 cents each 
they're quite the bargain, you can break 25 bits before you've caught up to the 
price of one new one.  And the new ones are just as easy to break too, unlikely 
it would last longer than 2 or 3 of the others, so you're still way ahead overall.

   Even if you don't build a full CNC, you should look at building a simple 
slide with stepper motor to control the drill feed speed.  That and aligning it 
so the bit shaft goes perfectly into the hole that the tip cuts will make the 
bits last much longer.  They still eventually dull and grab and then snap 
though, haven't gotten the stuff yet to resharpen them myself before they get 
too dull.

   And if you're using these by hand or most drill presses then guaranteed you 
were flexing the bits.  About the only way to even align my CNC accurately 
enough is to drill with one of the #80 very thin bits, note which way it's 
flexing as it drills, and then adjust until it stays straight as it drills.  You 
simply won't see the small amount you're flexing with a normal PCB hole size 
bit, yet it's still flexing every time around.  It may look straight to your 
eye, but you're still flexing it.  Eyeballing with hole bits just isn't good 
enough to tell, that's why I sacrifice one of my thin ones when aligning things.

   For reference I probably never got beyond 100 holes by hand even with 
alignment helpers etc.  With the CNC and stepper motor feed they go many 
hundreds of holes, some probably 1000 or 1500.  So you can bet it's your usage 
not the bit that's the problem..

Alan