Homebrew PCBs

Stefan Trethan wrote:
> On Mon, 18 Apr 2005 09:53:21 -0400, Bill Blackburn  
> <billblackburn@...> wrote:
> 
> 
>>Hi Guys
>>For the fellows who are mechanically machining their own PCB's, what is
>>the choice of Spindle Motors?  How do the RotorZip units work for this
>>application compared to using the Dermal units?  I was never very
>>impressed with the bearings in the Dermal Grinders.  They don't seem to
>>last and get loose rather quickly.  Interested in your thoughts on this
>>matter.  Thanks for the help.
>>Regards
>>Bill
> 
> 
> 
> i think the greater issue with dremels are the collets. People say it's a  
> gamble each time you change the tool if the runout will snap it  
> immediately or after 10 seconds.
> 
> ST


   LOL, I think it's more that 95% of people don't have a good clue what they're 
doing.  It takes extremely accurate axial alignment of the drill to the motion 
to use small bits.  Most people just don't even see how poorly aligned their 
systems are.  If the angle alignment isn't exactly parallel with the motion 
you're going to snap bits very often.

   #80 bit in the drill.  Hold a 1/64ths ruler behind the tip and move the bit 
up and down making sure the shaft of the drill moves exactly in the same line. 
Not  just to the 64th but over the same part of the line of the ruler.  Then do 
the same 90 degrees around.  That will get it close.  Then drill a hole, and see 
which way the bit tends to bow.  Adjust until you've gotten the bow to the 
minimum you can and you're done.  Then it's aligned accurately, and most bits 
will last.  I get plenty of holes per bit even with very tiny bits, and that's 
with a cheap dremel knock off or flex tool handle.  To tell you the truth I 
didn't even realize how crap my alignment was myself with the .039 etc bits 
until I started trying the #80s.

   If the angle isn't exact, and the drill makes a hole but by the time the 
drill is all of the way in, if it's even 1/10th of the bit diameter over you're 
putting a heck of a strain on the bit for every revolution and they will not 
last long at all.


   Another thing is most people don't realize how little cutting a small 
diameter bit does at say 10,000 RPM, and they feed too fast.  Bite off too much 
and it's going to snap in an instant.  20 or 30 K RPM isn't even too fast for a 
small bit with many materials, and you still can feed too fast.  And your hand 
generally isn't accurate enough for feed on very tiny bits, small jerks in 
feeding on a drill press means you'll break many more small bits by hand than on 
an automated system.


   Trivial to make enough automation to do say an IC tube with a line of holes 
too.  Go to Lowes and get 2 of the KV drawer slides.  Mount a platform between 
two and put the rails on a base.  That's your X to move the tubes.  Then another 
board, and put on two door hinges.  Two 4' pieces of wood on the door hinges, 
coming out to a vertex.  Basically a frame to get to 4' over from the hinges, 
far enough away and circular motion is basically linear.  Shift the alignment of 
the hinges until there is very little play by having them not exactly in line, 
almost binding even.  Then mount your drill at the point 4' away from the 
hinges.  That far away the motion is close enough to linear, at least for a thin 
drilled item like an IC tube..  Oh yeah they are three rail slides, take off the 
outer part and only use the inner and middle rails.

   One stepper motor and 1/4"-20 threaded rod to move each, use 1" long 
connecting nuts for the motion they have less play.

Alan