Homebrew PCBs

Hello,

BTW, in PCB's there is an effect call epoxy smear, which DOES cause 
havoc with platethrough holes. Anything you read in depth about PCB's 
will mention it... Epoxy is a thermoset, not a thermoplastic, but it 
still can smear the inside of the hole. When it does so in a multi 
layer board the "smear" covers the inner layers, and the PTH doesn't 
connect to that hole. It's part of the reason we can buy cheap PCB 
bits. A board house CANNOT afford to use anything but SHARP bits.

The Excellon machines Jan described are still used my many PCB shops 
today. Look for the signature green and orange paint scheme. And they 
still use the old floppies and even older controls. 
Sneakernet is still widely used. (which kinda makes sense when you 
consider that the boards layers themselves are stacked 
and "assembled" for drilling by hand. (Remember, board houses drill 
FIRST.)

As for the construction and backlash etc. in the PCB drills, these 
machines are built on and with huge Granite slabs, using air bearings 
and precision ground ballscrews with preloaded nuts. The 4 spindle 
type is pretty much an industry standard. You can usually find 
pictures of one of these on ebay, as they sell rather frequently. 
Use "excellon" in a search...

It's actually pretty surprising to see how "old" most PCB houses 
appear in their techniques and machinery. Living near silicon Valley, 
I've seen a few...

PCB ASSEMBLY houses, on the other hand, almost always have the latest 
and greatest... Nowadays they have to. Pick and place, reflow ovens, 
vison systems and xrays for BGA, etc. ..  

Hope this helps,

Ballendo 

--- In Homebrew_PCBs@yahoogroups.com, dg140@f... wrote:
> Hi Jan.  How did you account for backlash in your homebrew CNC 
rig?  What
> about those PCB drilling machines, what do they do for backlash and 
other
> error components?
> 
> ---
> 
> >Particularly if the bit is not NEW-sharp!
> >  The particular board which needs drilling is actually for the 
mechanical=