Homebrew PCBs

Bob,

We always used "diamond cut fishtail" router bits for profiling 
boards on Excellon Automation CNC routers. Almost every job was 
routed using .093" diameter bits. We would stack the boards two or 
three deep depending on the required accuracy. The spindles were 
started at 25,000 rpm and then the operator would manually tweak the 
speed until everything sounded right. If the spindle speed and table 
feedrate was not just right the bits could make a loud screeching 
noise. The table feedrate was set to around 50 inches per minute and 
was also adjusted by the operator for best performance.

Sometimes .062" router bits were used and these were operated at 
about 45,000 rpm but at a slower table feedrate with a maximum stack 
of two .062 thick panels.

The biggest mistake made with these router bits is to use them past 
their service life. I don't remember how long they would last before 
becoming dull but I think it was only about 400 or so inches. When 
the bits are new and sharp they will leave almost no dust in the 
routed path. When they start getting dull the dust will pack into the 
ends of the cuts especially on internally routed slots.

Another mistake is to set the plastic ring too far away from the tip 
of the tool. Excellon specifies .810" from the ring to the tool tip 
for drills but only .680" when using router bits. Many machine 
operators make this mistake and the extra flute length leaves the bit 
subject to oscillation. This problem can really affect the accuracy 
of the finished parts and break bits as well.

For "etch cutting" patterns directly into copper clad panels we used 
small size broken drill bits. It's easy to use a small diamond wheel 
to dress a broken carbide bit into a very effective cutting tool.

If I remember correctly we paid about $1.80 each for .093" router 
bits and purchased most of these bits from Tulon Corp. Hope this 
information helps.

Tom 

--- In Homebrew_PCBs@yahoogroups.com, "spoothammer" 
<spoothammer@h...> wrote:
> 
> Hi,
> 
> I hope I'm not re-asking a worn out question... but here goes. What 
is 
> the best tool to use to route printed circuit boards on an NC mill? 
I 
> have a Sherline mill with the NC kit, Xylotex controller, and 
Master 5 
> as the controller software. I am using Eagle PCB for designing 
boards. 
> I just need to know what the best (meaning least expensive but 
giving 
> good results & life). What does LPKF and the other board router 
> devices use? Is Grizzly a good source? Tool steel or carbide? 
> 
> Thanks!
> 
> Bob