Zoran,
There are calculations we used for the various feeds and speeds but
most of this was done automatically by the machine. What you need to
know is the chip load for the bit size you are using. The chip load
is how many mils (.001" = 1 mil) the bit goes into the board per
revolution. Your feed rate is then calculated by multiplying the chip
load by the spindle speed. For example, a bit requiring a 3 mil chip
load at 60,000 rpm equals 180 inches per minute feed rate.
There are more calculations required to arrive at the surface feet
per minute for a bit size etc. I don't know how to post these
equations in this message because they are complex. There is a chart
with all of this information on it and perhaps I can photograph or
scan it into the Photos section. The bottom line on all of this is to
just get your machine going any way you can and adjust the speeds for
what works and sounds good to you.
The Excellon drilling machines have a built in software page called
a "Diameter Page" which contains drill bit size and feed rate
information. This chart can be user edited to get the results you
want. The machine looks at this chart and adjusts the spindle
parameters as needed. These charts are set up in ranges such as .020"
to .030" etc. Every size in this range will have the same feed and
speed. If needed, the Diameter Page data could include a feed and
speed record for every drill size you wanted to enter.
Some CNC drill programs contain the feed and speed data from the CAD
system and the drilling machine will use that info. The problem with
this is I never once saw a CAD system that could get even close to
having the correct feeds and speeds. So we always edited that part of
the program and let the machine take over.
An experienced machine operator will always tweak the spindle speed
while the spindles are drilling until everything sounds right. You
can actually hear the difference as you change the speed so you just
keep tweaking until the spindles are "singing". The only time we got
out all the charts and did calculations was when a customer was
hanging around. This way they thought we really knew our stuff and
were getting their money's worth! As soon as they left we went back
to "winging" it!! We bent a lot of rules in those days to get the
jobs out the door. It really was a lot of fun back in the old days.
Anyone in the PWB business can tell you similar stories.
Tom
--- In
Homebrew_PCBs@yahoogroups.com, "Zoran A. Scepanovic"
<zasto@y...> wrote:
> Hi all,
>
> I'm on the way of making PCB drillin machine, and I would like to
get some
> info on the spindle speeds and feed rates for different drill
diameters
> needed for drilling FR-4/FR-10 boards.
>
> (Maybe Tom has the answer!)
>
> --
> Sincerely,
> Zoran A. Scepanovic
> zasto@y...
>
> [Non-text portions of this message have been removed]