12 Dec
2025
12 Dec
'25
9:30 p.m.
On Fri, Dec 12, 2025 at 9:50 PM devin davison via cctalk
<cctalk(a)classiccmp.org> wrote:
It's been a while since i last wrote to the list.
I have been reading up a
lot on early cnc systems.
While recently picking up some left over tech from a shutdown machine shop,
spotted a early cnc system with some kind of minicomputer attached. Looked
to have some kind of tape drive and paper tape punch. It looked like it was
stored under a leaky roof, ball of rust, it looked too far gone to salvage
anything useful.
About 15 years ago, we had a Bridgeport Series II CNC mill with an
original DEC LSI-11 processor board stuffed into a slot in
all-Bridgeport hardware. In addition to manual operation on control
switches, it had a Remax paper tape reader and a serial port to slurp
up G-code.
Because the PDP-11 only had 16K of RAM, you had to either run jobs
from paper tape (which nobody wanted to punch in this century) or
dribble the G-code in a manner described as "drip feeding". Given
that a lot of modern designs coming out of your CAM engine are upwards
of a megabyte, that's a lot of dripping.
In the end, it was more trouble than non-technical folks wanted to
deal with so it was scrapped for the price of scrap steel. I was
allowed to strip whatever I wanted - I kept the PDP-11 CPU and the
Remex reader.
I have no idea specifically what programs were used in the 1970s to
generate the G-code (though G-code can and was written up by hand).
-ethan