Ubuntu
Linux and the Enhanced Machine Controller (EMC) are used to control a three axis Computer Numeric Controlled (CNC) minimill
This page provides a brief description of my conversion of a
surplus MTI seamsealer into a four axis minimill for use in (small) 3D
milling applications. The conversion is completed and working fine; the
machine has been used for years to fabricate printed circuit boards (PCBs) for
electronics projects, coasters (my Smith Chart and Morse Coaster designs) and
other miscellaneous engraving projects.
The conversion is made possible through the good works of
the folks at NIST and the current community of developers that maintain and
enchance the EMC at LinuxCNC.org.
Purpose
This minimill conversion was initially conceived
as a means of fabricating circuit boards for electronics and microwave
applications. After building one circuit board for a stepper driver,
I realized there was value in automating the PCB process --
especially for drilling small through holes as doing this manually with a Dremel
tool is nearly impossible!
Platform
A surplus MTI seamsealer was made available by my employer. The specifications
from the manufacturer's previous web site may be seen here. The unit is now apparently out of production.
In any case, the machine is basically a six-axis (X1, X2, Y, Z1, Z2, and a Rotary Axis) device originally designed to
make precision welds for electronics packaging (i.e. hermetic covers). I'm using three
orthogonal axes to accomplish my goals for the minimill.
Stepper Drivers
I replaced the desk/rack-mount computer
and motor drivers with a single four-channel board from HobbyCNC. These
drivers supply 3 Amps per coil of unipolar drive and are easily
interfaced to EMC through the printer interface. One catch in this
process is the Allegro/SanKen SLA7062 driver chip wants a one
microsecond,minimum, setup time for the Direction signal before the
Step signal arrives to step the motor; this is configured using the standard
setup parameters in the EMC configuration file.
Computer
A Compaq Presario 2100 (not the machine in the photo below) laptop
controls the minimill. This machine is WAY smaller than the
original computer console and has run Linux (Ubuntu) for several
years. I just installed the
standard (live) distribution after doing the machine latency test, as
described
on the EMC web site. The computer is plugged into AC power and the
printer cable leading to
the minimill is connected to the parallel printer port.
EMC Distribution
The EMC distribution employed on the laptop is the
http://www.linuxcnc.org/hardy/ubuntu-8.04-desktop-emc2-aj13-i386.iso
distribution image. I adjusted the .ini file to match the
leadscrews and stepper motors, as needed. The machine is working great with no
known issues; I just generate a gcode file, load material on the machine, zero
the axes, and out comes a PCB or part! For PCBs, the cool thing is no chemicals
are required and the holes are drilled in just the right places for through hole
parts everytime.
Current Activity
The minimill is being used on an as-needed basis to make circuit boards and
engravings. My latest projects on the minimill were a little time-domain
reflectometer and a power meter circuit that is based on the Analog Devices AD8307 log
amp/detector. Information on these projects is available in the Files section
of the NFARL Yahoo group under the DIY_Homebrew directory, if interested.
Photographs
Finally, some photos...
Here is a slide that shows the machine running a little engraving job for the family.
These
two photographs show printed circuit boards made on the machine -- it
cuts isolation traces for the necessary circuit traces and drills
holes for thru-hole components, as needed.
