Bob's Minimill Conversion

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.

PCBs photo        AD8307 Pwr Mtr PCB

If questions or comments, email Bob

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Originated 2010-01-15
Revised 2010-01-22