Re: Threaded Rod WORKS!

--- In CAD_CAM_EDM_DRO@y..., "cncdxf" <cncdxf@a...> wrote:

> Chris,
> What if the person has a 6" X 6" cutting area and the
> threaded rod is off by .005 or more over that distance. The
> machine will still be a learning tool and it can turn out great
> parts for RC cars and planes.

Very true. My first CNC device was a X-Y table with solenoid pen
control - basically a pen plotter used to win high school science
fairs. Used 10-24 threaded rod - which if I recall had 0.006 of
backlash or something horrid like that. This device was programmed
in assembler via a Motorola 6809 processor, and could do lines and
circles via a part program, or "free hand" mode - where the pen would
follow a joystick. Monopolar 4-phase steppers (mail-order from some
place in Mass), powered by TIP120 Darlingtons, sequenced by a port
chip hanging on the 6809 bus. Wanted to use it to layout PC boards
using resist ink but never got around to it.

The best part was doing the circle routines in assembler w/o the
trig functions or lookup tables. It can be done, and fast too!

My second CNC project (2.0) was composed of 2x4s, plywood, cabinet
drawer slides, three monopolar steppers (higher voltage MOSFET
drivers with V/R current limiting, zener flybacks), more threaded
rod, RC car bearings etc. It was a 3-axis 'mill' - using a Dremel
tool for a cutter. Used it to carve out foam patterns for casting
into aluminum. Powered by an 8088 PC, out a wirewrapped i/o port
card, programmed in C under Turbo C 2.0 or something old like
that... Could perform 3d lines, 2d circles/arcs. Executed a 'part
program' composed of X,Y,Z commands, both relative and absolute, as
well as commands for arc/circles etc.

CNC V2.5 was the same as 2.0 only I attached shaft encoders, and had
the previous 6809 system display the shaft positions on an LED
display (open loop DRO). Ported most of the control code to Linux on
a '486. Used it as a CNC drill to drill (via Dremel) flame baffles
for propane furnaces. Did some X-windows programming under Linux for
tool path 'verification'. Build an EDM power supply and software
support. Burned some holes through many objects using 0.5mm graphite
pencil lead for an electrode. These days I'd probably try 0.020 inch
Tungsten TIG electrodes.

More recently I've played with PICs and steppers, evaluating how to
limit acceleration and velocity of the same steppers. So far so good.

Generally all of this stuff was really inexpensive, yet extremely
instructive. I sure learned a lot. My next project will probably
involve buying a large cast iron object from Grizzly (knee mill?),
and hanging some larger bipolar steppers onto it etc... Probably
throw a few PICs in there for good measure too. As soon as I can
sell off my wife and kid to gain some spare time I'll get back into
all this fun stuff!

-Bill