Computer-Controlled Router Table Balsa Cutting: INTRO
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Computer-Controlled Router Table for Balsa Cutting

Owen White

owhite@tigr.org

Beware all ye who enter: CNC tables are not cheap. CNC tables
do not save time. CNC requires you to learn lots of user-hostile
software. CNC tables waste a lot of balsa wood. CNC tables are not
always incredibly accurate. Perhaps its not exactly worth the
effort. Quoting one respected curmudgeon:
       "Still dont see what you cant do with a sharp number 11
       exacto blade and a ply template for cutting ribs".

              -Dereck Woodward.

Time. If you look at the text below describing the process you can see
there is an increased amount of design that has to happen in
CAD. Fortunately I have a lot of extra time during business trips and
I have so far always had a backlog of planes that I have designed
compared to the planes I have had time to build.

Functionality. CNC tables do not do everything. Just cause you cut
parts you still have to put the thing together. Its just sort of like
having the kit company in your basement. Someday we'll have a system
that lets you start with a balsa tree, push it into a machine, and get
a complete plane as output.

Accuracy. My table has a resolution of 1/200ths of an inch. At first
glance that sounds pretty good. But there can be a little bit of slop
in x-y mechanism, minor slippage of the board can cause problems, and
sun-spots activity appears to effect the quality of the process. The
final result is that when you cut plywood parts where tab A is
supposed to fit into slot B with zero gaps some work with the x-acto
will still be required.

Why I did it. Despite considerations against its value, I built
a CNC router table to cut balsa wood for RC planes. I enjoyed making
it and I enjoy using it. It was extremely interesting engineering
project. I find long-term construction projects to be quite gratifying
and I'd do it all over again. Another factor I spend a lot of my time
on business trips running AutoCAD.  So I can design plans on my laptop
and then come home and cut parts. One thing I'll say is that it is
absolutely the world's most incredible feeling to see stuff that once
existing on a computer screen appear in three dimensional space. There
was also the time a neighborhood kid saw the device and remarked in
complete amazement: "Its like a balsa wood printer!". Real world
advantages are, once the parts are designed revisions are quite
easy. There is an alignment factor; when -all- your ribs are
identical, and you put them together on the board they fit together in
a way that just isnt really achievable from any other method. (Well
okay, any other -scratch- method). Having rapid access to a fresh set
of balsa also makes you a more courageous pilot. It increases my
confidence that after a wreck I can retreat back into the basement and
punch out a fresh set of balsa parts.

Costs: I paid $700 for the table. $250 for a mechanism to give
me movement in the z-axis. $300 for drivers. Power supplies were
surplus. The dxf to gcode software was $500. The gcode to motor driver
software was $150. AutoCAD is expensive but there are
alternatives. Computer prices vary, someone just asked me if I would
take a more than adequate 486 off of his hands for example.

Process. After you've built your table here are the general
flow of activities:

(Okay, I was kidding about that last point). 

Additional information:


Gallery:

bronco1 bronco2 bronco3 bronco4 bronco5

A flying mailbox, the NewBee.

Dah flounder.

Still on the board: The Tempesto electra.

Most of the dxf files of the plans and flat-part layouts for the above
models are available on request. 
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