this review I will show you how to setup and operate the CNC
Foam Cutting Machine that we built in Part 1 HERE.
A CNC Foam Cutter will allow you to quickly build wings, fuselages
and other shapes from various weights and types of foam. The
machine uses a temperature controlled hot wire to cut (by
melting) the foam to the correct shape. The machine is a 4-axis
machine and has two independent sides, so different shapes
can be cut on each side. This machine will cut tapered shapes
as well as straight shapes.
this review Hobby CNC provided a FOAM Pro Major Electronics
Combo while Precision Tech Machining provided the lead screw,
lead screw nuts, bearings and bearing blocks. Gilles Muller
provided the GFMC software and A Main Hobbies provided a ProTek
1010b+ iCharger to use as a hot wire power supply.
is where we left on on Part 1:
130 oz-in Torque Stepper Motors
this machine can cut:
Expanded polystyrene "breadboard foam"
Blue or Green Extruded Polystyrene Foam Insulation
will need some basic tools:
Steel Wool (for cleaning the wire between cuts)
really handy tool to have when cutting foam is a metric tape
measure. I found this one at Ace Hardware for under $10 bucks.
The GMFC software uses all metric, so this tape will help you
measure your machine and position the foam before cutting.
it comes time to selecting the cutting wire, there are lots of options.
The perfect cutting wire would be readily available, cheap, very
small in diameter, would not stretch when it got hot and be very
Steel Wire (Also called Stainless Steel Fishing Leader)
by most fishing places, cheap
hard to find very small diameters
Wire (Most hobby shops carry this)
by most hobby shops, small diameter, cheap
Little Stretch, Strong, Small Diameter
tried all these and prefer the RENE-40 wire for several reasons.
It does not stretch as much as stainless steel or Nichrome and it
is very strong and comes in a small diameter.
Products LLC has been selling small amounts of RENE-40 wire (50
feet) to the hobbyist for many years. There RENE Cutting Wire is
0.014 inches in diameter and at the time of this writing was $36
install the spring you will need a spring, crimps and the RENE cutting
wire. I found my spring at Ace Hardware, C-141 a 5/8 x 2 1/2 x 0.072
Utility Extension Spring. Use the spring on one side and the other
side will attach to the screw going through the block. Use the crimps
to secure the wire into a loop. It helps if you can loop the wire
through the crimp at least 1 extra time. The crimps I used were
Du-Bro Catalog number 896. The RENE wire is strong, but very stiff
and does not bend well so take care not to make sharp bends with
need to install the wire so the spring is a little stretched. Exactly
how much you will need is hard to describe with out some way to
measure it. You can study the spring in the picture above to get
an idea. When you cut a tapered wing this spring will have to stretch
to make up the extra distance as the two axes move out of plane.
is a better way to tension the wire, but you have to build a bow
and support the bow. The bow hangs under the machine so you will
need to add legs to the machine. With this method, the wire tension
stays constant as the axes move out of plane. Searching the web
will yield more than a few examples of how to do this. If you cut
a lot of highly tapered shapes, this is the best method for tensioning
are 3 kinds of foam that I'll look at in this review. Each has their
place, and I will explain the common uses of each.
most common is white or "breadboard" foam, also
called Expanded Polystyrene. This is the foam that most ARF's (if
they use foam) will use. White foam comes in various densities including
1lb/cubic foot, 1.5 and 2.0 lb/cubic ft. Generally 1.5 or 2.0 lb
foam will produce the best combination of strength and weight. The
higher density foam will require more heat to cut as well. Typically
the white foam sold at the big-box home improvement stores is the
lighter 1lb foam and has "regrind" or recycled foam pieces.
This foam will not cut as nice and the wire may drag or hang in
spots. For the best cuts, try and find "virgin" foam that
has no "regrind" in the 1.5 or 2.0 lb densities.
typically denser than than the white foam and it generally does
not come in various densities. I have not worked with the green
foam, but from my experience the pink foam cuts just a little nicer
than the blue foam. I've used this foam with great success in my
Combat airplanes. Depron is also an extruded polystyrene foam that
comes in many thickness that are popular with electric foamies.
foam is cool stuff. It is by far the most "crash resistant"
of the foams. This foam has large beads and wings cut from this
material absorb impacts very well. This for is also much less stiff
than with the other kinds of foam. The disadvantage of EPP is you
will probably have to order it, and shipping can be expensive. If
your going to make a plane to bump around, this is the foam for
Expanded polystyrene "breadboard" foam
improvement stores, insulation supplier
Blue or Green Extruded Polystyrene Foam Insulation also can
be purchased as "Depron"
improvement stores, insulation supplier, Mail Order or Hobby
how does this thing cut the foam anyway? The theory is simple. A
tensioned wire is heated by an electrical current source, this causes
the wire to heat up. The heat that radiates off the wire
melts the foam. Enough heat is generated by the wire that the foam
will melt in front of the wire as it moves through the foam.
amount of power that runs through the wire and the speed that the
wire travels is important. Set the power too low, and the wire will
cut by contact. Too high, and the amount of foam that is melted
will be excessive. Also with too much heat, the surface of the foam
is distorted. Cut too fast or slow and you will either cut by contact
or melt too much foam.
that Power = Volts x Amps, you can read more HERE.
For a typical power supply (not a special constant current power
supply) you hold the voltage at some level, and the amperage will
fall out depending on the resistance in the wire. To make the wire
hotter with a typical constant voltage power supply, you dial in
more voltage. This will cause the amperage to go up and thus the
wire will be dissipating more power.
Example of cutting by radiance from the
GFMC help file
know what your thinking, but how do you get an accurate size shape?
The answer is with the software. Kerf is the distance that the wire
needs to be offset. The GFMC software allows you to insert two different
kerf values. The GMFC will cut tapered wings, and on the tip (normally
the side with the shorter chord), the Kerf will be bigger than the
root because the wire is moving slower. To compensate for that,
GFMC has two Kerf values (S and S/2).
the software cuts any shape, the left and right axis must move to
the same percentage of the line that you are cutting. For example,
if you are cutting a tapered wing with a 10" root chord, and
a 8" tip chord - the wire must move faster on the side of
the larger chord. So when the wire is at 10% on the tip - the
wire is at 10% at the root. Also the wire will enter and exit on
at the same time from the leading or trailing edge.
Wire Power Supplies
cut the foam you have to provide power to the wire to heat it up.
You can do that with AC (Alternating Current) or DC (Direct Current)
electricity. A search on the web produces results for hot-wire power
supplies of both types that you can buy or build yourself. The best
is the Direct Current variety because of heat control and heat stability.
confuse the cutting wire power supply with the one that will supply
DC to the HobbyCNC controller board! These MUST be two separate
power supplies! For the HobbyCNC board I used a converted ATX
400W computer power supply. The HobbyCNC site has these instructions
on how to modify the power supply for use when it's not in a computer.
this review A Main Hobbies provided a ProTek 1010b+ Charger. ProTek
has introduced their 1010b+ advanced battery charger that has some
unique software that will allow it to be a foam cutting power supply.
The best part is you can power it with a 12V power source and get
up to 40V output! It also has an easy to read LCD that will let
you dial in the amount of voltage and readout the amperage. A stable
power supply is very important to getting consistent cuts
with the machine.
ProTek charger comes well packaged in a full color box. The
ProTek 1010b+ can charge up to 10 Amps. It comes with a board
to connect to 2S through 6S LiPo batteries. It also comes with
a temperature probe for safe charging and alligator clips. The
manual comes on CD and can also be downloaded HERE.
The ProTek 1010b+ will charge or discharge several different
chemistry batteries including Lilo, LiPo, LiFe, NiMh, NiCd,
and Lead Acid. In addition to being a charger, it has software
to drive a brushless DC motor and be a foam cutting power supply.
The 1010b+ charger also supports the open-source software Logview
that can display, plot and analyze the charge and discharge
data. You can also update the firmware via the included USB
cable from the Internet HERE.
Heat Control (Included with the HobbyCNC board)
not a power supply, the HobbyCNC board comes with a wire heat circuit.
This circuit has two positions, Auto and Manual. On the Auto position,
it will interface with the GFMC software to vary the heat as the
wire moves around the shape. One example where this works well is
going around a square corner (like in a spar slot), the software
will reduce the heat to for a sharper edge. There is a switch to
change the mode to manual, and in this mode you can press the two
buttons (up and down) to vary the heat of the wire. The HobbyCNC
board can handle up to 35 Volts DC of voltage at on the bow power
supply terminals. To power the bow you can build your own power
supply from parts with instructions from the HobbyCNC site.
the HobbyCNC and the GMFC software work together, the quality of
the cut is definitely better. The software knows when to dial the
heat down. It does this around corners and when the wire speed slows
down. The HobbyCNC board acts like a valve on the current, so you
need to supply the board the maximum voltage that you are going
to cut. The HobbyCNC board will then supply less voltage out when
the GMFC software demands it.
ProTek will simply supply a constant voltage current to the cutting
wire. It will maintain a constant voltage to the wire. The ProTek
does a great job of maintaining a constant power to the bow. As
a bonus with the ProTek, you can also charge up to a 6S LiPo battery.
This charger has also been recommended on other R/C Sites for it's
precision while charging. The ProTek has an internal DC-DC converter
that will let you output up to 40 volts on the wire. This is handy
when you want to clean the goo off the wire.
either setup you need to provide a power supply. With the HobbyCNC
board, you will need at least a 24V 2 Amp supply. The HobbyCNC site
has instructions on building one of these for about $75 bucks. You
cannot use a converted computer ATX power supply with the HobbyCNC
setup. The ProTek charger isn't so picky and I was able to power
the ProTek with a 400W ATX power supply.
cutting power supply you choose will depend on your needs. If you
need the most accurate cuts, then use the HobbyCNC setup. The ProTek
has a nice LCD panel that gives you great information when cutting
foam. Having this data will help you set up the machine the same
way each time you use it. This is a feature that the HobbyCNC board
is lacking. The ProTek also does double duty as a kick butt 10 Amp
6s LiPo charger.
GFMC software is used to drive the HobbyCNC board and make cutting
files. It has several special functions, particularly for cutting
wings. It can cut just about any profile, so you can cut pieces
for fuselages. I've even used it to cut foam blocks to help me transport
my planes to the field.
GFMC you will tell the software how big your CNC machine is and
what kind of foams you will be cutting with. The program will allow
you to create and name various types of foam where you can preset
the cutting speed and the kerf. You can also have multiple machines
with different settings.
GFMC has so many features and functions, watch the video below for
a quick introduction.
GMFC software was primarily designed to cut wings, although other
shapes can be cut. For cutting wings, the program will allow you
import an airfoil profile and add features to it like spars and
other cutouts without having to draw them in a CAD program.
you don't need a CAD (Computer Aided Design) Program Either...
You can import airfoil coordinates from a .dat and .cor files. A
.dat file is a standard way to store the airfoil coordinates in
a text file. A .cor file is a CompuFoil
format that also stores the coordinates in a text file. The
.dat/.cor files are common files for storing airfoil coordinates
(without spar slots and other cutouts) and you can download thousands
of airfoils HERE.
They both can be opened in a text editor like Microsoft's Notepad
program. Both .dat and .cor files are text files with airfoil coordinates
in "unitless" dimensions. GMFC will export a profile to
.dxf so you can open it with a CAD program and create more complex
shapes such as hollow wing cores. You can also import a .dxf file
of an airfoil or any shape from a 2D CAD program.
cut shapes other than wings, you can draw that shape in a 2D CAD
program and save that file in the .dxf format and import it to GMFC.
Once you import the file, you will need to edit the points of the
shape by telling GMFC the zero/starting point and the direction
of the cut.
feature that I really like about the GMFC software, is that you
only need to purchase a license for the computer that is going
to run your cutting machine. You can download
and install GMFC Pro on your other computers, and the "cutting"
feature will be disabled after 30 days. You will still be able
to use the software to design your cutting profiles. I normally
design the cutting profiles in my office (in the big comfy office
chair of course!) and then transfer them to the computer in the
shop via a USB stick.
Setup and Calibration
First you will need to set up the GMFC software to work with the
HobbyCNC controller board. Goto GMFC>Table configuration...
to run the motors in half-step mode, so I removed the jumpers from
the HobbyCNC board.
the steps per revolution, screw thread and the table size.
Once you have the table setup you can power on the HobbyCNC board
and jog the machine around manually. This way you can check the
operation of all the motors.If you need to troubleshoot
- DO NOT DISCONNECT ANY OF THE MOTORS WITH THE POWER ON!!! This
will blow the stepper motor driver chips.
you are done moving the machine to the extremes and checking for
binding, move the machine to the home position and zero the machine.
the machine a distance and measure the actual distance it traveled.
Start with something small like 20 mm, then do it again for something
bigger like 500 mm Do this a few times in each direction. If you
are loosing steps, you have too much friction in the mechanical
assembly or have the table settings wrong.
The Kerf is the amount that the machine needs to offset the wire
to account for the amount of foam that is melted by radiance. To
determine the Kerf, a test cut must be made with the same type foam,
the same speed and the same power to the wire. For example, if you
were cutting a 100 mm X 100 mm square, and the test cut was only
98 mm tall, you would put the kerf as 2 mm. To make a text cut,
GFMC has a cutting file that is used where the large side is 80
x 40 mm and the small side is 40 x 20 mm.
cutting the foam, I like to set the kerf in the foam management
setting to zero for S and S/2. This step isn't necessary because
you could add or subtract to the kerf that was set when the test
cut was made, but it does cut down on any potential math errors!
keep from wasting foam on test cuts, I prefer to use the machine
to slice 10 mm off the end of the foam block. Then I cut those pieces
into 150 mm long lengths. Using a few pins, stand one up on either
side of the machine. Set the machine up as if you were cutting one
continuous block of foam.
the test cut, measure the block height (not width) and subtract
the difference from the size the block was supposed to be and the
size it is and put that value in S for the large block and S/2 for
the smaller block. This is your Kerf. For this task I prefer a metric
machinist rule. You can also use calipers, if you are careful to
not squeeze the foam. The calibration takes 5-10 minutes and uses
very little foam.
often should you calibrate the machine? First you will need to calibrate
the machine for each type of foam. Then you will need to calibrate
when the temperature changes. I can't give you a good idea on how
often to calibrate for temperature, but if you want the most accurate
cuts, you will need to calibrate often. Next any time you change
cutting speed, you will need to calibrate.
There are two ways to design a cutting profile. You can use coordinates
from a .dat or .cor file or import a .dxf file from a 2D CAD program.
With the .dxf method, the only extra step is to define the zero
point coordinate and the cutting direction. Other than that, the
steps are identical. GMFC will preview both the root and tip profiles
as well as the wing planform (top-down view). To see the top down
view, goto View > Wing.
set up a cutting profile goto Project > Current Panel Configuration....
a basic introduction of aerodynamics, NASA has a good site: HERE
some explanation of chord, camber and other wing terms check NASA's
is the height of the foam block. In the image above it would
be the distance between the two horizontal blue lines.
is the distance between the root and the tip.
amount the tip profile is set back from the root profile (horizontally)
amount the tip profile is higher than the tip (vertically).
Check this box input the dihedral.
this box if you are cutting a wing panel. This will allow you
to add spars to the wing. On more complex profiles (even airfoils
that you have drawn the spars in) you may want to make sure
this is unchecked.
this will allow you to put in a thickness to offset the cutting
in to account for a wing skin.
this grays out the sweep back option and centers the root and
tip so the wing has the same sweep on the leading edge and trailing
this box to select a different profile from the root and the
to select a profile
is the chord in millimeters. See the image above.
Edge Margin (mm)
is the amount the wing is set back from the front of the foam
Edge Margin (mm)
is the amount the wing is set back from the rear of the foam
is the amount of degrees difference between the root and the
is the distance between the profile and the bottom of the foam
changes the camber of the wing.
changes the thickness of the wing.
that the cutting line is offset to account for wing skins.
now for that extra step when working with .dxf files. Goto File
> dxf/Hpgl Import...then select a file.
press the button.
and you will get something similar to the image below.
hover over the very last point in the trailing edge and right-click
then select "Define Zero Point Here". Then press the
you need to check and see where the cutting line is. It should be
on the outside of the profile. You can check by going to Cut >
Panel Cut.... and selecting cancel. The cutting lines will be shown
on the profile of the airfoil.
the lines are on the inside of the airfoil, the numbers are going
the wrong way. Press the
button and right click over the zero point and select "Reverse
When you are ready to cut a profile goto Cut > Panel Cut.....
(Right Wing / Top first)
which wing panel to cut and if to cut the top or bottom first.
the Profile box is check then the software will compensate for
kerf, otherwise it will cut directly on the line. If the Ref.
Lower Surface box is checked, then all the wing cores in a multi-panel
wing will be at the same height so you can vacuum bag these
you to select trimming the foam block before, after or while
option allows you to position the block. For wings that have
taper and dihedral you may have to play around with the block
positioning until you don't get an error in the bottom left.
allows you to "simulate" the cut to view it in an
allows you to cut a panel that's bigger than your machine and
allows you to select where to section it.
you to select the foam type and speed
you to make more than one cut at a time. Great for production
work. This program stacks the wings the height of the foam block
that you entered and will cut the profile one right after another.
you have adjusted all the parameters, power up the HobbyCNC board
and turn on the wire heat. Then press Cut.
the CNC machine is the first step in an adventure. Once you start
using your machine, you will discover new ways to make foam cut
shapes. Like a good airplane or helicopter, you will learn to "tweak"
it the more you use it. In this article, I described how to run
some of the basic features of the GMFC software. As you get familiar
with the software, you will see that I have hardly scratched the
CNC machine and the GMFC software can be used to make many different
shapes. I've cut wings, fuselage pieces and even repair parts! This
machine will let you make single or multiple shapes quickly.
really enjoyed writing these two articles. Building the machine
was fun and now that it's complete there is almost no limit to what
I can make!
The comments, observations and conclusions made in this review are solely with respect to the particular item the editor reviewed and may not apply generally to similar products by the manufacturer. We cannot be responsible for any manufacturer defects in workmanship or other deficiencies in products like the one featured in the review.