The original design was built in order to cut RC wings (even tapered wings - where one side is different then the other side)
Polystyrene (EPS and XPS) will cut using a hot wire - other foams - like polyurethane should only be cut with a blade or saw.
When cutting, be careful !!! - wire will get hot, and some people may be allergic to the EPS fumes - always work in a well ventilated area.
Step 1: Over View
The first prototype was made out of wood, but didn't look "professional" enough, so I decided to go with a more robust design made of steel.
The design can be modified to almost any size. Keep in mind that for longer travel you will need a longer lead screw.
The problem with a long lead screw is that because it its own mass, it will "wobble" in higher speeds.
One way to overcome this problem is to move to a larger diameter lead screw.
Another way is to move to a chain or belt driven design. Belt driven machines are usually 8' and longer but require the use of micro-stepping. An example of a machine larger then 8 foot would be a surfboard foam cutter.
Some surfboards are up to 12 feet in length, the only way to cut these boards would be a belt driven or chain driven mechanism
I will try to cover this topic in the future with a sample machine and pictures...
We started out building a machine to cut wing cores, but soon after we discovered a huge interest in the machine for other industries - like moldings, architectures, surfboards, Logos, props, packaging Willow Sills, Casings, Wainscoat , Fascia, Crown, Parapets, Wallcaps, Pediments, Quatrefoils, Columns
Step 2: The Y axis - Vertical axis (step #1)
probably need 10" max travel on the Y towers.
If building a hot wire CNC foam cutter for props, crowns, moldings
You would probably want to go with a 4' x 4' (X x Y)
EPS Foam billets are usually 3' x 4' x 8' or 4' x 4' x 8'
XPS foam comes in sheets of about 4' x 8' x (1" or 2" or 3" thick)
If building a CNC foam cutter to cut Polyurethane foam - FORGET IT
Polyurethane foam should not be cut with hot wire, but a blade or a saw
There are CNC foam cutters for Polyurethane that work similar to a band saw
But use a abrasive wire instead of a saw - click here for more information
In this section we will build the two Y posts or towers (Y axis).
The posts can be found at the fence section at Home Depot
You can replace these posts by any other post as long as you
are able to keep them from vibrating during the cut.
Any vibration of the posts will result in vibrations on the wire
resulting in "waves" or not smooth cut of the foam.
The following can be found in the drawer section, you will need two 16" drawer slides
The Home Depot Catalog number for 24" slides made by Liberty 7-81266-18070-4
Step 3: The Y axis - Vertical axis (step #2)
Cat num: 204-008 Home Depot num: 6-39426-48607-7
measure 6" from the base, and screw in (or use a rivet gun) the slide to the post
Make two of these units - one for the left side of the machine and one for the right side of the machine.
Step 4: The X axis - Horizontal Axis (step #1)
Here is the Home Depot Catalog number for the part below:
"Half Base" made by Company named Simpson
Catalog number : C751-973
Home Depot num: 044315-10350
these parts were punched and then bent, when we decided to make our own parts we had
them laser cut and bent - then powder coated
Step 5: The X axis - Horizontal Axis (step #2)
You will need two of these units, one for the right side of the machine and one for the left side of the machine.
Step 6: The X axis - Horizontal Axis (step #3)
We used large 5/8" screws to hold the post in place on top of the U shaped X carriage.
Now make the 2nd one - again you will have a total of two units.
Step 7: The Lead Screw (step#1)
online, stainless steel threaded rods.
For this section, I used a lathe and a set of tap and die.
There may be ways around, but I chose to go the safe route.
We later had ACME nuts made just for us - if you are interested in purchasing
ACME nuts Please visit our online store at http://www.8linx.com/cnc/online_store.htm
There are a few differences between threaded rods and ACMEs. Usually ACME
have a lower inch per turn.
A later design, we used ACME screws that can be found on ENCO - search www.use-enco.com for ACME threaded - here is the exact link
Step 8: The Lead Screw (step#2)
will turn 10 times and during this time it will advance 1 inch. If you use 3/4-6 ACME
rods and ACME nut - this means the ACME screw
will turn 6 times and during this time it will advance 1 inch.
When calculating the steps-per inch on a machine you need to know the ACME
value and the stepper motor steps.
For example: using 1/2-10 ACME with a stepper motor driver at 1/2 step - to
calculate the steps per inch follow these steps 10 turns per inch times 200
(which is the usually stepper motor steps per turn) times 2 (this is the half step
of the stepper motor driver) the total comes to 4000. This means that the
resolution of your machine will be 4000 steps per inch
If you decided to go with the ENCO threaded rods, you can buy from them the ACME nut as well. Here is the link ACME Nuts
Step 9: ACME Screw (step #3)
A better way is to make this "Coupler" out of rubber - this will help in case the motor shaft and the threaded rod are not aligned.
We later moved to ACME screws that can be found on www.use-enco.com. These ACME screws come is 3' and 6' lengths. Since their diameter is 1/2" and the motor shaft is 1/4" you will have to machine these ACME rods to 1/4" diameter. Use your lathe of stop by at a machine shop and they can do it for you.
Step 10: ACME Screw (step #4)
The last picture on this page shows that the two "T" brackets are facing each other,
This is where the hot wire will connect. For those who wish to mass produce wings,
simply add one or even two more "T" brackets and you can cut 3 cores at a time.
Step 11: The Software
1. FoamWorks software will work with the electronics in the package below - has CAD
capabilities as well
2. GMFC - needs a timer module - without the timer the package below will not work
3. Mach3 is a generic CNC router software will work with the package below, but you need to
be able to generate 4 axis g code.
4. KCAM - same as above - generic CNC router software - will do nice PCB boards as well
5. DeskCNC - is an additional hardware board that connects to the PC via the serial port and
its output is the electronics
package below, not very easy to put together but doable.
All of the software above other then DeskCNC require you to have a printer port on the PC
If you are going to cut wings or simple shapes we would recommend the use of Foamworks
If you want to cut complicated shapes and multiple shapes we would recommend DeskCNC or Mach3. We currently use AutoCAD to draw the shapes, then convert them into G code using DeskCNC, and the last step is to run the machine using Mach3.
Here are some tutorials for all 3 software packages - we have spent many hours creating them, and they are free of charge to use or distribute !!
Step 12: The Electronics
You can search ebay and look for "4 axis stepper motor driver".
Then you will have to find 4 stepper that will match the drivers - pay attention to the type of driver you are getting. Some will work with Biploar motors and some will work with Unipolar motors.
The last step is to find a power supply. The power supply should be around 24V 5A, but its best to get all of the electronics from one source.
If you can't find anything on ebay try this
The Electronic box works together with the software you choose.
Make sure that the electronics you select can be programmed to accept pulse and direction for each of the 4 axis.
Mach3, KCAM and Foamworks will all work fine
Mach3 will only drive the electronics. Foamworks will also generate a file called "DAT" file, and with this file it will also control the electronics.
Sounds complicated, but take a look at all these web sites and after a while things will start making sense.
Mach3 - www.artofcnc.ca
Foamworks - www.foamwork.net
Step 13: The Stepper Motors
There are only two coils, and current must be sent through a coil first in one direction and then in the other direction; thus the name bipolar.
Bipolar motors need more than 4 transistors to operate them, but they are also more powerful than a unipolar motor of the same weight.
To be able to send current in both directions, engineers can use an H-bridge to control each coil or a step motor driver chip.
In a unipolar stepper motor, there are four separate electromagnets. To turn the motor, first coil "1" is given current, then it's turned
off and coil 2 is given current, then coil 3, then 4, and then 1 again in a repeating pattern. Current is only sent through the coils in
one direction; thus the name unipolar.
A unipolar stepper motor will have 5 or 6 wires coming out of it. Four of those wires are each connected to one end of one coil.
The extra wire (or 2) is called "common." To operate the motor, the "common" wire(s) is(are) connected to the supply voltage,
and the other four wires are connected to ground through transistors, so the transistors control whether current flows or not.
A microcontroller or stepper motor controller is used to activate the transistors in the right order. This ease of operation makes
unipolar motors popular with hobbyists; they are probably the cheapest way to get precise angular movements.
(For the experimenter, one way to distinguish common wire from a coil-end wire is by measuring the resistance.
Resistance between common wire and coil-end wire is always half of what it is between coil-end and coil-end wires.
This is due to the fact that there is actually twice the length of coil between the ends and only half from center (common wire) to the end.)
Step 14: Finalizing the machine (step #1)
I use strong spring to keep the cutting wire tight. The spring also keeps the wire tight when cutting a tapered wing.
You can get the spring in your local Home Depot. On some designs I have seen people using a bow instead of the spring design. I got better results with the spring, but feel free to experiment
Here is a setup which I also use on my foam cutting bow. The router speed control can handle up to 15A And the power supply can supply up to 3.5A which is more then enough current for a 30" wire. (about 1.5A) The low voltage power supply is used to isolate the main voltage (110V) from the cutting wire.
Another way to go would be to use an isolation variac - here is a good choice for one
make sure to get the isolation version !!!
Step 15: Finalizing the machine (step #2)
The router speed controller connects to the mains voltage and its output goes to a transformer (should be isolated)
These transformers can be found in surplus stores like www.allelectronics.com
Another way to go is to use an insolated variac - this is better since it provides isolation from the main power.
You can find this variac at http://www.action-electronics.com/variac.htm
Almost all variacs are NOT isolated, and by being not isolated, the user may get "zapped" if not careful. Use caution when powering the hot wire, try to stay at low voltage (below 50V), in some cased you may need to go beyond 50V - in case you have a long wire. make sure never to touch the wire or the springs.
A hot wire CNC foam cutters as its name - cuts the foam by melting it before having contact with the foam EPS foam - expanded polystyrene at 1LB density can be cut at speeds from 10 to 20 inch per min XPS foam - XPS foam has an innate combination of properties that make it one of the most efficient insulating materials available. The closed-cell structure, responsible for the foamÃ¢â¬â¢s excellent moisture resistance, also contributes to its high compressive strength and superior thermal performance extruded polystyrene foams may need to cut at a slower speeds, from my experience, when cutting XPS foam, I use a thinner wire - about 0.4mm. XPS cut are generally smoother then EPS foams.
Another kind of foam is EPP foam (the kind they make the Zagi wing flyer) - EPP (Expanded Polypropylene) EPP foam doesn't dent or break. It has a "spongy" quality to it, so on impact it compresses and pops back to shape
We started out using stainless steel wire as our hot wire, this will work well, but the wire will not last long and can break under to much tension. If cutting a 2LB foam for a large project, wire breaking during the cut can cause a lot of $$ At a later stage we moved to Nichrome wire. Nichrome wire will last longer and will not break even when red hot. Keep in mind that the wire will tend to stretch when heated, so a spring is needed to keep it from sagging
The software I use is foamworks (www.foamwork.net)
This software is the most popular foam cutting controller software, and also not to expensive (about $50) It will control up to 4 motors and let you cut tapered wings and other shapes, take a close look at the site There is a lot of useful information there, and even a link where people