This article will show you how-to build a CNC hot wire foam cutting machine. Foam is a great building material that is lightweight and inexpensive. With a CNC foam cutter you can quickly build complex shapes including wings and fuselages.
The machine works by moving a heated (hot) wire through foam. The heat of the wire melts the foam leaving the desired shape in the foam. When you are finished you have a “shuck” (unused part) and a “core” (used part).
This is the first in a two part series that will show you how to build a CNC foam cutter. The second part will cover the hot wire and hot-wire power supply as well as operating the machine with the software and various cutting techniques.
This machine can be built using a drill press, band saw or jig saw, a metal chop saw, hand drill and simple hand tools. You will also need basic electrical tools such as a volt meter, soldering iron, wire strippers, flush wire cutters, flux and solder.
I wanted to purchase materials locally, as a result much of the CNC machine materials were purchased at the local big-box home improvement store.
The heart of the machine is a HobbyCNC FoamPro kit that include a 4 axis stepper motor controller circuit board and four 130 oz-in stepper motors. The machine will be run by Giles Muller Foam Cutting Software (GFMC Pro). The machine also has a few purchased machined parts. They include 1/2-10″ lead screws that are machined on either end, bearing blocks and motor mounts.
Degree of Difficulty
Good Building Skills
Time Required to Build:
More than 25 hours
Width (wing span):
Length (wing chord):
Motors: 130 oz-in Torque Stepper Motors
Foams this machine can cut:
- White Expanded polystyrene “breadboard foam”
- Pink, Blue or Green Extruded Polystyrene Foam Insulation
Materials and Hardware
In the article I show you what I used to build this machine. Chances are that other ways, different methods, materials and different hardware will also work. With the exception of the Ultra High Molecular Weight Polyethylene (UHMW) plastic, some electrical supplies and the bearings, all other materials were purchased locally at the “big-box” home improvement stores and the local auto parts store. The bearings were purchased in the skate board section of the local sports store.
HobbyCNC First Look
- Detailed Instructions
- Easy construction
- Excellent Tech Support
Hobby CNC offers a FoamPro kit that includes a stepper motor driver board kit (unassembled), four 130 oz-in stepper motors, hook up wire and a printer port cable. The stepper motor controller board is connected to a printer port on a computer and controlled by software designed to run a 4-axis CNC machine.
The kit includes nearly everything that you will need, but you will need to provide a case for the board, a cooling fan and two power supplies. One power supply will power the stepper board and the other will power the hot wire to cut the foam.
Dave from HobbyCNC provides excellent tech support through a Yahoo! group which you can join after you purchase a HobbyCNC kit.
|The HobbyCNC package comes well protected in lots of of bubble wrap. The kit includes the board and a large bag of components.|
|Yikes, Look at all those parts! Once you organize the parts it will make it much easier to find the ones that you need when putting the board together.|
|The kit includes capacitors, voltage regulators and resistors.|
|The HobbyCNC board is well marked and easy to read. The instructions are detailed and complete. The stepper motor chips come in an electrostatic safe bag.|
Precision Tech Machining First Look
- Excellent fit and finish on motor mounts
- These machined parts make building the machine easy!
|Precision Tech Machining Introduction
Precision Tech Machining is a full service machine shop that also offers products that help the hobby CNC machine builder. The offer ACME lead screws, lead screw nuts, bearing blocks and motor mounts. These products makes it easier to build a CNC machine without having a mill and lathe in your garage.
|Lead screws come machined on both ends to accept the bearing blocks and a drive coupling. Used in the review are two 24″ and two 48″ lead screws. All lead screws are 1/2″-10 ACME threaded rod.|
|Four Bearing blocks and two motor mounts make this machine easy to build without a mill and a lathe. The vertical axis bearing blocks (center – four required) we specially designed for this review.|
All holes for 8/32 screws were drilled with a 3/16″ drill bit.
Cutting of the “Super Strut” material is done with a metal chop saw. This chop saw was purchased at a discount tool store for $50 and has worked well for many projects before this one. Use a tape measure to measure the lengths. Use a T-Square to make sure that the guide on the saw and all cuts are square. Measure to the outside of the saw blade and leave about 1/32″ between the mark and the blade. You should cut all pieces to +/- 1/16″ tolerance or better.
The “Super Strut” channels are bolted together using spring nuts. These are inserted into the channel and are held in place using the springs that are attached to them. The base machine builds very quickly. When tightening the parts use a square to ensure that the channels are at right angles.
The aluminum was cut using a jig saw and a metal blade. The brackets for the vertical axis start out as L stock and are trimmed as shown. Use a file to clean the edges up. You will need to make four of these.
The holes for the bearings are drilled in a few steps to make sure they are in the right place. Using the multi-step process will help prevent the drill bit from “walking” and drilling off from where you intended it. First, measure and mark where you want the hole. Then use a punch to mark the spot. Then use a center drill (short stubby drill bit in the middle) to drill a starting hole. Then use a twist bit to drill the hole. When you are done debur the holes. I used the drill press to keep the holes square.
Assemble the four vertical axis brackets according to the images. Multiple 5/16″ washers act as spacers. The ID of the bearings is actually 8mm (0.3149″) and the bolts shoulders are 5/16″ OD (0.3125″), but once the bolt is tightened, there is little slop.
When purchasing the “Super Strut” Pick out pieces that the bearings will fit into. I had one piece that I had to open up using a hammer and some plastic blocks. Test the brackets on the “Super Strut” to make sure that the bearings ride on the top and side of the rail. If the “Super Strut” is dirty, you may need to clean and polish the areas that the bearings ride on. In the picture on the right you can see most of the pieces for both vertical axis laid out.
The 0.5″ thick UHMW (Ultra High Molecular Weight Polyethylene) plastic moves up and down the vertical axis and has the hot wire attached to it via the 3″ screw. It electrically isolates the wire from the rest of the machine. The UHMW has a low friction coefficient and is simple, eliminating the need for several more bearings.
The 3/4″ steel tube takes the bending load from the wire by letting the plastic block slide up and down. You will want to take some 000 steel wool and dish soap with warm water and polish it until it is smooth (It doesn’t have to be shiny). Having the lead nut tight against the UHMW plastic ensures that the plastic won’t bind on the 3/4″ steel tube.
Prior to final assembling the vertical axis, you will need to install the slack adjustors. The slack adjustors are two “L” shaped pieces of aluminium with a 1/4″ diamter screw in each one. The 1/4″ diameter screw is adjusted very close (without touching) to the 3/4″ steel tube. These screws prevent the plastic block from rocking back and forth when the wire changes direction. Adjustment of the screws will be covered in part 2, since it requires the hot wire to be installed and under tension. The brackets are held on the plastic block with (4) 8-32 screws and nylon lock nuts.
When assembling the bearings to the bearing blocks and the lead screws, parts should easily assemble and may require some light tapping to assemble. If more force than light tapping is required, some rework will be required for a good fit. If you force the bearings onto the lead screws and the bearing blocks you will have excessive friction that the stepper motor will not be able to overcome the friction.
The moving parts of the vertical axis are tied to the axis with 1/8″ thick 4″ L brackets. You will need to drill holes to mount the bearing blocks. Be sure to leave about 1/4″ between the bearing block and the bracket to leave room for the screw heads. On the top add the 4″ long aluminum for the vertical axis motor mount.
Mark where the lead screw needs to go through the vertical axis and cut a “U” shape. Drill a 3/4″ or larger hole with a hole saw and then cut to the tangents of the circle with a jig saw. To align the horizontal lead screw I used 2 pieces of wood that were cut together so they had the same height. A table saw makes this task easy. Simply place the wood under the bearing block and mark the Super Strut to drill. Drilling the holes a bit oversize will allow you some adjustment. Leave the screws loose so you can adjust the lead screw later. Install the screws to attach the lead screw nut to the vertical axis.
Once the vertical axis and the horizontal lead screws are installed, you can align the horizontal lead screws. The easiest way is to move the vertical axis to the front end of the horizontal axis and then tighten the screws holding the bearing blocks on that side. This will align the lead screw to the bearing block. When the front side is done, move the axis to the rear and tighten those screws. Repeat on the opposite side horizontal axis. I used a 1/4″ drill bit, a clamp and 1/4″ ID fuel hose to move the horizontal lead screw.
Now that the basic construction of the machine is complete, it’s time to add the HobbyCNC motors. I started by adding the vertical axis motors by using the Precision Tech Machining motor mounts. You can align the motor side to side visually, and I used a ruler to align the motor fore and aft. Simply measure the shaft of the motor and set the shaft of the lead screw to the same distance. Mark and drill the holes. The 1/4″ ID fuel line can tolerate slight misalignments.
Mount the horizontal axis motors by drilling the mounting holes in the aluminum stock. Drill the center of the mounting bracket just a bit larger than the 1/4″ ID fuel tubing. Make sure that the clamp that is closest to the motor is 0.4″ from the base of the motor to clear the “Super Strut”. Slide the second clamp on the hose and install the motor. Drill a 1″ circle in the side of the “Super Strut” so you can tighten the hose clamps. Insert the motor by sliding the fuel hose over the motor shaft and tightening one of the hose clamps.
Install the wood that will form the base for the foam to sit on. To save in cost of materials, I made 2 strips of wood to support the outer edges. Nail the strips of the wood to the base. Now the basic mechanical construction is complete.
Now that the mechanical construction is complete, it’s time to build the the HobbyCNC board. The first step is to organize the electrical parts. You can identify the resistors by the color bands on the body of the resistor. In addition I used the multi-meter to measure each resisters resistance prior to inserting it into the board.
In the far left picture, the basic construction of the board is completed. The only remaining parts are the electrostatic sensitive stepper chips and programmed PIC. At this point you will complete the TB5 test to check and make sure that 5 volts is present at the test pad. This indicates that all the components are installed correctly prior to installing the stepper chips.
The HobbyCNC board is enclosed in a plastic case that is not included in the HobbyCNC kit. The directions specified a part that could be ordered from an electronics supplier, but I found that a case from the local Radio Shack that worked (P/N 270-1809). Cut a hole in the top case for the cooling fan in the location specified in the directions. Here a hole saw or jig saw will work. Route the wires for the fan to the inside of the case and use the supplied template to layout the front panel. The front panel houses the switches and connectors for the HobbyCNC board.
When it comes time to install the heat sink to the stepper motor chips, you will need to drill and tap the aluminum bar that is supplied with the kit. It is a good idea to use some heat sink compound to help transfer the heat from the chips to the bar. This is the same stuff that is used on computer CPU’s and can be bought at Radio Shack. Once you tighten the heat sink on the chips, you should have a little squeeze out from the heat sink compound. Make sure that the bar does not extend down past the bottom of the chip, or you will short the chip out.
Install the board in the plastic case and make the connections to the switches and banana jacks. Also run the power into the box and hook the negative side to TB5 and the positive lead to the 8 Amp fuse. Run the other side of the fuse to the positive side of TB5. I installed banana jacks between my power supply and the HobbyCNC box so I could use same power supply to charge batteries when I was not cutting foam.
Once the HobbyCNC board is completed, you will need to complete the Vref test before hooking up the motors to the board. With the stepper chips installed, apply power to the board and adjust each axis potentiometer (small blue adjustable part) to the correct voltage (see instructions for the correct voltage). This will set the amount of current that goes to each motor, so it’s important to set it correctly. Do this before hooking the stepper motors up!
Once the VRef test is complete, route the included hook up wire from the HobbyCNC controller board to each motor. Make sure that you plan your wire runs carefully, the kit includes just enough wire. I located the HobbyCNC controller in the front center of the machine. The horizontal axis wires are the shortest with the rest going to the vertical axis motors.
When soldering the wires of the motor to the hookup wire, the motor will have 8 wires and the hook up wire will have 6 wires. Two pairs of wires on the motors are “common” and must be twisted together before connecting to the hookup wire.
I drilled some holes in the motor mounts and secured the hook up wire to the mounts using a zip tie. This provides strain relief to the motor, ensuring that the moving motor doesn’t have it’s wires pulled out.
Connect the parallel cable and 12V power supply to the HobbyCNC board and you are ready to fire the machine up. If you turn on the power supply, all 4 motors should “lock up” and hum (with or without the computer connected). This indicates that all four stepper circuits are functioning correctly. Do NOT connect or disconnect the stepper motor wires to the board with power on the board, you will blow the stepper motor chips!
In this first part of a two part series, we covered the construction of a hot wire CNC foam cutting machine. The mechanical and electrical construction was covered.
In the next segment we will cover installing the hot-wire and hot-wire power supply and how to setup and operate the GFMC software. Drawing cutting shapes in the computer and the differences in types of foam will also be covered.
With a CNC Hot-wire Foam cutter you will be able to make many complex shapes including wing cores and fuselage parts quickly and easily. Using the HobbyCNC and Precision Machining Tech parts makes the construction of this “scratch built” project fast and fun.
RCU Forums: batchelc
|Precision Tech Machining
|GMFC (Foam Cutting Software)