The AeroForm is unique in that it uses strings (drive lines) instead of traditional lead screws to move the hotwire. These lines are wrapped around each of the four stepper-motor shafts and precisely reeled in and out by the control board. With the drive lines, there is no friction and no backlash, meaning the hotwire moves smoothly even when the motors reverse direction. Eliminating the expensive lead screws also greatly reduces cost, making a true CNC foamcutter available to many schools, clubs, and hobbyists for the first time. Controlling the non-linear drive lines and providing all the other functionality of the AeroForm is a complex task. The custom SpecCNC control board uses a Parallax P8X32A chip with eight parallel processors, which together have more than 500 times as much processing power as the guidance computer that landed the Apollo astronauts on the moon.
The first prototype of the AeroForm was built in 2014 with the aim of creating an affordable CNC tool for teaching aeronautics. After years of improvements to the electronics, firmware, and mechanical design, the AeroForm was producing airfoils similar in quality to those made on a professional CNC foamcutter costing many thousands of dollars. Searches for prior art revealed that the line-driven design had been developed several years earlier and published in German by Hans Seybold. The AeroForm can therefore be seen as a compact and highly refined version of Seybold's design. In the spirit of its predecessor, no patents are being sought on the basic AeroForm design, keeping it in the public domain.
The AeroForm cuts expanded polystyrene (EPS) and extruded polystyrene (XPS) at feedrates up to about 240 mm/min. Extremely durable Expanded Polypropylene (EPP) can be cut at feedrates up to about 120 mm/min. It is the responsibility of the user to consult the relevant Material Data Safety Sheets (MSDS) for the material being cut and avoid exposure to hazardous fumes, dust, and fibers. The AeroForm should always be used in a well-ventilated area.
The AeroForm is designed to run stand-alone (headless) without a dedicated computer or internet connection. This is a major advantage in classrooms, at club events, and even in home workshops where a computers and connectivity issues can cause major headaches. The AeroForm has a simple four-button interface coupled with sophisticated on-board processing. By selecting different shapes or airfoils, and then adjusting the scale, taper, rotation, alignment, cutter offset, and feedrate, it is possible to make tens of thousands of unique aircraft parts, from a variety of different foams, without using a computer. For even greater control, advanced users can edit the simple text files on the included micro SD card using free programs like Notepad (Windows), TextEdit (Mac), or gedit (Linux). Unlike most other CNC machines that are built on complex software, drivers, and internet licensing, the AeroForm will continue to work reliably for years into the future.
Small foam parts are typically difficult to make with hotwires because the foam melts and distorts. The relatively low temperature and precise control of the AeroForm allows it to cut airfoils with chords as short as a few centimeters. Parts like fuselages can be made with wall thicknesses down to about a millimeter in extreme cases. At these small scales, experimentation is often required to find the right balance of temperature, cutter offset, and feedrate needed to produce good results.
With practice and careful supervision, the AeroForm can cut wings with chords up to about 14 inches. Fuselages with 7-inch cross sections or larger can be made in halves. Such parts are easily assembled into model aircraft that are much larger than the machine itself. Building aircraft from smaller parts has many advantages including 1) any taper is reduced and cut quality is improved, 2) hollow parts built in sections, such as top and bottom halves of a fuselage, are not blemished by the hotwire cutting into and out of the cavity, and 3) carbon fiber spars and other structural elements can be buried in the glue joints. When these joints are sanded and covered, they are nearly invisible.
The AeroForm works by moving a hotwire that melts and collapses the foam, generally without touching or burning it. When the machine is properly configured and the wire is wiped clean after every cut, it produces very few fumes. Like nearly all CNC machines, however, it should be used with proper ventilation to prevent fume exposure. Be aware that other work with foam, especially sanding, can create dust and fibers that may also be hazardous. Safe practices such as wet sanding, use of protective eyewear and gloves, and regular cleanup with a HEPA vacuum are recommended. To protect our waterways, never wash foam dust down the drain.
The AeroForm is constructed from furniture-grade poplar and birch because wood is non-conductive, so the low-voltage hotwire will not short circuit if it contacts the frame. Wood is also strong and light, allowing the AeroForm to be carried easily by one person. And wood parts can be replaced and modified by the user, for example, to build a larger machine using the same hardware and electronics. Because the hotwire motion is relative, its cutting accuracy is far better than the tolerances of the wood frame. Slight variations in the frame dimensions therefore have no discernable effect on the accuracy of machine.
The work surface on the AeroForm consists of two removable slats that can slide from side to side. This design provides maximum flexibility when cutting tapered parts; one or both slats can be positioned to support the foam while not interfering with the hotwire motion outside of the foam. This flexibility is especially helpful when making shorter tapered parts such as stabilizers and fuselage ends. The removable slats also allow the hanging bow to be quickly placed on top of the table, making the machine easier to transport.
The AeroForm is designed and manufactured in the United States. The CNC controller is made from US-built circuit boards assembled by Worthington Assembly, the Massachusetts-based board house for CircuitHub. The core of the CNC controller is an eight-core microcontroller made by Parallax Inc. of Rocklin, California. The cable work is done by Charlton Precision Products of Kingston, New York. The poplar and birch frame is made by Green Mountain Wood in Chester, Vermont. Stainless steel braces and bracket are laser-cut by the MTG Inc. in Westfield, Massachusetts. A few components that are not available from US manufacturers, such as the power supply, stepper motors, and screws are imported.
The only parts that are likely to wear over time are the hotwire and the drive lines. Because the hotwire operates at relatively low temperature and is automatically turned off between cuts, it can potentially last for years. The life of the hotwire can be extended even further by quickly wiping it clean with a cloth or paper towel after every cut. This will prevent foam residue from becoming burned onto the wire surface. Finally, the drive lines may eventually become flattened to the point where they wind over themselves rather than coiling cleanly around the motor shafts. The drive lines are inexpensive and easily replaced. These parts are available as part of a refurbishment kit or can be purchased from other suppliers.
The AeroForm is a mechanically simple machine that is intended to provide years of trouble-free service. Each machine is pre-assembled and fully tested prior to shipping. The only moving parts, four stepper motors, run very slowly under a light load. The rugged control board has high-conductivity silver traces, is designed to run cool for long life, and is well protected within the frame. Parts that may wear out, such as the hotwire and drive lines, can be replaced with easily attainable supplies.