Hot-wire foam cutting answers

What cncfoam.com is, accounts, browser support and getting started with the free hot-wire foam cutter.

• Is cncfoam.com really free, and what's the catch?
  Yes — the browser tool is free, forever, with no catch. You can design, simulate, export G-code and stream to your machine without paying or even signing in. The shape li…
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• Do I need to install anything or create an account?
  No install, ever. cncfoam.com runs entirely in your browser using WebGL for the 3D view and WebSerial/WebSockets for streaming — there is nothing to download and nothing…
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• What kinds of machines does cncfoam.com support?
  It targets hot-wire foam cutters: two independently driven towers carrying a straight heated wire. Today it fully supports 2-axis (a single X/Y tower, wire mirrored) and…
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• Can I use cncfoam.com without owning a machine?
  Absolutely, and a lot of people do. The simulator is a complete design-and-preview environment: load or generate a shape, scale and position it, watch the wire animate th…
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• How is cncfoam.com different from DevFoam, GMFC or LightBurn?
  The biggest difference is that it runs in the browser with zero install and is free. GMFC and DevWing/DevFoam are capable but are paid, Windows-native programs; LightBurn…
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Turning a text prompt into a cuttable foam shape with the AI shape generator.

• 📌 What kinds of shapes can it make right now?
  Six families: - NACA 4-digit aerofoils (e.g. NACA2412 wing 200mm chord 600mm span) - NACA morph wings — interpolates two profiles along the span (NACA2412 to NACA0009 mor…
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• 📌 How do I use the AI shape generator?
  Open the tool (cncfoam.com/), look in the top header for the purple ✨ AI button. Click it. A small dialog opens with a text input and six example chips. Click an example…
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• не рівний різ а зубчиками
  стл файл 3д в якому лінії рівні а при різі зубчики
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• Is this a real LLM (Claude/ChatGPT) behind it?
  Not today. The current version is purely procedural — it's pattern-matching regex against your prompt, picking the right recipe, plugging in your numbers, and outputting…
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• Why doesn't my prompt work?
  Most common reasons: 1. The shape family isn't supported yet. See the list above. If you typed "crown moulding" or "saddle" we don't have a recipe. 2. You used imperial.…
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Designing and building a DIY hot-wire foam cutter — frame, towers, wire tension and motion.

• What does it take to build a basic hot-wire foam cutter?
  At its core, surprisingly little: two towers that each move in X (depth) and Y (height), a length of resistance wire stretched between them under tension, a way to heat t…
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• What frame material should I use — aluminium extrusion, wood, or steel?
  All three work; the priority is rigidity and squareness, not the material. Aluminium V-slot/T-slot extrusion (2020/2040) is the popular choice: precise, easy to bolt up,…
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• How big should I build my hot-wire cutter?
  Size it to your real work plus margin, because bigger costs rigidity and money. For RC wings, a 1000–1300 mm wire span with ~300–400 mm of X/Y travel covers most panels.…
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• Horizontal or vertical wire — which layout is better?
  Both are common; it is mostly about what you cut and your space. A vertical wire (towers side by side, wire upright, foam pushed through horizontally) is the classic wing…
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• How do I keep the two towers square and parallel?
  This is the single most important build step on a 4-axis machine. If the towers are not parallel and their X/Y axes not aligned, the wire is skewed and every cut is off.…
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Steppers, drivers, wire, pulleys and the mechanical parts of a foam-cutting machine.

• NEMA 17 or NEMA 23 steppers for a foam cutter?
  NEMA 17 is almost always the right answer. A hot wire pushing through foam needs a tiny fraction of the torque a printer or router demands, so the common 17HS series (aro…
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• GT2 belts and pulleys — how do I avoid backlash?
  GT2 belts have very little inherent backlash if installed right. Use genuine 6 mm GT2 belt with matching 20-tooth pulleys and toothed idlers, set the pulley grub screws o…
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• What is wire lag (bow) and how do I reduce it?
  As the wire melts through foam it meets resistance and bows backward in the middle, lagging behind the carriages — like a bowstring. The faster you feed or the cooler the…
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• What's the best way to attach the wire to the carriage?
  Use a connection that is mechanically secure, electrically solid, and re-tensionable. A common approach: a small insulated post or pivot arm on each carriage, the wire wr…
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• How hot should the wire get, and how do I control the heat?
  Just hot enough to melt a clean slot at your feed speed — typically a faint glow in a dim room, not bright orange. Too cold and the wire drags and tears; too hot and you…
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Controllers, wiring, stepper current, ESP32/FluidNC setup and streaming G-code.

• What controller board should I use for a hot-wire cutter?
  The modern, recommended path is an ESP32 running FluidNC: cheap, Wi-Fi and USB built in, supports the multiple independent axes a 4-axis cutter needs, and configured enti…
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• Why FluidNC on ESP32 instead of GRBL on an Arduino?
  Three big reasons for a foam cutter: axis count, connectivity, and configuration. A 4-axis cutter needs four independent motors (X, Y, U, V); classic 8-bit GRBL is built…
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• How do I wire stepper drivers to the controller?
  Stepstick drivers (A4988/DRV8825/TMC2209) plug into carrier sockets and take four wires to the controller logic — STEP, DIR, EN, and GND — plus motor power (VM/GND) and t…
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• How do I set stepper driver current (Vref) correctly?
  Set current to roughly the motor's rated amps (a hair under is fine — foam cutters barely load the motors, so you can run conservatively and stay cool and quiet). For A49…
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• How do I control the hot wire from the controller (PWM, relay, M-codes)?
  Treat the wire like a spindle. The simplest is a relay or MOSFET switched by the controller's spindle-enable output, turned on/off with M3/M5 (or M8/M9 in some setups). F…
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Hot-wire G-code explained — XYUVA axes, M-codes, feedrate and FluidNC/GRBL dialects.

• What G-code does a hot-wire cutter actually use?
  A small, friendly subset. Almost everything is G1 linear moves (coordinated straight cuts) with a feedrate — there are no arcs or tool changes. A hot-wire job is basicall…
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• What do M3/M5 and M8/M9 mean on a foam cutter?
  They are the wire on/off switches, borrowed from spindle and coolant codes. M3 (spindle on) or M8 (coolant/flood on) is repurposed to energise the hot wire, and M5/M9 tur…
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• What are the X Y U V axes and how do they map to my machine?
  On a 4-axis hot-wire cutter the wire stretches between two towers. X and Y drive one tower end (depth and height), and U and V drive the other end independently. When X/Y…
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• Why is there a pre-heat dwell (G4) at the start of the file?
  A cold wire tears foam and bows badly. The G4 dwell is a short, deliberate pause right after the wire is switched on, before the first cut, that lets the wire reach cutti…
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• Why does cncfoam.com only emit G1 moves and never rapid G0?
  Because a hot-wire cutter has no safe 'rapid' — the wire is always hot and always in or near the foam, so a fast G0 positioning move would race the wire cold-or-hot throu…
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Technique: balancing feedrate against wire heat, kerf, clean edges and cutting wings.

• What feedrate should I use for EPS versus XPS?
  It depends on density and wire heat, but as a starting point: light EPS (expanded, the white bead foam) cuts fast and forgiving, often 15–25 mm/s; denser XPS (extruded, t…
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• How do I avoid a melted, droopy, rough surface?
  That look means too much heat for your feedrate — the wire is melting a slot wider than itself and the edges sag and re-fuse. The fix is almost always to lower the wire t…
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• Why is my cut wider than my design (kerf)?
  The wire melts a slot slightly wider than its own diameter — that gap is the kerf, and it makes outside cuts a bit smaller and holes a bit bigger than the nominal path. H…
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• How do I cut a clean airfoil or wing?
  Start with a good profile (a real airfoil coordinate set, or the built-in wing generator), mount the foam blank squarely, and tension the wire hard. Use a moderate, stead…
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• How do I cut tapered or swept wings (the morph)?
  That is exactly what a 4-axis (X/Y + U/V) machine plus a two-profile morph is for. You give the cutter a root profile for one end and a tip profile for the other; the wir…
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Choosing foam — EPS, XPS, EPP and densities — and what cuts cleanly with a hot wire.

• EPS vs XPS vs EPP vs EPO — which foam for what?
  EPS (expanded polystyrene, white bead foam) is cheap, light and easy to cut — great for big parts, cores, masters and packaging; its bead structure leaves a slightly coar…
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• Can I hot-wire cut polyurethane (PU) foam?
  Not well. Polyurethane does not cleanly melt-cut the way polystyrene does — instead of slicing, a hot wire tends to char, gum and smoke, leaving a rough, sticky edge and…
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• Can I cut foam board, Depron or fan-fold?
  Yes — thin sheet foams like Depron, fan-fold (FFF) and thin XPS hot-wire nicely for flat-plate RC models and prototypes, but they are usually so thin that a straightedge…
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• What foam density is best for RC wings?
  For most RC wing cores, lower-density EPS around 20–30 kg/m³ is the common choice: light, easy to cut, and stiff enough once sheeted with veneer, fibreglass or tape. For…
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• Is it safe to cut polystyrene indoors?
  With ventilation, generally yes for EPS/XPS at a correct low temperature, but never in a sealed room. The cut releases styrene vapour and fine particulates that are irrit…
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Using the cncfoam.com tool: loading shapes, morphing, STL export and streaming to your machine.

• 📌 Can I cut a 3D model (STL or OBJ) on a hot-wire machine?
  Yes — cncfoam.com can import an .stl or .obj and work out a cut automatically. Open ＋ Load parts → Import STL / OBJ. The important thing to understand: a hot wire only ma…
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• 📌 My Inkscape SVG won't load in the tool — what gives?
  Almost always one cause: your SVG was originally a DXF that you opened in Inkscape and re-saved as SVG. Inkscape's DXF importer leaves a pile of junk in the block — most…
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• How do I load an SVG or DXF into cncfoam.com?
  Open the tool, click ＋ Load parts, and pick your file as Profile A (SVG, DXF, or G-code). The tool samples the outline into a cut path and drops it into the workspace, wh…
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• How do I morph between two different profiles?
  In ＋ Load parts, choose the Two-part morph option, then load Profile A (left end) and Profile B (right end). The tool blends the two outlines linearly along the span and…
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• How do I export an STL of my cut?
  Load or generate a shape, then open the Download / stream menu and click 3D (STL). You get a file (cncfoam_result.stl) of the carved 3D solid — the actual shape the wire…
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Machine builds and setups shared by other makers.

• What does a minimum-viable foam cutter actually cost?
  Realistic budget for a working 4-axis 500x500x500 machine, built from scratch: - ESP32 + FluidNC controller (Bart Dring 6-pack): €60-80 - 4× TMC2209 drivers: €25 - 4× NEM…
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• Can I run the foam cutter in an unheated garage?
  Yes — actually better than a heated one in some ways. Stepper motors run hotter under continuous use, so a cold ambient helps. The wire reaches its own working temp regar…
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• What's your wire mounting setup? Looking for ideas.
  I use a spring-tensioned setup on both ends: - Wire is crimped to a small terminal lug at each end - Lug screws onto a 3D-printed insulator (so the PSU current doesn't go…
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• Show us your setup — workshop tour thread
  Drop a photo of your hot-wire setup with details: motors, controller, frame material, foam stock, what you mainly cut. This thread is the show-and-tell — comments encoura…
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• My setup: 800x600x300 wing-cutter for RC slope soaring
  Built around an old aluminium printer frame. Bigger Z (tower spacing) for long wings, shorter Y (height) because aerofoils aren't tall. - Controller: ESP32 + FluidNC, cus…
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