Knowledge base

Hot-wire foam cutting answers

A searchable, curated library of answers on foam cutting, machine setup, G-code, FluidNC/GRBL and the free cncfoam.com tool. Most questions are already answered below — search or browse by topic.

Category: All General ✨ AI helper Building / DIY Hardware Electronics G-code Cutting tips Materials / foams Software / tool My setup

Browse answers by topic below, or use search. New to the tool? See how cncfoam.com compares to GMFC, DevFoam & JediCut, or read the hot-wire foam cutting wiki.

Category Cutting tips · 23 matches. Clear filters.

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…
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…
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…
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…
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…
Why does the wire lag behind on corners and curves?

Because the wire bows under cutting resistance: the carriages reach the corner before the sagging middle of the wire does, so corners get rounded and curves trail. The fa…
How do I cut letters, logos or signage?

Hot-wire cutting is 2.5D: it extrudes a flat profile straight through the block, so letters and logos come out as prismatic shapes (the outline pushed through the foam's…
How do I cut a shape that has internal holes?

A taut hot wire is a continuous line anchored at both ends, so it cannot plunge into the middle of a block to make a fully enclosed hole the way a laser or router can. Ev…
How do I get a smooth finish instead of a rough one?

A clean hot-wire finish comes from the wire melting, not tearing: aim for a taut wire, the lowest heat that still cuts at your feed, and a steady feedrate. Rough or fuzzy…
How do I cut a long block in multiple passes?

If your part is longer than your travel or you want to reposition stock, plan registered passes: cut a section, then move the foam to a repeatable reference (a fence or p…
Why don't my two ends (left and right) line up?

On a 4-axis machine, mismatched ends usually mean a setup or sync problem, not a design one. Check that the towers are square and parallel and that both sides have the sa…
What's the smallest detail I can cut with a 0.3mm wire?

Rule of thumb: minimum feature size = 2× wire diameter + kerf margin. For 0.3mm wire and ~0.5mm/side kerf on EPS, that's about 1.6mm minimum. Trying to cut a 1mm slot wil…
Wire keeps breaking near the end of long cuts — why?

Common causes, in order of likelihood: 1. Wire is too hot. Heat work-hardens the wire over time; combined with thermal cycling it eventually fatigues. Drop temperature 5-…
How do I handle the start-point — where do I put the wire before pressing Run?

By default the tool's serialiser emits G92 X0 Y0 U0 V0 at the top — that tells the controller "wherever I am right now is zero". So jog the wire to the front-bottom-left…
Can I cut multiple parts from one foam block?

Yes, in two ways: 1. Load each G-code separately, position with OFFSET FROM 0,0 to a different spot in the material block, cut. Repeat. Re-zero the wire at start of each…
Can I pause a cut mid-job and resume?

Depends on your controller. FluidNC supports ! (feed-hold) and ~ (resume) over the control character interface, and the tool's USB / Wi-Fi streamer's Pause / Resume butto…
What feedrate should I use for EPS / XPS?

Depends heavily on foam density, wire diameter and wire temperature. A starting point: - EPS 15kg/m³ (cheap white packaging): 15-25 mm/s with 0.3mm Kanthal at ~80°C - EPS…
My cut comes out wider than the shape — is that kerf?

Yes. Hot-wire "kerf" is the gap between the wire's physical diameter and the actual cut width — the foam melts back from the wire. With a 0.3mm wire on EPS at moderate te…
My cuts smell terrible / are the fumes dangerous?

EPS and XPS produce mostly styrene + CO2 when melted with a clean wire. EPP and PE are cleaner. Polyurethane foam is BAD — it produces isocyanates and HCN; do not cut PU…
How do I avoid the \"melty\" droopy face on slow sections?

Slow = more heat per millimetre delivered. Two fixes: 1. Lower wire temperature on slow profiles. Some controllers can drive the wire PSU off the spindle PWM — set it to…
What's the difference between G0 (rapid) and G1 (cut) for foam?

G0 = rapid travel, wire off (M9). The machine moves at maximum speed between cut features. G1 = controlled feedrate, wire on (M8). The tool generates one M8 per contiguou…
Should the wire be perpendicular to the foam or angled?

Perpendicular to the cut direction at the moment of cutting — but for a hot-wire that's automatic. The wire is straight, it spans the two towers, and the foam is between…
Why is my cut wavy/jaggedy instead of smooth?

Usually one of: 1. Wire tension is too low. The wire bows on direction changes. Add a spring or increase your clamping force. 2. Feedrate is too high for the foam. Wire d…

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