1. Introduction

1.1 The principle of four-axis cutting

A resistive wire, heated by an electric current, is moved through a block of polystyrene (EPS or XPS), Depron or EPP by a computer numerical control machine. When the heat is set correctly, the wire does not touch the material: the material vaporizes just before contact, over a width called the kerf. The machine is driven by HotWire4X, installed on a computer connected to the machine’s electronic interface by a USB cable.

A four-axis machine moves each end of the wire independently: the carriage of side 1 (in blue in the software) and the carriage of side 2 (in red), each following its own path in its vertical plane. The wire, stretched between the two, thus sweeps a ruled surface: a tapered wing panel, a cone, a part whose two faces differ.

A HotWire4X project therefore describes two paths, one per side, their spacing (the distance between the two cutting planes, that is, the width of the block), their relative position (the sweep horizontally, the dihedral vertically) and the position of the whole in the block of material.

Two things make the quality of a four-axis cut:

• synchronization: the wire passes through the points with the same number on both sides at the same time; the two paths must therefore have the same number of points, distributed so that the wire does not skew (chapter 4);
• kerf compensation: the wire is offset by half a kerf from the drawing, and since one side often moves more slowly than the other, the kerf does not have the same width on both sides. HotWire4X computes it segment by segment from two measurements made once and for all on each material (chapters 5 and 7).

Two-axis cutting, where both ends of the wire follow the same path (lettering, sheets, silhouettes), is a special case: both sides receive the same path, which the software does by itself when only one path is imported. There is therefore no separate “2-axis” mode.

1.2 What HotWire4X can do

The software is organized in tabs, each devoted to a type of part or to a step:

• Wing: a panel or a complete wing made of several panels, from wing profiles, with sweep, dihedral, twist, and the structural elements (sheeting, spar, hinge, kerf, X leading edge). The tab prepares the cuts itself.
• Sections: a fuselage or a volume cut into successive sections, drawn freehand with smooth curves, then nested automatically on sheets.
• Views: a volume obtained from two silhouettes (a side view and a top view, for example) cut from the same block, turned a quarter turn between the two passes.
• Assembly: the three-dimensional mock-up of all these elements, to check the proportions.
• Design: the general workshop, where you import or build the two paths of any part, point by point.
• Cutting: the preparation and the execution of the cut on the machine.

Two tools complete the set: the vectorization of an image (a logo, a drawing, a cut-out photo becomes a path) and the bank of reference images (a plan or a photo placed behind the drawings to trace over them).

Everything that has no dedicated tab is done in the Design tab, which accepts any closed or open path, imported from a vector drawing or composed in the software: raised lettering and logos, sheets and sheeting, molds, cones and pyramids, slicing and cutting sheets to size (the guillotine), block dressing, packaging parts, scenery for models. The only requirement is that of the process: the part must be one that a straight wire can sweep.

1.3 Compatible hardware

HotWire4X drives machines equipped with one of these interfaces:

• an Arduino Mega 2560 with a RAMPS 1.4 shield and the HotWire4X GRBL Mega 5X firmware;
• a BigTreeTech SKR Pico v1.0 with the HotWire4X grblHAL firmware;
• the IPL5X interpolator of the 5X-Project, used by the FilChaudNX and CNCFAB machines.

The software runs on Windows 10 and 11 (64-bit) and on macOS (Apple Silicon: M1 chip or later). Details of the hardware, the boards and the firmware are on the site’s system requirements page.

Design, machine configuration and machine tests are free; a license (chapter 16) unlocks G-code export and direct USB cutting.