Inkscape for Laser Cutting

Introduction
Inkscape is a free vector graphics tool you can use to draw and process files to be cut on a laser cutter, such as those at FabCafe, MONO and FabLab.

It is similar in functionality to CorelDraw, which is the standard package used by most laser cutters. The common file format between the two is SVG. Unfortunately SVG is somewhat outdated(?) and has several shortcomings that you will need to be prepared for. Most of these problems can be handled in Inkscape. If you do your work correctly and check all the boxes, your saved SVG file should import to CorelDraw with little to no additional work needed. If you follow my advice and that of ATXHackerSpace (linked below), you will either have a perfect import with no effort needed, or will have all the tools within your SVG file to identify problems quickly and adjust them properly.

What is 'kerf'?
Kerf is defined as the width of material lost due to a cutting process. In a chop saw, it is defined by the width of the saw blade and teeth. In a laser cutter, is defined by the diameter of the beam. There is always some additional loss due to the TYPE of material and it's thickness.

In addition, on thicker materials, the laser tends to V the cut instead of ||

There are many laser cutting kerf charts on the internet. Just google for "Laser cutter kerf" or better yet, include the brand name. Here is one such chart: 

Materials 	    Thickness 	Average Kerf
 * Acrylic 	    1mm-3mm 	0.18mm
 * Acrylic 	    5mm-8mm 	0.21mm
 * Acrylic 	    10mm-15mm 	0.3mm
 * Acrylic 	    20mm 	0.32mm
 * HIPS, PETG, Styrene, 1mm-3mm   0.45mm
 * Birch plywood 	    0.8mm 	0.08mm
 * Birch plywood 	    1.5mm 	0.16mm
 * Birch plywood 	    3mm 	0.2mm
 * Birch plywood 	    6mm 	0.22mm
 * Birch plywood 	    12mm 	0.3mm
 * MDF 	            3mm 	0.16mm
 * MDF 	            6mm 	0.2mm
 * MDF 	            12mm 	0.28mm
 * Veneered MDF 	    6mm 	0.17mm
 * Greyboard 	    1200u 	0.08mm
 * Greyboard 	    2400u 	0.12mm
 * Paper 	            90–350gsm 	0.08mm

u indicates microns
 * paper is measured in GSM

Prepare your workspace

 * In document properties, set the default units to mm and size the paper according to the size of your material
 * Avoid using the material edge as an edge of one of your cuts. This is risky if the dimensions are critical, and could damage the laser bed. Instead, keep all of your design within a border around the edge of the material. You can place guides from the rulers around the edge of the work area.

Notation for the laser operator (even if that is you)
In order to notice if the image imports out of scale and to fix it when it does, you need a scale marker. Somewhere OFF of your work area, draw a box and set it's dimensions. Within the box, add some text which describes the precise size of the box. For example, a 300 x 100 mm box. If something goes wrong importing, you need only refer to your box, select ALL of your objects (including the box) and scale until the box matches the rulers in CorelDraw (or whatever package the laser uses)
 * Place a dimension marker

The operator needs to know which lines to CUT and which to ETCH. Some laser cutter drivers act like a printer, and have pre-defined color coding. Others let the operator choose just before commencing cutting. Off page, place a few small rectangles. Fill the rectangle with solid, primary colors. Use ONLY RGB values. So, RED - 255,0,0. Green - 0,255,0 etc. Now define with some text which color you will use for cut lines, and which will be etching (if more than one etch, indicate percentages as well). '' Assure that when drawing your objects, you ONLY use these colors! It is easy to accidentally nudge a color slider. Double check your object properties!''
 * Place a cutting/etching legend

Good object preparation

 * Review the notes above about using only primary colors for your objects!
 * Set your default line width to 0.0254 mm and assure all of your cutting lines are this width. (Adjust as necessary as per the laser cutter specifications)

Links


This page by ATX hackerspace in Austin Texas covers some very critical points about importing Inkscape files to CorelDraw. When taking their advice, be sure to convert inches to metric! Of particular importance, you need to scale your data UP to 106.667 percent before you save your SVG file. Why? Inkscape uses 90 pixels per inch, while CorelDraw uses 96 pixels per inch. Another good point to save time on the laser cutter path is to set line width to precisely that of the laser cutter. In their case, 0.001 inches (that's 0.0254 mm for us metric users).