Laser cutter class: Difference between revisions

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We also have to specify the line separation. This is the distance between raster lines, and the smaller the number the higher detail we can produce, but the more raster lines (and so more time) is required to produce the image. We'll pick 0.1mm, as this is a good quality, and works well for the speed and power we used.
We also have to specify the line separation. This is the distance between raster lines, and the smaller the number the higher detail we can produce, but the more raster lines (and so more time) is required to produce the image. We'll pick 0.1mm, as this is a good quality, and works well for the speed and power we used.
!!! images
Finally, we'll select the red layer. This layer will also be Cut mode, with the same speed and power as the black layer. However, unlike the black layer, we need to adjust the position of the cut because this will need to fit snugly with the black acrylic insert. To do this, click the advanced button and make sure Sew Compensation is checked. RDWorks gives this a strange name; to the rest of the laser cutting world, this is called kerf compensation. We need to specify the kerf size, which for acrylic is about 0.15mm, as listed in the manual. We might end up adjusting this later depending on how well the fit is.


  !!! images
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Revision as of 15:32, 14 December 2016

This page is the overview for the laser cutter class. The class is a project-based introduction to the software and hardware of the laser cutter, intended to teach participants in the class everything they need to know in order to use the laser cutter. We assume no prior knowledge of the software involved, only general knowledge of how to use a computer.

This class is broken into three main parts: part 1 deals with the design of the laser cut object using Inkscape, part 2 deals with the use of the laser cutter software, and part 3 deals with the operation of the machine itself.

This page is currently a work in progress, and should be used right now only for planning purposes, not as an actual resource for learning yet. When this message goes away, this page is considered usable as a learning resource.

Project Overview

In this project, we will create a laser cutter merit badge that employs many standard techniques in laser cutter design. This won't be a complete, in depth overview of the laser cutter and everything it can do. Instead, you'll learn a variety of standard techniques, along with the processes required to make use of them on the laser cutter, so that you become comfortable with the machine. These techniques include some basic design skills, preprocessing, vector cutting, vector engraving, press fit design, cut order optimization, and the general control of the machine. You will not learn laser safety: you must go through a separate training session for this. Please see the Laser Manual for more information about laser safety training.

This class has one suggested prerequisite, namely the class on design software, which will give you a more complete understanding of Inkscape than is provided here. While the prerequisite is not absolutely required, it's suggested because it helps you understand the software at a more general and fundamental level than we teach in this class.

Part 1: Design using Inkscape

In this part of the project, we will design the merit badge, both the physical aspects and its realization in software. There are therefore 2 main steps to perform here. The first step is to sketch out and decide on the overall design and dimensions, the second is to translate this into a precise sketch in Inkscape. This particular merit badge will be made of acrylic, but the steps described below work for pretty much any material you can cut on the laser cutter, provided it has sufficient thickness.

Rough Sketch

The merit badge we'll make will be based on the Noisebridge logo, as sketched below. We'll have an inset central Noisebridge logo out of black acrylic, and the rest out of blue acrylic. The outer portion of the logo will be engraved, as will the text.

Laser cutter class part 1 0.png

Precise Sketch / Inkscape

We can get the Noisebridge logo in SVG format from the identity page. The direct link to the SVG file is https://noisebridge.net/wiki/File:Noisebridge_logo_not_by_idiots_for_cnc.svg. We'll open the logo in Inkscape and make some changes. Make sure to resize the canvas and save it as a new file. It's also useful to set up some grids. Millimeter units are generally the most useful.

Laser cutter class part 1 1.png

Before we go any further, it'll be useful to resize the logo to be 60mm in both dimensions. This will make it easier to align things later. We'll select everything (control-A) and then set the size in the toolbar. Make sure the units are millimeters.

Laser cutter class part 1 2.png

Now on to the real editing. First, let's get rid of the text, since we don't actually want that in the final logo. We can just select the text and delete it.

Laser cutter class part 1 3.png

Next, we'll remove the negative space from the inner part of the logo, because we want the inner part of the logo to be solid black. To do this, we'll need to use the path editing tool in the toolbar on the left. We'll just select the nodes for the inner paths and delete them.

Laser cutter class part 1 4.png Laser cutter class part 1 5.png Laser cutter class part 1 6.png Laser cutter class part 1 7.png

Now let's make the pill shape around the outside. We'll use the rectangle tool and round the corners. I'll make the height of the rectangle 10m more than the diameter of the logo (70mm), and the width will be three times the diameter plus 10mm (190mm). The corners will be rounded with a radius in both directions of half the height of the rectangle (35mm), to produce an actual semicircle instead of just a rounded rectangle. We'll also position the rectangle so that the logo is centered on the left end's semicircle. Again, make sure that all the units are in millimeters. Additionally, it's useful to make the fill of the pill shape partially transparent, or to use only a stroke, so that we can see the logo underneath it. You can also reorder the objects after you make the pill the right size.

Laser cutter class part 1 8.png

Finally, let's add the text. We should leave some space on the right end so that we can optionally add a hole for putting the badge on a keychain or something like that. We'll adjust the size to be pretty big but not too big.

Laser cutter class part 1 9.png

Looking at the overall size, it's a little large. Let's make it smaller. Select everything and scale it proportionally, so that the height is 30mm. Make sure that the proportional resizing lock is enabled so that the width is scaled automatically in proportion to the height.

Laser cutter class part 1 10.png

The design is now done, and we can save the file.

Part 2: RDWorks/LaserWorks Laser Cutter Software

In this part, we'll go over how to import files into RDWorks and prepare them to be laser cut. We'll need to perform a number of steps, including a pre-processing conversion of the file into a usable format, an assignment of cutting properties appropriate for the material and process type, and an optimization of the cut order.

Converting to DXF and importing to RDWorks

The laser program RDWorks can accept a number of file types, but unfortunately SVG isn't one of them. What we'll do, then, is convert our SVG badge into a DXF file, which RDWorks can use. Before we do this, however, we'll need to perform some preprocessing steps. If we just save a DXF directly, without performing these steps , RDWorks will interpret the file incorrectly, like so:

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As you can see, there are lots of extraneous lines. If we left them in, they would be cut by the laser cutter, leading to an incorrect piece. To fix this, we need to eliminate all the bezier curves in the image.

With the image loaded up in Inkscape, select everything and convert all of the objects to paths (Path > Object to Path).

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Next, we'll ungroup all of the objects (Object > Ungroup>. This is especially important because we have text, where the whole text object is a group composed of multiple smaller objects for each letter.

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Finally, we'll flatten out all of the bezier paths (Extensions > Modify Path > Flatten Beziers). We'll pick the flatness to be 0.1, which is the smallest we can produce with this tool. If we need a smaller size, we can always scale up the objects first, then apply the tool, then scale it back down.

!!! images

Now we can save a DXF. In the save dialog window, select Desktop Cutting Plotter (AutoCAD DXF R14) (*.dxf) from the format dropdown menu. It's the longest entry in the list, which is useful to know if you plan on doing a lot of laser cutting.

!!! images

We can now import the file into RDWorks. In a new document, import the DXF file just created (File > Import). Be sure to use import, not open, as the open dialog window only supports RDWorks' own RLD format.

!!! images

We can now see that the imported image has none of the extra lines that we had earlier.

Assigning Paths to Layers, Setting Layer Parameters (Blue Acrylic)

Because we're going to be using two different kinds of acrylic, and doing two different kinds of lasering, we need to assign the paths to different layers so that we can use different properties for each. We'll also need to have two separate patterns to send to the machine, one for the blue acrylic, and one for the black acrylic. We'll go through the process for the blue acrylic first.

Notice first that all of the paths are currently black. This means that they're assigned to the black layer. Layers are identified by color alone. Select the outer rings of the Noisebridge logo, and the text, by clicking the paths and/or click-dragging a marquee. Now assign them to the blue layer by clicking the blue square at the bottom left of the work area.

!!! images

Now select the inner part of the Noisebridge logo and assign it to the red layer.

!!! images

We've assigned three different layers because each will have distinct properties. The black layer will be a simple cut. We don't need it to be precisely sized because its just the external edge of the badge, and doesn't have to interlock with anything. The blue layer will be engraved, not cut. And finally, the red layer will be cut, but needs to have its size tightly controlled to adjust for the fact that when you cut material, the cut has a thickness, and the resulting piece is not precisely the size you've specified in software.

We'll now modify each layer to specify its different properties. Double click the black layer in layers tab at the top right of the work area. This brings up the layer properties pane for the black layer.

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Since we want to cut this layer, we'll set the processing mode to Cut.

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We also need to specify the speed and power for this layer. The blue acrylic I'm using is 3mm, so we look this up in the laser manual's section on known materials, so the speed is 20mm/s and the power is 55%, but the acrylic you use may have different settings. We'll enter these into the speed and power fields of the layer parameters pane.

!!! images

Next, we need to make sure no special size adjustments are being made, so click the advanced button as shown below and make sure none of the boxes are checked. We'll see these again for the red layer.

!!! images

That completes our settings for the black layer. We can now move on to the blue layer, which is for engraving. Click the blue swatch of color on the left side of the layer parameters pane.

!!! images

As with the black layer, we need to set the processing mode, but this time it should be set to Scan, which tells the laser cutter that it should raster scan inside the paths rather than cut along them.

!!! images

We'll also look up the speed and power settings for engraving and enter those as before. Acrylic engraves at 400mm/s and 5% power regardless of thickness.

!!! images

Next we'll set the parameters specific to scan processing mode. In the bottom of the pane, we'll select the scan mode to be X Swing. There are four options here, X Swing, X Unidirectional, Y Swing, and Y Unidirectional. The X and Y options determine which directly the raster lines move, and we want X because that's fastest (it only moves the cutting head, rather than the whole armature). The Swing options specify that engraving should happen when the cutting head moves both left and right, whereas Unidirectional specifies that engraving happens only in one direction of motion. Swing is faster, but produces lower quality engraving. We pick X Swing because this project doesn't require very high detail.

!!! images

We also have to specify the line separation. This is the distance between raster lines, and the smaller the number the higher detail we can produce, but the more raster lines (and so more time) is required to produce the image. We'll pick 0.1mm, as this is a good quality, and works well for the speed and power we used.

!!! images

Finally, we'll select the red layer. This layer will also be Cut mode, with the same speed and power as the black layer. However, unlike the black layer, we need to adjust the position of the cut because this will need to fit snugly with the black acrylic insert. To do this, click the advanced button and make sure Sew Compensation is checked. RDWorks gives this a strange name; to the rest of the laser cutting world, this is called kerf compensation. We need to specify the kerf size, which for acrylic is about 0.15mm, as listed in the manual. We might end up adjusting this later depending on how well the fit is.

!!! images

Optimizing Cut Order

Simulating

Downloading to the Machine

Part 3: Laser Cutter Machine Operation

Parts of the Laser cutter

Moving the Cut Head

Moving the Cut Bed

Changing Manual Cut Head Speed

Focusing the Laser

Loading Files

Changing Layer Settings

Tracing a Bounding Box

Performing a Dry Run

Performing a Powered Run (ie Actual Cutting)

Cleaning the Catch Tray