Standard Procedure to engrave PMMA
Note: this tutorial references documents found here: Referenced Documents for Engraving PMMA Tutorial.
- With a 2D drafting program, open a *.dxf file such as 10-4LineTemplate.dxf. Go into the layer manager and change all layers to the smallest possible lineweight. Print this file after choosing a laser configuration (create one if none listed).
- Open the laser cutter driver to adjust settings. In manual settings load the 10-4LineTemplate.las file. The final cross-section should look like goodEngraving.jpg, not badEngraving.jpg. The difference is a final low-power pass on each engraved line to help reduce surface features on the sides of engraved channels. Low-power is represented by the single blue lines on top, medium-power by underlaid green lines below, and high-power by red lines for through-cutting.
- Choose a substrate PMMA material and measure the thickness of this material at the location of engraving/cutting. PMMA can vary by over 10% in thickness throughout a modestly sized piece, so take care to note where you are engraving as engraving depth is sensitive to substrate thickness. In manual settings, enter the thickness where the substrate will be cut/engraved.
- Within the laser cutter driver graphic user interface, use a pointer to print off of the edge of the material by starting the print within a cm of the edge of substrate. Print the file.
- The correct number of passes corresponds to the number of the line (out of the 10 engraving lines) that looks approximately like goodEngraving.jpg. The channel should be reasonably smooth-sided, with a roughly-defined bottom and well-defined side tapers. Repeat this procedure for the 4 cutting lines to determine the number of passes for cutting through material.
- In a 2D drafting program, lay out your drawing using the “0” layer as shown in rawLayout.dxf. Paste these “0” layer lines into a copy of 10-4LineTemplate.dxf. This assures correct coordination with 10-4LineTemplate.las. Use the layer manager to set all lineweights to the minimum setting.
- Since the laser cutter engraves/cuts lines in the order they were drawn, determine your cutting order. You will note in badOrder.jpg that there is a region (circled) that is wider than other engraved regions. This is because some lines in this region are engraved on PMMA that has been preheated by engraving other lines drawn in this region. There are regions (see arrows) where channels are blocked. An alternate order of engraving/cutting is shown in the goodOrder.jpg. This is accomplished by allowing engravings to cool by interspersing through-cuts, and by always through-cutting prior to engraving where there are intersections between through-cut and engraved lines. The 10-4LineTemplate.las file reduces through-cutting speed to promote better substrate cooling during engraving.
- Once you have determined a draw order, for each engraving line in your layout overlay the number of medium-power lines you determined was optimal in the previous step, followed by one low-power line on top. For through-cut layers, overlay the correct number of high-power lines. Delete all “0”-layer contents to avoid unnecessary printing. See finalLayout.dxf as an example.
- Using the print procedure previously outlined, print your layout.
If you have any issues using this tutorial, please contact any of this page's authors. You may wish to make fine adjustments to power, speed, or PPI. If so, please refer to the following presentations illustrating the effects of changing each of these parameters:
As shown in these presentations, 2%, 800 PPI, and 100% are generally good engraving power, density, and speed settings. The 10-4LineTemplate.las file varies this formula only for the finishing low power pass at 0.5% power, and for the slow through-cutting at 25% power / 20% speed.
- Laser Driver
