Painting in engraved detail gives your design an additional unique factor and makes less likely to scream “I’m laser cut!” In the old days of hand cutting materials, you would have to sit there for hours, carefully applying masking tape of fluid in strategic areas to ensure a crisp paint edge. Like trying to paint straight stripes on a wall, only on much smaller scale.
Fortunately, should you choose to try paint filling your laser cut engraving, your can mask required areas with laser cut precision. The acrylics are cut with protective paper on, and all areas with heavy raster/vector engraving are ready to be painted. Other materials can have transfer tape applied to top surface on request. The exceptions to this are leather and felt because transfer tape does not stick well to those. Some woods can present the same problem also, so experimentation is always advised. Protective paper and transfer tape are not the same thing. Protective paper is the brown film on both sides of acrylic sheets and is applied at point of manufacture, which means that, by default, all our stocked acrylic has protective paper on both sides. Transfer tape is the light-coloured adhesive sheet that is stuck on to keep all the parts in place when the cut design is removed from the lasercutter.
Transfer tape over acrylic, over bamboo ply
There are two main factors in this process: digital, which is your design; and physical, which is the actual painting.
Let’s start with the digital. Whether you’re using a raster fill or vector engraving, you need to use the heavy lines/fills, which you can also read about in this forum post. A vector outline around your raster fill will also give a crisper edge, which works well on larger, less detailed areas. Small details end up too cluttered, and the extra engraving time adds to the making cost.
Vector outline on the right, and how it comes out (after painting) on white acrylic and Eurolite Italian Poplar
You can see that there’s some paint bleeding on the plywood resulting from insufficient adherence of transfer tape to wood surface. Getting optimum masking results with porous materials like sorft plywood will require experimentation.
If you’re using vector engraving only, experiment with doubling or even tripling your lines to make the detail more obvious, like in the Sammich Midi boxes
Top to bottom: raster fill, raster fill with vector outline, single vector outline, multiple vector outline created using the “expand” command. Left to right: file, Eurolite Italian Poplar, white acrylic.
You can see that in the example of multiple vector outlines the lines need to be much closer together to give a solid line effect. To see whether your design is at the right scale, print out the image at 1:1 using stroke width of 0.02mm.
At this point you will upload your file and enthusiastically wait for your “another exciting shipment from Ponoko” with all its Yippee! goodness.
The real work begins once you open you package. Firstly, very very carefully peel the transfer tape off the top of the sheet. Now if this is acrylic, it should be pretty straight forward because the protective paper is stuck firmly to the material, and there is little risk of it lifting off. If the material is anything else, i.e. it is protected by transfer tape, you need to peel off the top layer with caution, as not to raise off the masking layer.
Once the transfer tape is off, vector engraving is ready to be filled in. Use a blower brush to get rid of the residue from raster engraving first. You can either use Indian ink or spray paint or model making paint such as Tamyia.
This is how you do it with a paint brush:
If your engraving is detailed and close to the edge, do no spray directly out of a can, as it will result in overspray. Options in this case are ink/paint with a fine brush, or you only have spray cans, you can spray a little bit of paint into the lid and dip your brush into that. Usual spray painting safety rules apply.
This is how you spray paint your engraving:
You can safely use spray paint if your engraving is limited to centre of the sheet, the edges of which can be easily masked.
Acrylic on the left, Poplar on the right
The next step is waiting for the paint/ink to dry, and then you can gleefully spend hours grinding down your nails as you peel off all the tiny bits of paper. To save your fingers and nails you can use a sharp, pointy blade. Be careful not to scratch your material.
If everything goes to plan, you should have paint fill that looks something like this:
Here are some more tips on engraving: