Earlier this month, I was working on a plywood project on which I wanted both clean laser cut lines (free of the smoke marks that often appear, especially on thicker plywood and MDF) and the ability to add color to the work without creating a separate silkscreen or stencil. I found that painter's tape or other low-tack paper masking tapes solve both problems. The process I used follows.
Laser-grade plywood or MDF
Sprayable clear wood sealer
Step 1: Apply Painters Tape
Apply painter's tape or other low-tack paper masking tape to both sides of the work piece for best results. If the work size is larger than the width of the tape, make sure each strip overlaps, but only by about 1/8".
The lower-tack the tape, the less likely it is to pull up the grain of the wood when removed.
Applying tape to both sides will prevent the appearance of smoke marks on both sides, but may not be necessary if only one side of the final piece will be visible.
Do not use plastic-backed tapes. Most will melt providing poor protection and possibly marking the piece, and vinyl tapes will emit chlorine fumes, which are poisonous and can damage the machine.
Step 2: Etch and Cut
If not intending to apply color to the work, etch and cut the piece as you normally would, but increase the laser settings (power up, speed down, or a combination thereof) for the etching fields by approximately 25% to account for the additional thickness of the tape. It's worth running a few small tests to dial this in. More power may be needed to cleanly etch through the sections where the strips of tape overlap. Vector cutting lines should not need to be adjusted. You're done!
If you are intending to apply color to the work, still perform the cuts, but only etch the fields in which you do not wish to apply color.
Step 3: Apply Second Tape Layer
If you are intending to apply color to the work, cover the target area with a second layer of painters tape. Being careful not to otherwise disturb the work piece to prevent the need for realignment.
Step 4: Etch Color Fields
Etch the field in which you wish to apply color, increasing the laser raster settings another 25% to account for the additional layer of tape that will need to be etched through. Again, performing small tests is very helpful in establishing these settings. Take care in realigning the work piece if it has been moved.
Remove the work from laser bed and work sheet, making sure not to remove any tape from the target area.
Step 5: Spray With Clear Sealer
Cover the edges of the work with tape and spray with 2 thin coats of clear sealer. This will prevent the colored spray paint from running beyond the tape lines by both sealing the pores of the target wood and creating a thin film adhering the sides of the tape more securely to the work piece.
Allow to dry to a tack between coats and before applying colored spray paint.
Step 6: Spray With Desired Paint Color
Spray the target area with 1-2 coats of desired paint color, and allow to dry to tack before removing tape.
Now to the results!
Left: A piece etched and cut without tape. There is some smoke marking around the cuts and on the back, but much less on this 1/8" plywood than there would be on thicker material.
Middle: A piece etched and cut with tape. There is no smoke marking on the cuts or back, but the etching is not as clean, since the laser had to cut through the tape first. This method may be best suited to piece that will be cut but not etched.
Right: A piece cut and etched with tape, with color applied. There are small gaps in some of the non-colored etching lines where the tape was not completely etched through. But with more fine tuning, this process look promising as a means to add color to laser etched pieces without resorting to the creation of an additional stencil or silkscreen.
This project was made at the wonderful, new TechShop Pittsburgh: www.techshop.ws.