Laser Tips and Tricks

Box and Organizer Making

There are many sites out there but boxes.py is reliable and widely used. It has parametric designs for compartment boxes, slatboard or DIN rail or french cleat wall organizing, wine racks and more. It builds in features like nodes and "loops" in the corners of fingerboard joints that help robustness and would be otherwise very annoying to draw out

Measure the actual thickness of your material with calipers, in mm, and enter that exact value in the thickness -- it governs the whole geometry of the joints, so get it right. The other most important parameter is the "burn" (kerf) -- the program will over cut the fingers and undercut the slots so that the actual output part fits tightly together. For plywood, dial in a value just short of where you'd need to tap the parts together with a mallet. For acrylic get the closest fit that leaves no residual compressive force on the pieces.

Read the note below on layer ordering, you'll want to move "blue" to the top in lightburn.

Recipes:

• 4.76 mm (0.19") baltic birch: 1.2 mm "burn" (kerf) at 25/75 (Dorian), 30%/100% (Tarkin)

Use your Layers wisely

Always order your layers as follows:

• all raster layers, so that you don't have inconsistent printing near the edges or other features and excess smoke that will hurt laser effectiveness
• engraving after rastering so that the lines are at the actual Z-height of the final work, and again so that you aren't shooting the laser at cut edges.
• cut all internal features before you cut the outside boundary, because the part can shift position once separated. Even if you are using tabs, your material might curl in the Z direction due to heat or bowed plywood. Finish dumping the laser heat into the part while it's a whole sheet and only then do your separation passes
• Large cutout pass -- after this, parts can shift on the bed
• (if called for) Tab separation. If you have plywood that is slightly bowed, or acrylic that might curl, consider knocking out part of the path or using a "tab" feature so that the sheet stays attached as a whole until you release all parts by severing the last few edged.

Be mindful that the laser is more aggressive when cutting small, close-by features than when doing large runs. When doing small features, you have:

• more and more heat building up in the location of those features (a bit in ply, significant in plastic), making the work easier to cut (i.e. as if you were working at a couple percent slower speed)
• if the laser is doing a lot of zigging and zagging, it similarly can make the laser cut comparable to what you'd see at a slower speed setting for long runs

• There will also be more localized smoke, especially in plywood if you are dumping in a lot of local heat; this counteracts the other two actions to an uncertain amount and can increase the effective kerf

Having read all that, you can probably forget it unless and until you care about having very fine detail, dimensional control on internal features, or are having problems with warping in plastics.

If you do see such problems, use layers to "interlace" the features and spread the heat input of your job out over time. That is, if you have a part with many small holes, in normal use you'd first cut all the holes on eg the blue layer, and then cut the part from the sheet with a red layer, and perhaps only then nick the corners with a green layer.

  +-------------------+
  |  o o o o o o o o  |
  |  o o o o o o o o  |

If you start noticing warping or inconsistent dimensions, you'd put the holes on different layers:

  +-------------------+
  |  1 2 3 1 2 3 1 2  |
  |  1 2 3 1 2 3 1 2  |

So that the cutter will dump heat into 1, 1, 1, 1, 1, 1; then into 2, 2, 2, 2,... (on the now-cooler starting side of the cut), then 3, 3, 3, 3,....