Create neat wooden furniture without laser aesthetics. The finger joint is very popular in wood laser cutting. It provides great strength and is easy to draw and assemble. But the dark edges are sometimes a bit too noticeable. Below we explain how you can easily mill them away.
Getting started
This technique works for all finger joint designs. The trick is to design the finger joints a little longer and then use an edge trimmer (flush trim bit) to mill them away. This works because the cutter has a running bearing that exactly follows the side of the object. To prevent the sole of the router from bumping over the fingers that stick out, use a small piece of wood next to the finger joints.
Material types
You can laser cut finger joints in all types of wood. In this example we use 9mm birch plywood, but the technique also works well in poplar and lime plywood, and also in MDF.
Supplies
-milling machine
-edge milling bit with ball bearing on the end. For example this. Make sure the shaft fits in your milling machine.
-3mm thick MDF board (or comparable thin plate)
-optional: 3mm radius cutter (for the finishing touch)
And of course your laser cut design.
Adjustments to your design
To be able to mill away the dark edges, the "fingers" must protrude a little. Because the thickness of plates can vary somewhat and because you want to have some clearance, a protrusion of 1mm is a good length.
You can draw finger connections by hand and therefore also add the extension manually. If you use a generator to make your drawing, there are some tricks.
Makercase does not have its own finger extension setting. But if you add 1mm to the material thickness and set that, you will still get a comparable result.
Boxes.py does have a finger extension setting. In the Settings for Finger Joints you can use extra_length. Please note: the unit is 'multiples of thickness' and not mm.
In Onshape you can use the LaserJoint script. This has an option 'Pin face offset' with which you can set the extension.
Check your design and let your wood laser cut.
Assemble
After receipt you can start gluing. Make sure you use enough clamps to ensure there are no gaps.
Milling
Now the milling can begin. Mount the bit in your milling machine and let it extend so far that the bearing is a few millimeters under the fingers.
Place the plate on top of your workpiece, next to the protruding fingers of the top. Start your machine and press the milling sole firmly onto the plate so that the machine remains vertical. Now drive the bearing along the entire edge to mill it neatly clean. Repeat for all sides.
After milling, a small edge will be visible. You can easily sand this away with 120 grit sandpaper so that everything looks neat.
Optional: round corners
If you have a milling machine at hand, you can use a radius milling cutter to give the edges a nice roundness. A 3mm radius cutter gives a subtle result.
Final result
Now you have a sleek piece of furniture or other object without those striking dark edges. This method is a lot less laborious than sanding, although that is also possible.It delivers professional results with minimal effort.
