Making Walled Scales

So this is going to be a pretty long, sort of how-to post about how I make knife scales that have walls. Basically all scales come in two different forms. The easier scales to make are flat scales. The name is pretty self-explanatory. A flat scale is shaped to the knife, and just has the proper through holes and countersinks for the screws. The more difficult scales to make, however, are the walled scales. One method of making these scales is to start with a thicker piece of wood and to mill out or pocket the inside of the scale, but without a CNC mill, doing it by hand it both tedious and very time consuming. With the tools I have available to me, I decided to try and makes walled scales using a combination of a 3D printer and the rest of the handle-making equipment that I already have.

To start off, it’s always nice to have the project knife on hand. This allows me to check fitment every step of the way and also allows me to create a CAD model for the walls.

Cropper Scan
Scanner image of pocket side of scale

Just for reference, the knife I am working on in this write-up is a Boker Plus Nano. It’s a pretty unique, compact knife that’s really quite affordable.

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Edited scanner image

I am really only interested in the walls of the scale and not so much the scale itself. Since on this particular scale, the screw holes don’t intersect with the wall, my task is a little simpler. The images was edited using GIMP.

InkscapeScreengrab
Vectorize in Inkscape

After editing the original scanned image, the image is then imported into Inkscape. Using the “Trace Bitmap” toll under the “Path” menu item, I created a vector of the inner and outer edges of the wall. Taking a set of calipers to measure the vertical dimension of the physical scale, I make sure that the vector in Inkscape has the same vertical dimension. Afterwards, I export the vector as a DXF.

SoldiworksScreengrab
DXF imported into Solidworks

Upon importing the DXF of the scale wall into Solidworks, I again check the vertical dimension, making sure that nothing has changed between the two different programs. Once verified, I simply leave the sketch underdefined and extrude the sketch to the appropriate thickness of the wall. Finally, with a solid model in Solidworks, I can export the file as an STL and print it on my 3D printer.

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Scale wall glued onto scale

After the print completed, I glued the scale onto a rather thin piece of wood. Using the metal liner, I was able to transfer the hole pattern using two different sized drill bits that closely matched the clearance hole diameters on the original scale. Unfortunately, when I was drilling the more centrally located small screw clearance hole, the drill bit walked quite a bit. I had to use a small file to “fix” the hole and elongate it such that the screw would still fit through. The wood is Myrtlewood Burl. It’s not a very dense or strong wood, but as a sort of decorative part, it suffices.

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Countersinking the screw clearance holes

Using a belt grinder and Dremel, I was able to easily remove the extra wood that was outside of the scale walls. In order to size the counterbores, I first assembled the knife. The impressions left in the wood by over-tightening the screws that held the knife together gave me a good sense of how and I should make the counterbores and exactly where to place them. Using a mill end in a Dremel, I carefully enlarged the screw clearance holes. This process involves a lot of stepping down small increments and checking to see how far down the screw sat in the scale.

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Test fit before coating and sealing

Before sealing up the scale in acrylic spray, I had a quick test fit to make sure nothing was sticking out, everything was smoothed, and the knife still can open and close properly. With a couple passes of acrylic spray, the outside of the scale is sealed. I usually leave the inside of the scale untreated.

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That’s it! I hope this walkthrough was useful.

 

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