3D Printed Customized 91mm Swiss Army Knife (SAK) Scales

Introduction

For those of you out there in the DIY community who have always wanted to personalize their 91mm Victorinox Swiss Army, look no further.  In  this INSTRUCTABLE you will find instructions and CAD files that allows you the freedom of personalizing your knife with new scales designed by you and printed on 3D printers available to the general public.  With the provided CAD files as a base, an individual with some basic knowledge in CAD can modify the files to include inscriptions, logos, or cool features not offered on factory knives.  Now I've always been fond of microSD memory cards and how much could be stored in such a small package.  My only problem is that it's compact size is it's venerability when it comes to getting loss.   So I thought it would be a perfect marriage to combine the versatility of a SAK with a microSD memory stick and add a compartment in the handle to store the card.

Unfortunately, time and a lack of access to a 3D printer limited this Instructable to just images from my CAD station.  If at the end of this Instructable you found it something worth your time and worthy of voting please do so.  If I were to win a new Makerbot 3D Printer, I promise to flood the Instructable community with my future ideas.

Thanks for your consideration.

p.s.  I will attach a variety of configurations under STL CAD format at the end of the Instructable.  Please check back in the near future for other CAD formats that are more customizable, ie STEP, IGES, NX6....

Design Stages

In my case, I took my trusted Victorinox model Compact as the guinea pig for this Instructable.  For those unfamiliar with this model it has a couple of features in the scales that most 91mm models do not have; specifically it has storage for a ball point pen and a standard sewing pin (great for digging out splinters). These scales are referred to as "plus" scales and can be found on a few selected 91mm models, but I digress. 

So I proceeded to remove the scales with a razor blade working it between the scales and the aluminum liners with a rocking motion around the three major rivet points or the brass pins where the blade rotate on.   With a little care, the scales can be removed without damage. Please be careful to not cut yourself.  Remember, the scales are replaceable but your hand works best with 5 fingers each.

Once the scales were removed I took a set of pictures of the inside surface of the scales.  It was critical that the image taken had to be as close to parallel to the scales as possible.  The pictures were imported into my CAD program with the setting of "True to Scale".  With the images of the scales displayed on screen I was able to trace the outline of the scales with a command called "Studio Spline" which creates a curve by the series of points I selected around the image.  The more points, the smoother the curve; but you get the idea.  I also traced out the additional features of the scales which included the clearance necessary for the rivets, toothpick, tweezers, pen, and the "Cross and Shield" logo.

Once all the curves were completed, they needed to be "Scaled" (no pun intended) up or down to match the size of the original scales.  For this step, I measured the actual scales with my Vernier calipers and found they were 3.55" or 90.17mm long.  Seemed a little odd this line of SAK was referred to as 91mm instead of 90mm, but who am I to judge. 

After generating a profile of the handle I was able to use the "Extrude" command to take the curve and extrude a solid to whatever thickness I wanted.  In the case of the original Compact, it was 0.15" thick. 

Adding the clearance features for the rivets, toothpick, tweezers, pen, and the "Cross and Shield" logo was accomplished the same way.  Trace out the curves and extrude them but with a "Subtraction" Boolean command instead of the "Create" command I used to make the base scales.

The microSD card holder was modeled using traditional CAD techniques.

Tools & Material

• 91mm Victorinox brand Swiss Army knife
• CAD software that allows editing of the following file formats:
  o STL
  o IGES
  o STEP
  o Solidworks (v11 or lower)
  o Unigraphics (NX6 or lower)
• Razor blade (to pry of scales)
• 3D printer
• Super Glue (gel form)
• Sandpaper (various grits)
• Masking Tape

Customize the CAD file

1. Import the whichever CAD files suits your software
2. Add TEXT to the surface of the scale
    a. Keep the size of the TEXT as big as possible to reduce the chances of writing becoming distorted.  Resolution capabilities vary
from printer to printer,  but a good size is a minimum of 6mm or 1/4"
3. Extrude the text in the positive direction for raised lettering (improves gripping of the knife) or in the negative direction for a flushed engraved look.
4. Add any features you like (use your imagination):
    a. micro SD card holder (already modeled in the attached file)
    b. flash light
    c. laser
    d. ruler

Print the Scales

1. Save the modified files as a STL format

2. Export to a 3D printer

3. Adjust scale to compensate for shrinkage (I printed in ABS on a Makergear M2 with 3% compensation for shrinkage)

4. Wait patiently for the parts to be printed (took me about an hour for both scales)

Clean Up the Scales

1. Carefully remove any support material that may have printed with the job.
2. Using progressively finer sandpaper, sand the scales to the desired finish (OPTIONAL)

Install the New Scales

1. Remove the old scales
a. Using a razor blade, carefully wedge the blade between the scale of the knife and the aluminium spacer
b. The original scales are pressed on over 3 rivet heads on both sides of the knife
c. Concentrate your efforts prying off the scales around these three points with a gentle rocking action of the razor blade
d. Save the scales if you want to convert your knife back to the factory condition in the future.
2. Dry fit your new scales onto the knife to check the alignment. If satisfied, proceed to the next step.
3. Apply a small drop of Super Glue to the 3 holes on the back of the scales which line up with the 3 rivet heads
4. Press and hold the scales together with some tape for 10 minutes.