3D Printed Knife Cover

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Eating at a picnic spot or wilderness campsite is great, but prep can be tricky.
You still want decent kitchen utensils, but for knives there’s a downside to having something sharp and pointy rattling around in your belongings!

When you have a 3D printer, problems like this have an easy solution…Capable and SHARP.

 

Printed in translucent PLA on a Malyan M200 (aka MP Select Mini) printer.
No supports; the bridging performance of the slicer and printer are great.
(so it ‘bridges’ the top parts without any sagging or dropped filament)

You can download the model at https://www.thingiverse.com/thing:2628653

If you have a different type of knife, you will need to create your own model.
It’s often best to create the real-world object in CAD first, then build your model around it. (So that you can ensure it all fits together)
Here is a quick guide to modelling a knife blade in Fusion 360;

1. Capture

The cover needs to fit well, so the first step is to measure the knife!
For flat objects, a good technique is to photograph it against a calibrated background like this cutting mat.

Insert the picture into a new Fusion design using the Insert > Attached Canvas feature. Select the plane and the file, and press OK. Don’t worry about the size in the first step.

Now, to calibrate the size of the sketch, right-click on the canvas in the browser and select Calibrate.

  • Zoom in on one end of your ruler or grid, and carefully click on the start point.
  • Then zoom out, zoom in on the other end, and carefully click on the end point.
    This tool isn’t as easy as it could be – a tiny text box pops up somewhere on the screen – you’ll have to find it.
  • Type in the real distance between those two points and press enter to size the canvas correctly.
    For example – if you used the ‘0’ and the ’15’ in the picture below, enter ‘150 mm’.

2. Sketching

There is no “make this an outline for me” short cut, but it’s fairly easy to draw around a canvas.

  • Create a new sketch on the same plane as the canvas.
  • Draw, trying to match the lines up with the photograph.
    • Don’t worry about getting it right first go, you can come back and move the lines around.
    • For curved shapes like a knife, the Spline tool is very useful.
      Place the points down first, then click on the tick mark.
      Come back and click on the points, then adjust the handles to set your curve.

Once the outline is in place, we’ll want to draw some vertical lines into the sketch.
Why? Because a knife is not a single extrusion, the cross section changes in interesting ways. Ensure

The best tool to use on a shape like this is the Loft tool.
It needs a sketch at each section of the shape:

3. Sections

Sketches need to go on planes, so first let’s create some.

The Construct > Plane at Angle tool creates a new plane from a line.

  • Select a line from the first sketch, then use the Plane at Angle tool.
    Adjust the angle to ensure that the plane is at a right angle to the canvas and first sketch, and click OK.
  • Repeat for the rest of the object, and name your planes sequentially.

Create a sketch on each of these planes, with the cross section of the knife at that point based on measurements – eg the blade cross sections are narrow triangles, intersecting with the ends of those lines. The handle is a narrow trapezoid.
Note: Make sure your section profiles intersect the knife outline; use ‘project’ on the plane-construction lines and have those lines be coincident or midpoint to the ends.
This is to make the loft operation easier.

4. Lofting

The Loft tool is similar to the Extrude tool. However, the shape of the cross-section changes smoothly from one sketch profile to the next. (and the next, and the next…)

Consider this air duct joiner that goes from square to round.
The Loft tool is perfect for this shape – a sketch is created at one end with a square, and a sketch at the other end with a circle, and a loft is created from one shape to the other.

Those cross section sketches made previously are now going to be lofted.

Open the Loft tool and select the knife point, then each profile in order.
You can see that the tool tries to figure out the shape, but it doesn’t quite look right.
It’s necessary to add guide rails – click the “Rails” mouse pointer icon in the dialog, and select the guide lines.
Note: You may encounter difficulties getting every profile to loft together in one operation. It is fine to loft in separate stages; For this knife the blade was created in one loft operation, and the haft was joined on to the blade in a second operation.

And ta-da! A reasonably accurate knife blade model, ready to build a cover over.