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How to trace knife designs into NanoCAD

If you’re like me you’ve been working from templates or simply drawing freehand at this point when making your knives. I’ve moved my designs from photoshop, to Tufnol templates and now finally I thought it was time to digitise them by scanning my knives into a nanoCAD drawing so that I can have everything laser cut and have a consistent product.

Laser or waterjet certainly modernises the whole knife-making process and saves you quite a bit of time. If you add up the time it takes to trace the blade onto the steel, cut it out, grind the profile, mark your holes, drill the holes, chamfer the holes, and radius any sharp corners, I’m sure you would be surprised how long it takes to complete all those steps.

That is the time you’ll save just by having your blanks cut and it only compounds the more often you do so. It’s worth mentioning that while someone else is cutting your knives out, you can be busy with other tasks. Bonus!

Required Items:

1. Digitise your knife

I have a Hewlett Packard multifunction printer (feel free to use what you have available), so I just poped my knife template into the scanner, scanned it, and saved it as a jpeg file. You don’t need colour for this step, so a simple black and white image is perfect.

If you don’t have a scanner, your mobile phone is a great option. Simply position your template on a neutral background (white/grey) and make sure your phone is as level as possible. Usually, the two crosshairs will overlap when you’re level. Snap, save, and transfer to your computer.

 Scan knife sketch or template
Scanning…..

2. Insert Image

Inserting your scanned image into Nanocad (Autocad is virtually the same) is quite easy.

  • From the menu, select: Insert -> Insert Image from File
  • Browse, and find your saved image and hit OK
insert image into nanocad
Inserting the image into NanoCAD

3. Increase Image Transparency

I found this to be a very worthwhile step to start with, as it allows you to easily see the lines you’re going to be drawing when tracing the image.

Simply select the “border” (yes the border) of the inserted image, and either click the “Show Inspector” button on the toolbar, press Ctrl+1, or right-click on the image and select “Properties”. All work.

This will bring up the Inspector window. We’re looking for the Fade value under the Image Adjust section (it’s highlighted in the image below). Use any value from 80-90 so that you can easily see the lines we’ll be drawing shortly. If you can’t see the lines easily, come back and bump the fade value up.

You notice that the image’s transparency is increased.

Image Fade Nanocad
Setting the fade value of the inserted image.

4. Rotate the Image

If your designs are like mine (fairly big) your image will be inserted at an angle. It’s far easier to trace the design if the spine is horizontal, so we’re going to rotate a bit.

Your guess is as good as mine when it comes to what angle the knife is at or how many degrees we need to rotate it by. So Draw a line with the “Lines by Points” (Ctrl+Alt+L) tool so that it lines up with the spine of the knife.

Finding the image angle
Finding the Angle of the knife so that we can work with it.

Select the reference line you just drew and open the “Inspector” window as we did in the previous step. Scroll down to the bottom of the Inspector window and you’ll see the value for “Angle” (highlighted above). Note the value there (eg 303 in my case).

With the mouse drag and window select both the line and image (the window will need to encompass both). Once they are both selected, click on the Rotate Tool (Ctrl+E). In the command area at the bottom of the screen, it will prompt you to “specify base point” for the rotation. I like to select the center of the image (check if you have the snap to center on for this) for this but you can select one of the corners as well.

Next Nanocad will ask to “Specify rotation angle”, remember the angle value you noted down earlier. simply type in minus (-) and the value. eg (-303) and hit enter. This should get you close to zero degrees but double-check with the Inspector again. If it’s “360”, change it to “0”.

Rotate image nanocad
Rotated and ready for tracing.

5. Add New Layer/s

You’ll need to check with your preferred laser/waterjet service regarding their requirements for drawings. Mine specify that cutting lines should be White (Layer 0) and marking lines in Yellow (Marking). You can at this point at other layers if you would like. I sometimes add in a Layout layer (Cyan) which I use for proportions and evening spacing out handle holes.

Tip: Knife steel can harden when it’s cut with a laser. So for the hole placements, I mark these (Yellow layer) with a cross and circle, so that I can accurately punch and drill them later.

You can access the “Layers” settings from the Format menu.

6.addLayersv2 | Topham Knife Co
So many layers to choose from.

6. Check the Scale

In CAD it’s always, always a good idea to draw to scale (1:1). If you scanned your drawing, it’s probably on the money, but it’s a good idea to just check if that’s the case, so you’ll avoid unpleasant surprises down the line.

I simply draw a few vertical lines (tip, choil, butt of handle), and then some dimensions to double-check that the length is correct. Here you can see that the image was oversized by 5.782mm.

If you are out, you can scale or stretch the image until it is at your preferred dimensions.

  • The Strech tool allows you to manually drag a corner of the image.
  • The Scale tool, you need to specify a “Reference Length” by selecting the current image, and then your “New Length” in the command area. Make sure the reference length and new length reference the same portion of your knife. ie the blade, or overall length.
checking scale with dimensions
Bigger is not always better.

7. Add Straight Lines & Circles

Adding straight lines and circles to the drawing is straightforward. Simply draw them in, fine-tune their placements and you’re done.

Tips:

  • Circles should match the diameter of your small wheels attachment and or dremel tool, as it just makes life easier.
  • Offset the spine line, downwards to specify your tang width and heel height.
  • All holes and cutouts should be at least 60% material thickness (ie: 3.2mm stock >= 1.92mm diameter hole)
8.linesandcirclesv2 | Topham Knife Co
Starting to trace the knife.

8. Splines

Now there may be a way of doing this in a more correct fashion (large arc, radii, or polylines), but this works for me.

To add in the curvy sections of our knife the Spline tool comes in handy. It acts as the pen tool does in Photoshop, in that you’ll pick points along your curve and it will fill in / match the curve for you. When you reach your endpoint just tap the Enter key three times to close off the spline, otherwise it wants to circle back to the beginning.

fine tune your splines Nanocad
Add more points for finer control over the Spline curve.

Tip: I find that “Snap” points are useful when starting a spline, but worth turning off when you are drawing, editing the spline. It’s really frustrating when the point snaps to a point away from where the mouse cursor is.

Again, fine-tune the placement of the splines. When you are happy (you can’t go back), you’ll need to convert the splines to polylines in order to use Trim, Extend, and other commands with them. Simply select the Spline and type “Pedit” in the command area, and hit enter three or four times until the process is complete. Repeat for your other curves.

splines for arcs Nanocad

9. Add Fillets and Radii

When it comes to knife design, it’s good practice to avoid introducing potential stress risers into your design. (Read: How to prepare your blade for heat treatment) Nanocad allows us to add fillets and small radii to all the sharp corners/transitions in our design. Here I’m adding a 3mm diameter (1.5mm radius, larger than 60% of the stock thickness) to the corner of the handle cutout. You’ll note I’m leaving material around my hole/s and handle so that the tang retains its strength.

fillet and radius corners

And that’s it.

I know I didn’t show the steps I took to add my pinholes and or handle cutouts but if you followed along this far, it’s just applying the same principles over and over again. Draw line/circle, offset, trim/extend, fillet. Rinse and repeat.

10. Finishing Off

To finish the drawing off, clean up your drawing by removing the inserted image, unwanted layout, or marking lines, trim off any lines and then save as a DXF file (or whatever file format your service provider needs).

Checklist:

  1. File is built at a 1:1 scale
  2. All stray points, duplicate lines, empty objects and text areas have been removed
  3. No shapes have open contours
  4. All shapes have been united, combined or merged
  5. All objects are on the same layer
  6. All holes and cutouts are at least 60% material thickness
  7. Two objects cannot share the same line nor intersect.
12.PlotcaddrawingNanocad | Topham Knife Co

You can also print (Plot) the drawing with a 1:1 scale just to double-check as some printers may have a slight varience which you can correct by setting the “Scale”. If you’re still not comfortable committing to having your blades laser cut, you can print off your designs and use them as templates.

Let me know in the comments if you’d like me to follow this post up with a more detailed video if that would help.

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