Making a Celtic Knot

The best reference on this is George Bain’s wonderful book:

For more on this artist see:

Given a simple design:

re-creating it in Carbide Create is quite straight-forward.

First, import the pixel image as a background reference:

Set Background


Use the Polyline tool to roughly draw some of the desired geometry:

and repeat for all the shapes involved:

If need be, adjust the Grid size:


Since the design is symmetrical, once one part is made it may be copy-pasted:

and then mirrored and dragged into position:

and this process repeated:

At this point, the geometry may be duplicated and placed on a reference layer:



For any given part, use Trim Vectors:


Then use Join Vectors to close the elements:


Then repeat for each part…

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Eventually arriving at:

…as requested on support…

Then select all the geometry and rotate it 45 degrees:

It is then a matter of selecting the geometry which represents each length of board:

Grouping it:

and dragging it out of the way:

Selecting the remaining geometry:

Rotating it 90 degrees:


and repeating:

At this point the geometry may be left-aligned:

and distributed vertically:

at which point the background may be hidden:


Then use the polyline tool to draw in the outline of all the boards:

Repeating until one arrives at:

Space things out a bit:

Select all of the board outlines:

and offset by tool geometry plus 10%:

Distance: 0.275in (assuming a 1/4" tool)
Offset Direction: Outside

Then assign toolpaths.

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Increase the Stock size as necessary and select the original geometry:

Then assign a No Offset Contour toolpath to a suitable depth:

Then select the original and offset geometry:

and assign a Pocket toolpath to half the stock thickness:

Then select the board outlines and the offset geometry:

and assign a Pocket toolpath which starts at the bottom of the previous pocket and cuts through (assuming workholding which will hold things in place) or to tab height:

If using tabs select the part outline geometry:

and Edit Tabs:

Adding as many tabs in suitably unobtrusive places as is necessary to hold things:


Then assign an Outside Contour toolpath which starts at tab height and cuts through:

which all previews as:

Then the geometry may be arranged so as to be optimally cut out of the boards in question, minimizing waste.

It will then be necessary to cut matching half-laps on the bottoms of the boards — probably the easiest way to do this would be to make a fixture would allow clamping the boards upside down using the top half-lap to register things, then cutting the other half-lap adjacent to it, using an inset V perimeter pass (you’ll need a narrow V endmill) to prevent the boards from being cut apart — this is left as an exercise for the reader.


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