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The Canadian Korona

I decided to make a crokinole board. That would have been the next project for me in the woodworking class, but since I had access to a proper CNC machine, I decided to use it.

Crokinole is a Canadian version of Carrom, a disc flicking game. A similar game in Finland is called Korona, which is internationally known better with its Latvian name Novuss, even though Korona/Novuss is more closely related to pool.

The idea is to create a crokinole board with a two colored design on it. Originally, I planned to mill two colors of wood into two pieces that would slot nicely together, but I preferred the surface of plywood to planed and glued wood, so I ended up making the design separately from the machined base.

Files

All laser cut files are designed to be cut from a 3mm thick 61 x 61 cm plywood board. If the plywood is thicker, the milled base board should be thinner. If the plywood has a bigger area, then you could use the full design as the cut file.

Materials

Amount Part Details Link
1x 61 x 61cm plywood 61 x 61 cm birch Link
1x 61 x 61cm plywood 61 x 61 cm eucalyptus Link
1x glued timber 2000 x 800 x 27 mm birch Link

Design

Drew a sketch with iPad Notes.

Recreated the sketch with Affinity Designer.

Autodesk Fusion is an idiot, and does not let me define the size of the imported svg with either dimensions or direct numbers. The only way to scale the design is with percentile number, that reset every time I move the svg around. It is impossible for me to get the proper positioning and size for the design like this.

After a bit of googling and watching unhelpful Youtube videos about weird tricks that work on very specific kinds of designs, older versions of Fusion or force me to redesign the who thing in Inkscape from scratch, it dawns on me that it is a DPI issue. Autodesk Fusion defaults svg to 96 dpi when importing, and if the file was created with different DPI, it will be sized wrong. So I got to Affinity Designer, and select correct dpi from the export settings.

Had to redo that again, as I noticed that I had too steep angles in my design. Needed to round them so that the milling bit would fit.

Next, I needed to buy wood. In two different colors.

No go

Then I ran into problems. There were three

  • The board is too small to be accepted as a assignment for CNC machining week. It is less than 30 inches in diameter at its largest.
  • The wood that I ordered did not arrive on time.

Doing it

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After a couple of weeks, the wood did arrive. But I had to change my plans a bit. I really did not like how planed and glued birch looked as the the playing surface, so I switched from actually milling all of the pieces from the wood, and instead milled the body, and attaching a laser cut plywood on top of it. The design would still be cut from two different woods, but only from plywood.

At this point, I redesigned the files to fit this new design. I designed the whole thing around these dimension. The only thing I changed was the removal of 3mm of material from the playing surface to account for the laser cut plywood.

To avoid link rot, and given how hard it was to find precise measurements, I will duplicate the measurements from that link in here:

Crokinole Dimensions

  • Overall playing surface diameter: 26” (13” / ~330mm radius)
  • Outer circle diameter: 24” (12” / ~305mm radius)
  • Middle circle diameter: 16” (8” / ~203mm radius)
  • Inner circle diameter: 8” (4” / ~102mm radius)
  • Ditch: 2” (~51mm) minimum
  • 20 hole diameter: 1 3/8” (35mm)
  • 20 hole depth: 1/4” (6mm)
  • Dividing circle lines: 1/16” (1.5mm) to 1/8” (3mm)
  • Discs: 1 1/4” x 3/8” diameter (32mm x 10mm) Standard Crokinole discs
  • Rim: 1 1/2” (1/2”/12mm taller than the playing surface)
  • Playing surface: 1/2” thickness on most boards.

I decided to mill the whole thing with a 20mm flat end bit. 20mm to make it faster, and flat end to make all corners tight. In this design, as everything is accessible by the bit directly from above, flat end can finish each corner really well.

I had some trouble getting the final contour cutting to do what it was supposed to do. For some reason, when I tried to select the bottom outer edge, it would mill the contour lines as if the model was the hole I wanted to make. I do not know why it did that, but it fixed itself after I tried to route it again with the sketches hidden.

So I went milling, following the same procedure as with the shoe rack.

At first it faced the playing surface.

Then it milled all gutters and the mid hole as a pocket. And cut all the edges with the contour setting.

The whole milling process was really messy, with sawdust flying everywhere. This was most likely a combination of a couple of factors:

  • Birch might be heavier that other woods, thus it was not suctioned that well.
  • The suction machine in the workshop had some problems that day, it would not suck with enough intensity.
  • The bit was longer than normal (and hanging even lower) to account for the 27mm thickness of the stock. This meant that the brushes of the vacuum suction pipe did not touch the stock.

The contours did not cut all the way through. It left a paper thin layer of wood around the board. To get it off, I first used a knife to remove the layer, saw to cut off all the tabs, and a sanding machine to finish the rough edges.

Laser cutting the design

I had two designs ready for the board. One inspired by middle eastern mathematical patterns and one inspired by celtic knots.

As is intended to use birch and eucalyptus plywood for the design, the final color will be quite light.

I did some tests to figure out what kind of offset the inlaid eucalyptus pieces would need, to account for the kerf of the laser. In the end, it became clear that there was no need for any kind of offset. The pieces would lay flush and tight enough even without one. The idea was to glue the pieces to the base plate and sing them all in epoxy anyway, so any kind of looseness that was not visible to the naked eye wasn’t a problem.

Assembling it

After laser cutting, I glued all the laser cut pieces on the top of the machined board, arranged in the proper pattern.

Still not ready

Now I have a pretty design on a wooden board, but it is not playable. The board still needs the outer walls and a way to laminate the playing surface. The outer walls will likely be done with three layers or 1mm plywood. Plywood at that thickness should be bendy enough to circle the outer areas. If not, then I need to use even thinner veneer.

Before the outer layer, I most likely need to apply the lamination. If I do it after the walls are done, I risk it pooling at the edges, making it look bad. I will most likely laminate it with some form of epoxy resin, making sure that I can get an even coating everywhere. And to make sure that the walls can still be placed, I need to tape the edges, so that I can remove the resin from there. If resin proves problematic, normal lacquer might still do the thing.

I did make a pouch for the crokinole pucks during wild card week.