Introduction: 2-3/4D Sculpture?

Sculpture can represent many things to many people? Religion, a famous person etc, but in this instance I want my sculpture to "Take Yourself To Another Place"? Yes, to invoke a memory, a wish a mindset. Perhaps a coral reef or The Olgas, a bunch of flowers, field mushrooms...let your imagination drift?

A condition of the Instructables Sculpting Competition for which this Instructable is an entry, was for an "....awe inspiring sculpture.." OK, I take that to mean a 2D - 3D form that in the eye of the beholder is remarkable and amazing! I needed to challenge my skillset and come up with a shape that one might say, "How'd they do that?" Well my tools are a CNC machine, and along with Fusion 360, I'm always modelling and sculpting wood. My CNC is a 3 axis conventional machine, none of this 4th and 5th axis stuff! This limits what I can turn out, notionally a 3D form but not truly, more like 2-1/2D. In other words it has a length, width and height but no part of the form can overhang another in a single cutting setup! Purely because the cutting tool is fixed to operate perpendicularly, so can't undercut.

But let's push the boundaries a little here and go for 2-3/4D (pseudo 3D). We can invert our model and machine from both sides, or all 6 if a cube? That's more steps but a greater challenge to overcome. Now we're talking! Also let's use a shape that can appear inclined and rotated and still be able to be machined perpendicularly! In fact let's throw in a heap of similar shapes all at different levels and orientations to really impress?

Now I had my manifest and set out exploring ideas, What shape lends itself to this?......a cone perhaps? It can be radically tilted but a tool can still machine the internals.Therefore after a bit of doodling in the Sketch environment of Fusion 360, I came up with this. I'm not going to show you step by step how to exactly build this, but will offer some clues on how to overcome some hurdles and let you be the sculptor you never knew you had in you?


Wood - man made or natural. In this case 26mm (1") thick x 250mm x 200mm (10" x 8"). It can be any size really limited to the travel of your CNC and the length of your cutting tools.

Step 1: Sketching

Just like an artist you need a canvas! In my case I decided on an object confined to being around 200mm (8") x 140mm (5-1/2") x 26mm (1"), Using small dia cutting tools limits the timber thickness because you don't want the collet to crash into the material. I draw up my rectangular boundaries on two planes, the ground plane and 26mm higher. In Plan view I start drawing my circles and arranging them. I'll use 3 different sizes, each with an opening at both ends. In SURFACE mode I Loft between bottom and top circles to create my initial bodies. I then start to orientate each body and move them around, always keeping in mind the outer perimeter boundaries of your wood? I start copying each body and moving them around to suit. Once I've decided on the layout I Thicken each Surface Body by 4mm (5/32"). This converts each shape into a Solid body. In the picture you'll see the radiated line effect on each body? That's because you have a Solid body on top of a Surface body. Delete your surface bodies. Now you need to fine tune, move and orientate every Solid body to fit within your outer boundaries and to your eye be visually appealing? There's a Screencast movie that shows that process.

TIP? Just bear in mind here, that you will have overlapping bodies where it will be impossible to machine! Don't fret about trying to come up with geometry to deal with these situations? Your tool will just cut perpendicularly down from the top body's boundary to the lower and you'll be left with that void filled in!

Next you need to trim where one body intersects another and trim away the offending projection. There are a couple of ways of doing this but probably the easiest is to select the offending mother body and use Split Body in the MODIFY drop down. Then use the face of the inner cone of the adjacent connecting body to split the mother body. Then delete the new projecting body. See pic 6 above, where all the projections have been removed bar one, which I left as a curiosity?

Step 2: Tabs?

If I was to proceed to Manufacture I could auto add on Tabs to hold the piece? This won't work for such an organic shape. I need to add the Tabs as part of the original model body. This is where from experience you\ll know the number, size and best location for these? I decide on four rectangular Tabs notionally 10mm x 3mm (3/8" x 1/8"). I want to set them just below the top circumference thickening of of the largest dia cones.

TIP? On a new ground plane XY - New Sketch, project the outline of the Body (By now you've joined all the bodies to become one?) You need to decide on the dia of the cutting tool you're going to use to cut out the perimeter this body? I'll use a 6mm dia (1/4") Therefore my Tabs need to project out 6mm (1/4").

Once you've finished your Sketch, extrude each Tab individually by 3mm (1/8") and offset vertically, using a side view to fine tune placement. Then view your model from the top and look out for the Tabs piercing through the inner cone face, or not penetrating the outer cone face completely. Push Pull the Tabs to suit, or in some cases trim off the projection using Split Body.

Congrats if you've got this far, as it's now time to Manufacture?

Step 3: Manufacture

"Manufacture" is the term Fusion 360 use for the CAM operations. We have to machine both sides and will require two setups (Top & Bottom).

TIP? You need to always be thinking, "How am I going to hold the work piece down?" Never underetimate the forces generated when machining! Even with quite small dia cutters, the forces generated are enormous and good clamping is necessary.

With consideration to the above, allow yourself enough material around your model to clamp onto AFTER deducting the dia of the perimeter cutting tool! I always draw pencil lines to show the "safe" zone for clamping. You'll notice the scars on the end of my clamps where I miscalculated? Its the collet nut on deep cuts that tends to crash into the clamps.

For the top side I'll have a Contour cutout using a 6mm dia (1/4") end mill, followed by a 3D Adaptive cut using a 3.15mm dia (1/8") end mill. Lastly, a Scallop cut using a 2mm dia (3/32") Ballnose. For the Bottom I'll repeat the Adaptive and Scallop as for the Top.

Fusion 360 manufacture Top and Bottom toolpath simulation screencasts above.

Step 4: In the Real World?

Well it's one thing to say you've designed your sculpture, but the proof's in the making! Above are progress pictures. I used Beech as it machines well without too much grain standing up. Machining time is another consideration for any of these complex enterprises? The Top and Bottom took 10 hours! Much slower using smaller dia tooling, but with delicate work you need to err on the cautious side? I've seen work shatter due to using too large a cutting tool.

In years past when single 45rpm records were produced, musical artist's recording company's produced 'A' and B' sides to a record. Sometimes the 'B' side became the hit and sometimes both sides, known as a double 'A' single? Well I reckon my sculpture is a double 'A' as both sides are equally inspiring! :)

Sculpting Challenge

Runner Up in the
Sculpting Challenge