Preparatory work

Small size project/test


I went to the Second maker square at Carreau du temple and followed a tutorial on how to make frames from DM Makers. My first aim for this week was to reproduce the same worklow. The constraints to take into account were: -
a wide enough frame -
reinforcements -
chamfered upper faces so that the canvas would be strechted without being constrained by the wood. DM Maker milled plain wood with Techshop CNC based on CAM models in Fusion360. As for WoMa they are used to VCarve with layered DXF as input and the material I will be using is plywood. The first task was to translate one way of doing into the other. Also I wanted this frame to be a gift so I had some constraints from the recipient. He wanted a multi-frame or a panoramic one. I picked the firt option as it could involve joinery. I also wanted some criteria to be respected:
- Small frames that could be separated when painted and reunited afterwards
- Frames that could be used as a grip while painting
- Mostly right angles so that the streching of the canvas would be easier I used this project as a CNC test. The reinforcement part had to be thinner than the frame so it would involve pockets. The chamfer of the upper face would involve a V-shape end-mill. I also wanted to test bending wood, so I designed a part to overline the two frames once fitted together. This part will have two kinks, I imagined those kinks made possible by parametric karf.

Drawing with Fusion

1. Sketch the frame (width 3.5cm)
2. Sketch the reinforcement part (sketched separetly because they will be esxtruded at different heights)
3. Extrude both (frame: 18 mm and reinforcement: 12.2 mm)
4. Combine the 2 bodies
5. Chamfer with distance and angles the inner *face* (distance 10 mm angle 30°)
6. Export sketches as DXF
7. Open Rhinoceros
8. Create collection of layers (CUT ON, CUT IN, CUT OUT, POCKET)
9. Assign layers to curves
10. Create polylines for the lacking geometries
11. Add circle at CUT IN angles so they don't come out rounded
12. Trim/join circle and polyline
13. Export as DXF to VCarve

Source file to load here

Vshape anticipation

In order to chamfer Vshape endmill had to be used. The slope is function of the mill, I picked a 120° one with a 7 cm diameter. That's why at first I put a width of 3.5cm for the frame, so it would be chamfered all along. But I forgot to measure the height of the conic part which was 2.3 cm (thicker than my material).

Not could I chamfer all the way down only up to the reinforcement. The angle of the resulting slope being 30°, I arbitrarily chose a chamfer distance of 10 mm.
As tan(30) x 10 = 5.77, the chamfer height would then be 5.77 mm and the reinforcement 12.23 cm (18-5.77).

Kerf

I did a lot of research on kerfing as I intended to test bending wood. There is such an example on a shelf at WoMa. The bending of the example comes from alternate incisions on both side and from a spinal depression.
Picture! I wanted to test something slightly easier: cuts on the whole width but not going through the material only throught 3/4 of it.

First you have to know the curvature you want to obtain.
The formula for such a pattern are those ones:
Length = radius x pi
Inner radius = Outer radius - 3/4 material thickness
Outside length(Lo) - inner length(Li) = the material length to be removed (R)
R/end-mill width = kerf number (Kn)
Lo/Kn = Kerf spacing (Ks)

I considered building a small table based on kerfing

Main piece conception

I had to reorient my project idea as Thomas pointed out that there was no joinery involved. The frame was only meant to be a test/practice, to better understand the end mill characteristics. We finally had less time with the CNC than expected. So the time devoted to test was reduced to zero. I found my inspiration on Pinterest . I liked the design, the press and fit joinery and its biomimicry inspiration, also it was only made of 2 different pieces.

Two pieces compound

Fusion 360

I used my rests of trigonometry to fullfill this project. To calculate the slot width I had to know the material width and the angle formed between the pieces.
- I decided to do 27cmx27cm square pieces because my first idea was to make a shoe rack out of it. My shoe size being 41, my shoes are 27 cm long. Also 27 is easely divided in 3.
- The slot length was either 1/3 or 2/3 of the square length with a round end. I tought this would provide some liberty. After completion I think a sharp end would have helped the assembly process.
- The plank was measured with a caliper and was 1.84 cm wide
- The slot width was the tricky part. My calculation was w = tan(30°)x1.85 + 1.85/cos(30°) = 3.21cm I made a sketch on Fusion 360 in order to check, with the sketch dimension I obtain 2.184 + 1.1 = 3.284 cm

Slot width

I couldn't figure out the reason of discrepancy between the 2 methods.

Once the dimensions computed I parametrically designed my pieces in Fusion. Once done I extruded then (1.85cm thick) and moved them in 3D to mimick the final geometry. This process validates the dimensions. My first try showed me an error in the slot width, the second an error in the slot length. I corrected them until the visualization validated my dimensions.

The same checking process was done later in Rhino.

Rhino

Once the design done, I had to export in dxf format to Rhino to close the polylines (Join + Trim tools) and to add layers. Layered dxf are read in VCarve, this enable toolpath to be computed for each layer separately. The names should enclose all the information needed: the cutting type, the cutting depth and the endmill used.

Source file of the hive furniture to load here

VCarve Pro

1.The DXF is imported in VCarve.
2. The board dimension are defined
3. Untick XY Datum position offset
4. Click Ok at the bottom of the Job Setup

job setup