Fab Academy 2018 - Thierry Dassé

Week 8 : Computer controlled machining

Group assignment

Computer controlling machine

An old Table

Table legs I own an old table with Louis XVI style legs but without top. I put a broken marble top but have thought to make another one for many years.
I wanted the top to be contemporary and not as classical as legs.
I started to think of a rectangular shape but with chamfered pockets on the top.
To see render between legs and top, I started to design simplified legs on Blender.

Table top

First, I wanted to make a Voronoi diagram on the top but with many holes on it, my table wouldn't have been usable.
I simplified it in three pockets on the top.
To design it, I first made a sketch on librecad because it's quite easy to make polylines with parallel edges and have round corners with filet tool.
Then, I transformed lines to shapes with width using path to outline tool on Inkscape.
Then, I imported the result in Blender to make the volume with lines at different height.

At the end, I think it could have been easier to make it directly with Freecad. I tried with :

There are two limitations on Freecad. First, on a 8mm pocket, you can't make a 8mm chamfer. 7.99mm is possible but chamfer has to be less than 8mm. Second, the chamfer is always 45°. I didn't find a way to modify the value. In my case, I wanted a chamfer width 30mm width and an angle depending on pocket depth.

Table top on librecad Table top on inkscape Table top on blender Table top

Table on Blender
Table on Freecad

Milling

milling machine To mill my table, I used a 1000x500x22 mm MDF sheet and Vcarve software.
I first create a new project and put enter my MDF sheet dimensions x : 500, Y : 1000 and thickness : 22.
Then I export my table top in .stl and import it in Vcarve.
I choose a 10mm spherical mill. First, I set layer thickness to 1mm and start the mill. It was very slow and when I had a look to the timing, the duration was 68 hours. I changed layer thickness to 5mm, increase the speed and my table top will be made in 2 hours and 43minutes wich is better.
During the milling, I made the file to cut ouline with a 6 mm cylindric tool. Duration was 4 minutes.
I didn't have enough time to make a finishing path and have to make it by hand but result satisfy me.

Vcarve Vcarve Vcarve Vcarve Vcarve

Feet design

I also made table feet. Two feet are linked with a piece to maintain them vertical.
I used tenons and mortises to assembly pieces together.
I designed all on Inkscape for 22mm thick plywood and made a render on Blender to verify geometry.
feet design feet render

Feet SVG file

Feet on Vcarve

I also use Vcarve pro to make feet. I divide my pieces in two files to mill them.
I couldn't import svg file directly so I exported my sketch in dxf and pdf from Inkscape.
Size were not scaled good in dxf file but in pdf so I used this file format.
I first define material size : 600mm width, 1200mm height and 22mm thick wich is sheet size and maximum size on our shopboot CNC.
When I wanted to put my pieces on, I see that orientation was not good so I selected all lines and made a 90 degree rotation.
I first selected internal lines and use pocket menu, select a 6mm mill.
Then, I selected outline and use outline menu, select a 6mm mill cuting external and add tenons

feet on Vcarve feet on Vcarve feet on Vcarve feet on Vcarve feet on Vcarve

Feet1 and Feet2 vcarve files
Feet1 and Feet2 toolpaths files

Milling feet

After milling my feet, I assemble pieces. With a 6mm diameter tool, my holes are round rectangle because Ididn't want to make extra holes. So I add to file for tenons to enter in mortises.
After that, I assembled with a hammer. Feet are really stable and press-fit.

milling feet feet assembling feet assembling