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8. Computer controlled machining

The assignment this week required that we design, mill, and assamble a big object. As I am needing a table at home, I decided to make one. Unfortunately, our machine is not big enough to make a very big table, but I designed a table for my living room.

Design of the table

The design of the table was done using the free version of the software Autodesk Fusion 360. I have done the following steps.

  1. Defined the necessary parameters for drawing the table. The max width the machine we will use can handle is 40 cm, so I decided to design a table 50 X 40 X 40 cm (length, width, and height). The variable heigth_top is half of 50 because the top piece will be duplicate to avoid drawing twice the same piece.

  2. I started creating a new sketch to design the side piece using the plane XZ. First, I added a but square in the length and width of the side piece (both size width. Then, I draw two holes where will be placed a support for the side piece in the lenght 2*thickness. The two wholes was placed in the same distance of the edges top and side (dist_hole). This is necessary to create the support of the table in the correct place in the side and top piece. Lastly, I drew in the top of the square the shape of the press-fit that will connect the side with the top piece (using the size of thickness).

  3. Create a extrude using the sketch from step 2, selecting only the inside of the drawing.

  4. Add a new sketch, now to draw the top of the table. I drew only half because the other half of the top will be exactly the same, so it is only necessary to duplicate the extrude. I drew a square 25 X 40 cm (height_top and width). Then I drew two holes with the same dimension and placed in the same position as the ones from the step 2.

  5. The extrude of the top piece were a combination of some operations. First, extrude the sketch from step 4. Extrude the difference of the press-fit from the side piece removing from the top piece. Duplicate the object and turned 180° (using its side line) and moved up thickness to be in the same level as the first object. Then join both parts to make one single one.

  6. The result of the drawing until now, both pieces side and top.

  7. To design the support, I extrude the holes from both pieces (side and top).

  8. Then, using the two object from step 7 were connected using the command Loft. This command connect two selected objects and it is possible to create a joing object.

  9. The other side of the table is exaclty the same, so the side piece and its supports were mirrored using a plane placed in the middle of the top piece.

Download the F3D file from the design using Fusion

Milling pieces

From the previous design, still using fusion, it was generated the lines of the objects that can be sent to the mill machine. I used the machine (Shapeoko)[https://carbide3d.com/shapeoko/] to mill the pieces of the table. The machine has a work area of 400mmX400mm, but it is possible to find a good position for milling bigger objects. The machine has its own software program to make the toolpaths, which is very easy and straightforward to start with CNC milling. However, sometimes the drawing from Fusion 360 scales wrongly and we could not find a reason for it. I have tried to scale the drawing by 1:5, since the objects are too big. This is an important information, since the dimensions of the objects should be adjusted to the correct value, otherwise the table would be smaller than expected.

  1. From the design on Fusion, it was generated the drawing of the pieces using the menu DESIGN > Drawing > From Design (for more information on how to use this functionality take a look on the assignment week 04 here). It was included one drawing for each part of the table using the respective views. this was resulted.

  2. The file was imported into Inkscape and removed all unnecessary lines. It was added as well the amount of pieces each drawing need to be milled in the machine: 1 top, 2 sides, and 8 support pieces.

    Each part was imported separeted in the software of the mill machine (Carbide Create), because it would not be possible to mill all pieces at once. Before including the pieces in the software, they were changed to the correct scale (by multiplying per 5). This software generates the G-code (.nc file) with the configuration and the drawing to mill for sending it to the mill machine. The first piece to be milled was the supports of the table.

  3. In the first part of the configuration, the software were setup using Cutting Parameters: 3mm for Depth per Pass (how deep the machine will mill next round over the lines of the piece) and 1.429mm for Stepover (to avoid pieces free during the operation of the machine, the user can add points where the machine will stepover to keep the piece fixed). Feed Rate is the actual size of the material used (424.180mm). The sedond part of the configuration, it was adjusted the Start Depth to 0mm, the Max Depth to 18mm (the thickness of the material), and the direction of the milling process Outside of the lines.

  4. Bellow you can see the drawing ready to be milled. It was export as .nc file that will be used in the next step.

  5. The .nc file was imported in the software Carbide Motion that is the software that controls the mill machine. The niddle were positioned in the bottom left of the material (in the red dot in the previous image), using the arrow commands from the software.

  6. And the position reset to zero.

  7. The first attempting of mill failed because the drawings were too much close the edge of the material, and the machine missed one corner. It was removed the first piece and the other were adjusted to fit the material setup in the machine.

  8. Then it was milled the side pieces. To save time, because the machine would need to work for a log time, only the press-fit of the side and top pieces were milled in the mill machine. The big lines were cutted using a chainsaw. The same configuration described before were used. This step were applied to the top piece as well.

Download SVG file from the drawing

Assembling together

After preparing all pieces was time to assemble them together. The press if of the side and top pieces were good, however the support were bigger than it was supposed to be. The drawing had a wrong scale when imported in the software of the machine. The supports were milled again, now using the correct scale.

First the supports were sticked together using pressure machine for clip. I decided to use two times the material in the support for a better structure of the tabel. After that, they were glued in the top piece of the table. The same were done by each side, but using also glue in the press-fit of the table to guarante the pieces are sticked together.

The table were kept under pressure in the edges for 30 minutes to guarantee there was no spaces between the pieces. After taking out the tension screws, I sanded the table to avoid waves and have an aligned table. Bellow the resulted table from this assignment.

Group Assignment

Ingegno - Computer controlled machining

Last update: August 30, 2022