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8. Computer controlled machining

The assignment for this week was to make (design+mill+assemble) something big (~meter-scale). I decided to make a table, but with an interesting design․ The legs of the table should look like butterfly wings․

Group assignment

During the group assignment we watched a video titled “5 Types of Woodworking Joints” and I decided to use two of the options shown there.

  1. Mortise and tenon

  2. Half lap joint.

  3. 5 Types of Woodworking Joints During the group assignment, we got acquainted with the process of following the safety rules while working with a CNC machine and the parts of the machine.

Safety rules

  1. Always ensure that you wear proper ear protection and safety glasses when operating a CNC machine.
  2. Don’t operate it alone!!!
  3. If you have long hair, ensure that you keep it covered when you operate the CNC machine.
  4. Keep your hands away from any moving parts during the machining process.
  5. Stand away from the machine whenever it is operational. You should also warn any other people near the risk of being too close to it.
  6. Ensure that you turn the machine off completely and clean it whenever you have finished using it.

Safe distance is very important.

In our FabLab we use ShopBot CNC machine. Before cutting, we got acquainted with softwares that are used with this machine. There were 2 - VCarve Pro-ShopBot Edition and ShopBot 3.

Parts of machine

Spindle is a key part in CNC machines. Tool Holding Mechanism

  1. Collet Chucks
  2. Hydraulic Chucks
  3. Shrink-Fit Tool Holders The Tool Holding Mechanism has different sizes, according to which end mills are inserted. We press the end mill into it and then assemble it into the spindle.

End Mills - are the important part of CNC milling

We also learned how we can change tool.

Basic Settings in VCarve Pro:

Tabs are for safety. They hold the workpiece if it tries to move during cutting, keeping everything stable for a perfect outcome.

start depth refers to the initial vertical distance the cutting tool plunges into the workpiece during a milling operation.

We can use tools that are in software or we can create it by clicking on “Edit”.

Testing process

After that we tried to arrange the pieces in a square circle so that they all fit and do not fall out.

For that we made a 2D drawing of rectangle, we divided them into 10 pieces to understand whether they fit or not, how much space stayed between them.

The dimensions in 2D was 80mm x 200mm, but as we can see in picture it was a bit different.

After that we made 2D drawing that was an 80mm equilateral quadrilateral. After cutting it, we measured it and it showed ~79.80 mm on both sides and it almost fit into the frame.

Individual assignment

Design process

First, I got the shape of the butterfly wings with the help of the Inkscape program.

Afterwards, I drew one wing of the butterfly, and I got the second part with the help of Path Effects’ Mirror symmetry tool.

Then, I exported the drawing in svg format to import into FreeCad as a sketch.

After making certain modifications, the butterfly wing got the following appearance

Since I haven’t decided on the number of table legs and the size of the table yet, I made up my mind to make a parametric design in order to easily change the dimensions later.

Furthermore, I added the two round platforms to the legs of the table which can also be used as a shelf, and I finally designed the top of the table․

In our FabLab we use ShopBot CNC machine.

Before I started the cutting process, I laid out the drawings of my mock-up table using Inkscape to get an idea of how it would fit on the existing plywood 10mm.

For cutting process we used VCarve Pro-ShopBot Edition and ShopBot 3 softwares.

First I needed to generate ShopBot Part File. Here are the steps.

Toolpath generating

  1. I imported dxf files VCarve Pro-ShopBot Edition and arranged it.

Also circles were added where I needed to put clamps.

After that I started to generate Toolpath with Profile toolpath.

After that I also added cut depth, tool, machine vectors and added tabs.

I got the warning because material thickness is smaller that maximum tool depth.

Then I selected 3D view .

I saved toolpaths to file.

Here is the machine code.

Cutting process

Then, I opened ShopBot 3 and adjusted X,Y,Z axis positions.

After that I started cutting process.

Here is the process of cutting.

Assembling table parts

After all parts were cut I started assemble them.

The top of the table fit but have a space and I didn’t want use glue that’s why I used wood putty and its really helped.

Here is how my table was at the end of week.

Conclusion

This week was quite hard but also helpful and informative. I learnt a lot of new tools in FreeCad and again did a parametric design that helped me make my design flexible. I never made something big with CNC machine, because CNC that I used was planned for small parts. I enjoyed this week especially when I was assembling my tables’ parts and got the result that I wanted.

Files