7. Computer-Controlled Machining
Hero shot
Group assignment
It's time to get to know the CNC. We have a Mekanika model.
In order to do that, we've created a simple square part using the machine's various cutting and engraving options:
- a round hole
- a rectangular pocket
- a notch with dogbones for nesting
- bridges to prevent the part from jumping off the table
Part design
We used Freecad to create a parametric square part using spreadsheets.
The parameterized parts are :
- the side of the square
- the part thickness
- the radius of the fillets
- the round hole diameter
- the X position of the round hole
- the Y position of the round hole
- the kerf
- the notch length
- the notch width
- the rectangular pocket length
- the rectangular pocket width
- the rectangular pocket thickness
- the X position of the rectangular pocket
- the Y position of the rectangular pocket
Easy part construction
To avoid drawing the different parts by manually entering each measurement, we've used the symmetry (horizontal, vertical) and constraint (horizontal, vertical, radius, diameter) options.
The symmetry and constraint steps must be performed one by one to avoid errors.
Once all the parts have been constrained, they are linked to the parametric table.
An error may occur from time to time. The solution is to remove redundant constraints displayed in the sidebar.
When the part design is ready, all lines and points are green and the message "fully constrained" appears in the sidebar.
Preparing the file
Once the object has been created, we need to prepare the file so that we can start working on the CNC.
To do this, we must first register the various mills and their parameters in Freecad.
To get the right cutting parameters and avoid complicated calculation, we had 2 options :
- Sylvain Denis' online calculator (great job, thanks ! :D ) already adapted for the Mekanika
- Dominique Lachiver's online calculator
Using the CNC
Safety
Safety is essential in the Fab Lab (even more with this kind of machine). The first step is to have and use personal protective equipment (e.g. ear muffs, goggles, dust mask, and gloves especially for moving the boards).
It is also important to unplug the spindle before changing the tool on the machine !
Changing the tool
First step is to change the tool and make sure that it is correctly fixed.
Think about preparing the right pieces (in our case, the mill was to big) !
Placing the board
Object cut with the CNC
Link to our Group page
Individual assignment
CNC Project
Design
Mill
Assemble
Files and resources
My files
Resources
- Dominique Lachiver website : interesting website IN FRENCH (created by a retired teacher) to learn digital manufacturing
- Our group page