CNC Tests
Today I made the first tests with the CNC. I decided I would not wait for our concept to be final to start understanding the machine. And it was a good idea, as I learned a lot of details that will have an impact on the final file to import in Master Cam.
I had prepared a simple sketch in Rhino to work with:
I had prepared a simple sketch in Rhino to work with:
The idea was to pocket the shapes (shape A) in one piece and to pocket around the shapes on the other (shape B) so they would fit in.
- For some reason, I could not implement the pocket function for the shapes. Master Cam was saying there was an error as the lines were not closed. It also said sometimes that the lines were not on the same place. I guess this was true for the shape B, as the lines in Rhino are a whole and are lower on the Y axis. Maybe that was the problem?
This time flat. But the same errors occurred. So I build a similar file directly in Master Cam. This was a great exercise and I learned a lot about the different cuts and how to build the paths so my two pieces would fit together.
I ended up CNCing more that only two files. Here is a pictures of the work:
I ended up CNCing more that only two files. Here is a pictures of the work:
On the lower left you can see I pocketed the shapes counterclockwise. So the cut was inside the shapes lines. On the lower right is the other part that should fit into the first one.
- The circle ended up being too big because I pocketed it clockwise, so the cut happened on the outside of the line. Obviously, the shape will not fit as the circle whole was pocketed on the inside. The pocketed whole ended being smaller than the shape.
The pieces would now fit, but there is another problem:
When I pocket inside the lines, I am using the diameter of the bit. So there is too much space in between the two parts. So, I have to consider the dimensions of the bit when creating the shapes in the original file, before importing it in Master Cam.
Summary:
Advice from Ben Light, ITP resident:
Summary:
- use the flat bit to pocket areas;
- consider the bit dimensions for any shape that has to fit into a whole, to avoid extra space;
- find out how to pocket open areas;
- find out how to pocket curves.
Advice from Ben Light, ITP resident:
- When creating shapes, consider the material. Per instance, wood volume changes with temperature. So if you build two parts that join, you must have a little tolerance for the wood to expand;
- when creating the original shapes: never use the same exact dimensions for the shapes to fit. Always add a 0.01 tolerance. Per instance, the part that has to fit into the whole needs to be smaller of at least 0.005 or 0.01 in the Y and the x and the Z axises.
- If you build a part that is a square, when building the whole, the bit will round the edges. When pocketing the extruded shape, it will create sharp corners. So the part will not fit into the whole that has rounded edges because there is a tiny triangle that wont fit. So, when you create the file of the part that need to fit in, always use rounded corners based on the bit radius!;
- in Master Cam, always position the origin of your model at least 2 inches from the real origin so when you set the Z on the CNC, the point that it might create will not appear on your part;
- if building a slider section to insert a shelve in a wood section, always make the slide pocket longer (at least the dimension of the diameter of the bit) than the width you need for the shelf as the bit rounds the corners! so if you make it longer, the shelf will have enough room to fit in;
- when you pocket an area, always pocket further than were you are gonna cut the part, because if you don’, the pocketing will stop directly at the edge of your geometry and will not pocket the edge of the geometry. You can see on the first picture that this is what was happening on the top right test. I pocketed an area and then made a contour cut around the full geometry clockwise. But I stopped the job as I saw that it would leave an edge that was not pocketed. So pocketing more means will allow the edge to be pocketed too.