6. Large format CNC (computer controlled Machining)¶

During this week we tested the CNC machine and tuned in the ideal settings Group Assignment - Large format CNC (computer controlled Machining)

Design¶

I wanted to design a small coffee table, and have finger joins to connect the top and bottom, and a cross lap to create a unique and stable support in the middle.

Let’s Sketch the first part of the center and extrude it to the same thickness of our material (12mm plywood)

The top is a simple “Slot” Shape, with a thickness of 12mm to match our material

Here are the fingers, that will go through the slots

Added the 2nd middle support, and had it at a 90 degree angle

Next I added the top and bottom of the table

The top part will connect with finger joints, but I also wanted to double up the thickness with another top that will be glued on (just as an additional finishing step). It will also have a 3mm engrave so that we can add some acrylic in the middle

Here are all the parts laid out!

DXF View

DXF File (after all changes listed below) Coffee Table DXF

Cutting¶

Now comes the time for cutting!

I loaded up my files in VCarve Pro, and used these settings. Our tool was a 1/4” bit The Feed-rate was set to 90, and the speed at 19,000 RPM. These numbers were based on our tests in the group assignment.

For the middle part, we don’t want to cut through, so we made the depth 6.5mm

and here is our toolpath

Plywood was the selected material, and it creates very messy edges. Unlike MDF which has a very clean, ready to paint finish.

Whops! The Cross Lap doesn’t exactly fit. It was not deep enough, and no matter how much I tried to get it to press fit it didn’t work.

So we need to adjust and re-cut, the new design added 2cm to each side of the slot in the Cross Lap. Using a rubber mallet it managed to snap together as a tight press fit. The new Cross lap measurements were correct.

This time around it fit flush, and so did the top and bottom. We can now see our initial coffee table.

I added some glue to add the 2nd top. This is just an additional step I am adding, and not part of the Week’s requirements.

Added clamps, but made the mistake to use thin cardboard rather than thicker material, and the wood ended up having clamp marks on them sadly.

For the middle part, I wanted to use Acrylic, so I head down to the laser cutter and used the same file to just cut that one center part of the design I made. Speed 110mm/s, power was 60, again based on our group tests during the laser cutting week.