Week 7: Computer Controlled Machining

What is a CNC Machine?

CNC stands for Computer Numerical Control. A CNC machine is a type of machine that can cut different material according to specific computational directions given to it by a computer program. Technically, both laser cutters and 3D printers may be considered as CNC machines as well since they also operated and move according to numerical controls determined by software. Less formally, CNC machines generally refer to machines that are larger and cutting wood or other materials with drill bits.

The CNC Machine at Fab Lab Kerala:

Here is a picture of the large CNC Machine (with computer). It's called a Shop Bot.

Here's another view also showing the computer with software.

Behind the computer are three switches, to control the power for:

• The machine movement in 3 directions
• The spindle, which holds the bit which cuts the material
• The vacuum or dust collector

We'll say more about our machine and other things in the group assignment page for this week.

CNC Design Project - Design & Laser-Cut Prototype

Back to Fusion 360...

Here is first draft of my project, which is also related to my final project:

Only problem is that parameter for thickness doesn't work well:

So I went back and did the project again.

This time I was very very very careful with the parameters from the beginning:

All the measurements defined in terms of parameters and all sketches constrained:

Here is the final version. I can change any parameters and nothing bad happens.

Now it's time to export. We arrange and export the sketch as .dxf:

Few important notes:

• To find 'Arrange' go to 'Solid'->'Modify'->'Arrange'
• Make sure only the components you want to arrange are selected. (if you drag box over the area you may inadvertly include edges or other)
• The arrange envelope has 2 tabs: object and envelope. Envelope creates the space; make sure its dimensions can include all components.
• To export, right click on the arrangement in the browser, and select 'Export..' from there.

Now we are cutting in the laser cutter as a test before cutting a full scale version in plywood.

Here is the assembled model from cardboard. Actually it fits pretty well. It is 1/4 scale. Good job.

Just a few issues:

• Forgot to include kerf on the vertical edes. Kerf need to be everywhere!
• The mouth is fine for laser-cutting, but for CNC will not be able to cut the sharp corners.
• The door on the back will be a problem.

CNC Design Project - Redesign & Kerf-Bending

First we redesign the mouth. The top corners with circles, like an exaggerated dog-bone.

Next we consider to use kerf-bending to make the back door, as in the following example from Sreyas:

This kerf-bending technique cuts entirely through the wood, in contrast to some techniques that cut a groove 90% or so through the wood.

Here's my design:

CNC Design Project - CNC Cutting

Setting up for printing: we screw the board to the sacrificial layer and calibrate in all 3 directions.

Then we make an air rectangle around the border of what we plan to cut to ensure that the spindle will not go over the screws.

Used software "Vcarve" a.k.a. "Vectric". Here's the initial set-up. Some guidance:

Cutting process: It took just over 1 hour and we only used half a sheet of the 12 mm plywood.

CNC Design Project - Sanding and Processing

Cutting tabs: it was easier with the chisel and hammer than with the knife. But the tabs generally worked well.

Sanding: We used a power sander, but for the small places that didn't work so we cut sandpaper to fit on a small handheld 3D-printed holder.

Fitting it together and final result: it fit perfectly, just a bit tight but with a hammer it forced in and cannot easily come out.

CNC Design Project - Hero Shots + Design Files + Kerf-Bend

Zip file containing .svg for laser prototype, .dxf for CNC cutting, and design file in .f3d.