8. Computer controlled machining¶

Assignments¶

Group assignment

Test runout, alignment, speeds, feeds, and tool-paths for your machine

Individual assignment

Make (design+mill+assemble) something big.

Group Assignment¶

In group assignment our instructor helped us in understanding the operations of the machine. We did alignment, testd cutting and feed settings, generated toolpaths for the machines. For detailed documentation go to our Group page

Speed Settings
There are two types of speed you need to feed in the cnc machine- feed speed and spindle speed.

Spindle speed is the speed at which spindle of the machine rotates. The spindle speed in the machine is denoted by a number followed by S. They are 4S, 5S, 6S, 7S. 4S being the slowest and 7S the fastest.Tha maximum spindled speed at 100% is 3200RPM.

Feed speed is the speed at which the tool moves in the cutting direction for cutting the material. The harder the material the lower will be the spindle speed. It is usually defined in feet per minute.

Steps for cutting

Design the files in 2d format. For this you can use any vector software like Adobe illustrator, coreldraw, autocad etc.
Export the desing in the .dxf format.
Import the .dxf files in the Aspire software for creating toolpaths.
Export the gcode of the toolpaths and save it in the flashdrive.
Plug the flashdrive in the controller of the machine.
Clamp the board
Set the origin.
Start cutting.

Cutting bits

For cutting the plyood/mdf we used 6mm carbide drill bit. Every bit has two parts- Body and the shank. Shank is inserted in the spindle and body has flutes which cut the material .

Operations of the machine are expalined below in individual assignment

Individual Assignment¶

Design¶

I designed below cabinet for storage purpose. For designing, I used Fusion360 software.

Steps

First, I set various parameters( Modify –> change parameters), so that later if I want some changes it would be easy to modify the design.

Draw the sketch(R) of the base and set constraints and dimensions. For the slots, I added 1mm clearance to the thickness of the materials so that it would be easy to insert the parts in one another.

Extrude(E) the base to the thickness of the material.

Use rectangular patterns(Create –> patterns –> Rectangular patterns) to create three copies of the base.

Draw a sketch of the left end and set the dimensions.

Extrude, and create one more copy and move to the right side.

Next, create the back side to close it from the back side. Add four notches at the sides(two each side) so that it places perfectly at its position and fit with other parts.

Create left and right panels. I would have to use hinges so that these panels/doors can be opened and closed. I added one mm clearance in these too so that these open and close freely.

Add appearance(A). I used oak wood as the material.

Save the sketches of all parts as .dxf (Right click on sketch and save as dxf).

Cabinet V1 by narender on Sketchfab

Click here to donwload the fusion file.

Processing the design for CNC¶

For generating machine codes we used Modella software. It is a software for generating tool-paths for the machine. You can use this software for most of the CNC routers.

Steps

Create a new file, in the first window, set the length and breadth and thickness of the wood that you have. I had 750X1550mm wood of 15 mm thickness.

Add all the parts which can be fit in that area(File –. open). Align them in a way so that there is minimum wastage of the wood. My design has 8 parts but I was able to fit only 7 parts in the given area. I had to cut one part separately.

Check if there is any open curve or not. This is the important step as to cut the whole part it must have to be a closed curve.

Create fillets. I used the T-bone fillets. The need for using fillets is because usually the end mills are cylindrical in shape so it can’t cut inner corners sharply and due to this the parts won’t come in contact when you assemble them.

Click on tool-path –> 2D profile toolpath. Here, fill the start depth and cut depth. Use cut depth 0.2-0.3 mm lesser than the thickness of the material, otherwise, the tool will go pass the wood and damage the CNC bed.

Select the diameter of the end mill. Pass depth is the depth which tool cut in one pass. Stepover is the tool height from the cutting surface when it’s moving from one point to another without cutting.

By clicking on “edit passes” you can set the no. of passes in which whole depth would cut.

Add tabs at few placed in all parts so that they remain in place after cutting.

Cutting¶

First I clamped the plywood on the CNC base. For clamping we had screw clamps which tightly hold the board onto the platform of the cnc. This is a very important step because if the board is not well clamped then it can move while the tool is cutting it.

Next, insert the cutting bit in the collet. I used 6mm downcut CNC bit.

Set the z-axis’ origin.
This tool is used to set the Z cordinate of the machine precisely, the X and Y home positions can be set via Teach pendant but the Z cordinate is set 11mm above the surface using this tool

Loading the files into the machine

Save the processed file into the flashdrive and plug it in the controller of the machine.
This is the controller of the CNC. The feed rate and the spindle speed is controlled by Teach pendant in this machine unlike other ones, in which the feed and spindle speed is given in CAM Software. Button x, y, z are used to move the tool head along three axis. Move the toolhead above the point on the board from where you want to start cutting. Then press xy=0 to set it as the origin. Then, open the file using the menu button and start cutting.