7. Computer controlled machining¶

This week I made a table for kids in a school.

1. Group assignment¶

Babken introduced me to the main principal safety rules using the CNC machine based on the manual

PROTECT: Turn OFF your router or other power tool before loading or positioning a workpiece or adjusting the position of the tool. Do not change router bits or other cutters without first unplugging the power tool or having a positive system to make sure the power tool is not accidentally activated. It is your responsibility to use it safely.
AWAKE: Never operate the tool when you are fatigued.
EYES & EARS: Always protect your eyes and ears when operating your ShopBot.
ATTEND: NEVER leave the tool unattended while it is running. A cutting error or workpiece slippage that the tool cannot detect might occur. Some person unknowledgeable about tool operation might approach and start the tool. Or some other unexpected event might occur.
TO_STOP: During a cutting or motion process, the SPACEBAR on the computer keyboard is a Panic/Stop/Halt button. Hitting the bar will stop the tool’s movement. Your ShopBot PRSalpha also has a remote STOP Button that interrupts power to the stepper motors and the spindle or router after it is pushed. You should locate the STOP Button convenient to your tool and workstation.
POSITION: The safest location for you during the operation of the tool is within easy reach of the computer keyboard or STOP Button and well away from the path of the tool. Because bits can break and fly loose during cutting
BE_SMART: Most importantly, never place yourself at risk during a cutting or machining process by placing any part of you near the cutting path or by attempting to move or adjust the workpiece or active tool. SHOPBOT IS A ROBOT, BUT YOU ACTIVATE ITS MOVEMENT AND YOU TURN ON AND OFF ITS POWERED CUTTING-TOOL.

For this machine, it is very important to be careful.
It is not a small machine, and the power of it, it’s huge.

2. Individual Assignment¶

I started creating the legs of the table.
As this is my first time, I don’t know how to do it with a curve shape, so I started to designed it as a “cross-shape”.

2.1. Parts¶

2.1.1. Upper leg¶

I called it “upper leg” as this have the joint in the bottom, this means that for connecting with the other leg, you will have to put it from the up.

The lenght of the leg is an estimation of how well-suit it will be for the legs of the kids. In total it measures 500mm.
The width of the material is 10mm measured with a caliper.
As the width of the material that I used is 10mm, I had to consider the top of the leg to be part of the total of the size of the leg.
This can be a little bit complicated to understand so I will go by parts from the top to the bottom.

Why these measures?

120mm is the width of the leg (personal measure).
80mm is the width of the “conection” of the leg with the table (personal measure).
10mm of the top is the length of the connection between the leg and the table (not a personal measure, we calculate the width of the material with a caliper).
490mm is the length of the leg, not counting the 10mm of the connection (not a personal measure).
10mm in the middle is the joint size with the other leg (not a personal measure).
150mm is the 30% of the total size of the leg. (personal measure).
50mm is the most down part of the leg, where the leg will touch the ground (personal measure).

2.1.2. Downer leg¶

This leg is called “downer leg” because is the leg that we will put in the bottom so the “upper leg” will connect from the up.
This leg has the same measures as the upper leg, but as the size of the joint of the “Upper leg” was the 30% of the total, this will have eventually 70%.

2.1.3. Table¶

The table was very simple to make, it was made by only create a circle and have an estimation about the diameter.

2.1.4. Joints¶

The joints were a little bit difficult to make as Babken told me to create different models and “call” them to eliminate their size on the “2.1.3 Table”, so it would be easier in the future if we want to change a parameter.
In other words, the joints are not a solid figure, but it is a “void”.

2.1.5 Parameters¶

[APART] The “Inside Corner” Problem.¶

It is a good idea to learn more about this issue before start cutting. The “Inside Corner” problem it’s all about cutting the inside angle keeping in mind that it will be impossible to reach all the way into an inside angle with a rounded bit.
You can learn more about this issue in this website that talks about this issue. It is a very good one and all about this explanation comes from this website.


This is where the “Dog Bones” and “T-Bones” enter to the game.

Dog-Bone¶

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T-Bone¶

Do it automatically!¶

Vcarve does this automatically. But the only problem is that this tool is not parametric. Scaling your design after inserting fillets will scale the fillets as well.

It is best to insert the fillets after the design is complete.

Continuation of the individual assignment:¶

2.2. Creation of the Comb¶

So as any machine that cuts, I had to measure first the “kerf” of the End Mill. So I used the same comb from my assignment of the laser cut and as it was a parameter figure, I just had to change some number so the holes will match with the End Mill of the machine, and as well with the width of the table.

End Mill: 6mm
Material_Width: 10mm

2.2.1. Vcave for the Comb¶

I exported the file as .dxf and then I opened it with the program Vcave.
As the webpage says: Vcave provides a powerful but intuitive software solution for creating and cutting parts on a CNC Router. It gives you the power to produce complex 2D patterns with profile, pocket, drill and inlay toolpaths, plus gives you the ability to create designs with v-carving textures as well as import and machine unlimited Vectric 3D clipart or single model files.

First we select the size that we are going to work with or “job size”

We import our file to the program.

Then we select the Cutting depth.

The starting it will be 0mm and the cut depth it will be 10.7mm.

This is a very important thing as well. You have to choose the type of end mill that you will use. In this case is the end mill of 6mm.

As well, we are going to change the number of passes that the End Mill will do in the material

Now we are going to choose the this option of “Adding tabs to toolpath”. This will create some tiny connection between the figure that we are cutting and the material, so it will have more hardeness when it’s cutting so it will not move that much.

The preview of the “toolpath” it will look like this:

Now if we click on the option (insert name), we will see the direction of the cut of the End Mill all over our figure.

Now we will export the file to our command console.

But before cutting we need to calibrate the machine and unlock the spinning of the End Mill.
As well, make sure to make the material that you are going to cut steady.

In this case we are going to use simple clambs as shown in the figures below

For the testing you should take the metal sheet and make the End Mill touch it.

Once you finish with this, you can continue.

|It is very important to start the spinning of the End Mill before you start cutting.
For this just unlock the power of the spin with the key. The key should be turned to the right and the red switch should be situated on the “on” position.| |--------------------------| || || || ||

2.3. Changing the paremeter of the joints¶

Due to the joint test that we did with the comb, the perfect size of the joints was 9.7mm. Even if the width of the material was 10mm, the connection between the legs and the table was more solid when we put a hole of 9.7mm.