Computer Controlled Machining

This week assignment was to make "something big" with computer-controlled machining. My first thought was to make a chair for my "reading time" during work. What does this mean? At lunch, I ate my dinner ASAP in order to buy a coke and start reading alone, far away from people. It is not that I dislike people, but I prefer to spend my time reading a book than any social activity (Don't judge me as I don't judge you :) ). The following images show the design of the sparse pieces of my chair that I made in Onshape.

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At the end, the chair can recline.

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However, before to mill my work, I needed to make a test in order to check if my joints were going to be rigid enough. For that I drew a small circle in order to check if it work.

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So, before using the milling machine it is needed to create the path that the drill bit will use follow. For that we use the program VCarve Pro. When the program is opened, select File->New. The next screen will be displayed:

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The next fields are explain: JobSize(X & Y): indicates the size of material it is going to be milled. Material(Z): indicates the thickness of material. In my case it will be 18 mm. This is important because several parameters inside the file are related to this measure. Units: choose units I fill the information as is shown in the next picture.

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The process to make the VCarve file is pretty simple 1) Import the files you want to mill. In my case I had them as vectors, so I went to File->Import->Import Vectors. Arrange the elements in a way the space is not wasted.

2) Afterwards, draw small circles where you think the screw for holding the MDF are best located. I got the following:

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3) At the top right corners there is a tab named Toolpaths. We are going to use it as it follows: Select the option "Drilling ToolPath". A side window should open with lots of information. Fill the spaces as the next picture shows:

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Then select all the circles and press the button "Calculate". This is done to know where to drill the screws with the security the drill bit will not collide with them.

4) Create fillets: the drill bit cannot make a 90° cut inside the material. It will leave a small corner with a curve which size depends on the drill bit radio. In order to solve this we create fillets. Select the "create fillet option":

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Fill the next window as it follows

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Click every corner where the fillet is needed. The following images present a piece without and with fillet.

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5) Then select "Profile Toolpath". The file created in this step will determine were the drill bit will mill the MDF. There are two classes of profile works:

A) Machining Vectors - Inside: Cutting vectors that are inside other pieces. From example, a circle inside a square.

B) Machining Vector - Outside: cutting vectors that are contours of a piece.

When making paths, separate them depending if they are outside or inside. However, in every case, add "tabs". Tabs are small non cut pieces of materials that prevent it to get out will it is being milled.

6) Finally, export the data into ."sbp".

7) Now, is time to use the millin machine, the ShopBot. It is actually pretty easy. First it is needed to turn it on, turn to the right the key beside the turn on button, and press reset. Afterward we open the program ShopBot3 and do the calibration of the Z axis. For that press the next button:

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Then calibrate the X-Y axis pressing the button display below.

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Finally, open the file and start milling.

God is good and in my first try the test results were satisfactory. The joing was good enough for my chair. I made the VCarve files for the pieces of my chair and sent them to mill. However, at the moment of buildinf the chair, I found that in this ocation the joints were not entering smoothly. I had to use the esmery to reduce the corners of the joint and create a small slope. The next images shows the process of building the chair.

The final product:

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Download all the files from here.

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