7. Computer controlled machining¶
Individual assignment¶
- Make (design+mill+assemble) something big (~meter-scale).
- Extra credit: don’t use fasteners or glue.
- Extra credit: include curved surfaces.
Group assignment¶
- Do your lab’s safety training.
- Test runout, alignment, fixturing, speeds, feeds, materials, and toolpaths for your machine.
The link to the safety trainin is here.
Designing¶
This week we are to make something big using the CNC machine and to do so, the first thing we have to do is designing. I will be using Fusion 360 software to design a furniture with minimum of 1 meter length. I decided to make a shoe rack for my shoes at home. For now since its the learning stage I thought of not doing complicated designs so will be doing a simple shoe rack designing and making. The joints I would be using are the finger joints to attach different parts of the shoe rack.
Firstly I did a simple designing work on a piece of paper defining the different parameters like the length of the shoe rack, the width, the size of the finger joints and lots more. So my simple sketch looks something like this.
Now I started designing it in Fusion with the pre defined parameters. In fusion I created the sketch using the line tool and the fit point spline tool and defined the parameters as and when I went on designing the shoe rack bit by bit. After giving all the dimensions and after finishing the sketch my shoe rack sketch came out to be something like given in the following image.
Next I extruded all the bodies to 18mm since the thickness of the ply wood that we were using was of 18mm in thickness size. To have a visual of how my shoe rack will look, I had to join the finger joints and make the shoe rack stand in the design. To do so I used the Joint function under the Assemble tool and to make the joints I had to create another sketch and define the poins that I have to join. Before we can joint the components, we have to make components out of the bodies and then start joining. After joining the components, my shoe rack looked something like given in the image below:
Since the designing part is done, now its time to do some projection of the bodies created so that we can export the sketches in dxf format. You go to Create sketch>> Project/include>> project and then select the bodies to be projected and it will be done. Next up you right click on the projected sketch and then export the files in dxf format.
Once the dxf files have been saved, you are done with the designing part.
CNC cutting¶
According to Wikipedia Computer Numerical Control and commonly called CNC is the automated control of machining tools (such as drills, lathes, mills and 3D printers) by means of a computer. A CNC machine processes a piece of material (metal, plastic, wood, ceramic, or composite) to meet specifications by following coded programmed instructions and without a manual operator directly controlling the machining operation.
A CNC machine is a motorized maneuverable tool and often a motorized maneuverable platform, which are both controlled by a computer, according to specific input instructions. The input of instructions in CNC are done through G-code. G-code is the common name for the most widely used numerical control (NC) programming language. It is used mainly in computer-aided manufacturing to control automated machine tools. G-code is a language in which people tell computerized machine tools how to make something.
The CNC machine operates in X,Y and Z directions where Z being the vertical direction. Now I take the dxf files in the shopbot controlling desktop for cutting. To do so first we have to create a tool path in G-code format which is the language the CNC machine understands. To create the toolpath you open the dxf files in Aspire software which will help create the toolpath for the designs. Now i opened the dxf files in the Aspire software which shows the designs as shown below. 6 of the design bodies on the left part are mine and the other 2 belongs to a friend of mine who needed extra ply wood as his design was quite big compared to me so I let him use the remaining part of the board.
Now you have to define the geometry, number of flutes, feeds and speed and other settings which you require as shown in the image below.
For my cutting the settings were made like;
- Number of flutes: 2
- Pass depth: 3.5 mm
- Stepover: 1.2 mm
- Spindle speed: 18000 r.p.m
- Feed rate: 50 mm/sec
- Plunge rate: 30 mm/sec
You have to arrange the parts in such a way that the ply wood is not wasted. We use circles to make drill holes in the ply wood so that while cutting the board is steady and doesnt move for smooth cutting. You have to make a separate tool path for the drill holes. The tool path for the drill holes came out like this.
And the tool path for the parts cutting came out somthing like shown in the image below;
Once the toolpaths have been generated, you have to save them in sbp(shopbot part file) format. Now we open the command console of the shop bot where the toolpaths will be uploaded and will be fed to the shopbot for cutting. We have to do zeroing here also just like we did during pcb milling and to do so you just click on the zero axis and then do the zeroing there as shown below;
Now you upload the drill hole sbp file first for drilling holes for screwing the board to the sacrificial layer of the shopbot machine and start cutting.
Once done with the drilling holes, you have to screw down the board to the sacrificial layer manually to keep the board in tact while cutting the parts. I screwed around 8 to 10 screws in the holes that I drilled before.
To start the process of cutting the parts, first you have to start by passing the command to cut from the command console and then press the run button from the shopbot which will initiate the cutting of the parts.
It took around 25 minutes for cutting all the parts. I took out all the parts for assembly and smoothening.
Since the cutting part is done, the CNC room was a mess with saw dusts everywhere so being a responsible CNC machine user I took a broom and started cleaning the mess that I have made so that the next person to use it will be able to use it straight away without any dust particles in the room.
Now I took the parts outside the lab for filing it and to smoothening the parts to make the finger joints fit perfectly. Took me around half an hour to do so.
Now the only thing left to do is the assembling of the parts. My shoe rack came out to be something like shown in the following image. These are the ready made parts for my shoe rack.
Design files(dxf)¶
DXF 1
DXF 2
DXF 3
DXF 4
DXF 5
DXF 6