Computer Controlled Machining
CNC What is it?
Computer numerical control (CNC) is a manufacturing method that automates the control, movement and precision of machine tools through the use of preprogrammed computer software, which is embedded inside the tools.
CNC is commonly used in manufacturing for machining metal and plastic parts. Mills, lathes, routers, drills, grinders, water jets and lasers are common cutting tools whose operations can also be automated with CNC. It can also be used to control nonmachine tools, such as welding, electronic assembly and filament-winding machines.
Materials and equipment
- CNC machine
- 18mm MDF
- 1/4'' mill
- Safety equipment
First of all, we must bear in mind the identification of the CNC equipment
Generic CNC machine: The machine in charge of carrying out the roughing and cutting of MDF for our project. Workarea: 122 x 244 cms.
Chiller: The equipment that has the function of cooling the spindle that rotates at high revolutions. It should always be kept at room temperature.
Dust extractor: This equipment has the function of extracting the dust and chips generated by the CNC milling machine. From time to time you have to do the respective cleaning.
Security zones are also very important.
The CNC milling machine has an area delimited with a yellow tape. The marked area must be respected for the safety of the operator.
Finally the Personal Protection Equipment (PPE) to work safely on this machine.
In this case we need the mandatory use of ear plugs to mitigate the noise generated by the CNC machine and dust extractor. The use of gloves to handle MDF sheets and fasteners is very important to take care of our hands. The use of minor tools is also necessary to extract some pieces of the platform.
Finally we installed the milling cutter in the head to get our machine ready.
My Design
In this activity I decided to design a Montessori table and chair for kids.My goal is inspired in the image below.
Design Process
STEP 1:
Determine the measurements of the table. Using AutoCAD software, the table was drawn. Width 5 cm for joints.
STEP 2:
A 2.4mm depth of MDF material was used for this design, so the height of the joint will be 2.4mm
STEP 3:
As well as we kwow, the borders will be circular beacause of the cutter, so , for best results we need to make additional circles on corners, like image below. We use 0.5mm of circular radius.
STEP 4:
In the tests we realized to consider a tolerance of 0.05 cm (0.5 mm) in both sides.
STEP 4:
Completing the design of the table.
STEP 5:
Now, the design was exported in DXF format.
STEP 6:
Next, the DXF exported file was imported on Rhinoceros 5 software.
STEP 7:
We can see the design in all views (Top, front, right, perspective)
STEP 8:
Activate RhinoCMA 2018, MILL.
STEP 9:
We'll see some options for MILL. Select Stock Box. Copy Model Bounding Box, Height (H), and set 24 mm.
STEP 10:
Select Align, Set World C.S. option. Next, select Set to part box, Highest Z, South West.
STEP 11:
Next, select Work Zero option. Select Set to Stock Box, Highest Z, South West.
STEP 12:
Those settings are set to align x,y,z in zero.
STEP 13:
Next, the milling settings. Select 2-axis dropdown list and choose Profilling option.
STEP 14:
Select curves or edges, first for inside elements.
STEP 15:
Now configure the Profiling Parameters, Tool option, Select Flat Mill and set 6.35 mm on tool diameter (1/4 inch), next put a name for new tool.
STEP 16:
On Entry/exit parameters, set None in Entry Motions and None in Exit Motions.
STEP 17:
On Cut Levels, Set total depth 25 mm, (1 mm additional tolerance). Set Depth Cut to 8. This means 3 passes of 8 mm and last 1mm.
STEP 18:
On Cut Parameters, check Use outside/inside for closed curves box. Now select Inside. Then select Generate button.
In Feeds and Speeds menu, I can set the parameters of the feed rates. The most critic for me is Cut (Cf) and Transfer (Tf). The units are in mm/min.
STEP 19:
Repeat the process with outside curves/edges . Use the same cutting tool settings, on Cut parameters change to Outside. Then select Generate button.
STEP 20:
Next, Put the inside options first, outside after.
STEP 21:
Finally, Select Setup1, right click, select Post. Type a name, check .nc extension (G-code). The copy on usb drive.
Cutting Process
We assuming the MDF board is correctly adjusted on the platform of CNC machine. A 1/4 inch diameter cutter ready to cut.
STEP 1:
Put USB stick on DSP.
STEP 2:
Move axis X+ X- Y+ Y- Z+ Z- to calibrate the axis x,y,z origins using the DSP, next save position with XY-0, Z-0 buttons.
STEP 3:
Next, push RUN/PAUSE and select the .NC file we generated on Rhinoceros 5 software. Then push green button OK to start the cutting process.
STEP 4:
Some photos of the process.
STEP 5:
We did the similar steps, but now for the Montessori chair.
Download
Project files and plans are available here
Takeaways Assignment
- I had to be very careful on this type of machine, since it uses rotating tools at high speed. Use the corresponding PPE.
- The lace technique helped me a lot to make a piece of furniture, however, the milling tool, being cylindrical, does not leave the cuts straight, therefore the dog bone technique must be performed, so that it can fit perfectly.
- It would be very useful to use a vacuum bed, since placing adjusters loses working space.