8. CNC - Machining¶
Week assignment
- Test runout, alignment, speeds, feeds, and toolpaths for your machine (group).
- Make (design+mill+assemble) something human scale size (individually)
Group test¶
Machine specs.: RaptorX-SL
- Working area: 3,200 x 2,010 x 300mm
- Clamping area: X -3,500mm x Y -2,200mm
- Positioning speed X+Y/Z: maximum 40,000mm/min
- Working speed: maximum 20,000mm/min
- Step width X: 0.0213mm
- Step width Y+Z: 0.0113mm
General steps¶
- Measure the material. Each board could be slightly different.
- Prepare the file, we used RhinoCAM. This is the most time-consuming part.
- Prepare the file for the screws. Some boards could be bended so adding additional screws prevents parts from coming off.
- Upload files to the cloud.
- Fix the material to the table.
- Download the files in the machine computer and set the origin (X,Y,Z).
- Set the proper end-mill.
- Turn on the vacuum.
- Set the screws
- Start with the screws-file.
- Then, set the screws on the spots.
- Run the file with the design.
- Vacuum the wood chips.
- Take out the cuts, remove the end-mil and put it away.
For the test we used a 6mm end mill one flute o’flute. We left 30 mm to set the screws on the borders of the board and also created a screw file.
Test we cut.
Setting the files on the board area.
The first thing was defining the material size and creating a rectangle with the full shape of my board and do some points that will be engraved to position the screws.
Settings for the cut We used a ∅6 mm Down cut Flat end mill. The formula used to calculate the tool’s feed and speed was: Feed rate = N x CPT x RPM
- N = number of flutes
- CPT = chip load
- RPM = spindle rotational speed
These are the parameters we used:
Stept to set the machine¶
Position 0 of the machine is set by default on the bottom left corner. The X-axis is defined on the longest side of the machine.
Removing the dust collector makes it easier to change the tool. We used the machine’s wrench and key to release the collet and holder.
We decided not to use the right corner of the bed as it was not even. Overuse wore it out. So, we had to set the 0 for X,Y for the origin of our board. To set the Z-axis, we have the auto-leveler, which should be set right under the tool.
We use the remote control to be able to set the origin correctly, but it is quite annoying.
Things to bear in mind:
- Make sure dust-collector is on.
- Make sure you know where to find the emergency buttons.
- Wear safety glasses, closed shoes, and earmuffs.
- Do not go near the machine or put your hands on it while it is working, we only have 2.
In the image you can see how the piece came off while it was being cut. This was because the bridges were very weak. As the board was a little bit bended, or first piece poped out and we decided to change the bridges in order to get a proper cut.
When finishing a job you have to do the following steps:
- Move the axis away so you can reach the cutout pieces
- Turn off the machine and dust collector
- Proceed to remove the material. You may need a stake and a mallet.
- Clean the parts with the vacuum cleaner, they are easier to remove.
- When you’re done, vacuum your moo, take out your board, put it where it belongs same for the protective gear, and leave everything as you found it.
The speed test¶
The RPM/FeedRate test shows that the results were better using lower speed. We decided that the best parameter was a speed of 5000mm/min at 20000rpm However, the instructors recommended us to use a setting of 18000rpm at a feed rate of 5400mm/min.
Kerf test¶
The final test included:
- Thickness of cut for fit.
- Radius for fitting a wooden rod.
- Tab ladder fit with different lengths.
- Flexible surface with plywood.
Make something human scale size¶
For this part of the assignment I choose to do a stool that can be used as a small table. I wanted my object to be simple, versatile, portable and easy to disassemble so I could carry it in a suitcase.
I used Rhino to design my stool and I made a 3D model to be sure that everything matched. I just draw the outlines and change the colors of the layers to use them for the different processes. I wanted the stool to have a big handle and to look a little bit chubby. That’s why I decided to use the rounded legs.
In order to be sure that everything was going to fit toghether I overlaped them and check the tolerances. I used 2 different tolerances. For the legs I needed a tight joint and for the top part a more looser joint because it was going to be a not-so-perfect cut. Another factor to consider was that the wood I used was really soft. So, it was easily compressed.
After finishing my design I upload it to the cloud and open it again from the Lab’s compueter where I could access RhinoCAM. By this time, I had forgoten some of the settings I need to do in order to get a proper file to cut. So, I requied a lot of help fom Josep.
I decided to do a documentation of all the settings in case I have to use this machine again.
First, I measured the board that I was going to cut. There’s something tricky about the thikness. It might not be the same on different areas of the board. In my case there was 1 mm variation. My stool was pretty small so I decided to fit it on one side of the board.
Board size: 2500 x 1250 mm
I went back to the computer, created a board and set its size. Also, I selected the top point and afterwards I created a rectangle with a 30 mm offset were I was going to set the screws.
The distance between two parts must be bigger than 2 times the tool diameter.
I set the tool (6mm Flat end-mill) with the following parameters:
- Holder diameter: 30mm
- Holder lenght: 45mm
- Shank diamter: 6mm
- Tool lenght: 35mm
- Shoulder length: 27mm
- Flute lenght: 27mm
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Tool diameter: 6mm
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Speed: 18000rpm
- Direction: CW
- Plunge, Approach & Engage: 2250
- Cut: 4500
- Retract & departure: 2250
I took screenshoots of all the settings in case I needed to cut something else in the future. Certainly, this is something that I will not remember.
To define the tool I used the best test parameters on the group assignment. To define the tool I used the best test parameters on the group assignment. Josep recommended me to use 18000rpm for the speed.
To define the correct parameters to be used to mill we used the following equation: chip load = SPEED (mm/min) / ( RPM * Flute number) By knowing Chip load, RPM, and Flute number, we were able to calculate the speed: SPEED [mm/min] = chip load * RPM * Flute number
Screws settings I used¶
My board was a little bit bent and my stool was small, so I knew I was going to need some additional screws. During our class demonstration on how to set up the board, we learned that to add additional screws, we needed to create a file to avoid the machine milling over a screw. The settings I choose for this were the same ones that we used for the test. I took some pictures while we were defining the settings and I also reviewed this with Josep. This step is to secure the wood, which makes the process safer.
For this procedure, I needed the tool to engrave the points where I was going to set the screws. I used the same tool I used for the rest of the cut.
Joints holes settings I used¶
I used this to create the holes for the joints. One of the hacks they taught us was to create the joints by making controlled holes. The file is similar to that of the screws but instead of engraving the wood it makes a hole. So, I changed the total cut depth from 3 to 15.2mm. However, I had to lower the Rough Depth parameter to 1/5 of the total depth so that teh cut was gradual. I wanted to try this way of making the joints and I was surprised by how accurate the result was. Everything ended up fitting perfectly.
Pocket settings I used¶
To make the holes where the woods would fit, use the pocket. I wanted the joints to be visible so I had to be very careful with the tolerances.
Internal cut settings I used¶
For the internal cut, the handle, I had to be careful with the number and the size of the bridges. I didn’t want there to be too many, but I didn’t want my piece to come off before I finished cutting. I set them to 3. I chose them to be rectangular and put 4mm for both the height and the length.
Exterior cut settings I used¶
For the bridges I used almost the same parameter that I used for the internal cut but I added one more bridge. For the cut, I just changed the option for Closed Curves from Inside to Outside.
File ready to cut.¶
First I needed to run the file to set the screws points. Then I could get on the machine bed to put the screws so that my board does not move during the cut.
The cut¶
While the machine was cutting the pieces, I checked that everything was going well. There was a minor problem due to the plate being slightly warped.
Sanding¶
In this image we can see that the top piece was not perfectly cut. It remained like a sheet of thin wood on the surface. To solve this problem use four different sanding processes.
- Manual: Sanding papers 80, 120 and 360.
- Sanding power tool for the borders, the legs and the X shape.
- The Dremel for the t-bones holes.
- The Electric Wood Router to round the edges of the top piece and grip.
The bullnose router bit is designed to cut a perfectly shaped half-round profile.
Additional tools I needed when using the router:
- Wood jaws
- Sandpaper
Make sure you wear the safety goggles to prevent wood trimmings from getting into your eyes. Also, I didn’t practiced before trying on my stool and I burned the wood 😬
First things first, secure the wood, ensuring minimal movement when you’re working. Use wood jaws to prevent damaging the wood.
Then, Place the Router on the Tool. The router should have a long central crew where all the blades are going to be fitted. You may have to remove any blades that you have previously used then fit the bullnose router bit onto it. Turn it slowly until you have a small amount of it just below the router. Secure the bullnose router bit in place by fitting a nut onto the bottom of the long central screw.
When turning on the machine it is important to press towards the wood edge and move the lathe with a constant speed. If you stay in the same place for a while, the wood burns. If the pressure varies, then the surface will be uneven.
After finishing the job, smooth down the edge using sandpaper. This wood was extremely soft, so it was very pleasant to sand it.
The stool¶
Find all the files here: