Computer Controlled Machining
Week 08
This week we dealt with the handling of a large CNC machine. In the group assignment we should test runout, alignment, speeds, feeds, and toolpaths of the machine. In the individual assignment we should make something big with this machine.
Group assignment
For this week it was necessary to drive to the FabLab Kamp-Lintfort, because neither my FabLab DEZENTRALE Dortmund nor the FabLab HRW Bottrop have a big CNC milling machine. A little trip, one might say. Where is this Kamp-Lintfort? Far away, off the track, somewhere on the A40 and then almost near the Netherlands. So get in the car and let’s go. After an hour we finally arrived, got out and admired the FabLab. A dream for students. If something like this had been offered to me earlier as a student, I would have been deeply thrilled… If only the Ruhr area had something like that (call!). Here are some impressions of the really beautiful FabLab Kamp-Lintfort:
Especially beautiful the wall full of exhibits.
Many thanks at this point to local instructors Ahmed and Marcel from Kamp-Lintfort, who kindly took care of us for this assignment and also looked after us during this time! Thank you, I had a lot of fun with you!
The complete range of fab tools, workshops etc. can be found on the FabLab Kamp-Lintfort website.
Safety instructions
Next, we received a safety briefing for the large CNC machine from the local main instructor Ahmed. I am very grateful to him for the friendly reception and care on this day. It is the machine elsign EasyWorker MasterPro 2513, which has a working area of 2600 x 1400 x 300mm, the machine has a general dimension of 3200 x 2300 x 1700mm and has a weight of 1400 kg. The Axis resulotion is 0,02mm and the precision of repetition is specified as +/- 0,005mm. The spindle can reach a maximum speed of up to 19.000mm/min. The machine was explained to us from all points of view, then possible dangers were mentioned. There are countless safety switches, at every point of the machine including the remote controller. Here some pictures of the machine:
Preparing the CNC-machine
The machine has an automatic toolchange with 6 slots. 5 of them are filled with milling cutters with different diameters. In slot 1 there is a 2mm milling cutter, in slot 2 there is a milling cutter with 4mm and further up to 10mm in slot 5. For our projects we will take the milling cutter from slot 2 with a diameter of 4mm.
The control of the CNC machine runs via a control station which is directly connected to the machine. We have received a comprehensive introduction to the software, including possible sources of error. We used the CNC control software from elsign, which also generated the paths for the machine for us. After having learned how to handle this user interface, we were now allowed to do the practical part.
The machine can be controlled via software or remote control. Here is a video of the homing and the manual control of the machine.
After resetting the machine, we had to home it first, i.e. tell it where the endstops and the position x=0 / y=0 are in the absolute range. Then we wanted to determine the tool length again. We could find this out with the help of the tool length measurement tool, which we placed under the milling cutter. We approached it with slow step numbers and then activated the automatic z-measurement function. Then it moves slowly and exactly until the probe is triggered. The program automatically calculates the length and calculates the correct parameters for the tool and the Offset z-heigh. The whole thing looked like this:
Before we were allowed to start, we had to buy wood for milling at the DIY store. I decided to buy screen printing plates with a thickness of 15mm. Screen printing plates are multiplex panels in which a screen is pressed onto the plates during the manufacturing process. The result is positive screen prints with many small dots or negative screen prints with small indentations.
I placed the material on the top and determined the offset, i.e. the relative point to the absolute point, which will later be the starting point for the object to be milled.
The vacuum table also had different surfaces, which could also be controlled individually.
Last but not least, you have to consider three points regarding safety before you can theoretically start the machine:
- Is the dust holder down?
- Is the vacuum pump on?
- Is the ventilation system switched on?
The ventilation system? The FabLab is very well equipped and has its own adjustable ventilation duct. These can be adjusted by rotary switches so that, depending on the machine used, the exhaust air is only exhausted where it is needed and thus no unnecessary power is lost.
Test object
I needed another test object that I could mill. For my later idea I had to have something that really fits. So again a press-fit construction. This led me to design the following parametric objects. I measured the parameter material thickness with the help of a caliper on the wood itself. The following model was created:
The file had to be exported in DXF format from Fusion 360 and loaded into Rhino to merge the lines there. There was another advantage of Rhino: you could specify different layers and later tell the machine what the outside, inside or pocket layer is. When you load a DXF-File, measure everything again. I had somehow a bug with the software (WIP-version) and the scaling wasn’t right. When reloading the DXF file everything was correct. An additional version that rotates the content was also created.
You had to execute two commands: Explode and Join.
After getting to know the machine under all relevant aspects and creating a template, we had to approach the software and load the dxf files. We entered the parameters directly, which were later relevant for us. In my case we only needed the offset mode. Then we had to load the data relevant for the material. The starting position had to be defined, where I decided to go down left. This is the point that corresponds to the previously relative “work” value X/Y 0/0. At the end it looks like the following:
Milling
Everything was ready to go - now it’s time to press the start button. I did my test runout with the previously described object. It was about finding out how good the alignment is for the CNC machine. The measured layer thickness should be about 15mm from the material bought above, the screen printing plate. In distances of 0,1mm the distances increased from gap to gap. The milling process then looked as follows:
The result was that the gap of 15.3mm was ideal. Accordingly, I added another 0.2mm, so it was 15.5mm at the end.
Individual assignments
Design my bookshelf
Now to my main task for this week: Make something big. Something big would have been a wardrobe for me - but not possible in one week incl. reasonable planning etc.. Apart from that I have a very nice and big solid wood cabinet. I don’t need to replace it. But in the new flat there is still plenty of space and for my household some objects have space requirement: books. Where to put all the books and literature. Sort them out? I already have - Magic Cleaning. Quite a lot has already been distributed outside. But another one or two bookshelves would be excellent! So I looked at two places. In the living room a big one made of solid wood or in the kitchen a smaller one, but perfectly fitting for the height of the window. After a joint discussion at home, we decided on the kitchen mini-bookshelf. So: make me a small kitchen mini-bookshelf. The first brainstorming was as follows:
An important special feature for the home is that the home must be robot vacuum cleaner compliant. After that, we always aligned all the new furniture. This, too, must for the most part conform to robot vacuum cleaners. Otherwise it is unacceptable. Thanks here to Xiaomi for commitment and development in this area. Our robot has the name Kiko and it’s hard to imagine the household without it. Let’s go to Fusion 360 and drawing:
There are many different ways to create edges in a milling model. There are different approaches and for each case you have to decide for yourself what is the most reasonable way. In my case it was about making the edges as good as possible so that later the small edge is connected directly to the other edge. A possible solution is a dog bone, which is a hole that is made at the corner to the edge so that the cutter can use this path and no rounded corners arise. There are several plug-ins for Fusion 360, such as Dogbone from DVE2000 or Dogbone from tapnair, which I used. After selecting the surface, the tool calculates the dogbones itself and draws them in. For some reason these were not considered later. Here only the hint for it. The files were then edited in Rhino like before:
After the model has been constructed in Fusion 360, the export as *.DXF to Illustrator has been done and since all elements have been merged, we now come to the main event. We start with the horizontal element.
After the machine has determined all zero points, the file has been loaded properly and all settings like ventilation etc. have been checked again. Now it could finally start. After the horizontal elements the vertical elements followed.
Towards the end: stacking, transporting home and assembling!
Here you can download the STEP-files for the mini-bookshelf and the test object:
Mini-bookshelf files
Test object files