8. Computer controlled machining

This week I worked on designing something on a meter scaled, and milling it on the big CNC.

Assignment

   group assignment
      do your lab's safety training
      test runout, alignment, speeds, feeds, materials, and toolpaths for your machine
   individual assignment
      make (design+mill+assemble) something big (~meter-scale)

Dimensions: 800 mm x 450 mm x 500 mm

Design on Fusion 360

Autodesk Fusion 360 is a software I used to design 3D shapes. I already discovered this software during my CAD week

We need to install a plugin in Fusion that will be useful for the design. It is Dogbones, we will use it at the really end of the design because it is hard to go back in the history and change after.

Here is the plugin for the dogbones

We will also need to arrange some parts in the design, the “arrange” box needs to be checked. Go in profil, preferences, design, check arrange.

So the workflow is first I need to draw the object in Design and then go in Manufacture.

First I wanted to draw something that fit with many rectangles, I started to design a box, with each piece assemble with kind of notches rectangles.

I draw the shape roughly by hand and add all the constraint to have the result I want.

But it was really messy and it took a lot of time.

So I decided that, for this week I will design a furniture for my van. My van is still under development and I have some ideas of the furniture I want to add in my van like a library or a chair with storage under.

First we drew on a paper the kind of furniture I want. I will do chair mixed with a storage cabinet under the bed. With my instructor we tried different kind of furniture I can have in my van, with different kind of furnitures, and the way to assemble it. We also took the measures directly on the van.

First I draw roughly the sketch in 3D with drawing on a sketch and some extrusions.

I designed a sketch with the value I took.

Then I extrude it from the height I want.

And I designed sketches on the face. I extrude it at -412 mm, because the thickness of the wood is 18 mm.

Then from that I did on each part of the furniture the sketch of the lines by projected some lines and I draw the rectangles that will do notches between two boards. I was inspired for notches by furniture that was made last year.

I drew each rectangles one by one by hand. I added constraints of equality between them and set one line at 30 mm, all the design change to have the rectangles equals. It is not really parametric design but if we change the value of 30 mm, the all rectangles will change, we will have to remove or add some rectangle to fit in the length of the shape.

After each sketch, I did an extrusion of 18 millimeters, the supposed thickness of the wood I will use. I did one extrusion directly according to the furniture body in doing a new body. And another one with an offset, to be farther from the furniture, just to see how the plank of wood will be.

I measured the thickness of the wood and it was almost 18 mm. I let 18 mm in my design to have a small clearance and be sure to mill it until the end of the wood. Thanks to the tests made in group assignement I know that there is not much clearance needed for the shapes to be press-fitted.

Then my furniture is fully done, and made up seven bodies.

From the bodies I extruded with an offset, I rotated them and put on the same plane to be able to have them on one piece of wood.

In red it is the final shape design, in blue it is each piece put on the same plane.

Then when all the shapes are plane, I added the dogbones thanks to plugin previously installed. I put dogbones with the diameter of tool I will use, a 10 mm milling bit.

I checked the measure of the tool, and checked if the 10 mm wirttent on the tool, is the same measure. I used a calliper to mesure it.

The dogbones are really important to add at the really end at the sketch. I tried to draw another 3D shapes after finishing those ones on the same file but Fusion didn’t want to add the dogbones from the plugin.

In manufacture, the workflow will go from left to right.

First I need to set the size of the wood I will cut.

Click on setup and the folder icon.

Here I will setup the milling, the model orientation with X,Y and Z. Y is the longest part on the device and Z is the milling down thickness.

The positive values of X will go to the right and Y go to the background. I select the orientation, and I can also draw some line to tell what is X, what is Y. This step is very important because it will influence the rest of the work.

I select the origin, the box corner.

The orientation needs to be really checked, to not do dangerous things. Then memorize the origin for when I will use the device.

I have to check that the dimensions are smaller than the piece of wood that will be cut.

Then I set the milling, there can be 2D milling or 3D milling, it is different kind of strategy of milling. Milling is removing material.

We need to define the tool that will be use, and also the speed of working.

The tool we will use has to be created.

It is a flat end mill. In the settings of the creation, cutter is where we set. It is a 2 flutes. We define all the length, the flute length (where we can mill). Cutting rate is where we can set the default value if for example we cut always the same material. For example cutting feedrate can be 3000 mm/min, the spindle speeed 10000 rpm. On post processor, we have the tool changer in the deivce, we have to tell on which number is the tool.

After select the tool, it put all the default parameters.

Geometry is where we want to mill, most of the time the bottom of the shape. We can add tabs. In action, we can see the simulation.

In passes, we can add the multiple depth, it is the maximum I can go down, for example 5 mm with a 10 mm tool is fine.

Then take time to check the simulation. If there is red stuff, it means that there is collision or problem. In simulate, statistic we can see the time of the milling.

I got some problems with the milling because of a too small piece on the design on this corner.

We can see that with the tool set for the manufacture, a 10 mm end mill, it doesn’t go on inside the corner.

Here is the error I get.

I tried to put a spearation between the contour and the hole but it didn’t work.

After thinking to a solution, trying to cut the piece with a diagonal cut to let the mill pass. I finally decide to remove the small piece and fill the gap at the opposite.

On the piece at the back of the furniture, before:

After:

To have a good milling process, I first cut the holes. The whole piece of wood is well maintained by the suction. If I had cut each piece of wood for the furniture first, it might have moved and do messy stuff.

So I selected all the holes to do the first file of the cutting.

Because of the tool I will use, a 10 mm flat end mill, I set multiple depth with each passing at 5 mm, the half of the diameter of the tool.

Then I selected the contour of each piece and set the same parameters.

I made a previous test with taking a corner of the furniture, to test that it fits well. I drew a sketch on the pieces, with rectangles. Then I extruded each piece of 18 mm and creat new bodies, and I moved them to be cut.

Then in actions, post process Fusion will generate the gcode for the machine. The machine is Mach2Mill.

Then open the gcode. The line G43 Z15.H8 needs to be deleted. (It is a compensation, the tool will mill 15 mm above).

Save, and then change the file format in .nc.

As a reminder :

  • First setup, the material size
  • The strategy
  • Contour is what we will use mostly for this week, or pocket
  • Select the operations
  • Simulate
  • Post process
  • Select the good machine
  • Delete the Z… on line G43

Here following the main parameters of the milling:

  • a 10 mm flat end mill tool (put on the 8 on the tool changer)
  • spindle speed: 10 000 rpm
  • ramp spindle speed: 5 000 rpm
  • cutting feedrate: 2 500 mm/min
  • lead-in feedrate: 2 500 mm/min
  • lead-out feedrate: 2 500 mm/min
  • multiple depth
  • maximum roughing stepdwon: 5 mm
  • tabs for the outlines of each piece

Test (from the group page)

Red shape : test of the Y axis with several widths. All these tests were carried out with the 2D Contour tool. Our speed was set at 2,000 mm/min for a speed of 10,000 rpm and removed 5mm of material at each pass. Results: - The leftmost line was not cut as it was too small in width for the bit: 10mm for 10mm. - The middle line was well machined. After having measured the passage of the milling cutter we observed a difference of 0,1mm between the drawn widths and the reality. - The rightmost line was well machined. However, during the machining process we observed a lot of vibration, which led to large deviations in the measurements. In some places (in the middle of the line) there were deviations of up to 0.5mm. - The lines are well within the required length of 800mm Conclusion: the machine is accurate to the hundredth on its Y axis. In addition, be careful with the spacing between two parts, vibrations can occur and create an inaccuracy of the dimensions.

Green shape : X axis test. This test was carried out with the 2D Contour tool. Our speed was set at 3,000mm/min for a speed of 10,000rpm and removed 5mm of material at each pass. Results: - The line is the required length of 617mm - There was a difference in measurement of 0.1mm Conclusion: The machine is accurate to one hundredth on its X axis

Purple shape : Z axis test. All these tests were carried out with the 2D Pocket tool. Our speed was set at 2,000mm/min for a speed of 10,000 rpm and we removed 1mm on the first pass, 2mm on the next and 3mm on the last.
Result: - Very accurate work from the machine we found no differences in dimensions. Conclusion: This machine is very accurate on its Z axis.

Yellow shape : Test of the interior angles with the dogbones and precision of the cutting. This test was carried out with the 2D Contour tool. Our speed was set at 3,000mm/min for a speed of 10,000rpm and removed 5mm of material on each pass. Results: - The dogbones were well made and allowed for the insertion of a shape with a right angle - The dimensions are exactly respected. Conclusion : The dogbones plug-in can be useful for our project.

Orange shape : Test of the trace tool. Single pass at 1000mm/min and 10,000 rpm for the spindle. Working depth 18mm. Result: - Very precise work, we also observed a difference of 0.1mm in the middle of the part, probably due to a too high stress on the bit which caused a vibration. Conclusion: Interesting result but will not be used for our personal work. This technique requires a lot of time and creates important constraints for the tools.

Black shape : This test was to find the value of press-fit. We did a test in cutting some holes at different values: 25.5 mm, 25.3 mm, 25.1 mm, 24.9 mm, 24.7 mm, 24.5 mm. We also did a shape to test these differents holes, a notch at 25 mm.

Result: - in the OSB wood, a 25 mm notch fir in a hole at 24.9 mm, so we don’t need clearance to do a press-fit. This test is working only for the kind of wood we cut, OSB. If we want to use another kind of wood, like okoume, we have to do again some test before milling the whole shape.

General conclusion :

Our professional machine is accurate on all these axes. Slight inaccuracies on the X and Y axes were found due to high stresses which led to vibrations. For our own work we can use the speed values of 3,000 mm/min for the feedspeed, 10,000 rpm for the spindle and 5mm thickness for the multiple depth.

Milling on the big CNC

The machine use for the milling is a big CNC with many part on it. There is the table where we put the material, with a sacrificial layer made of low density MDF. This table keep the material in place thanks to an air sucker under the table. The dimension of the maximum piece we can cut is 2400 mm by 1200 mm. There is some valve to open the air suction. Then there is 3 axes we used for the milling this week, X, Y and Z. There is a dust collector with vacuum of dust.

The machine works with command center with the button that up or down the skirt (1), the suction of the table (2) and the dust collector (3) switch on off buttons. There is the stop button use to trun off the device (4) and an emergency stop (5).

At the back there is a rack to hold the differents milling tool. It is improtant to select the right tool in Fusion, otherwise the machine will change the tool, it works with numbers from 1 to 8.

The dust is collecting in kind of trash can.

At the bottom of the device, there is a cooler to cool down the motor of the spinning of the tool.

The milling bit is old in a collet, that is screwed. The black object is the skirt, that help the dust collecting, it can be up or down, according to the position to the button on the commander center.

There is different size of collet, that match with the size of the milling bit.

First, switch on the machine by pushing the green button. Let the machine do the home process.

On the device remote. First we have to select output 6 so that the skirt goes down for the vaccuum of the dust. The output 6 has to be turned in red in the input / output menu. Then go back to the menu. Mode change the mode of moving.

The tool switch button in blue is to change the tool on the rack, and select the tool (3).

Then do the X and Y manually. Push on XY -> 0 (2). Then there is the toolset button to do the z at 0 automatically (1). We need to plug the probe height of cnc (in metal) to the device and the pliers to something connected to the milling bit. And then push the button. The Z has to be done with depressure.

To launch a file from the USB, click on file (4).

To do the Z, first we test the conductivity by holding the probe height in the air, to test that the device is seeing right the detector and won’t plung through the material.

Then we can do the Z on the wood with the suction depresure.

Here is the value, Z = 29.3 mm shown on the remote when the milling bit has touch the probe height.

For the machine maintenance, oil needs to be put on the rails. To do the, just pull lever and it will put a little amount of oil on the rails.

We also have a vacuum cleaner to suck up the excess of dust made by the milling.

So the correct tool has to be selected, then launch the file from the USB Key, check the output 6.

Apply the dust extractor, switch on the depressure and put on the skirt (on 1 on the command center) but we can lift it up to see.

The wood I used to mill my furniture is okoume wood.

One sheet of this wood is 2500 mm. Because the device only handle a piece of wood of maximum 2400 mm we have to cut to fit it well in the device.

We first try the device with the group of students we are at my lab, Agrilab. Here is the link to the group page about the work we have done in group this week.

First I launched the test to try to assemble the pieces and test if it fits well together. Took one of the corner of the furniture I designed. For this previous test, I was very lucky becuase it fits perfectly, the pieces didn’t move from each other, I didn’t believe it would work and I thought I would need to do the design again.

When the milling was done, the outlines of the test shapes were not really well cut. My instructor helped me in putting 0.3 mm lower for the height of the cut. To do that we place the milling outside the wood, have the tool at z = 0 with the remote arrow, and set the tool at z=-0.3 mm, and then click on the button z->0 to set a new z.

So now I started to launch the other files, one for the holes and one for the outlines of each part of the furniture. Here is the milling when it is processing.

And here is all the pieces when the milling has ended.

I was very surprise because the time was different from the simulation.

The first file for the holes was supposed to be 15 minutes and finally took 45 minutes for the milling. I assumed that the simulation didn’t take in account the fact that the milling bit take time to plunge and go up between each layers of the hole.

For the outlines it was almost the same, it took 33 minutes instead of 28 minutes for the simulation.

We can see clearly the tabs I add for the piece that will not move. I removed them with a cutter and it went pretty well to remove it.

We assemble the furniture with a hammer, but that was not really hard. Here is the video of the piece of furniture that assembled. (5 minutes)

And tadam, when it is assembled I can stand up on it, it is pretty strong.

And it fits in the van.

Before:

After:

Now I need to sand down the side to remove properly the tabs and fix it into the van and be smoother.

All the files

The Autodesk Fusion 360 file is about 20 Mo, I uploaded it in 3 parts. To open it download the 3 parts and click on the .zip.