Week 03 - Computer-controlled cutting

Goals

• Use computer-controlled cutting machines
• Caracterize the laser cutting machine (group assignment)
• Design a press fit parametric construction kit accountig for width and kerf
• Cut something with a plotter

Cutting tools

This week I was lucky to try our new waterjet machine! The model is a Protomax compact machine by OMAX.

The water is sent at very high pressure through a sort of nozzle containing a saphire. Some abrasive powder is also fed into that nozzle. The abrasive powder then takes the waterjet speed and is prjected towards the surface of the material. This machine allows us to cut a large variety of materials like metal, stone, glass...

We did a test on a 2-3 mm aluminium sheet.

The only parameter you can change in the software are:

• The cutting quality, going from 1 to 5 + a setting to move the head without cutting. The quality settings correspond to different speeds of the head.
• The path of the tool. Even using the auto mode you have to define the starting point of the path. Also, you have to take in acocunt that external cuts should be operated clockwise and internal cuts counterclockwise.

Here are some pictures:

Group assignment

One option for the group assignment was to characterize the kerf of the machine.

My comrade Lauriane characterized the kerf by cutting some square in 3mm plywood, then measuring their total length and comparing it to the length inside the whole. She found that the kerf is 0.268mm.

I was in charge of doing some power / speed tablesheet. Unfortunately this took me quite some time to execute each columns for a different speed, and at some point I didn't put my work at the correct origin (I still don't know if there's a way in Ruby to save your work's origin as in Job Control).

I finally gave up as this task was very time consuming but also felt quite pointless to me. Instead, I decided to do more kerf measurements, but for various materials and thus various power and speed settings.

Indeed, something bothered me about the kerf. I thought I heard during the course that the kerf characterized your machine (+ lens), but I believed that it would depend a lot on the power used (and thus correlated to the material you're trying to cut). I talked about such implications with people much more aware of optical science than me, and it seems that you have an Airy disk optical aberration on your focus point, which diameter is linked to the focal, the wavelength and if I'm correct to the energy of the ray.

I indeed found significative differences in my kerf measurements, and was satisfied with this first experiment with the kerf estimations.

See the group assignment page

Press fit kit

That was the big assignment of the week.

• Design: I decided to cut some little monsters with eyes, hands and tentacles. I wanted something quite funny, cute and wierd, and also use some curved shapes and no geometrical pieces.
• Machine: Lasercutting CO2 machine Trotec Speedy 360 120W with a 2,5" lens
• Material: I wanted to use black Carton Plume (approx 5mm thick), which consists of a layer of polyurethane (PUR) foam trapped between two layers of thick paper. I already saw that it can be cut with laser cutting machines (see sources below). I used Carton Plume from the Canson brand.

Caution Carton Plume resembles a lot to classical Carton mousse, but Carton mousse should absolutely not be cut in the lasercutting machine. It contains expansed polystyrene foam that burns and melts. Carton Plume is a labelled product that you can find under the brand Canson in France.

Sources :

• Trotec Laser website
• Wiki of Carrefour Numérique's Fablab
• Canson website
• I used this reference baught at Rougier et Plé

Speed and power settings

I also wanted to cut some test parts in rigid cardboard (approx 6mm thick). I tried quickly some good power and speed settings. For the Carton Plume I started with similar settings and it cut beautifully. I nevertheless diminished the power because there were some traces at the back. I ended up masing the back of my sheet with masking painter tape.

Settings for the Carton Plume approx 5mm thick:

• Power: 34%
• Speed: 0,8%

Slots tests accounting for kerf

I created a comb in Fusion 360 to use parameters for the thickness of the material and the kerf. I did a chamfer of 45°. I used a different value of the kerf (0.3mm) than what Lauriane ultimately found when checking afterwards (0.268mm). My slots have the following width:

• 1: thick - 2,5 * kerf
• 2: thick - 2 * kerf
• 3: thick - 1.5 * kerf
• 4: thick - kerf
• 5: thick - 0.5 * kerf
• 6: thick

I measured thick the thickness of the material with a caliper. For the cardboard I found 6.08mm and for the Carton Plume 4.90mm.

I exported these designs for carboard and for Carton Plume as dxf and cut two combs of each. Slots 3 and 4 were the better.

2D Design on Inkscape

I started creating my shapes in Inkscape. I wanted to visualize them and import them afterwards in Fusion to manage all the parametrics aspects for the press fit slots. I realised later that this was not as fluid as I expected.

Anyway here are my plain shapes without the slots:

Parametric design in Fusion 360

I defined some user parameters in a spreadsheet in Fusion 360.

Of course all the point of this slots is that they are correctly linked to the shapes. That's where it became a little bit trickier. Indeed, I've learned that importing a .dxffile don't allow me to use all constraints such as tangent. I thus finally used the following workflow:

• Create a new sketch on the xy plane
  • Import my .dxf file of the plain shape that I had previously draw in Inkscape
  • Move it where you have some space around
  • Finish sketch
• Create a new sketch on the xy plane
  • Create a fit point spline (closed) to fit the dxf curves in transparency
  • Modify its nodes and handles
    • If needed because I'll need to place a slot here: create a new node on the spline. For this you need to select the spline then right-click > insert spline fit point > click on the curve
    • Activate tangent handles by right-clicking on the node. The handles go from green to blue.
    • Finish sketch
• Hide the .dxf sketch
• Create a new sketch on the xy plane
  • Copy the original slot shape and paste it. Move it on the plane near your spline.
  • Rotate it and place it approx to where you want it to be, but not exactly (to be able to easily set the constraints) Important The slot must be placed on a convex face (meaning it its opening faces a concave curve).
  • Constraint the middle of the slot large opening to the spline node
  • Click on this node to make its handle visible (in blue, if not you need to go back in its sketch and activate tangent handle)
  • Click on the handle tangent then make it collinear to the slot large opening
  • You can add other slots according to the same logic
  • Finish sketch
• Create extrusion
  • Select the spline
  • extrude 'New Body' to distance thick
• Create extrusion
  • Select the slots shapes
  • Extrude 'Cut' to distance thick

Prepare the files for laser cutting

I had quite some troubles exporting and opening my file in .dxf to laser cut it. These are the problems I faced an the key points of how to solve them.

When you export your Fusion file in dxf you tend to export a lot of information you actually don't want, and some might even be missing. Also some splines are broken. To export the wanted geometries from Fusion :

• Create a new sketch on the xy plane
• Project all your relevant bodies shape on this plane. You need to select 'bodies' in the dialog.
• Create a rectangle around all the projected shapes
• Use the dimension tool to see (and if needed set to a simpler value) the dimensions of the rectangle
• Finish sketch
• Right-click and export to dxf

Unfortunately when I proceed this way I couldn't see correctly the dxf file in Inkscape. Indeed, it seems that Inkscape is not fully able to decypher dxf files. In particular splines were missing, which is annoying since I have a lot of them! That's how I solved the problem:

• I used an online converter convertio.co to convert my dxf to svg. I downloaded the converted svg file.
• When importing this newly converted svg in Inkscape, I can now see all the splines correctly, but the dimensions are wrong
• Lock the dimensions proportionnality
• Set them to the width of your rectangle in Fusion
• Set the stroke thickness to 0.1mm
• Set the rectangle width in Inkscape to fusion-rectangle-width+0.2mm
• Save!

Here are the shapes when I set the parameters as in the above window (for Carton Plume):

Operate the laser cutting machine

• Machine: Trotec Speedy 360
• Technical features: equipped with 2.5" CO2 lens or 1.5" CO2 lens
• Working area: 813*508mm
• Max. cutting thickness: approx. 12mm, depending on material
• Software: Ruby
• File formats required: prefer svg. Should also be compatible with ai, dxf, pdf, cdr + jpeg for engravings.

Safety rules

Some materials cannot be laser cut/engraved because they emit highly toxic gases, catch fire, melt or damage the machine.

Anyone bringing their own material must know its composition and provide proof of it, e.g. what type of plastic it is, could it contain fluorine or chlorine, etc.

You should always check that the focal length of the lens mounted on the machine is consistent with that indicated in the software and on the machine screen, and that you are using a suitable cone (long cone reserved for the 2.5" long focal length). The lens mounted on a grey frame has a 2.5" focal length, the one mounted on a red frame has a 1.5" focal length.

The operator must keep an eye on the machine at all times during machining, and be particularly vigilant for unusual smoke or flames. If flames appear, immediately notify a member of staff and be vigilant. If flames persist, switch off the machine by pressing the red emergency stop button. Use a CO2 extinguisher to put out the flames.

Once you've finished machining, don't open the hood immediately, so that most of the smoke and dust generated by machining can be extracted. Wait a few seconds until you hear a beep and the suction is quieter.

Switching on the machine

Make sure the top lid is closed, then turn the key clockwise. The machine switches on.

When switched on, the machine performs a number of initialization operations: please do not open the hood or touch the control panel until the operation is complete (indicated by an audible "beep").

Placing the plate

Open the cutting area and place your plate (after checking that your material can pass through the laser cutter); it should not protrude beyond the cutting area and should be as flat as possible. If necessary, elevate the table so that you can comfortably place your plate. This is done using the up-down arrows on the control panel.

Plywood less than 4mm thick can sometimes warp, so use tape in the corners to secure it to the tray and ensure that the board is flat.

Adjusting the height to the focal point

Because of the very principle of laser cutting, it's crucial that the (top) surface of your plate is positioned precisely at the focal distance of the lens, where the laser's rays converge.

At the Fablab SU, we can fit a choice of two lenses on the Speedy 360, one with a 2.5" focal length and one with a 1.5" focal length. It's essential to bear in mind which lens is mounted on the machine before preparing and starting any work. You can check this by looking at the lens ring on the head.

On the Speedy 360, focal length can be set manually using a template (each lens has its own template: use the gray template for the 2.5" gray lens, and the red template for the 1.5" red lens). The use of these markers is explained in the Speedy 100 documentation. They are stored in the red case on the left-hand side of the machine, on the lower cabinet.

But focusing can also be done automatically, thanks to an ultrasonic sensor positioned on the head. To set the focus automatically on the Speedy 360:

Move the laser head over the surface of your plate, roughly "in the middle" of your work. Check that nothing is obstructing the elevation of the plate. Check that the focal length on the machine's screen is the same as the lens mounted on the machine, and that the cone fits. This step is vry important, you may damage the machine otherwise. Simultaneously press the two up-down arrows on the Z axis. The platen moves up and stops at the focal distance.

Depending on their focal length, different lenses offer different advantages, making them more or less suitable for certain jobs. Similarly, several cones can be mounted after the lens. Note that the longest cone can only be used on the lens with the longest focal length (2.5").

If you realize that there's a problem (obstacle between the cone and the plate, wrong focus value on the computer, wrong cone mounted on the head...), you can interrupt the automatic focus by pressing one of the Z-axis arrows on the platen.

Reminder: the focus must be set each time a new plate is placed in the machine, even if it's the same material (small variations in thickness may occur).

Move the head to your work area

Place the laser where you want to start your work. You will then mark this location as the origin of your work.

• Usually, we use the top left corner as the origin of our work.
• Use the arrows on the control panel to move the head to the top left of where you want to start work (typically the top left of the plate if it's whole).
• A laser pointer allows you to pinpoint the position where the cutting laser will operate. If it's difficult to see on the plate, a blank sheet of paper can be placed underneath.
• Use a ruler to check that your work will fit into the planned position (especially when using a chute).
• If you're working on the edges of a plate, be sure to leave a 0.5 cm margin with the edges to avoid fire starting.

Bear in mind that you may first run a cutting/engraving/marking test on your plate or on a scrap before starting your machining. Find the right place for this little test to waste as little material as possible.

Preparing your job on Ruby

Ruby is the software used to prepare your job for the Speedy 360 machine. The interface is accessible from the browser. Use the shortcut on the desktop and register using the credentials shown on the green post-it note stuck to the tower.

Home screen

You can create a new template, import a file or use one of the templates in the list.

The workflow from model to machining is symbolized by the icons at the top of the interface. This menu allows you to switch between the different stages.

Check, modify or design the model

See the documentation provided by Ruby on the Design screen

Prepare for machining

See the documentation provided by Ruby on the Prepare screen.

Start machining

See the documentation provided by Ruby on the Produce screen.

Fabrication

I could first test on cardboard (this made me resize the slot deepeness d to a smaller value).

Then I cut my first elements in Carton Plume. I had to change my wvalue a few times (despite the comb, I was quite tired at that moment). Finally here are some tries with a little number of elements:

I liked it and cut more elements.

In the background you can have a preview of the deisgn I cut with the vinyl cutter.

Vinyl cutting machine

Design

I made an illustration of my press-fit kit. I used the plain elements designed in Inkscape, created a grid and added some text.

Here is a small test on this textile. I liked the texture of it (test n°1 and 3, the n°2 is a different flex so I didn't use that one)

Here is the design preview:

Here is how I made the grid design:

Operate the Graphtec Cutting Pro

Features

• Description: Plotter with a small cutter for cutting vinyl, flex, flock, cardboard...
• Maximum cutting width: 762mm
• Maximum plot length: 15000mm
• Usable film width: 920mm
• Compatible materials: Marking film, PVC film, fluorescent film, reflective film, polyester film (under certain conditions)
• Software: Graphtec Pro Studio
• Required file formats: dxf

Steps to operate:

Load material

• Position the roll of film between the two metal bars at the rear of the machine.
• Insert the front of the film in the cutting area, ensuring that the general lever are in the upright position and do not block film insertion.

The lever can be seen in the back, on the right of the machine

• Position the film correctly sideways: the left edge should be under one of the blue locking points, and the right edge under the blue locking line. Lock the smaller levers in the correct position.

Here you can see the smaller levers, behind the machine

• Position the front of the film correctly: the edge should be on the dividing line between the gray and black areas. You can recut the film if needed.

• Lower the large lever on the right
• Lock the roller to the rear of the machine, holding it in place on either side with the black clamps on the metal bar closest to the machine.

Detect material dimensions

• Switch on the machine (lower left switch)
• On the machine's control panel, click on 1 - rouleau limite avant. The machine will locate the left and right edges and move the front edge of the film back to the cutting area. If you're using a single sheet and not a roll, use option 3 - feuille

Start a test run

• If necessary, move the tip sideways to the desired origin and click on origin to redefine a new origin.

• On the machine control panel, click on the Cond/Test button for the first time
• Select configuration according to film type (condition 1: settings for classic indoor vinyl, do not modify)
• Click on the left arrow indicating the small test triangle in a square.
• Then click on enter
• The test starts. If all goes well, you can move on to cutting a file from the computer.
• You can also run tests directly in the software. It's often preferable because it will use the settings you update in the software, so it's an easier workflow if you don't rely on fixed presets.

Preparing your file on Graphtec Studio

• Import the dxf file to be cut

• Check dimensions

• Launch the Cutter menu from the top horizontal menu.

• Connect the machine thanks to the USB cable: it should appear on the right in the list of cutters, with the status Ready. A preview shows you where the work will be cut. If necessary, you can reposition it by modifying the position values.

Note: the bottom of the preview normally corresponds to the front edge of the film.

• At this point, you can also decide to mirror your design (icon "F") for flocking, or run several copies of the same design (the software automatically arranges them), or run the job several times in succession.
• You can then adjust the cut settings in the right menu: force, speed and acceleration.

• It's better to run a test from here, by clicking on the Test menu on the triangle shape.

• When you're satisfied with your settings, place the tip at the origin, click on origin, then click on the 'Send' button.

Unload the roll

• You can move forward the film to get a better view of the job, using the arrows on the graphtec panel.
• Unload the roll by lifting the locking wheels and the right-hand lever.

Fabrication

Material: cotton thick textile slightly waxed, white flex, fluorescent orange flex.

When flocking on textiles you have to be careful to:

• Cut the correct side of the flex (not the rigid plastic)
• Mirror the design

Here are picture of the press-fit kit + the plotted design:

Files

• Fusion 360 parametric CAD file

• Press fit kit export in .svg for 4.9 thickness, 0.268 mm kerf and 1.5 kerf correction

• Plotter svg file for the orange flex

• Plotter svg file for the white flex

• Power/Speed characterization svg file - text not vectorized

• Power/Speed characterization svg file - text vectorized