3. Computer Controlled Cutting - Personal¶
Part two of this week is to work on a personal project to explore using the various CNC cutting tools in the FabLab. For this project I decided to focus on a laser cut version of one of my final project proposals, a parametric cast / brace with a sensing apparatus for things like swelling, excessive force etc.
Goals¶
- [x] Cut something on the vinyl cutter Design, laser cut, and document a parametric construction kit:
- [x] accounting for the laser cutter kerf
- [x] which can be assembled in multiple ways
- [x] extra credit include elements that aren’t flat
Tools Used¶
TLDR; Nice images¶
1. Vinyl Cut a Thing¶
I was focusing on the design of the brace so for my vinyl cut project I decided I wanted to see some of my parametric forms in different colours.
Our machine is a Roland GRS-20, It was setup with a 45deg blade.
I pre-cut my vinyl into more manageable sections
- The rollers of the machine must be positioned such that the are on the material and also within the white highlighted area.
- The area between the inside of each roller determines our cutting area so it is usually a good idea to maximize the distance without causing issue where your vinyl can come loose when moving.
- Another key consideration at this point is that the piece so that is covers the light sensor on the front of the machine. this is used to measure the piece so it will throw and error if not done.
The clamp on the back of the machine is engaged, holding the vinyl in place
Select piece from menu
Note this dimension as this will be the art-board size in Inkscape
Open a blank Inkscape file and bring up document properties with cmd-shift-d. Enter the piece dimensions from the machine
Note the force setting for the machine, in this case:
- 20cm/sec for feed rate
- 90gf for knife force
- 0.25mm for offset
These are our standard setting for wall vinyl with a 45 deg blade.
Examples of different blade angles colour coded
Import artwork, I used .dxf as I find if very reliable for cutting and holding scale
Position artwork on board
Use cmd-p to print the piece and select the vinyl cutter from the menu. Under additional setting use Get from Machine to update the size to that of the current work-piece
Hold piece up to light to see cuts
For my second and third colours I added a box around each piece to make weeding easier
Lightly score the vinyl with a scalpel to separate the pieces from the rest of the vinyl
Pull away waste
Additional boxes make weeding more manageable
All three colours
Pre-cut some transfer tape and apply to the top of each piece
Trim around each piece to create a sticker
Then I cut each one into individual pieces
Cleaned down my laptop and chose where to stick them
Used tack tape to peel vinyl away from backing. Note; that if it wants to remain on the backing applying pressure with back of your fingernail can help
Place piece on laptop
Remove tack tape
Repeat for the rest of the stickers
And clean up after a job well done!
2. Parametric Brace¶
Design¶
For my parametric design i wanted to create a laser cut version of one of my proposed final project ideas using kerf bend cuts. There are 3 pieces that can be customised using parameters in Fusion 360 and when assembled form something that resembles a brace. While I more than likely will be 3D printing my final project I wanted to experiment with this model as laser cutting is so much faster to iterate through a design. I also like the possibility of including kerf style cuts in my print to allow select areas of the design to flex.
My idea started with a quick sketch as i find even the most basic one invaluable when working in cad
You can see the three different components:
- The angle bracket (Blue) that can be controlled in thickness, length and angle
- The bridge (Purple) that can be controlled in thickness, length
- The flexer (Red) that can be controlled in length
I started with the angle bracket, using the line tool to draw the basic shape
I then start to use sketch constraints to define my shape. Here the points on the right are made coincident
equal length constraints are added to the sections and the ends
I set up parameters for the key dimensions
And start to apply the parameters using the dimension tool in the sketch. Note that parameters can also be used in formula in the dimension
I add more dimensions including the angle
The shape is extruded using the e key from the sketch environment, the distance is the to the material thickness parameter
I create a sketch on the face of the part, the midpoints of each line are used to define the slot positions that will link the pieces together.
Note: I did later revise this sketch to have both slots on one side of the part as i thought it would be more comfortable for the user
The length and width of the slots are driven by the material thickness parameter
Tested different angle values to test if the sketch might break under some conditions
Bevels were added as finding features to aid in assembly
For the Bridge piece i started with a rectangle and used a control point spline to create clearance from the users arm
Again the was parameterized with the help of some construction lines and constraints
Part 2 complete
The flexer is a rectangle with an center point arc on each end
To create the cuts to make the part bend i decided to work in modules of 50mm
Sketch line and constructions lines make up the cuts, they make heavy use of the equal constraint to minimise the need for repetitive dimensions
To extrude e in the sketch environment. then select thin wall extrude for all my lines. The thickness is set to a kerf parameter. Doing it this way each cut is a rectangle rather than a line meaning I can remove bit of extra materials and hopefully make the piece bend easier.
This is then patterned to fit inside one of my 50mm modules
Then the pattern is then patterned` using a parameter that defines the number of modules
Flexible section complete
Parameters updated to more scalable values for my first estimate
Slot sketch added to surface to the flexer
Bevels added and final tweaking of parameters to final dimensions (excluding kerf and thickness which will be tackled in the next section
Fabricating¶
Moving on to the making portion of this week I have opted to use 3mm (nominal) MDF as we have a lot of off cuts around the lab I can use.
Never trust a nominal dimension, even though MDF is normally much closer to its nominal than plywood there is still always a difference between nominal and actual
One of my fellow students Diarmuid Kelly created a kerf test using rhino and grasshopper
I scaled the .dxf file to fit my thickness of material (this was a mistake, will explain in summary at the end)
I opened corel draw on the workstation connected to our Epilog Fusion Pro, the template we have set up keeps the artboard the size of the cutting area
ctrl-i to import in my .dxf file
I use the properties tab to set all the shapes to have no fill and set the stroke to hairline
Next step is to use ctrl-p to print the file and send it to the Job Manager
At this stage I loaded my material into the bed. As I’m cutting all the way through I’m using a honeycomb bed in the laser
Machine is turned on with a key
In the jog menu I position the laser over my workpiece
And use auto focus to set the focus of the machine
Parking the laser is useful as it moves it out of the way of the camera
This is the view from the Job Manager software, here we can position the artwork and also apply our settings. Note in this case i will be using the split by colour feature to apply different settings to different colour lines
The cut lines is use a 3mm MDF preset we have developed
The marking lines a much faster and less powerful setting is used
The piece is positioned with the help of the camera
Extraction is turned on prior to cutting and turned off in between cuts (once smoke has cleared) to reduce noise and power consumption
Hit the play button to start the cut
🔥Lasers🔥
Piece complete
For the x-axis a 0.1mm kerf was a good fit, tighter felt like it would damage the piece then removing
For the y-axis again 0.1mm kerf was a good fit
The values for kerf and materials thickness were then brought back into Fusion 360
To turn my 3D models into 2D files I created an offset plane and used project on the faces to create a sketch
The sketch can then be exported as a .dxf by right clicking
.dxf is imported into corel draw
I cut out the minimum parts required to test the fit
Parts complete
Test fit successful!
I bring in the rest of the geometry into my corel file
And use the print selection tool to separate and positions the last of my parts
The final result!
In Summary¶
As a primarily 2D workflow i see the strengths of both vinyl and laser cutting being there speed. Going forward in my project ill be using them to initial scale models and prototypes prior to 3D printing as the results are so much faster.
In my normal workflow the laser has primarily a tool for testing things that i will CNC at a model scale and i have really enjoyed that workflow
Things I would do differently next time¶
In my haste this week i ended up improperly using the kerf tool that Diarmuid made. Rather than updating the grasshopper parameters for selecting my material thickness i simply scaled the baked .dxf file. This means the kerf figures shown are not actually true to life. In this case i got away with it as scaling was close enough that i was only out by a few 0.01’s but if i had of be using thicker material or using a laser with a more exaggerated kerf this could have been a bigger issue.
See below link to to files created this week: