3 month project based on consumer heating. This was a fun project and some is shown below Full report and Appendix.
Rendered Exploded View
Category: CNC
DP402 Summary
This project was based around moving homes constantly. Our aim was to produce collapsible furniture that could be easily adapted to everyday life and small spaces that students and the like would normally have to live in.
Week 8 – Fusion 360 CAM for mould-making and casting
Design Rules for CNC/casting
Most important is to know your cutter shape and size. Any features have to be designed in accordance to the diameter of the cutter as this will restrict how far and deep the slots between features can be.
Try and keep the cutter as big as possible as it will reduce cutting time as well as the chance of the cutter breaking or chipping.
If you are making a mould;just like the vacuum former; you will need to use draft angles even on small/short features.
Absolutely no undercuts as the CNC milling machine is unable to rotate the bed or spindle
Making a 30 x 30 x 5mm tile in Fusion 360
- See SolidCAM post for a similar setup on SolidCAM
- Using the design rules above create your tile using Fusion 360 – with the front place in CAD actually the top of your model – CNC’s use a different coordinate system
- Move to the ‘MANUFACTURE’ tab
CAM Setup
- Click on ‘Setup’ > Ensure ‘Stock box point’ is selected in the origin box
- Under the ‘Stock’ tab > Selected ‘Fixed box size’ Set to 50x50x10mm with ‘Centre’ selected for the other boxes ; I always select ‘Fixed size box’ as then I always know that the scale isn’t messed up and can work with the size of the raw stock much more easily
- Under the Post-Process tab choose a suitable ‘Program Name/Number’ which includes enough details to not get confused with other versions of the file, in case you need to come back and change tool paths etc later
Milling Operations
- Right click on Setup > New Operation > ‘2D Milling’ > ‘Face’ ; For the first operation to get down to the correct level
- Select ‘Tool’ to create the new tool > Edit the highlighted settings which are the important ones for making this tile > click ‘OK’ and turn off coolant – OR choose from the existing tool selection > Samples > Metric – High Carbon Steel > φ3mm – flat (3mm Flat Endmill)
- Go to the stock selections tab > ‘Select’ box next to ‘Stock Selections’ > Click on the top surface > this picks the level you want to mill down to
- Heights tab > Set them all to from ‘Stock Top’ apart from depth which you can set to ‘Model Top’ > These are the levels your tool will retract to after each operation and shouldn’t be too close to the stock top nor too far to waste time
- Passes tab > This sets how much material the tool can remove with one pass > General rule is half the width of the tool for step over and 1/3 of tool diameter for ‘stepdown’
- Linking tab can be left as is. This controls the lead in and lead out
- Complete these steps again for the next tool operations – the only difference should be the levels and the geometry > all of the tool data and offsets remain the same as above
- I use the ‘Ramp’ tool to cut the contour and pocket in the same operation > this just cuts out time in Fusion 360 by remove the need to go through the set up process for the operations separately
- Check the tool path with the simulate function > Set the tool to be Shaft to remove the large tool holder blocking your view > Show stock > click play button at the base and ensure that all the material is removed > make sure that the mould left is exactly what you want to be left behind
Post Processor
Relatively simple > Click Generate and choose Grbl as the post processor > check you save it in a place that you can find it and check the file name is correct and identifiable
Here is the model with the tool path
Cutting the tile on the mini CNC machine
- Prepare the mill, by removing any waste from previous milling operations and apply double sided tape to the block of wax that you will cut your tile on – attach the tile to the centre of the bed
- Choose the cutter – use the one which you programmed in Fusion 360 – and install it on the machine. Two grub screws need to be tightened (one either side of the bit, as well as two for attaching it to the spindle)
- Load the GRBLcontrol program and use this to set the X and Y coordinates in the centre of the block of wax – click set home before moving on
- Do a test cut by raising the z home position and cut the air above the wax for about a minute just to check speeds, feeds and if anything looks amiss.
- Setting the z height – Very similar to that of the PCB milling machine – turn on the spindle and slowly move the z height down until it just kisses the wax, then set the home and lift it up slightly so it doesn’t crash when you start your operation
- Depending on the material override the feed to ~75% for pink foam or ~30% for wax
- Click send
- I stopped the milling machine at the end of the occasional operation to give it a vacuum and remove the waste material – This will improve the finish especially of harder materials as well as reduce the chance of the tool breaking.
- Keep watching it until the operation has finished then remove from the machine bed using a pry tool
- Vacuum the bed, ways, screw threads etc as well as the surrounding area, ensuring any tape is also remove from your part as well – leave it as you want to find it
- Deburr you wax part using a fingernail or the end of a ruler – but don’t press too hard
Problems
Ensure that the milling cutter is tightened down before each use – it wasn’t checked in my case and it just popped off when it had nearly finished (no harm done!)
This meant that the operation had to be started again and therefore took much longer than it should have
Casting with food grade condensation cure silicone
- Prepare a work area with some covering on the work surface as it can be quite messy
- Wear disposable gloves as well as a lab coat to protect clothing
- Use scale to measure out the silicone and curing agent in a coffee mug 1 to 10 ratio much easier to mix in than a disposable cup (excess can be peeled out after it has set)
- Mix well using a plastic stirring rod and leave for 10 minutes to let the bubbles rise to the surface
- Push into your wax mould using the stirring rod and fill up any others it you have any silicone left – try and remove any pockets of air
- It is quite good at self levelling so leave the silicone proud of the top of the mould so there is material left to fill any voids as it settles.
- Leave to set for at least 24hrs
- Peel it out of the wax mould and you should have a mould to cast into
Chocolate Moulding
Moulding with chocolate is relatively easy, just take your time and don’t burn it by putting too much heat into it too quickly. I tried to use the microwave to melt it but in suck small amounts found that difficult.
The best way is to melt the chocolate in a glass bowl over boiling water. Seeing as its a small amount I only needed to boil the kettle and transfer the water to the jug and place the bowl over this (with the water level just below the level of the bowl).
The chocolate came out of the mould relatively easily, and the details were quite prominent. One issue however is the flashing on the outside of the chocolate indicating that I overfilled the mould. It is also down to the ball nose end mill not leaving a square edge at the base of the chocolate, instead leaving a flange.
Week 7 – 3D scanning and printing
3d Scanning can be done in multiple ways and at multiple price points, either with handheld scanner for an iPad all the way up to full systems, e.g for car manufactures to scan clay cars.
They also have different degrees of accuracy, with hand held scanners being less expensive they will also produce less detailed scans, but still very much usable.
Photos to wire frame to surfaces
This is the process of taking a few images and importing them into a CAD software such as Rhino and creating a line drawing from the outside of the image and then building up a CAD model from that. This will produce a very accurate CAD model with clean surfaces, however it might be harder to get in the fine details for the thing you were taking photos of. You may also struggle if the object is very complex or if it has lots of small details on one face, making it difficult to get side profiles of these features.
The main steps are:
- Use a curve tool for draw the rough shape
- Clean these up with either rebuild curve or by dragging points on the curve
- Add in additional details such as the mouse wheel
- Use this wire frame to create surfaces which can be then used to 3D print
Photogrammetry
This is the process of taking lots of photos and importing them into a CAD software creating a 3D image using relative distances between the photos. This can normally done with an app as well as a corresponding desktop application as it can be quite intensive to create the model from the photos depending on its complexity.
3D scanning
3D scanning was done using scanners which attached to an iPad, making them very convenient to use; https://structure.io/
The scanning process is relatively simple as the app tells you what to do at each stage
- Launch the app and locate the box on the screen on the object that you wish to scan
- Change the size of the box to suit that of the object
- Click start and slowly move around the object ensuring that all angles are covered. It will tell you from time to time to stop and wait while it picks up all of the surface details.
- Send this via email from the app to start the next process
At this stage you can either use this scan to create a wire frame in a program such as Rhino and create the surfaces as above, or import it into a mesh altering software such as Meshmixer.
Rebuilding
As in the photo to wire frame method, the aim of this is to create a wire frame from the 3D model and then create new surfaces, which will overall give you a much better surface finish, but will be impossible to do on something organic such as an arm.
The 3D scan is brought in and rectangular surfaces are put in to create the main wire frames. Project to surface command is then used to obtain the exact curves. These can then be cleaned up or redrawn as above and then surfaces created using on to the multiple surface tools. This is the the most time consuming method but produces the best results and the highest quality surfaces.
Meshmixer
Meshmixer is a free software which allows you to create and edit meshes and 3D objects, such as 3D scans.
- Import you wire and use the simplest tools to reduce your work.
- Use the simplest commands first such as ‘Close Gaps’ – this command will almost always turn a lot of work into very little.
- The next best thing is to try and make the object a solid. I found it best to cap the base of the hand and set it at the desired angle. Use the Translate tool for this.
- Capping the base of the hand is done using the ‘Plane Cut’ tool. This acts as a knife and cuts a flat surface through your object.
- Use the tool ‘Make Solid’ to convert your shape into a solid. It isn’t perfect and left the space under my fingers a mess, mostly due to the lack of light when scanning and therefore details couldn’t be determined.
- Using the Sculpting tools the errors made by the scanner such as mussing out under the fingers can be corrected.
- This video shows the entire process of sculpting and editing the scan
3D printing
- Load the document into Ultimaker Cura which allows you to preview and edit the 3D printing details
- Once loaded, orientate the model into the desired place and ensure that it has imported in at the correct size. It is important to think about the orientation due to the layers as any overhangs which may require supports. Reducing the number of supports will reduce the print time as well as decrease the need for cleaning up after printing.
- Click Slice in the bottom right, then preview when this is completed.
- Under print settings you can choose the layer height – main time saver along with infill % – This will require the slice command to be run again
- Preview of the layers being built up; showing the support material
Final Image
Week 5 : Electronics Design
The task this week was to create the schematic, board layout and then mill the simple LED circuit board.
Autodesk Eagle is the circuit-board software that we used > Installing it was relatively easy as it was just a simple installation but to get the correct components for the FAB LAB, downloading the library of parts was done. This is to ensure that all of the pads are the correct size and can therefore be soldered easily.
This is the guide that I used > https://fablabbrighton.github.io/digital-fabrication-module/guides/guide-draw-circuit-in-eagle
Once you know where the library of parts is, it is relatively simple to use, but keeping it tidy is important to have an easy to read schematic and peace of mind that you have connected everything correctly.
Method for creating a new document
File > New Project > Right Click on the project > New > Schematic — Open in new window
Add Part > Search using *part* > All components that have 1206FAB as an option should be chosen
List of parts required is
- Red LED
- 1KOhm Resistor
- 10 KOhm Resistor
- Un-polarised Capacitor
- Omron Switch
- Resonator
- FTDI Header
- ISP header
- ATtiny44
Add all of the components to the schematic then change the values of the resistors and capacitor.
Right click on the component and click value > Type in the correct value so that you can use you schematic for soldering late on and correctly refer to it.
Moving on to Board
Generate Board > click OK on message box
Move components and rotate them to the orientation that is going to best suit the board layout
Change width of the trace in the top bar when drawing the traces
Change the tolerance : Tools > DRC > Clearance
Check errors : Tools > Errors
If any errors are due to the schematic, then that will need to be altered. However if the errors are due to clearance errors and traces slightly crossing, these will show up and can be fixed relatively easily. Most of the time they can be fixed in EAGLE, by either drawing the trace again and choosing a slightly different path, however if the stepping in the movement of the trace is annoying, Adobe Illustrator can be used to alter the traces.
The next step is to move it to Adobe Illustrator: File > Export > DXF > ensure scale isnt change and you save it in a suitable location.
In Adobe illustrator the main aim is to remove all line and text, leaving only the traces, pads and the outline of the board > The traces may need altering slightly from the EAGLE file so this is when you would do that.
This is when you would add a logo if you wanted to.
The outline width should be set to 3-5mm as this the components and the edge of the board enough clearance
The artboard now needs to be set the artwork size > this can be done in a simple step > Objects > Artboards > Fit to Artwork Bounds
This is a critical step to ensure the two tool paths generated have the same origin point and therefore match.
Print this as PDF to ensure the components fit. I chose to increase the width of the pads for the FTDI header to 5mm as they didn’t fit with the printout.
Save as a PNG > tick the box saying use artboard > 1000dpi > save somewhere you can find it easily
Go to > fabmodules.org > upload you PNG by selecting PNG from the drop down menu
> Select Roland Mill > PCB Traces for the traces and outline for the outline > invert the image
> set the x0 y0 and z0 to 0
> Set the yhome, xhome to 0 and the zhome to 10
> Set the tool Diameter to 0.4mm for traces ; 1mm for outline > no. of offsets to 0 for a test toolpath
The tool path should be generated when you click calculate
This is a critical check to ensure that you board will work > Make sure none of the toolpaths merge together. They can overlap but not merge.
Roland Mill
The mill is very easy to set up and has an automatic tool change which speed up the work.
Setting the x and y origin is simply selecting which axis and using the hand wheel to control how far across the cutter is.
Setting the z origin requires more skill > Turn on the spindle to full speed > select z axis > get it close using the hand wheel > change the step distance to reduce how fast the z-axis moves with the hand wheel > get the spindle to just touching the copper ; you should see a small amount of white power appear when you get close enough
Change the tool bit to the correct one for the operation > menu > click over to the one which says tools > select tool 5 for doing the traces > tool 1 for the outline
Load up the file using the blue square in the bottom corner > add your file to the menu and delete any others >
Send to the cnc and ensure that it doesn’t crash by watching it >
Once finished load the outline file and change the tool bit as above > Start the outline and wait for it to finish
Remove the finished PCB using a scraper and clean up any rough edges
Solder the components on as in last weeks blog.
Week 4 : Electronic Production
Surface mount components are very common and are what the majority of manufacturers will use due to the smaller size, compared to through components. It seems fairly easy to use them, although the mounting of these components, via soldering is vastly different to through hole components.
Through hole components have the obvious advantage of being self locating, so it is easy to manufacture. Surface mount components need to be held in place when soldering and so require skill to also locate them and make them straight.
Method
- Prepare the board for soldering by washing it in soapy water to remove any oxidation that may have occurred since milling.
- Gather all of the components and ensure you know what orientation they are supposed to be.
1x ATtiny45
2x 1kΩ resistors
2x 499Ω resistors
2x 49Ω resistors
2x 3.3v zener diodes
1x red LED
1x green LED
1x 100nF capacitor
1x 2×3 ISP header
- Tin the soldering iron by adding a small amount of solder and removing it using the wet sponge.
- Tin one of the contacts for each of the resistors, capacitors and the diodes.
- Do the same for one of the 6/8 legs of the Tiny Chips and the ISP
- Place the components on top of the solder and use a pair of tweezers to push it towards the board, therefore keeping it still. This is the hardest step, as if you have tinned the pad with too much solder then you will find it difficult to hold the component next to the board.
- Heat up the solder which you tinned onto the board and you should have attached the component onto the board.
- Then solder the other end/legs of that component, going back to add more solder to the other leg/end if there isn’t enough.
- To test the connection you should use a multi-meter on the most sensitive resistance setting. This will check continuity between the component. If the reading is 0 or very near to 0 e.g 0.003 then there is a short whereas if there is a reading of around the size of the resistors measurement then you cave it correctly installed.
- Check the overall circuit by applying 5v volts to the USB as in the diagram. S1 is shorted then the left LED should light up indicating that the circuit works.
Programming this chip requires it to be shorted and then the programming can begin.
*Update on Programming the programmer* 03/03/2019
Using these supporting blogs – Windows specific Installation
Installing the software was harder than following the links due to the lack of clear instruction on what parts are needed, especially for Git. The link for Atmel GNU Toolchain wasnt correct so I am unsure which I needed to install. I typed what the link was supposed to take me to into google and cap up with this website. Download all the files as a zip and then extract them in the desired folder.
I decided to create a different programs folder so I could better keep track of the software on my computer. I didn’t want to destroy anything.
Installations complete – all of the tools are located in F:UNI ProgrammingPrograms
Updating the path
Control Panel > Advanced System Settings > Advanced tab > Environment Variables
Under User Variables > Edit for Path > See below
Next it to download Zadig and run this to install drivers for the USB > where I got stuck
Windows didn’t like the USB and so every attempt failed to install the drivers.
I checked here for shorts between VCC and ground and found nothing amiss so it is a possibility that my PC isn’t compatible and wont recognise the USB.
Checking software installations
> Type make -v in GitBash
> Type avr-gcc –version FAILED
> Type avrdude -c usbtiny -p t45 FAILED
UPDATE 2 > 04/03/2019
Going into the Fab Lab today helped so much after the failed attempts at home. The main different being using an iMac rather than a windows computer. Mike in the Fab Lab also says that Linux works very well, so maybe a possibility of having a separate partition on a hard drive to set up a Linux OS on my PC.
The steps are as follows for Mac with the software installed:
- Download the firmware for the programmer > http://fab.cba.mit.edu/classes/863.16/doc/projects/ftsmin/
- Open the Makefile in a text editor
- Customise the make file > Edit the line with MCU = attiny45
- Customise the clock speed > Edit the line with F_CPU = 16500000UL
- Edit the programmer used to program your board > PROGRAMMER ?= usbtiny
- Plug in your board using a USB extension to not mess up your computer USB ports as well as the programmer > connect their 2 ISP headers with a ribbon cable in the correct orientation
- Open the Terminal > type pwd to check path Enter
- Type cd (space) (and drag the downloaded folder in) Enter
- Type pwd to check > should be the path of your folder Enter
- Type make flash > should come up with loading bars if working Enter
- Type make fuses > should come up with loading bars if working Enter
- Unplug both > re-insert your board > check mac recognises device in the system information > should show usbtiny
- Reattach programmer and ribbon cable
- Type make rstdisbl > blows reset fuse > should come up with loading bars if working Enter
- Remove solder bridge if successful and you should now have a programmer
The programmer was then successfully tested using Andrew’s code to a board containing an LED and switch.
Multiple programs were tested and all were successful.
Week 3 : Laser cutter: computer-controlled cutting (CNC)
Task: Produce a press fit kit (accounting for kerf) using the laser cutter
Making the Design
The main aim is to use parametric design software to ‘simplify the process’. Being able to edit the sketch automatically by adding parameters and using these to dimension the sketch instead of manually changing them.
First step was to create the rough design on Fusion 360 and then dimension it to ensure that it would fit together.
As you can see above the dimension with fx: 2.5 are the parameter dimensions. These are controlled by the parameter menu and are what you use to account for the kerf using these identities below: See my post about how to use parameters
+ addition
– subtraction
* multiplication
/ division
^ power
( following BIDMAS
) following BIDMAS
; delimiter for multi argument functions
Working out the kerf of the laser cutter is different for every material, due to the taper that it puts on when cutting. I worked out that the kerf was 0.125mm for 4mm Acrylic which is what I chose to make my model from. I decided to skip the card model as I felt it wouldn’t work very well with the clip mechanism that I was going to use and time would be better spent making it with either acrylic or MDF.
Overall 18 different versions were made on Fusion 360 to get the fit just right, and by doing several cuts using the laser cutter i worked out the correct tolerance as well as the correct dimension for the clip ‘nubs’. I do however have a graveyard of broken acrylic parts to show for it! The clips works by having a ‘nub’ which sticks out and slots into a cut out hole on the other piece. This allows the model to go together but it won’t came apart once assembled.
Assembling the completed part in Fusion was also relatively easy, although not as intuitive as Solidworks – much prefer Solidworks as it gives more control and the interface is more technical.
Material thickness – Acrylic – 3.91mm
Work and Personal Portfolio 