Tips for Newbie: FreeCAD, Cura, first 3D printer pitfalls and solutions
The ability to turn any imagined object into actual item-in-the-physical world has been a magical power beyond the reach of the common man.
“Personal” 3D printing gets us closer, but just like in the early days of personal computing, getting started involves struggling with the idiosyncrasies of experimental-stage tools and learning from other people’s mistakes / successes.
I am writing this guide 2 months after getting my first 3D printer. Waiting any longer I will begin to block out the painful beginning.
Buying a Printer
A 3D printer is a device that precisely deposits molten plastic layer-by-layer according to computer-generated instructions.
- Too clumsy to handle sticky liquid plastic poured from bottles so I went with 3D printer that uses plastic filaments that come in rolls.
- Too lazy to use apply tape or hairspray the printer bed for adhesion so I chose a printer with specially-coated glass bed. So far the glass bed worked so well that I plan to keep using it.
- Did not want to spend too much so I started with a non-enclosed Anycubic I3 Mega and then added an enclosed Anycubic 4Max Pro 2 weeks ago that came with the same kind of glass bed.
- Enclosed printer is much more quiet, easier to move around, and heats the bed more uniformly. I ended up with much much fewer (zero) bad prints so far compared to 3 on the open printer. Definitely worth the extra money. I plan to keep getting enclosed printers.
- I bought new machines from eBay, shipped directly from the manufacturer. I considered buying from Craigslist from local sellers who are either selling used machines because they have too many or people who tried to get into 3D printing, had difficulties, gave up and selling nearly new machines. I was not comfortable evaluating used machines and worried about trouble-shooting new machines being abandoned by newbies like me.
- I did not want to spend hours assembling machine from kit to save $100, because if the machine does not work, I would not know whether I assembled it wrong or I did not operate it correctly.
- Automatic bed leveling — I considered this feature but in the end did not buy a printer that include this feature, because re-leveling is not needed before each print. Typically once the bed is level, no additional leveling may be needed for a long time (months to years). This has been the case for me so far.
- Supported Filaments — so far I have only printed PLA, but my printers can also print other filaments like ABS. For getting started, PLA is sufficient.
- More than one printer? — I did not anticipate adding a second printer and so soon. But after experiencing how long it takes to print even a very small object (several hours minimum), I now understand why most people who own 3D printers have more than one. It is simply not practical when iterating through design changes to be significantly delayed by the 3D printing time.
- Size of 3D printer — unless you know you will be working on large objects, it is better to buy two smaller 3D printers than 1 larger one for the same money. The reason is that a larger printer will not print any faster, but having 2 printers will allow two prints to happen at the same time.
- Speed of printing — typically the low-end printers have heads that move about 60 mm/sec (or 10 grams of PLA per hour). Going faster will bump into the limit of the extruder motor + gearing’s ability to push / pull the filament into the hot tip, and the hot tip melting the filament sufficiently. These issues will degrade print quality. // Filament slippage and clogged heads are said to be commonly encountered problems even at typical print speeds. I have not pushed to higher speed for that reason.
Getting the New Printer to Print
The most intimidating part is leveling the print-bed.
Thickness of leveling paper: The instruction says to use a piece of regular A4 paper and the printer comes with a piece of paper labeled “For Bed Leveling”. However, the thickness of the paper is thicker than normal A4 paper?
My conclusion is that it is an approximation — main things:
- print head should not scratch the bed — that is too close
- print head is too far from the bed if the molten plastic gets dropped too high up, and does not stick to the bed.
- paper-thickness gives an approximation only. Once you start to print, additional adjustment may be needed.
- Most important: know which way to turn the adjustment control knob to move the bed closer or further from the print-head. I got confused a few times and made things worse.
If the first layer of plastic does not stick to the bed, then it will drift upward and cause subsequent (higher) layers to be placed in the wrong location or not stick to each other. If left running, the printer creates “bird’s nest” mess.
- It is a good idea to look at your print’s first few layers, to make sure they are sticking correctly before you leave the printer to complete its work.
2. Heated bed helps plastic stick to the bed— but too much heat will melt the bottom of your print and distort the resulting product. My printer’s PLA default bed temperature is 60 degrees C. I was having problem with adhesion and I increased it to 61 degrees, which solved the adhesion problem but I ended up with warping of the bottom of my prints due to excessing melting.
3. Uneven bed heating — both of my printers have parts of the bed that are hotter / colder than other parts. This appears to be less severe in the enclosed version. Getting to know the hot spots will help you place your more delicate print-features away from the hot spots to avoid warping.
FreeCAD (vs Fusion360)
I tried both and ended up mostly using FreeCAD.
- Fusion360 has a timeline interface that allows changing a previously defined feature by selecting it on the timeline. In contrast, FreeCAD uses an hierarchical object / operations-nesting interface.
- In FreeCAD, every operation creates a new entity in the model hierarchy. This mean if you go back to delete a previous entity, all subsequent entities may break. This means when I go back to change a previously defined feature in FreeCAD, I ended up having to re-do subsequent operations. This is rather tedious.
- Deleting an entity in the FreeCAD model hierarchy “releases” all the nested objects. They show up at the highest hierarchy level, rather than the level of their parent object. This makes complete sense because FreeCAD is nesting operations, not just objects. However, this was disorienting and confusing to me initially — kind of counter-intuitive as I had expected the model hierarchy to behave like nested file folders, which they are definitely not.
Figuring out how to move and look around the model from all angles is essential to using any CAD software. I am not going to waste your time on easy stuff like zooming (mouse scroll wheel) but will focus on a few things that too me longer to figure out.
- Holding down the middle mouse button allows panning.
- Selecting an object (by left clicking) and then holding down the middle mouse button allows dragging. Dragging and panning looks the same except dragging changes the mouse cursor into a 4-way symbol.
- Holding down the command key while dragging allows left clicking to change to model rotation mode. This is the most useful mode as it allows free rotation of the model in 3D space.
The shape of the model largely determines how challenging it will be to print. Separately, the size / weight determines how long it takes to print.
- Start Small , as small as possible — especially when first getting started. It will be faster to print and therefore faster to learn from mistakes. I started by designing items in the 10–20 grams range, which took 1–2 hours to print.
- Avoid Supports- supports may be needed when overhang exceed 45 degrees. For prototyping, I was able to make do with 70-80 degrees. In any case, supports are a pain because they have to be printed, removed and thrown away. Removing supports is tedious work. Also, support attachment points tend to scar the finished product, which adds to the list of reasons to minimize the need for supports as much as possible when designing. Because the need for supports is dictated by angle of overhang (relative to the print bed), pick the best printing orientation when designing and try to keep all features consistent with that orientation, as much as possible.
After exporting the STL file from FreeCAD, it is necessary to import STL file into slicer software like Cura to covert to gcode that controls the 3D printer.
- download a new version of Cura from the Ultimaker website, don’t use the version that comes with the printer manufacturer. Cura comes out with new and better versions quite frequently.
- Under “Settings — Printers: Manage Printers:Machine Settings”, you can customize the start and end G-code that gets appended to each gcode file that you generate for each specific printer on your list. You can Google your printer and probably find custom settings that others have used for your printer. Beyond that, you can further customize the gcode yourself.
- Orienting the model on the print bed — Cura either does not even try or does a poor job of placing the model to minimize need for supports. Play around with rotating the model and see how it changes the locations and quantity of supports. The goal is to minimize supports so that there is less work removing them.
- For prototyping, I find the Shell, In-Fill, and Support settings most useful. My goal in prototyping is to reduce the print-time (and wasted filaments). I consider the following to be pretty close to minimum.
- Shell: I have been able to use “Wall Line Count” = 2 and “Top Layers” = 4, and “Bottom Layers” = 3, “Top/Bottom Pattern” = Zig Zag, “Alternate Extra Wall” = Yes.
- Infill: I turned Infill off by setting density to 0 %.
- Support: “Support Placement” = everywhere, “Support Overhang Angle” = 75 degrees, “Support Density” = 5%
- Printing Screws — I started out with screws with size that perfectly fit into their corresponding holes. That approach produced screws that required a lot of effort to clean off 100% of supports and in the end still fit very tightly. Turns out this is a common observation and the solution is to scale STL in Cura so that the diameter of the screw-thread is reduced to 95–96% of the hole size.
- Mechanical Strength: Orientating Screws in Cura — the Z-direction is the weakest link in 3D printing. This means if a screw is printed pointing up (or down), then it is most likely to break when bent along its major axis / or even when tightened too much. Thus, the best orientation for printing a screw is lying flat on the printer bed, with major axis parallel to the printer bed. I learned this the hard way. Of course this principle is generally applicable, not just for screws but any object that will need to survive mechanical stress.
- Noise / location — 3D printer are loud, especially the non-enclosed versions. Because there is a need to check on the print and quickly stop the printer when non-adhesion happens, the 3D printer really cannot be located too far away. In the end, a walk-in closet worked best for my situation.