From Team 449 Wiki
3D Printers are a type of machine that use a process called Additive Manufacturing (AM). AM differs from many other manufacturing techniques that Team 449 uses in that it adds material little-by-little to make a part, rather than removing material like a saw, drill, or CNC router does.
This page contains instructions, and recommended best practices for working with 449's 3D Printers.
- 1 Definitions
- 2 Equipment
- 3 When to use 3D Printing
- 4 Design and Modeling Tips
- 5 Prep for Printing
- 6 Printing procedures
- 7 Other Notes
- 8 Example Parts
Model: The software CAD file that captures the geometry of the designed part. ".STL" is a common file format for exporting part models when 3D printing.
Part: the thing that is being printed in 3D.
Filament: A spool of thermoplastic that is melted, extruded, and then cooled to make Parts on a 3D printer
Extruder: The part of a 3D printer that melts the thermoplastic and deposits it onto the Model being built
Build Platform: The platform that the 3D printer prints onto
449 has two 3D Printers
Makerbot Replicator2 Specifications
The Replicator2 is a single-extruder FDM printer that prints using PLA filament ONLY. The User's Guide is located here.
The maximum build envelope for the Replicator2 is 28.5 L x 15.3 W x 15.5 H (cm) 11.2 L x 6.0 W x 6.1 H (inches)
3D Systems Ekocycle Cube Specifications
The Ekocycle Cube currently has two colors of proprietary filament installed: Natural, and Black. The proprietary filament cannot be replenished by generic filament at this moment; each cartridge has a chip that has a record of how much filament has been used, and it is unlikely that those chips can be reset. The Ekocycle is not generally used by 449.
When to use 3D Printing
3D Printing is an extremely useful tool for prototype manufacturing. There is minimal setup time, so it is cheap and easy to make single parts. Parts are lightweight, due to the plastic material and the ability to be filled sparesely. With 3D printing, it is possible to create parts with geometries that are very difficult, or even impossible, to create with traditional subtractive methods. 3D printed parts are not durable, but not particularly strong, and should not be used in structural applications.
Some good examples of when to use 3D printed parts:
- Housings for delicate electronic (encoders, IR sensors, RoboRios, etc.)
- Mounts and brackets that needs to accomodate multiple framing systems (e.g. 80/20 and speedrail)
- Sensor mounts where specific geometry is needed (e.g. hold a webcam at a 27 degree angle, or hold an array of IR sensors in a specific orientation)
- Adapters from COTS parts to standard hardware (sensor with a metric hole pattern onto 80/20)
- Unique shapes, especially 3D shapes (e.g. spirals and augers)
- Decorative elements
Design and Modeling Tips
Know the limitations of the printer
- 3D printers have difficulty in making overhangs
- Try to avoid overhangs and ledges.
- Try to avoid "bridges" than 0.15" long.
- The pre-processor software, known as a "slicer", can add support material if needed, but this uses more filament, increases build time, and requires more post-processing to remove the support material.
- The printers can handle outward drafts of no more than 60 degrees from vertical
- Try to keep outward angles at no more than 45 degrees.
- Know the build envelope of the printer
- Try to avoid parts that take up the entire envelope.
- Particularly try to avoid long parts up that take up the full width
- Long and/or wide parts will tend to exhibit warping on bottom face due to thermal contraction.
- It takes longer to print in the vertical dimension than the horizontal ones.
CAD Modeling Tips
- Start the CAD design on the front plane (i.e. z-axis is vertical), as this is the default orientation for the build platform
- Consider how the part will be printed from the beginning.
- Try to make bottom face as flat as possible, and seek to minimize overhangs that would require support.
- Interior perimeters (e.g. holes) tend to come out a little undersized, and Exterior perimeters tend to come out oversized
- The recommended compensation (add/subtract, depending on interior/exterior) is as follows:
- About 0.010" (~0.25mm) nominally to all holes
- About 0.015" (~0.375mm) for a close fit (i.e. to hold nuts in place)
- About 0.020" (~0.50mm) for a standard fit
- About 0.030" (~0.75mm) for a loose fit (or more, as desired)
- A 0.040in (~1.00mm) buffer will ensure full sliding clearance
Prep for Printing
Once the part has been designed, you need to export it and prepare it for Printing
Export part model as an .stl file
note, this needs to be updated with instructions for Autodesk Inventor
- Output as: Binary, Millimeters
- Deviation Tolerance = Slider about halfway
- Angle Tolerance = 5 deg
- Parts are often tweaked and re-printed several times. It is recommended to add some sort of version number to the filename.
- Filenames for the printer are limited to 30 characters. Please make sure your files names are shorter. Otherwise, characters at the end can get truncated. Since these are often uniquely identifying numbers, this can lead to confusion and incorrect part selection.
- Run the STL file through Autodesk Netfabb, and check for errors. Bad STLs will print poorly and result in holes and structural weakness. Fix the errors and re-export the STL. See here or here for a tutorial.
MakerBot pre-processor software
Makerbot Print is the MakerBot's pre-processor software (a.k.a. "Slicer"), and is available here. Use Makerbot Print if you don't need a USB connection to the Rep 2. If you do need a USB connection, use Makerbot Desktop.
- Click "Add File" to import your .stl model
- Customize the position and orientation of the part
- Rotate to get the correct face on the build plate.
- A single part will usually come out the best in the center of the build plate.
- You can also apply a scaling to the part (e.g. convert mm to in, or visualize a part a 1/2 size.
- You can put more than one part into a build.
- You can copy/paste the same part, or add additional parts
- If you fill up the build platform with multiple parts, it will take a while to run, but all parts will be ready when it is finished.
Settings for the pre-processor
- Rafts are pedestals of printed material that the pre-processor can include with your part. They help minimize warping due to thermal contraction. They break away very easily once the part is finished. However, they do take additional material and increase build times.
- Rafts are recommended for parts where the flatness of the base layer is important, or where the base layer has complex geometry.
- Supports allow parts with large overhangs or bridges to be built. They break away somewhat easily after building. They take additional material and build time.
- Supports are required for parts with lds overhangs.
- Recommended: 10%
- Minimum: 5%. Results in lightweight parts with short build times. Will not be very structurally strong.
- Maximum: 50%. Results in stronger, heavier parts that use more material and take much longer to build.
- Diamond (fast) and Hexagonal are recommended infill patterns
- Number of Shells
- Recommended: 3
- Minimum: 2. Results in slightly faster parts, at the expense of less strength and wall thickness
- Maximum: 5. if higher strength is required, particularly around holes and edges
- It is often beneficial to size your part such that thin walls (which require interior and exterior shells) are an even multiple of the extruded filament width, which is typically 0.4mm
- Layer Height is how thick the layers are when printed. Larger layer heights can reduce printing time, and should be used only for quick builds that don't have accuracy requirements (i.e. looks-like / feels-like models). Smaller layer heights are useful for final parts with critical vertical/angular features, but will increase build times substantially and are more susceptible to build failures due to clogged nozzles.
- Recommended: 0.20 mm
- Minimum: 0.10 mm
- Maximum: 0.30 mm
- Temperature is material/color dependent. MakerBot has recommendations here.
- The recommended temperature for MakerBot-braded PLA filament is 215 degrees C, with a range of 210 - 230, depending on how fast you are printing.
- Extruding Speed is how fast the nozzle moves when placing filament. Slower extruding speed provides greater precision and slower build times; vice-versa for faster speeds. Printing too fast can lead to chatter and severe inaccuracies around tight corners. User higher nozzle temperature for higher speeds, as the material needs to be extruded faster.
- Recommended: 80 mm/s
- Minimum: 40 mm/s
- Maximum: 100 mm/s
- Traveling Speed Is how fast the extruder moves when not printing. No need to adjust this setting.
- Recommended: 150 mm/s
Prep the Printer
The best print quality comes from preparing the printer and the build surface properly before each print. Below are recommended steps:
- Remove any tape from the build plate. Carefully scrape it away, so as not to damage the build plate.
- Clean the bare build plate thoroughly, by squirting it with rubbing alcohol and rubbing it with a paper towel. Let the alcohol dry/evaporate before proceeding.
- Apply two strips of blue tape. One aligned with the front edge of the build plate, and the next aligned right next to it. Take care that there are no folds or wrinkles in either piece of tape. Also take care that the two pieces of tape are aligned next to each other with no overlap, and minimal separation. It is OK to have the tape wrap around the edge of the build plate, up to 1" on the underside. You MUST dog-ear a corner of the tape so it is easier to remove later for both your and the next printer's sanity. You may also need to add a small strip of tape near the back of the build plate at the centre to aid in the bed levelling procedure. If the print will need the whole platform, apply a full-length strip to the back area.
- Use a squeegee or roller to apply pressure to the blue tape to increase its adhesion to the build plate.
- Gently clean the top surface of the blue tape with an alcohol-damped cloth before the build (not too wet, and use light pressure, you don't want to the blue tape to start disintegrating)
- Level the build plate before every print. Follow the instructions in the firmware.
Monitor the Machine During Printing
- Do not leave the machine unattended for long periods of time. Check on the build every 15-30 minutes. Online monitoring is being set up.
- Ground yourself before touching the machine while operating
- The machine can sometimes build up static charge. This can cause a static shock to occur if you touch the machine while it is running.
- This shock can cause the SD card to glitch and terminate the current build
- Monitor for a clogged extruder
- The machine will start clicking if the nozzle is clogged. This is from the extruded drive motor skipping as it tries to force more material into the clogged nozzle
- Also, visually verify that material is coming out of the nozzle
- Look for "air printing"
- Immediately cancel any build that start to exhibit signs of a clogged nozzle.
- Makerbot has instructions for unclogging a nozzle.
- Once you unclog the nozzle, start the build over.
Use Plastite-style thread forming screws to attach parts together
Plastite-sytle thread forming screws can be used to for low-strength low-cycle fastening into 3D-printed parts. These screws come in a variety of sizes and head styles: McMaster Plastite Screws. Recommended sizing for holes is shown below:
- M1.91 screws are 2.06mm wide. Recommend #54 drill (0.055"). Add >= 0.015", hole size is 0.070" (1.78mm) for good screw fit.
- #2-28 screw is 0.092" wide. Recommend #48 drill (0.076"). Add >=0.015", holes size is 0.091" for good screw fit.
- #4-20 screw is 0.127" wide. Recommend #44 drill (0.086"). Add >= 0.015", hole size is 0.105" for good screw fit.