3D Printing for FIRST Teams (8 of 8)

3D Printing for FIRST Teams

Authors: Kari Karwedsky, PTC, and Colm Prendergast, Mentor for FIRST Robotics Competition Team 1965

3D Printing Work Flow

The 3D Printing Work Flow that we use is composed of 7 steps.  

Step 1: Design your part using PTC Creo.

Step 2: Export Model from PTC Creo in .stl format.

Step 3: Prepare Model and Generate g-code file (or equivalent) for the printer.

Step 4: Prepare and Level the 3D Printer Build Plate.

Step 5: Load printer filament.

Step 6: Print Model.

Step 7: Clean up printed model.

In this blog post, we will look more closely at Step 7.

3D Printing Step 7: Clean up printed model.

Once the print job has been completed the first thing to do is to unload the filament. This is generally good practice and cleans out the extruder to avoid blockages. We usually run the load procedure first to ensure that the extruder flow is still smooth and there have been no problems encountered during the build process. After this has been verified remove the filament by following the procedure for your specific printer. The MakerBot procedure reverses the direction of the extruder stepper motor to push the filament out of the top of the printer. Gently pull the filament and continue pulling until the last strands have come out. This ensures that as much plastic as possible has been removed from the extruder.

With the extruder cleared remove the build plate and inspect the parts for any quality issues or warping. You are now ready to remove the parts from the build plate and remove any supports. Removing the parts and cleanup will require using sharp tools and this can be quite dangerous. 

Always wear safety gloves when doing this. This is what happens when you don’t!!!!

What can happen if you don't wear safety gloves

In addition to safety gloves the following tools are useful for removing parts from the build plate and part cleanup:

1. Craft Spatula: Lifting the Raft off the Blue Tape and separating the Part from the Raft.
2. Paint Scraper: Lifting large rafts/parts off the Blue Tape.
3. Xacto Knife: Removing Supports and Part Cleanup.
4. Craft knife set: Removing Supports and Part Cleanup.
5. Pliers/Wire cutters: Removing Supports and Part Cleanup.

These additional tools are illustrated below.

Tools for 3D printing cleanup

Start by using the Craft Spatula to lift up the edges of the rafts. This will most likely result in the Blue Tape getting ripped (which is fine).  Once all off the raft edges have been lifted if the rafts is still stuck you can use the larger Paint Scraper to level the raft and tape away from the plate. Do this carefully to avoid gauging or scraping the surface of the plate.

Using the Craft Spatula to remove a 3D printed part from the build plate

Once the parts have been taken off the plate the leftover tape can now be removed. Sometimes there will be residual tape adhesive left on the plate. This can be removed by using the sticky side of the tape to get it off. When the plate is cleaned of any tape or adhesive it is ready to use again. Keeping the plate clean will ensure that future prints are always made on a flat surface. 

The Craft Spatula can be used to separate the Parts from their Rafts. The thin flat edge of the spatula is ideal for this. This is a critical step. Sometimes areas of the part will not separate cleanly from the raft. This can be due to small unevenness in the raft structure causing the part to stick more forcefully in some areas and not others. 

Using the Craft Spatula to remove a 3D printed part from its raft

The most effective way to remove the raft is to try and remove it in one piece. Once the raft starts to break into pieces it is more difficult to manage. If you encounter resistance during this process it is a good idea to try and approach this area from a different direction. The scraping blade can also be used to separate difficult areas between the raft and part. Sometimes some force is needed so please wear gloves and be careful. 

3D printed parts and their respective rafts

Once the raft has been removed the supports can be tackled next. The Wire Cutters and Pliers can be used to cut away at the supports. You can use the Craft Knives and sharp blades to remove support material from the model surface being careful not to gauge the surface in the process. Since we are using a thick shell some amount of gauging can be tolerated without compromising the structural integrity of the part.  Depending on the amount of support material it can take a while to achieve good results. Removing supports can be one of the more difficult and time consuming cleanup tasks. Supports also have an adverse effect on the appearance of your final part. For these reasons it is always a good idea to design and place your parts to minimize the need for supports. Also, some printers support dual-extruders (e.g. MakerBot Replicator 2X). It is possible to take advantage of the second extruder to use a dissolvable filament for support structures. This can make this process much easier. Our team has never tried this.

The images below illustrate the supports being removed from the smaller pieces. As a reminder the full-size pieces were positioned on the build plate so as not to need supports.

Removal of supports from a 3D printed part

Once the rafts and supports have been removed the final tasks are any last surface cleanup and test fitting your parts. You can use the craft knives, blades and sandpaper to remove any surface imperfections. It is generally not a great idea  to use power tools for this (Dremel tool or sander) since in addition to scraping away any material the heat produced will also melt the plastic producing undesirable artifacts.

The image below illustrates the completed parts fitting together.

Completed 3D printed parts assembled together

The full-scale parts fit together as designed. A small amount of scraping at the bottom of the bore was necessary to achieve this. Sometimes the bottom of a model will sag a little as it is printed resulting in burs along the bottom edges that need to be removed. These are illustrated below.

Burs on a 3D printed model that may need to be removed

These burs can be removed by scraping the edges. The smaller scaled model parts did not fit very well since the scaling introduces errors in the sizing calculations. The scaled shaft was right are the minimum feature size limit recommended earlier (¼”) and was easily broken off. If feature sizes like this are needed the number of shells and infill percentages could be increased further to add more strength.

Finally, when you are finished cleaning up your parts you can add a protective coating to give a nice clean finish. XTC-3D® is an epoxy based protective coating for smoothing and finishing 3D printed parts. You can get some here (http://www.reynoldsam.com/product/xtc-3d/). This has been recommended to us but we have not tried to use it yet. Note that this will add more material to the surface of you part which may need to be considered when doing your design.

Happy 3D Printing & Good Luck with your FIRST Season!!!