3D Printing for FIRST Teams (6 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 4.

3D Printing Step 4: Preparing and Leveling the 3D Printer Build Plate.

When getting ready to print, the Build Plate must be prepared and leveled. In most cases 3D Printer Build Plates are either Polycarbonate plastic or Glass. The Replicator 2 shipped with a Polycarbonate Build plate which was light and permitted direct printing. However, there were many reports of the plates warping which caused print problems (prints would not adhere uniformly to the plate). We did encounter this and had our plate replaced by MakerBot. There is a Glass plate available for the Replicator2. The Glass plate is substantially flatter and yields much more reliable results. Newer MakerBot printers and those of many other manufacturers now use glass build plates. We have used a mix of the Glass and Polycarbonate plates. The Polycarbonate plates have worked fine for smaller models that are placed in the middle of the plate. Glass does yield better results for larger models that use more of the plate area. A MakerBot Replicator2 with the MakerBot Glass Build Plate is illustrated below.

MakerBot Replicator2 with the MakerBot Glass Build Plate

One drawback of glass is that the plastic will not stick to it. Generally, it is recommended to use Blue Painters Tape on the build platform. There are several options available including plate sized Blue Tape sheets from MakerBot or rolls of painter tape from any Hardware store. These have not proved to be the best options. The plastic is hot when it leaves the extruder and cools down quickly. As it cools it will tend to shrink. As it shrinks it will exert pressure on the tape and sometime pull the tape off the plate during printing. This results in the print warping while in progress. A tape with high adhesive properties will avoid this. We found the following tape that works really well (http://www.zoro.com/i/G4241036/). It also comes in 6� wide roles which will cover most of the Build Plate width. When putting the tape on the plate make sure that you apply a lot of pressure to ensure that it is firmly attached. Also ensure that there are no bubbles or creases in the tape. This tape can also be used on Polycarbonate plates to avoid potential scratching of the plate when removing the finished parts. Using this tape and Rafts has cut down on the number and severity of part warping issues that we have had. When done installing the tape insert the plate into the printer. The Glass build plate with the blue tape is shown below.

MakerBot Replicator2 with the MakerBot Glass Build Plate covered in blue tape

The next step is to level the build plate. Newer printers are doing a better job of automating the procedure. For the Replicator2 this a manual process that requires using a business card to judge the gap size between the extruder and the plate in different places. This is a difficult process to get repeatable because you are relying on (1) judging how easy it is to move the card under the extruder when it is in contact with the extruder and (2) the card can get compressed by this process resulting in uneven heights. Overall, this process is less than satisfactory and can take a lot of time to get right.

There are two simple ways that this can be improved. The first is to use feeler gauges instead of the business card. These are available in most hardware and automotive stores. We measured the thickness of the MakerBot reference business card and found it to be approximately 0.005� or 0.127mm thick. We experimented by using slightly larger and smaller feeler gauges but found the thickness of 0.005" to be the best options. A smaller gauge resulted in the plate being closer to the extruder which could result in extruder clogs. Using a larger feeler gauge increased the risk of layer separation during printing.

The second improvement was to get rid of the need to rely on feeling the pressure exerted on the feeler gauge while adjusting the plate-extruder gap. The feeler gauge is reflective i.e. you can see the reflection of the extruder (and hence the gap) in the gauge as it is lowered to the correct height. This is illustrated below.

Adjusting the plate-extruder gap

In this case the gap between the extruder and feeler gauge is minimized but the feeler gauge can still move freely. This is the ideal gap size.

Using this visual approach yielded more repeatable results. Once the plate is leveled the filament can be loaded.