Using the 3D Printer in the GVU

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Contents

The 3D Printer

The Dimension SST 768

What we have is a Dimension SST 768. It takes ABS plastic and a support material, and lays it out, layer by layer, to make whatever 3D model you want, up to 8x8x12 inches. The result is a fairly precise plastic version of your original model.

It sits in the GVU prototyping lab in the basement of the TSRB, so you'll need door access to the prototyping lab to get to it. In general, anyone can use this printer, so long as it is for a GVU project. For models that will take up more than 5 cubic inches, clear it with Scott Gilliland first, as the 3D printed plastic is somewhat expensive. Please be sure to only use it to prototype work that you yourself have designed, or have permission to reproduce. Remember that this is a learning and research tool more than anything else, so don't waste GVU resources on print jobs that are 'just for fun'.

Printing Using the Dimension SST 768 3D Printer

Below is a step by step procedure on how to use print using this printer.

Make a 3D model

The software that talks to the printer, CatalystEX, only knows how to read in one kind of 3D object file, an STL, so in order to make something, you have to make an STL of the shape you want. Usually, you'll be able to find some sort of "Save as..." option in your CAD software, so just export your model to an STL and you'll be ready to go.

On the computer next to the printer, both CatalystEX, Autodesk Inventor, and SolidWorks are installed. Inventor and SolidWorks are just two of many CAD tools available, including Rhino and Google Sketch-up; all that really matters is that you can produce a 'correct' STL file for the printer software to use. Learning to use 3D modeling software is beyond the scope of this document, but most software comes with pretty decent tutorials.

Another option is to make a model using Blender, the advantage being that Blender is free. The disadvantage is that Blender isn't really CAD software, so it's easy to make a model with points or faces where they shouldn't be, and thus confuse CatalystEX.

Import Model into CatalystEX

Catalyst's GUI is divided into tabs, and while you can add a job to the pack at any time, it's usually best to walk through each tab one at a time to see what Catalyst is planning to do with your model.

  • General: used to look at the model to import it see how it looks. You can also set the STL scale size and fill types here. The fill types control how solid parts are filled in. "Sparse" will make up internal structure, whereas "Solid" will make a truly solid part. Sparse fill works great for 95% of jobs, so you want to set this to sparse for most parts.
Catalyst Screen Shot
  • Orientation: Here you can reorient your model to get it to print using the least support material. Also note that pieces are the least strong vertically (the plastic can break between the layers), so if you're really looking for strength in a narrow spot, orient accordingly.
  • Pack: Here you can pack many objects into one printing session, and also get estimates for amount of material and time used to print.
Catalyst Screen Shot
  • Printer Status: Tells you interesting bits of information about the printer, including the amount of material left.
  • Printer Services: Tells you about various printers, if you have more than one on the network (we don't).

Use File-> Open STL to import your .stl file, set your options on the general tab, orient it on the Orientation tab, then use the "Process STL" button to convert that STL into a toolpath. A toolpath (saves as a .cmb) for this machine is the path it has to run the head around to create the model you want. After this step, it may report an error, meaning that it didn't like your model and can't figure out how to print something you gave it.

One very useful feature is the ability to look at exactly how a model will be printed on the orientation tab. Using the layer selection buttons, you're able to see your model divided up into slices, with red being a slice of your actual model and blue being a slice of the support material. You can further look at individual slices and see how each slice will be filled in. This will tell you if there are going to be any gaps in places you may not expect them, and will give you a good idea of what may stick together due to being too close. If you pay close attention to this, you won't have any surprises when your model prints.

There's also the ability to pack many models into one printing session, and this same tab can tell us approximately how much time and material will be used. This is handy so that you can avoid running out mid-model.

Before you print the model, make sure the machine is ready to print.

Get the Printer Ready

Be forewarned: **The inside of the Printer is hot. It can burn you.**

The main things you want to check:

Inside the Printer
  • Is a plastic tray in the printer?
  • Is the tray locked in position?
  • Is the tray free of all support material (to avoid scraping the print heads on it)?
  • Is there enough material in the printer to print all of your model?
  • Have you selected the proper fill types for what you are trying to make?
  • Is the little head-cleaning bucket in back empty?
Tray

Hit "Print"

You actually end up hitting print on both the computer and the printer, but now you should be ready to go.

Wait

You can see the estimated time and material remaining from the front panel of the printer. The printer is self-contained at this point, so you can log off of the desktop computer, and can leave the room safely if you want to.

Get rid of the support material

Once the print job finishes, remove the tray from the printer. You can either break off the support material, or dissolve it off using a strong base, such as in the Lye Bath (see below).

Clean Up

You need to clean off a plastic tray and re-load one, so the printer is ready to go for the next person to use it. There are chisels by the 3D printer, so clean the excess support material off of the tray, and put it back with the rest of the available trays.


Tips and Tricks

Snap-fit parts

If you print parts that should fit one inside of the other, with no clearance, they will fir somewhat tightly. If you orient the parts so that the faces that contact are printed vertically, they'll have ridges on them, allowing the parts to 'snap' together. This is very useful for making lids that snap on to cases.

Thickness

Image Showing different levels of thickness

Walls are printed as 2 sides with zig-zag filler in between. If the wall is thinner than 1.5mm, then the printer gives up on putting in this filler, and you just get two walls. If you make the wall between 1.25 mm and 1.38 mm, however, the printer will print 2 walls and a third in the middle. At 1.25 mm it goes back to just two walls, with those walls getting a little "unstable" at .76 mm. Finally, at the thickness of .05mm on the model, the printer gives up entirely and prints nothing.

These results were gotten by printing very thin point, and seeing the results along the point.

For cylinders, you get a circle filled in with zig-zag patterning, then a hollow tube, and eventually just a dot. It's worth noting that you can get thinner dots than walls.

Proximity

It appears that you can print two walls 0.2 mm from one another without them "sticking" to one another. Further, if you leave near-zero space between two parts in a model, and then print them, they will "stick" together, but can be pulled apart later.

This seems to also apply for circular walls, regardless of orientation (for example, if you have an axle in a hole, 0.2 mm space should be enough.)

Tray Reuse

Technically, the plastic trays are single-use, but we re-use them all the time. We have had some trouble, however. It seems that after many many prints on a tray, the support material may fail to stick to the surface, and as the part is printed, the support material warps and bows upwards. The end result is that the part is printed wrong and may even get knocked around by the printer head. If this happens, you may want to toss the tray out and try again on another tray.

This is especially likely if the tray has been put in the solvent bath, because the surface then becomes more slippery and the support material is less likely to adhere.

Tight Corners

While the printer can print 90 degree angles fairly reliably, it sometimes has problems getting the plastic to bend consistantly around corners tighter than 50 degrees. The tighter you go with these, the worse the corner may come out - outside edges especially.

Printer Cartridge Info

The cartridges can be swapped out mid-cartridge, and reused later. If you take a cartridge out of the printer, please label it with the amount left in it. In theory, the cartridges are moisture-sensitive, but we haven't had any problems storing them in the open so far.

Also, if the end of the plastic thread falls into the cartridge, you'll have to open it up to re-thread it. This can be done using a 7/64" allen wrench.

Finally, the cartridges are "chipped": a chip keeps count (rather inaccurately) of the amount of material left. Thus, even if a cartridge feels "full", it may be at 0%.


Lye Bath

We have a chemical tank full of a strong alkaline by the sink. This is useful to dissolve the support material from hard-to-reach areas of a model. (For models with less support material, you can often just break the support material off).

The lye in the bath is strong enough to burn skin if left in contact for more than a few seconds. Luckily, it does wash off, so if you get any on you, just rinse off in the sink. If you manage to get any in your eyes, don't hesitate to use the eye wash station. (You should already know where that is). Also, use the black rubber gloves next to the lye bath when placing or removing parts from the bath.

To turn it on, flip the switch, hit the reset button, and then check the water level. The bath is heated to 70 degrees celsius, so it will evaporate the water out whenever it is on. Thus, turn it back off when there are no more parts in it. Also, when starting it up, make sure it has enough water in it, and add more if needed (more info is posted on the wall)

The lye may take a few hours to work. Eventually, it will become saturated with the support material and turn milky-white, and will need to be changed out. If this happens, just find Scott and ask him to do this.



Acknowledgements

This document has been reproduced from the most excellent tutorial [1] found at the CS 7470 Fall 06 Website, with permission from Jay Summet.

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