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Printing With Support - Extreme Overhangs
Printing with support is required when plastic must be deposited on a layer where there is no or insufficient plastic on the previous layer. This includes steep overhanging surfaces, straight overhangs, and fully suspended islands. Learning to print objects on a 3D Printer that require support structures will dramatically expand the potential of your printer and give you the confidence to undertake printing tasks that perhaps you had previously avoided. It would seem though that nature doesn't like to follow design guidelines like the "45 Rule," the idea that overhanging surfaces should not exceed 45 degrees thus avoiding the need to use support; and many of the most compelling objects to print require the use of support.
The following procedure is done using the slicing engine Skeinforge. Other tool-path generation programs with the ability to generate support structures should produce similar results.
Select a Model to Print
Artec produces a number of small footprint, high resolution, high detail 3D Scanners. They have a gallery of scans available for download on their website. A scan of a decorative mushroom (image: Artec3d.com) provides nearly every genre of needed support and in addition to being an excellent test piece, it will leave you with a good looking replica of a scanned mushroom. Before printing, the STL from Artec should be given a flat bottom and checked for manifold. You can find the appropriately modified STL on thingiverse, here.
Prep your printer
Stringing is an undesirable artifact caused by plastic oozing out of the hotend nozzle when the printhead is moving from one printing location to another. The effect is unintended 'strings' of plastic spanning various parts of printed objects. Stringing in combination with support can bind the lattice together making removal difficult and adding additional surface artifacts detracting from the overall appearance of the finished object.
Skienforge will print the support structure, or lattice, at the standard feed-rate for your profile. If you run the first layer of your print slow to help adhesion (default for many profiles), that speed change will not apply to the first layer of support. The support lattice is built as a single trace of plastic, laid down like like a ribbon, looping back and forth like switchbacks on a mountain. As such, making sure the first layer of support is firmly attached to the print bed can often mean the success or failure of the print. There are some things you can do to help ensure the first layer of the support lattice sticks to the build surface even with the increased speed.
Ensure a smooth build surface. A fast moving nozzle close to the print bed can catch on flaps of tape or air bubbles. While larger widths of Polyimide Tape can take some practice applying, I have a hard time recommending anything else. A single piece, carefully applied, will give your bed a smooth long lasting surface with excellent adhesion. Polyimide is also known by the trade-mark 'Kapton' if so licensed through DuPont. As Polyimide tape is manufactured and sold all over the world I believe it is worth a purposeful shift towards the term Polyimide.
Provide a level print bed. A level printing surface means every thin trace of support will be laid down at the intended height. A slope can cause some traces to be laid down too high from the print bed and prevent them from adhering.
Clean the print bed. Dust from the air and oils from your hands can prevent proper adhesion of the plastic to the print bed. A quick wipe-down with Acetone will help this. Note that Acetone is a solvent of many plastics and should not come in contact with an Acrylic print bed.
Support Settings & gcode generation
Navigate to the Skienforge interface. In ReplicatorG this is done by selecting the profile you want to modify and clicking ' edit.'
Those using the current version of ReplicatorG will need to first select the 'Gcode' menu item 'Edit Base Profiles' to display the available profiles for modification. I'm using a MakerGear extruder on the Thing-O-Matic and and currently running our 3mm ABS filament produced from a grade of ABS named PA747. I'm printing at 0.2mm Layer Heights and a trace width of 0.4mm. Hence the naming convention: MG PA747 pt2, 4. After you click edit, Skienforge will open in a new window. Navigate to the 'Raft' tab and scroll all the way to the bottom. For starters you can copy what I've found to work well for and later adjust if need be to match your particular machine.
The description of the values under - Support - are:
Support Cross Hatch: OFF - this will create support more like a grid compared to a zig-zag ribbon which can be more difficult to remove. We have it off.
Support Flow Rate over Operating Flow Rate: 0.6 - the extruder will deposit 60% of the amount of plastic usually extruded for the profile. Higher means thicker support, lower corresponds to thinner weaker support. This is the number most likely to be adjusted should you need to fine tune.
Support Gap over Extrusion Width: 0.05 - defines the distance from model to support as a percentage of Extrusion width, in this case 5%.
Support Material Choice: Everywhere - Several options are presented. 'None' (explanatory), 'Empty Layers Only' (used when placing a print some height above the print bed), 'Exterior Only' (The standard supporting lattice), and 'Everywhere.' No reason not to cover all use cases and select 'Everywhere'
Support Minimum Angle: 55 - The degree of overhang after which Skienforge decides it is time to add some support structure. The de-facto value is 45 but most printers with some active cooling can handle a bit more. Try 55 and decrease if there is unwanted drooping, curling, or 'noodling.'
Also: Removing support can sometimes be a stressful to the object you are attempting to release from it's grasp. I also set all extra shells to 2 under the 'Fill' tab giving the print a little extra strength so I don't have to worry so much about the print potentially breaking apart during the process.
Thats it! Save changes and close out of the window.
Generate your gcode as usual making sure 'Full Support' is selected under 'Use support material.'
Select Full Support
Printing (adjusting settings & reprinting)
Now comes the exciting part; printing the mushrooms. This model generates a large amount of support structure. I'm using our Glow-in-the-Dark plastic that, while looking amazing, does cost a bit more than standard varieties. It is perfectly acceptable to burn through some cheaper Natural ABS during the learning period.
Start building the print as usual but babysit the first couple layers to make sure everything is getting off the ground all right. It should be apparent early on if your support is too thick or too lean. Good support is firmly planted to the print bed with obvious spacing between the support pattern. If adjacent support traces are touching, go back and reduce 'Support Flow Rate over Operating Flow Rate.'
You want the support as weak as possible while still providing a base for the printed model. Here you can see a flimsy support lattice slightly warping in on itself as the ABS cools. This is perfectly acceptable and in some ways a sign your support is on the right track.
If all went as planned, you mushrooms have finished printing and you can see the full effect of the support. It engulfs all but two top hats. Great work.
Carefully remove the finished print and examine your handy-work.
Take a look at that mess. It isn't pretty, but it's fine looking support. Good visible spaces between the lattice but enough structure to provide solid support for the model. From here you can also get a good look at the part of the top mushroom that Skienforge felt could make it on its own.
Before removing the support the whole print came to 62 grams, or about 2.2 ounces.
Using a combination of pliers and fingers, carefully start to strip away the lattice. When done correctly, long ribbons should peel away at once.
Do what you can with your hands, then move to the pliers being careful not to scratch the sides of the print. Lastly, if need be you can use tweezers or a set of picks. Remember to save all your support and mix it with Acetone or MEK to make ABS Glue.
When I finished removing all the support I weighed the model again.
29 grams, ouch! A full 53% of that model was support structure. How about aesthetics, how do things look. Here are shots of the two kinds of support we are interested in. Support laid on top of the printed surface and support beneath a printed surface.
You can see that there are some visible artifacts left over, some of which could probably be cleaned up more with tweezer work and/or sanding. All in all though, the support came off decently well. Considering you are printing the same material at the same temperature, it is fairly convenient that you can define an arbitrary surface for which plastic will only temporarily adhere. Now, lets have a look at the finished product.
Now that is a pretty good looking luminescent fungus. Pat yourself on the back, good job. If this is your first experience with using support, congratulations, it only gets better from here.
While a good portion of the print was support and some of it still stuck around after cleanup, it was all a necessary evil allowing you to print otherwise impossible geometry. One can reduce the amount of support needed by increasing the minimum angle for support in Skienforge once your other settings are dialed in well enough to support steeper angles. Better would be a more intelligent support structure algorithm similar to the ones employed by some high-end commercial machines; building only small columns of support lattice that branch out at the last moment to hold up the print. Regarding ease of cleanup and aesthetics, the inevitable future of water soluble support will make cleanup a breeze and produce much smoother surfaces. It will not however decrease the material cost as currently any available water soluble thermoplastics such as the PVA we carry is more expensive than other more common plastics like ABS and PLA.
If you have any tips or tricks for printing with support; help your fellow men(and women) and leave them in the comments.