Rafts, Skirts & More

There are several different elements within a 3D print. This is a list of common items that may be included with a model when printing. The advantages, disadvantages, and notes are from my experiences. Other users may have additional experiences to share.

The Introduction to 3D Printing video illustrates many of these elements.

Raft · Skirt · Brim · Infill · Support · Perimeters · Vase Mode · Start Points and Retractions · Prime Pillar · Ooze Shield


Raft

Rafts are like a foundation for a print. They work well for many prints. "Raft Offset from Part" adjusts the margin distance from the model to the edge of the raft. Be sure to make it wide enough to have something to grip onto when you want to tear it away after printing.

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Skirt

Skirts outline a print at the start of the print job. Set one or two outlines to get things flowing well and to see the overall space and placement of the final print. I use a skirt on nearly every print.

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Brim

Brims are wide skirts that are attached to the model. They can be created instead of a skirt by setting "Skirt Offset from Part" to 0.00 or to a very small number so that it barely sticks to the model. Brims help prints stick to the print bed. They can be more than one layer.

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Infill

Infill is the material printed inside of the model. There are options for density and style along with more detailed settings for angles, if desired.

Notes

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Support

Support is necessary when a model has overhangs to print. If it is possible to rotate a model so that it can print without support, it is usually worth trying to do that.

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Perimeters

Outline/Perimeter Shells are the outer boundary of a print. Increasing the perimeter shells can make a print more solid and hefty as well as decrease translucency.

Notes:

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Vase Mode

Vase Mode, also known as "Spiral Mode," can be selected by checking the box for "Single outline corkscrew printing mode (vase mode)" in Simplify3D. In this mode, the model is printed just as one perimeter shell with no infill. After any bottom layers, the print head spirals around as it prints extruding constantly along the way.

The geometric bowl in the Introduction to 3D Printing video is printing in vase mode. This link will take you to the moment in the video where that is printing: Vase Mode Bowl.

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Start Points and Retractions

Random Start Points Optimize Start Points Choose Start Points Only Crossing Open Spaces

Retractions occur when the motor pulls the filament back up into the nozzle a little bit. This typically happens when the printer shifts to the next layer or when the print head moves from one area of a print to another. When there is a retraction, sometimes a little blob of filament sticks to the print and makes a tiny bump. Additional settings are available within Simplify3D to try to minimize these bumps. For example, in the "Advanced" process settings within "Ooze Control Behavior" there is an option to "Only retract when crossing open spaces" and I often try this to help.

In the print preview mode, you can see the retractions and get an idea of where they may affect your print. Un-checking and checking the box for "Retractions" within the preview can help you see them more clearly or select coloring by "Movement Speed."

One way to control how the retractions may appear in your print is to set the "Start Points" within the "Layer" tab.

Paying attention to layer start points can really help improve the look and feel of the final print.

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Prime Pillar

Prime Pillars are particularly useful when printing with more than one extruder. When printing with dual extrusion, for example, while one extruder is printing the other one may ooze out some material and not be quite ready to print when it is its turn. The prime pillar is printed first for each layer, so the extruder will be ready when it starts printing the layer of the model. Also, with the oozing there may be drips that will catch onto the model if the waiting extruder goes directly to the model. The prime pillar will catch these drips since it is printed first.

To help prevent falling pillars and to have more control over the pillar location, I often add to the workspace a tiny model that prints just one or two layers. Using a raft will help the pillar stick to the bed and the tiny model next to it will increase the raft size. Having the pillar far from the primary model helps when the pillar is catching ooze strings. With this technique, I have been able to avoid ooze shields. For example, I set the pillar to be in the North position and place the tiny model separated from the primary model in the y-direction. The pillar is then North of the tiny model and far from the primary model.

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Ooze Shield

Ooze Shields are useful when printing with more than one extruder. When printing with dual extrusion, for example, while one extruder is printing the other one may ooze out some material and not be quite ready to print when it is its turn. The ooze shield is printed first for each layer (or after the prime pillar if included), so the extruder will be ready when it starts printing the layer of the model. Also, with the oozing there may be drips that will catch onto the model if the waiting extruder goes directly to the model. The prime pillar will catch these drips since it is printed first. The ooze shield can protect the model from drips.

I have been avoiding ooze shields by using distanced prime pillars when possible.

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Abby Brown
Torrey Pines High School, San Diego, CA
November 2018

www.abbymath.com