3D Printing Concepts

3D Printing can be incredibly versatile once you get beyond the basics, but getting there is daunting. Here's some information on the 3D printing process that will help you as you move forward.

Slicing

Slicing is the process of turning your 3D model into a toolpath for your 3D printer. We call it slicing because the first thing the slicing engine does is cut your 3D model into thin horizontal layers. MakerBot uses a few different slicing engines in our software, and all of them let you change settings that affect the way they generate a toolpath for your model. If you're having trouble getting your objects to come out the way you want them, the answer may be somewhere in these settings. Here's an overview of some common concepts in 3D printing and what your options are.

Slicers

MakerBot Slicer. The MakerBot Slicer is MakerBot's own slicing engine. It’s super fast, and we’re adding improvements all the time. MakerBot Slicer is the slicer used for the three default profiles in MakerWare, and it's also available in ReplicatorG 0037 and later.
Skeinforge. Skeinforge is an extremely customizable slicing engine that has given most of us our best prints but it's also slow and has a steep learning curve. Skeinforge is the primary slicer in ReplicatorG.
Slic3r. Slic3r is a slicing engine created by the open source community. It's never been optimized for use with MakerBots, but we've made it available for experimentation in the most recent versions of ReplicatorG.

Layer height

Layer height is basically equivalent to vertical resolution in 3D printed objects. It's like pixels in a digital image, or thread count in sheets. The thinner the layer, the more layers per millimeter and the smoother the texture of your built object. The only problem with small layers is that they make you build take longer -- for every layer you print at a layer height of .3 mm, you have to print three layers, each one taking just as much time, at a layer height of .1 mm.
The standard nozzle size on recent MakerBots is .4 mm. That's about the diameter of the plastic noodle that emerges from your extruder, and, theoretically, .4 mm is the highest layer height you can print with this nozzle. But at that layer height, each extruded noodle of plastic would just barely touch the top of the previous layer, making for a weak object. We generally don't try to build things with layer heights higher than .34 mm with a .4 mm nozzle.
The other end of the layer height spectrum is also complicated. By making adjustments to slicing settings, some MakerBot users have achieved layer heights well under .1 mm, but fairly low layer heights should be achievable out of the box. Start with a .15 mm layer height on The Replicator or Replicator 2X, or .1 mm on Replicator 2 and work your way down from there.

Build speed

Build speed is a combination of a couple of different things: The feed rate is the speed at which your extruder is moving. The flow rate is the rate at which plastic is extruding. With stepper motor extruders -- a category that includes all MakerBot extruders since the MK6 Stepstruder -- it's generally best to set these both to the same speed, so when you set your Feedrate in ReplicatorG or your Speed While Extruding in MakerWare, you are editing both of those rates.
The tradeoff with build speed is between fast build times and high object quality. Very fast build times can cause rough textures and breaks in the extruded noodle of plastic.

Temperature

Extrusion temperature is the temperature the extruder heats to during your build. It depends on a few other variables, mainly the properties of the plastic filament and your build speed.
Different plastics melt at different temperatures -- and in different ways. PLA makes a solid to liquid transition, like that of ice to water, and melts at extrusion temperatures from about 180C up. It also gets shinier and, with translucent colors, clearer when it's extruded at higher temperatures. ABS makes a more gradual transition, and softens enough to be extruded somewhere around 215C.
Higher build speeds require higher extrusion temperatures. That's because our plastics take time to melt, as well as high temperatures. The faster the plastic is being pulled through the extruder, the higher the extrusion temperature needs to be to melt it quickly enough. We use a temperature of 220C for ABS and PLA at speeds of 40 mm/s and lower, and 230C at speeds up to about 100 mm/s. These temperatures are optimized for use with both kinds of plastic, but PLA can often extrude at much lower temperatures.
You can also adjust your build plate temperature if you're using a bot with a heated build plate. ABS really needs to be printed on a heated surface, and should stick well to Kapton tape over heated aluminum between temperatures of 100C and 120C. PLA sticks to non-heated surfaces, but larger PLA objects print well on plates heated to between 40C and 60C.

Shells and Infill

Each layer of a given object is going to be divided into two parts: shells and infill. The shells, also known as perimeters, are extruded outlines defining the shape of the layer. Extra shells strengthen objects. Infill is what happens in the space left over. It's usually extruded in some kind of pattern -- the MakerBot Slicer and Skeinforge both use a hexagonal pattern for infill by default. The main setting you're dealing with here, though, is infill percentage. More infill will make an object stronger. Less will make it lighter and quicker to build. Before you build something, think about how much infill it will actually need. Objects for display often won't need more than 10% infill, while even objects that are going to see hard use rarely need more than 80% infill. Not using more infill than necessary will help you save time and plastic.