What do digital desigers need to know about creating digital designs for a MakerBot! Feel free to edit this page to add your own insights!
- Overhangs - If you want to design an overhang, you can get away with making gentle slopes. For example a wine glass will actually print out on a MakerBot. The slope of the overhang should be about 45 degrees or half the width of the free space extrusion, whichever is steeper for the given distance. What this means is that if you can, design the overhang at an angle so that the material builds upon itself out to the edge. This would eliminate the need for support material. To get things to attach horizontally, you've got to either suspend gravity inside the MakerBot or add supports or develop a support material extruder. Adding supports such as vertical 0.35mm walls every 1cm should be more than enough to bridge a void and you can snip them away later!
- Supports — Single thickness walls (0.35 - 0.5 mm every 1cm depending on skeinforge settings) and perforated walls work well for this, as they are generally weaker and easy to break off. Place supports with some cleverness to take advantage of bridging.
- Corner Warping - If you make something wide and long and flat, the corners will curl up a bit because the material shrinks just a bit as it cools. The way super expensive machines deal with this is they heat up their build platform or the entire chamber and then cool it down once the thing has been made. Experiments await for those who want to try pointing a heat lamp at the build platform or a heat-sink style build platform made of a PCB.
- Wall thickness — Objects meant to be water tight should be at least two wall thicknesses thick, three might be better. Skeinforge defaults to two layers per wall, so walls thinner than four wall thicknesses build faster if skeinforge doesn't have to make a layer a fraction of a wall thickness thick.
- Moving Parts — Before you upload your model, be sure that there is enough clearance between moving parts such as gears, cogs, links in a chain. If you do not, your prototype may be a solid, non-moving object. To ensure the parts of your model move, you may need to make clearance adjustments.
- Cylinders and circles —
- Small circles: You can print very small circles, but not accurately. At some point, the number of points in the circle is too much for the cpu on the controller to handle. If you reduce it to a hexagon or a triangle, it helps a bit. For the most part, 5mm is the smallest hole has been accurately printed without a bit of trial and error and adjusting how it is drawn to get it to print the size you want.
- Large circles: While you can print larger circles, the number of points on the circle continues to come into play and if possible, printing a hexagon or multi-sided object will be easier. In addition, hexagons (or multi-sided objects) can be laid on their side for printing versus attempting to print a cylinder on it's side.
Tips for designing a part to be dimensionally accurate:
- Dimensions above a certain size are easy to get accurate down to the motor resolution (0.1mm).
- Curved surfaces generally have better surface finish than flat ones.
- Things that generate a closed tool path with no breaks give a higher quality part. In other words, if you make a wall one extrusion width, it needs to be a closed curve or over a certain length or it won't build reliably, and oozebane becomes critical. If you make it two or four thicknesses, it becomes its own closed curve.
- Things that generate short toolpaths, even if they are closed curves, are a problem, as with towering turned on, the plastic doesn't have enough time to cool, and the result will sag or wiggle as the head passes over it. If towering is turned off, narrow towers become weaker and generate lots of strings unless oozebane is well calibrated.
- Some of the dimensional accuracy relies on the extrusion rate and other factors being calibrated correctly.
File preparation is an important part of 3D printing. If the source file is not converted properly data can be lost, resulting in a part that looks different than you expected. The program, Skeinforge, that the MakerBot uses to create the toolpath (GCode) requires STL files in millimeters (mm).
Almost all of today's CAD systems are capable of producing an STL file. For the user, the process is often as simple as selecting File, Save As and STL. Below are steps for producing high quality STL files from a number of today's leading CAD systems.
If you are unsure that your file is properly exported there is a free program you can download called MiniMagics. This is an .STL file viewer software that allows you to import, save and compress STL files, as well as view parts and detect bad edges and flipped triangles.
Most CAD packages will have a couple of options that affect the quality of the STL. Changing a "Deviation" type of value will alter the overall output or tessellation. Changing an "Angle Tolerance" type of value will alter smaller details in your file. The tighter these parameters, the more triangles placed on the surface of the model. Simple geometries tend to be a few hundred kilobytes in size. Complex models will range from 1-5MB in size and still produce good parts. For many models, files larger then 5MB may be unnecessary and often result in more time to get your quote and models back.
In all cases, export your STL file as a binary file. This saves on time and file size.
Please note, these are general guidelines and may not work or in some cases, produce the best possible STL file. You will need to consult your specific CAD programs user's manual for specifics.
STL File Size & Faceting
Angle, Deviation & Chord Height (Faceting & Smoothness)
If your part was rougher or smoother than you had hoped, you can change the angle, deviation and chord height to create the right outcome. Faceting is determined by the relative coarseness of curved areas of the adjoining triangles. The most common variables are deviation or chord height, and angle control or angle tolerance. Following are three examples of various STL faceting outputs determined by varying angle, deviation and chord height: Coarse faceting (poor), excessive fine faceting (fair) and good quality faceting (best).
Coarse Faceting (poor): When the faceting is too coarse you can see flat spots on curved surfaces. The flat spots in the STL file will show up when the part is produced. Coarse faceting is almost always caused by the angle setting being too high, or the deviation/chord height settings being too large, or a combination of both.
Excessively Fine Faceting (fair): Fine faceting can cause delays in processing and uploading of parts because of the larger size. Increasing the resolution excessively does not necessarily improve the quality of the produced part. This is caused by the angle settings being too low, or the deviation/chord height settings being too small, or a combination of both.
Good Quality Faceting (best): The happy medium between the two extremes is good quality faceting, just detailed enough so that features build to the file dimensions, while being simple enough to maintain a manageable file size.
The build process for these machines is based on the extrusion of a melted ribbon of plastic (typically ABS). The ribbon is extruded in successive layers in the Z axis to build the model up. The important distinction here is that this process is an additive process and not a removal process, such as is typical for traditional machining. As a result the process has both strengths and limitations. Although the model material is quite strong, typical performance of the plastic with respect to material properties should not be used. The level of cross lattice bonding of the polymer that is typically available in the material is not available in this process and, therefore, standard documentation on the performance must be applied
Typical Equipment Capabilities and Limitations
Usable Build Area: 100mm Width x 100mm Depth x 130mm Height
X/Y Positioning Resolution: 0.085mm
Z Positioning Resolution: 3.125 microns
Typical Z-layer height: 0.3725mm
Again if you've got guidelines, tips, or tricks for designing for MakerBots, edit this page!