About this 3D model

( Just in case the text formatting were jerked up, the article in PDF format is available at http://www.thingiverse.com/download:2091544 ) I have my Thing-O-Matic for a year now. From time to time, I tried to calibrate it to print parts to fit. Finally, I got it done (See http://youtube.com/watch?v=lQbvfiZAm-c). It turns out I just had the edge width and the scaling wrong. If you also have the problem to print parts to fit, read this article. It might work for you too. Here are the symptoms of the problem I'm trying to fix. 1) A printed plug is impossible to fit into its printed hole. 2) Small parts (around 1 cm size) are too big, while larger parts (around 10 cm size) are too small. Instructions Okay okay, let's see what our 3D printers should be offering first (if configured correctly). See http://www.youtube.com/watch?v=lQbvfiZAm-c . The video shows two parts, an S-Shape hole and an S-Shape plug http://www.thingiverse.com/download:141737 . The plug and the hole are edge to edge touching each other in the STL file. As show in the video, I can actually plug them together just by pushing real hard with bare hands, no tolerance compensations in the design, no drilling or filing, they just fit. The S-Shape is chosen deliberately as it shares a lot of common features with interlocking designs. Designing is fun with interlocking designs. ( A more fancy result, same premise, http://www.youtube.com/watch?v=O3dJsjv-8vA ) This article is intended for Skeinforge (SF) calibration, and I did my calibration with ABS plastics, Thing-O-Matic (0.4mm nozzle, firmware 4.1) and ReplicatorG+Skeinforge 50. Before the calibration Temperature will affect the actual amount of the extruded plastics and, therefore, the realized line width. Though it is not necessary, I strongly recommend you to figure out the strongest bonding temperature initially, see http://www.thingiverse.com/thing:35088 . You really need every bit of available bonding strength for printing large ABS objects. If you are using ReplicatorG, please disable its user interface "Use Print-O-Matic". This named-funny-UI is just to override some Skeinforge variables without your notice. It is easier to calibrate your 3D printer to fit without this named-funny-UI . You can do it by unchecking the checkbox "Use Print-O-Matic (stepper extruder only)" in the "Generate Gode" window (See http://thingiverse-production-new.s3.amazonaws.com/assets/95/f2/da/5d/af/disable_replicator_setting.png ). If you insist to use the user interface "Use Print-O-Matic", you won't be able to adjust the infill width such that you would end up with a fragile printout (See Section Calibrate infill). Here is the list of necessary variables for this calibration to work, * Carve/Extra Decimal Places (float) : change to 5 * Carve/Edge Width over Height (ratio) : nozzle diameter/layer height * Inset/Infill Width over Thickness (ratio) : nozzle diameter/layer height (initially) * Dimension/Filament Packing Density (ratio) : needs calibration (equivalent to the reciprocal of the extrusion multiplier in Slic3r) * Scale/XY Plane Scale (ratio) : needs calibration Before the calibration, you need to increase Carve/Extra Decimal Places (float) to 5 . This variable is to control the significant digits of the values in a gcode file. There is no point to reduce precision at this point. Precision is king if you want to print parts to fit. Calibrate line width If you are having problems to print parts to fit, your 3D printer is probably drawing lines wider than Skeinforge expecting. In my case, SF is expecting 0.4mm , while my 3D printer is drawing 0.64mm (See http://thingiverse-production-new.s3.amazonaws.com/assets/b9/49/7b/db/d0/IMG_20130225_124259a.jpg ). The optimal line width that your 3D printer can do is the same as its nozzle diameter, so you want to enforce that to optimize its ability to print small features. To calibrate the line width to optimal, * 1a) set both "Carve/Edge Width over Height (ratio)" and "Inset/Infill Width over Thickness (ratio)" to "nozzle diameter/layer height" . * 1b) set both "Speed/Feed Rate Setting (float)" and "Speed/Flow Rate Setting (float)" to the same value. * 2) print the thin wall model http://www.thingiverse.com/download:259710 , and measure the wall thickness with a caliper. * 3) adjust "Dimension/Filament Packing Density (ratio)" . * 4) repeat Step 2 and Step 3 until the measured wall thickness meet the nozzle diameter. As a starting point, the new value can be estimated by (measured width)/(nozzle diameter) x (old value) . The goal of this section is to fine tune the volume of the extruded plastics to match the expected line width. Therefore, Filament Packing Density (ratio) is not the only option. There are a brunch of variables which can alter the realized line width, e.g. e-step per mm , changing the flow rate relatively to the feed rate, etc... . Just pick one and stick to it. It probably can work just fine. Just to remind you: when the amount of extruded plastics