(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 Im 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, lets 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). If you insist to use the user interface Use Print-O-Matic, you wont 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). 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 is too little, it will not make the wall thickness smaller than the nozzle diameter. Instead, you will have some spongy like walls with wall thickness roughly the same as the nozzle diameter (See). If it is simply impossible for you to calibrate the wall thickness to the nozzle diameter, you may substitute the nozzle diameter by a bigger value (say 0.1mm bigger) and try again.

Calibrate scale Once you have the line width right, you can go on to calibrate the scale, here is the procedure: 1) Print the 20mm test cube http://www.thingiverse.com/download:139958 2) Measure the size of the cube with a caliper (Caution: measurements must be done after the cube fully cool down) 3) Divide 20mm by the measured size, and set the value to Scale/Xy Plane Scale (ratio).

The measured size should become approximately 0.5% to 1% smaller than 20mm after the line width calibration,. This difference is probably caused by the plastic shrinkage, which can be fixed by adjusting the xy scale. After the scaling calibrated, the ability of your 3D printer to print parts to fit should have improved dramatically. You can print the test plug http://www.thingiverse.com/download:139973 or the S-Shape plug http://www.thingiverse.com/download:141737 to verify. (Note that, the S character in the S-Shape plug is not symetric. Fitting the S character upside down wont fit)

Please be reminded that, even after the line width and the scaling calibrated correctly, smaller holes (diameter smaller than 3mm) will still be too small due to the arc issue. The Skeinforge Stretch plugin can handle the arc issue, and gets the smaller holes to fit. The Stretch plugin worths a shot, just enable it to try. The default setting is a little bit conservative. You might need to adjust Stretch/Perimeter Inside Stretch Over Perimeter Width (ratio). The default value is 0.32, and I need to increase it to 0.72 to get a perfect 2mm diameter hole.

Источник: http://www.thingiverse.com/thing:35088

Автор: download

Лицензия: Creative Commons - Attribution