3D 打印笔记 - 打印的圆洞内径偏小
最近在制作磁铁版本的效应器和滑车，需要打印机能够精确打印 12mm 直径的圆洞，用来放置直径刚好 12mm 的圆形磁铁 尝试调参数，经常得到的结果是直径刚好，而整体 size 偏大，反过来整体尺寸刚好，圆洞直径又偏小，放不下磁铁。 这里有一篇文章提到在 3d 打印机上，圆洞的边数和圆的直径有关，最好是直径的两倍，比如 12mm 的最佳边数为 24. 不过很多时候圆洞的边数不是控制的了的，比如放大缩小，这样的条件限制太不灵活。 http://hydraraptor.blogspot.com/2011/02/polyholes.html ---- 要让打印机能够印出大小完美的圆，首先要仔细校准打印机的流量。 http://www.deltarap.org/printing-undersized-holes/ https://github.com/alexrj/Slic3r/wiki/Calibration 印一个薄壁，用卡尺量厚度，把预设的挤出宽度和实际打印的厚度的比值填入 Slic3r 的 Extrusion multiplier，或者 Cura 的 Flow ** 这里有一个 tip，用卡尺量厚度的时候，尽量量最顶上的那条线，下方的线可能因为被挤压而改变线宽，理论上最顶上的线才最接近真实的挤出宽度。** ### Extrusion multiplier Tuning 1. Measure your filament and enter it (measure across multiple places using digital calipers and enter the average to 2 sig figs (2.8 or 1.7 respectfully) 2. Enter your nozzle diameter (no need to measure, just enter the number you bought it as. Nozzle diameter only affects bridging. 3. Set your Extrusion Multiplier to 1 before beginning this process 4. Print the [_40x10.STL](https://github.com/ahmetcemturan/SFACT/blob/master/calibration/_40x10.STL) file. 5. Open the Gcode file and look for the value for perimeters extrusion width. Take a note. 6. Using Calipers measure the wall thickness of all 4 sides of the thin wall cube. Throw out the largest value, and average the other 3. (Be sure you measure from the top of the box, not the bottom, the bottom might be flared out because of the 1st layer not being perfectly level. Also if you have big variations it is a good idea to measure the side that is extruded last as the extrusion will have mostly stabilised by then (after the Z-move). Try to measure the smallest number of layers possible from top as the slightest vertical misalignment of your layers will increase the measured value. Ideally a single layer would be best but very difficult with regular calipers. (Make sure the measuring device is not biting into the filament during measurement.) 7. Now you have the theoretical Slic3r width and the measured width. Divide the Theoretical Value by the Measured value. If You had previously 1 in extrusion multiplier then just enter this value. If You had some other value there before then multiply this value with the just obtained value and enter the Result into Extrusion multiplier. 8. Re-Slic3e and Re-Print the file with the new value. Remeasure. It should be spot on. If not You can iterate (repeat the process with the enetered value). ## 其他 ---- 这里有一篇 fine tune E steps 的文章，不过我觉得让线材挤出一定长度，再用实际挤出长度得出来的比值就可以初步校准 E Steps 了，不用像下面提到的那么麻烦。 http://reprap.org/wiki/Triffid_Hunter%27s_Calibration_Guide 用到的 stl： [cube stack test](http://www.thingiverse.com/thing:24238) 基本思路是用 95% 的 infill 来打一个金字塔，观察每层的线之间是否有空隙，如果有空隙就用 M92 Ennn 来增加挤出量（E Steps），没有空隙就减少挤出量直到看到空隙。 ### E Steps Fine Tuning 1. Now, with everything very close to ideal values, we can finally dial E steps in that final little bit! Find an object with flat tops on a number of levels, such as [this cube stack test](http://www.thingiverse.com/thing:24238) (scale this object by 250% after loading in Slic3r) 2. ** Slice at 95% rectilinear infill** . Use the **lowest layer height** you're comfortable with - the lower the layer height used for this test, the finer your resulting E steps calibration will be. I use 0.2mm for first run, and if I'm feeling ambitious I'll repeat this process at 0.1mm. 3. Print. 4. Ignore the first 5-6 layers because they're too sensitive to the exact height of the first layer. If it's obviously over-filling or under-filling, alter E steps or Z=0 point and restart the print. 5. Observe infill. If you can't see tiny little gaps between the lines, reduce E steps by 0.5% every 2 layers until you can see tiny gaps. 6. Observe solid top layers. If you can see tiny gaps, increase E steps by 0.5% every 2 layers until there's no gaps in the top. 7. Send the new E steps to your printer with **M92 Ennn** without even pausing the print - you will see the result in a couple of layers when the change is this small. 8. Goto 5 until the infill has tiny gaps AND the solid top layers do not. 9. Now, your E steps value is extremely fine-tuned! Save this value in your firmware's configuration and flash to make permanent.
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