Calibrate your 3D printer to print parts to fit
by whitemousegary, published
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.
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Glad to hear that. Please tell me how's your machine doing after you did the full calibration. It would be excellent for me if you can report flaws in the article.
This is the most comprehensive calibration procedure I've ever seen. I'm not even done with the full calibration and I can already see a significant difference in print quality. Thanks!
Just finished 4 Wall-Blocks on my RepRapPro.
In Slic3r i adjusted the extrusion multiplier to change the flow ratio.
Test1: Flow Ratio 1 Wall 0,79mm with standart settings (callibrated the Steps/mm of extrusion material before)
Test2: Flow Ratio 0,9 Wall 0,7mm
Test3: Flow Ratio 0,8 Wall 0,63mm
Test4: Flow Ratio 0,6 Wall 0,48mm
I'll have to check tomorrow in the sunlight how smoothe the surfaces came out. the biggest difference yet is the teh stability when squeezing
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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 flow rate and, therefore, the realized line width. Though it is not necessary, I strongly recommend you to figure out the strongest bonding temperature initially, see 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 thingiverse-production.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 can adjust *"Dimension/Filament Packing Density (ratio)"* for the line width calibration, instead of adjusting *Speed/Flow Rate Setting (float)*; and you don't have to change *Carve/Edge Width over Height (ratio)* and *Inset/Infill Width over Thickness (ratio)*.
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)
- *Speed/Flow Rate Setting (float)* : needs calibration
- *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 thingiverse-production.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,
- 1) set both *"Carve/Edge Width over Height (ratio)"* and *"Inset/Infill Width over Thickness (ratio)"* to *"nozzle diameter/layer height"*.
- 2) print the thin wall model thingiverse.com/download:259710 , and measure the wall thickness with a caliper.
- 3) reduce *"Speed/Flow Rate Setting (float)"*.
- 4) repeat Step 2 and Step 3 until *the measured wall thickness* meet *the nozzle diameter*. As a starting point, the *new flow rate* can be estimated by *(nozzle diameter)/(measured width)*(old flow rate)* .
Just to remind you: when the flow rate is too low, 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 thingiverse-production.s3.amazonaws.com/assets/3a/04/82/c9/c7/wall_calibrate.png ). 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.
Flow rate is not the only option to calibrate line width. There are a brunch of variables which can alter the realized line width, e.g. *"Dimension/Filament Packing Density (ratio)"*, e-step per mm etc... . Just pick one and stick to it. It probably can work just fine.
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 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, thingiverse-production.s3.amazonaws.com/assets/f3/c5/51/32/08/scale_calibrate.png . 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 thingiverse.com/download:139973 or the S-Shape plug 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 won't 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 reprap.org/wiki/ArcCompensation . 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.
If you did follow my instructions and reached here, you might have noticed something undesirable. The 20mm cube (15% infill) becomes very fragile (appliable to any *non 100% infill objects*). We can fix it by decreasing *Inset/Infill Width over Thickness (ratio)*. The new value ...
- *Inset/Infill Width over Thickness (ratio)* : *(nozzle diameter - overlap)/layer height*
In particular, I need 0.01mm overlap to enforce the infill lines to fuse with their siblings for 15% infill (of course, 0mm overlap for 100% infill). See [please add an image]. Note that, the *ReplicatorG UI "Use Print-O-Matic"* won't allow you to make this change; please, give up that UI.
The reason to the fragile printout is that: when you calibrate your line width, the surface beneath is rock solid; while the surface beneath infill is sparsely filled. Without a solid surface to support, the infill lines become narrower. Filling up areas with lines too narrow, we have the infill lines loosely bonded to their siblings, i.e. fragile.
You might be confused by the suggested change; indeed, you should be confused. The naming of *edge width* and *infill width* are awkwardly misleading. Both named after *width*, but behave in opposite manners. When you increase *edge width*, SF will extrude more plastic to realize the increased width, and spaces the lines accordingly. On the contrary, when you increase *infill width*, SF WILL NOT change the extrusion rate, but it will still do the spacing with the increased line width... (whatever...). Let me translate it for you. *Edge width* means the width of lines literally, but *infill width* means *line spacing* instead. So, if the infill lines are too far from their siblings, we decrease infill width (i.e. *line spacing*).
In case you really need some extra strength, you can consider using wider lines for printing. You can do it by simply setting (no need to calibrate line width again)
- *Carve/Edge Width over Height (ratio)* : *your desired width / layer height*
- *Inset/Infill Width over Thickness (ratio)* : *(your desired width - overlap) / layer height*
Don't worry, using wider lines is perfectly fine if Skeinforge knew it.
**Something counter intuitive about the calibration**
There is one thing worth noting that my 20mm cube before the line width calibration is actually closer to 20mm in size (See thingiverse-production.s3.amazonaws.com/assets/f3/c5/51/32/08/scale_calibrate.png ). This is a little bit counter intuitive. What really happening is that ABS plastic will shrink (a lot) after they cool down. So, if the dimension is right before any scaling, the size of a printed object should always be smaller than we expecting (See the second graph). We can also see why it is so using the first graph. In the ideal scenario, the mapping between the ideal case and the expecting case is a line with a 1:1 slope. *The wider than expecting realized lines* shifts the mapping upward, and shrinkage makes the slope less steep, so we have a small range of good mapping near the intersection (See the first graph).
**Two popular wrong interpretations**
By the way, I would like to clarify two popular wrong interpretations of the problem. When I look for reasons for the symptoms above in the internet, I keep seeing people saying it is caused by "plastics shrinkage" or *"the arc issue"* reprap.org/wiki/ArcCompensation . For "plastics shrinkage": its true that plastics will shrink after they cool down, so a printed hole (e.g. thingiverse.com/download:139973) will become smaller. However, its printed plug will also shrink by the same amount. Therefore, a printed plug should fit into its printed hole regardless of shrinkage. For the arc issue reprap.org/wiki/ArcCompensation : it will only affect smaller holes, not the larger one. The author is too conservative when he deduces the implications of the formula in the page. ABS plastics can tolerate a tiny bit of deformation. From my experience, if you try to fit a metal rod into a smaller ABS hole, as long as the difference in diameter is within 0.05mm, a fit will still be feasible (the tightness will vary though). To make it easier to read, I re-parsed the table (see thingiverse.com/download:139948 ). It shows that a 10mm diameter hole will be 0.008mm smaller than it should be, which is not enough to cause a tolerance problem. To a pair of hole and plug, the arc issue will only become a problem unless the diameter is smaller than 3mm.
This is it. The information mentioned here is probably mentioned somewhere else already. I just meant to put them in an organized manner as a note for myself. If I missed a citation, please show me. I'll put it back.
PS: 2013-05-01 - My 3D printer is delivering printouts reliably with precision and strength for quite a while now. It's time for me to say goodbye to test shapes. For the time being, I kept a small portion of the test shapes I printed for some good reasons. This is the last picture of them before I throw them all away, thingiverse-production.s3.amazonaws.com/assets/be/9a/23/9c/e8/IMG_20130501_070417.jpg . Cheers, fingers crossed...
Why the wall thickness didn't change after modifing the flow rate?
* Did you disable "Print-O-Matic" UI?
* Did you press "Save all" after editing profile?
* Did you re-generate G Code file after editing profile?
* Are you using the profile you edited in the "Generate GCode" window?
* This shouldn't be necessary, anyway, are you using SF50, ReplicatorG40 and the latest firmware?
Do I need ReplicatorG for this calibration to work?
* No, you don't need ReplicatorG. This article is intended for Skeinforge 50, not ReplicatorG. You just need Skeinforge for this calibration to work. ReplicatorG is not necessary at all.
There are two thin wall models. Which one should I use?
* Use the one matches your expecting line width. (e.g. 0.4mm line width vs. 0.4mm thin wall; 0.5mm line width vs. 0.5mm thin wall)
* *Both should should be just fine initially. However, when you calibrate the infill width to a smaller value, SF might think the thin wall model should be filled (which can mess up your measurement). Using a matched thin wall model can stop SF from filling the wall.*
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