Here are some objects that I printed and used to calibrate my printer. They aren't the only ones available but they worked for me. Search "calibration" on Thingiverse to find other tools.
It takes some time to get a printer working well and it takes vigilance to keep it printing well.
The first time I printed this rectangle I saw I was getting places where the nozzle was so close to the glass that nothing was being extruded. In other places it was above the glass and plastic was dropping down.
I talked a little about bed level as a possible cause of clogging in the last post and mentioned that I reinstalled the springs under the bed.
Using what I saw in the test print, I carefully adjusted each corner to get the bed as level as possible. Then I used the bed leveling option in MatterControl to fine tune it. Another test print looked much better with an even layer of PLA in each of the rectangles.
Before you can get accurate dimensional measurements, you need to make sure the extruder motors are outputting very close to the right amount of filament. Checking the extruders is an easy test and doesn't require any part to be printed.
I measured 120mm up from the top of the extruder body and made a mark on the filament there. Then I used MatterControl to send the command to extrude 100mm of filament. This is the length that comes off the roll and NOT what comes out of the nozzle.
Next, I measured from the top of the extruder up to my mark. If 100mm was extruded, the measurement should be 20mm. In my case it was 27mm. I asked for 100mm and got 93mm so I was under extruding but by less than I expected.
The formula to calculate the E (extruder) steps is:
Expected measurement / actual measurement X current steps
So, 100 / 93 X 117.3 = 157.32
I set that step and ran the test again. This time the mark ended up at 20mm where it belongs.
A test cube is probably the first thing most new 3D printer owners try.
This cube is Thingiverse 214260. I took 33 minutes to print on my MakerFarm Pegasus when sliced with MatterSlice using .2mm layer thicknes
I like this one because it has the X, Y and Z marking so I don't have to remember to mark it. It is infilled to make it more rigid so takes longer than the hollow calibration cubes you will also find on Thingiverse.
The first time I printed the cube it came out with a lot of shifts in the Y axis and the X, Y and Z dimensions were also off. I tightened the Y belt and used the formula here to make a adjustments to the steps.
The formula for using a calibration cube to set the X, Y and Z steps per millimeter is:
Expected measurement / actual measurement X current steps
I printed it again and got a whole new set of wrong dimensions. You can see some ghosting in it too. After chasing numbers for a few tries, I decided just changing the steps settings wasn't working.
A little online research turned up several articles that claim adjusting steps based on measurement is never a good idea. The step setting should be based on mathematical calculations that take into account the actual mechanical parts used in the drive chain for each axis.
The math is given in on Triffid Hunters calibration guide page at http://reprap.org/wiki/Triffid_Hunter's_Calibration_Guide.
I didn't do the calculations. MakerFarm already figured that stuff out so I went back to the recommended setting in the firmware they provide.
Then I took a very close look at the hardware mechanics and finally found out why my numbers were off. You can read all about that process in my Circles Have Me Going in Circles post. Now my cubes are pretty good.
My recommendation is to use the cubes as a check but don't use them to adjust the steps except, maybe, for very precise final adjustments. Before doing that, find out what is really throwing your dimensions off.
To test for and get rid of the oozing and stringing I used this helpful guide from MatterHackers and the test object they offer in the article.
I have been seeing stringing in the prints I did so I was hoping this would help me get rid of it.
For the first plot I used the settings the article ended up with as the mid point of improvement from their testing. That was 2mm of retraction and 150mm travel speed.
My test came out with essentially no stringing at all. So what to do. I see stringing in my prints but the test says there is none. I just got a bunch of nice 10mm cubes.
Make magazine uses a pretty tough one for testing 3D printers in their annual shootout. I printed that next.
Plenty of stringing to see in this print. Although, I am pretty impressed with how well the Pegasus handled the points on these pyramids. As the points get smaller, the printer spends less time going around them and the plastic has less time to cool. That makes pointy things hard for 3D printers.
There are so many factors that can effect stringing it was hard for me to know where to start. I tried to break it down and tackle one potential cause at a time.
Extruder temperature is definitely a factor in stringing. The higher the temperature, the more stringy the plastic will be.
Filament manufacturers put temperature ranges on the packages and I started with that. For this red PLA from eSun, the recommended range is 190-220 degrees C.
After some experiments printing single walled cylinders and checking them for oozing and stength. Lower temps mean less ooze but also can cause weak prints. I settled on 190 degrees C as an OK balance of strength and oozing. This can vary by roll and even by color so I will have to watch each one I try.
I will also try reducing the temperature below what eSun recommends to see if it helps even more. See the torture test below. I am still trying to improve that one.
I adjusted the E steps above but I wanted to see if it needed any fine tuning. I used the same cylinders I printed for the temperature test to check extrusion.
First, I saved the g-code for the cylinders to a file and opened it with a text editor. I was looking for the extrusion width that was expected. In this case 0.67mm which is pretty typical for a .4 mm nozzle.
I used my digital calipers to measure the wall thickness of the cylinders I printed at several points around the perimeter. Since they were printed as a single perimeter, that number should be 0.67mm.
It is important to measure at the top since the bottom of the part will be a little oversize because of the heated bed and pressure from layers above. I also tried to get just one layer between the caliper jaws but that is hard to do.
The measurements I got ranged from 0.67 to 0.71. Not bad but I did tweak it just a little.
To make the adjustment I divided the expected measurement of .67 by the average of my actual measurements, .69, to get the percentage I would need to modify the extrusion rate by. .67 / .69 = .97 or 97%. I then plug that number into the slicer software.
I know some people change the filament diameter to adjust the flow but why? The multiplier is right there and that is what it is meant for.
That did reduce the stringing slightly.
This is supposed to be the key to string control. The MakerFarm default setting is 1mm. I upped that to 2mm of retraction and then went all the way up to 6mm but didn't really see any difference in stringing or oozing. You might see different results. I settled on 2mm as my setting.
I set mine at 150mm/s which is what the MatterHackers guide suggested. They claim anything over 150 wont make a significant difference.
MakerFarm says 2mm and I left it there. I might try a smaller number if I am printing parts with tight spacing and getting strings.
I have improved the stringing from my printer but I still feel it can be a lot better. I will continue to work on it by changing one setting at a time and seeing if it reduces the strings.
3D Benchy is a cute little boat that will test the accuracy and capabilities of your printer.There are details and features in this object that will test almost every aspect of your 3D printer.
When you download the file from Thingiverse you get a couple variations for single and multi extruder printers. There is also a .pdf file with the full set of measurements so you can compare the ideal to what you actually get when you print it.
If you have children or grandchildren they will be happy to take your test models off your hands. No need to scrape these!
Thingiverse number 1363023 is a very tough test of printer adjustment and capabilities. It will really show you what needs to be tweaked to get better prints.
Getting perfect prints of this one is something to strive for but I know, in reality, I will never get there. That is the whole idea of this test - to see just where the print quality begins to drop off.
This probably shouldn't be your first print but, if your Benchys are looking good then give it a try. You will learn a lot at the very least.
Here are the tests included in this one print (from Thingiverse):
There are a couple smaller version of this object but they don't include as many tests. They can be handy when you what to try some changes but not wait for the big one to print.
I am still working with this model and probably will be for as long as I own a 3D printer. It really shows were improvements can be made.
Testing and calibration is important with any new 3D printer. You need to get it dialed in for the filaments you use and the projects you print. I know this is something that I will continue to do.
From the last few posts, it must seem that testing and calibration is all I have done with my Pegasus. While I have done a lot of testing, I have been printing other things too. I am getting good use out of my machine. I will be talking about some of those projects in future posts but a few include:
Your comments and questions are always welcome. Do you have calibration tests you prefer? Please let us know what works for you.
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