The C2 Printer Leveling Project

The leveling of the print bed is crucial to getting a great print. If the print bed is not level, then all sorts of problems can occur.

While investigating the best method to level the print bed, I became aware of an engineering issue with the aluminum support bracket and the 4 steel nuts / screws which the print bed magnets stick to. The holes for the screws are 5.5 mm in diameter, However, the screws are a mere 4.88 mm in diameter. This disparity between the diameters can lead to a sloppiness of the nut's relative X-Y position within the available hole space.

So, why does that matter at all? Allow me to explain.

Let's start with a relative distance of 1 mm. 10 sheets of 20 weight copier paper laid as a stack will equal a thickness of 1 mm. The vertical accuracy of the C2 printer is rated at 20 microns, or 0.02 mm. In the last example, we used 10 sheets of paper to get 1 mm. With 20 micron thickness, you would need 50 sheets to get 1 mm of thickness.
Referring to the steel nuts which support the print bed, a 0.1 mm relative X-Y displacement will result in a unwanted shift in the vertical distance which is dependent upon where the print bed magnet contacts the nut's surface.
This inaccuracy leads to an unstable shimming process where you get the print bed leveled nicely. With removing the print bed to remove the printed object, when you put the print bed back, it is a great chance that the print bed is no longer level.

I started the FreeCAD program and designed sleeves for the screws which hold the steel nuts to the aluminum support. I leveled a small section of the print bed and printed the sleeves. I then removed each screw / nut from the aluminum support, added the sleeve and put the screw / nut back together onto the aluminum support. (The fit is very tight!)

With the sleeves in place, the screw / nut combination are now co-axially centered within each mounting hole. Removing and replacing the print bed is no longer a leveling issue.

Which now leads to the next item: thin washers - 0.2 mm thick to use in the shimming process.

Again, using FreeCAD, I designed shim washers which are 0.2 mm thick I printed a few on the C2 Printer. With the steel nuts X-Y position fixed, it is relatively easy to remove the nut, add a thin washer and then re-secure the nut.
Referring to the leveling procedure posted in the Troubleshooting section: Instead of placing addressing label pieces on the mounting nut, with this setup, you simply unscrew the nut, add a shim washer and re-secure the nut.

CURA is able to import the *.obj files attached to this thread.

Tools:
5/16 or 8 mm wrench to hold the steel nut
3 mm Allen wrench to hold the screw​

 

A follow up to the project:

In case anyone is wondering if a C2 printer can print a single layer object with a nominal thickness of 0.2 mm, please have a look at the next image:



Some additional information:

Metal to metal contact can have friction given enough pressure (like a magnet sticking to a refrigerator door as an example). To mitigate this friction issue, I applied a "dry lubricant" to the magnet surfaces of the print bed. Dry lubricant is wax based instead of oil based. Thus it won't evaporate over time like WD40 will. Dry lubricant can be found in automotive parts stores or automotive parts section of large retailers like Walmart.
The procedure is simple, soak the end of a cotton swab with the dry lubricant. Cotton swabs are sold in most pharmacies. With the wet end of the swab, wipe the magnet surfaces. Simple, right? Give the lubricant a minute or two to setup before placing the print bed into the C2 printer.

If you are wondering what the numbers are in the above image, in Part 2 of the leveling procedure found in the Troubleshooting forum, I mention measuring the thickness of the 2 printed lines (front, middle and end). The top left number covered by the micrometer is .27 mm. As you can see, my print bed is very level.

What is a good thickness to look for before finalizing the fine adjustment?

During my research on the print bed leveling, I found that a line thickness between 60 - 80 % of the nozzle width is desirable. A thickness approaching the nozzle width (greater than 80%) will not adhere to the bed properly. A thickness less than 60% can potentially lead to gouging of the print bed surface sheet.
For a standard nozzle width of 0.4 mm, the line thickness should be somewhere between 0.25 mm to 0.32 mm

Other considerations while leveling your print bed:

Use the same filament during the procedure. A change of color or manufacture can have an unwanted effect on the line printing during the leveling procedure.

Always select the same temperature for each printing. Again, changing the printing temperature during a leveling procedure will affect the line thickness and can potentially throw you off-track.

If the print bed surface sheet has gouging in it due to the print bed not being level, change out the printing sheet. When you put down the new sheet, be careful not to trap any air bubbles. The print bed sheets can be purchased from the partsbuilt.com online store. During the Fine Tune Z Offset adjustment, the C2 printer will do the auto-level procedure where it samples 9 points of the print bed. Gouging can adversely affect the calculations during the sampling.

And lastly, clean the print bed surface with alcohol to remove any finger prints. 91% isopropyl alcohol can be purchased at most pharmacies. Be careful when looking for this item as some stores place it in along with the more common 70% isopropyl alcohol. 70% alcohol has too much water and takes too long to evaporate.

 

This is why we switched over to using it for all of our high detail work.

 

I added an update to the Leveling procedure in the Troubleshooting forum which lets people know to come here for more information.

 

Some more information concerning the Fine Tune Z-Offset wizard.

!) after adjusting the bed offset with the wizard, if you do not print a test line and save the settings, the software will not save the new height. So, when you make a height adjustment using the bed up, bed down buttons in the wizard, you must print one test line before saving the results.

2) When making a mechanical adjustment to the print bed height (shimming a post), you must exit the wizard with the save and exit option. And then restart the wizard in order to get the new mechanical heights of the print bed measured. What I found was when I shimmed a post during a Fine Tune Z-Offset procedure, the new height was not recognized although logically, printing a new test line should have shown a change in the height. Apparently, the software is at the issue.

3) The Z-Offset Adjustment wizard measures only at the front left spot of the print bed. It is possible that one of the other posts could be higher than the front left post. When starting the Fine Tune Z-Offset wizard, lower the print bed by 0.1 mm before printing the first Test Line.

And in general, if you shim the front left post, you should restart with the Z-Offset Adjustment wizard as the last measured Z-Offset distance could be too close to the nozzle.

 

More information for verifying that the print bed has a good level:

If a filament line looks like the image below, that is a sure fire indicator that the filament is not adhering to the print bed.


When printing with a raft, if the corner of the raft looks like the next image, that corner WILL lift from the print bed as your print continues.



And finally, I am attaching a simple object for checking the level of the print bed. Use the Low Quality Robo3D C2 profile. You will want to observe the printing of the raft - layers 1 & 2. It is at these layers that imperfections in the print bed leveling will manifest itself.

If you see the above mentioned problems with the filament / raft, abort the print and fix the problem.

 

And one other item of interest. The BuildTak product which is used to cover the print bed: it is not as flat as you would hope for - i.e. variation in thickness. So keep this in mind if you have to replace the BuildTak sheet. Might be a good idea to re-check the print bed leveling after replacing the BuildTak.

 

Further Update:

After getting a very level bed, I had to remove the bed for a large print. When I started another print, the indications were as if the bed had not been leveled. I was thinking "What the heck is going on?".

While thinking about the friction caused by the magnets in the print bed, I tried removing and reseating the print bed. After re-starting the print, the level of the print bed had been restored. So, if you run into this situation, just try reseating the print bed before panicking and going through another bed leveling procedure.

 

New Update:

As a final test of the bed leveling, I designed a model for testing the level. This model is a single layer square. It is printed with no adhesion support (like a raft or brim), highest quality profile. If the print bed level is within spec, you should get a square. The square is 120 mm x 120 mm.

First attempt:


Second attempt after shimming:


Third attempt after shimming:


While the third attempt is not perfect, it is a square without tangled filaments (like the first 2 attempts). So if you are successful in printing this square, you can rest to know that your print bed is correctly leveled. BTW, the print time is around 4 minutes.