Levelling the bed nightmares!  

Re: Levelling the bed nightmares!

Hi Mark

Welcome to the forums.

There is someone else here having similar issues with that print. I wonder if is is something in the gcode causing the problem. Have you tried slicing it yourself? The original STL can be found here: http://www.thingiverse.com/thing:246198 Can I suggest that you download, slice and print to see if the problem goes away?

With regard to the levelling, I think there are quite a few people with similar issues. It seems that PR had a poor batch of heated beds which were not very level and this causes the glass to be bent when clipped in place and, depending on the degree of bending, calibration can be very difficult.

What you could try is to clip the glass in place and with a steel ruler, see where the low points are. Generally the high point seems to be near the centre. You then put packing pieces between the glass and the bed (Note - they must electrically insulated from the bed) where the clips are. Get the glass as flat as possible and then level it.

Ok, the thermal transfer from the heater to the glass will not be ideal, but at least the bed will be level.

With regards to re-calibration after a print, I also have that problem, but I have found a work-around. Note that this works for me; I would appreciate if you could confirm whether it works for you.

So, after a print, remove the last print and home X and Y.
Home Z then raise Z 10mm and repeat.
Preheat bed and extruder, Home Z, turn off stepper motors and check calibration. Calibration should now be OK.

Note that I have slightly amended firmware in that I have set the Z axis to home to zero and not the 0.23mm in the Prusa firmware. This is simply because I calibrate to 0.1mm at the corners and 0.04mm in the centre. My bed is bent by about 0.1mm. I set my slicer to use a bed roughness of 0.05mm to compensate for the difference.

Peter

Re: Levelling the bed nightmares!

Hello PJR,

Thank you so much for your help. With regards to that model, I did slice it myself 🙂 I did not use the default one on the SD card. I found the link from the Prusa website and sliced it myself using the Slic3r I downloaded from here using the correct profile.

I'll check if I have a bent glass. Did not consider that an option because I never though the glass would be bent 😉

Re: Levelling the bed nightmares!

Hi Mark

Toughened glass is very difficult to make flat due to the extreme temperatures involved in the toughening process. Also due to the thinness of the glass, it will bend to match any irregularities in the heater PCB.

At the moment, you have a couple of options; work with what you have or see if you can find replacement parts which are flatter.

As I mentioned earlier, a steel rule across the surfaces will show the lumps and bumps; if you are aware of those it is much ewasier to adjust for them.

Peter

Re: Levelling the bed nightmares!

I found it to be really really touchy. You will need to spend some time on it. I suggest working on opposite corners also note the the adjustment screws catch in the frame hole so make sure it is seated each time you make a move.

Re: Levelling the bed nightmares!

I also had difficulties levelling the bed. On mine, two opposite corners would rock - you press down on back right and front left comes up - press down on front left and back right comes up. Adjust back left or front right to make them lower, and then they are too far away from the nozzle!
In the end I worked out that the metal frame underneath the heater (the one that is tie wrapped to the 3 linear bearings) was causing me the problem. There was just too much play caused by the tie wraps not being tight enough. I removed them and fitted new ones - as tight as I could - but the problem remained. In the end I removed the tie wraps and fastened the linear bearings to the metal frame using thin steel wire. This removed all play and rocking from the metal frame and allows me to level the bed above that.

Re: Levelling the bed nightmares!

David

That usually indicates that the frame is very slightly twisted. You have to check that all 4 feet are perfectly level. If one (pair) is touching, put a small object under is (about 2mm high) and a quick push down on the opposite pair squares up the frame.

Peter

Re: Levelling the bed nightmares!

Hi again,

I got a new glass plane from PR. Thank you for the support and very fast shipping!

While it has made things better the bed is still not 100% level. Did anyone ever implement the auto-levelling feature? I know it's in the firmware but hashed out because I searched for it.

If anyone has ever done it or has any pictures, please share them 🙂

Re: Levelling the bed nightmares!

Not sure if this helps but if you have a small level I would use one and adjust as needed until it is leveled.
The glass you can check with a straight edge. Lay it across the ends and look to see if it touches it all of the glass. Or shine a light on the one side and see if you have bleed through. If you do then the glass isn't flat.
Good luck.

Re: Levelling the bed nightmares!

Mark

It's almost impossible to get a perfectly lever toughed glass, due to the manufacturing process. Use the edge of a steel ruler across the diagonals to see how much deviation there is. Turn the glass over and do the test again.

It's probably the heater PCB that's pulling the glass out of shape. Loosen the 4 nuts under the corners of the PCB and "jiggle" the heater a tad. This may help any bend in the heater, caused by forcing the screws into the Y carriage. Tighten the nuts, fix the glass and test again.

The glass is usually high in the centre. You can insert small heat-proof packing pieces between the glass and the heater where the clips are.

The glass does not need to be perfectly level to produce great prints. The first layer can be adjusted in the slicer for any minor irregularities in the bed.

Peter

Re: Levelling the bed nightmares!

Hi all,

Thank you very much for the replies. I will keep on trying to get it level, because although I am getting great prints I know they can come a little bit better.

Peter you are talking about the bed roughness level right? I will try playing with it a bit.

Thanks and Best Regards,

Re: Levelling the bed nightmares!

Yeah, that's the one. If you set it to 0.05 with a layer height of 0.2, the first layer will be printed at 0.25. At the points where the gap is 0.2mm, the filament will be squished on to the surface, giving a better stick. At the lower points, where the gap is slightly larger, it will print and stick normally.

Peter

Re: Levelling the bed nightmares!

Thanks very much Peter. Will give it a try and post results here! 🙂

Re: Levelling the bed nightmares!

For what it's worth, I found that my glass plate was very slightly curved. With the convex side up, the nozzle crowded the bed, resulting in a thin first layer and problems with adhesion. With the concave side up, the prints turn out OK. To make sure I always know which is which, I took a diamond-tipped Dremel bit and scratched a small 'CONC' in the (unusable) corner of one side, and a small 'CONV' on the other side.

This may or may not work for others, depending on how distorted the plate is. Anyway, it's working for me.

Re: Levelling the bed nightmares!

I found leveling the bed a bit fiddly as well until I found this tool on Thingiverse. http://www.thingiverse.com/thing:115671 It is really helpful in leveling and understanding the flatness of the print bed on my i3 because I can see the deviation as numbers and figure out how to adjust for it. I modified it to fit my set of calipers and use it to level/check my bed prior to a print.

Here is a picture of the tool in action.

I've found the tool useful not only for leveling the bed but also to check and adjust the level of the x-axis gantry relative to the y-axis rails. I move the bed fully to the front out of the way and mount the calipers on the gantry and measure to the top of the y-axis rails. I then manually twist the z-axis threaded rods on either side to get the same measurement to both rails. This is done with the printer off.

For bed leveling, I turn on the printer and preheat it to the temperature I plan on using. Don't rush the warm up time, give it plenty of time as I found the dimensions will continue to change as everything heats up.

After everything is warm I auto-zero the print head and disable the steppers. I then move the print head to the front left corner and use the calibration card/paper to set the height of that corner as usual. I then move the print head out of the way and use the calipers mounted to the x-axis gantry at the same spot and measure the distance and set it as my zero point on the calipers. I then slide the print bed to the left rear corner and adjust the left rear knob until I also get a zero reading there as well. I reposition the calipers to the right side of the gantry and adjust the right rear corner until I get a zero reading, and finally slide the bed and do the same on the right front corner.

After I have all corners adjusted, I then go back to the front left corner and re-zero the calipers. Now without adjusting the bed, I go back and measure the corners, the center of each side, and the center of the bed and write down the deviation from the initial zero measurement. Positive values mean the bed is a little lower than your zero, and a negative means it's a little higher. This gives you an idea of the flatness of your bed.

Using this technique, I figured out my print bed is a little higher in the center. Now when I go back and check level, I set the print head distance there, and measure and zero the calipers. I then measure the sides and corners with the calipers and use that data to figure out the best compromise for the final adjustment.

Here is a picture of my measurements before my last print. The print head spacing was a little tight using the card in the center, and based on those numbers, I decided to adjust the right side down to match the left side which proved to be the best compromise. If the center was a little loose, I would have moved the left side up to match the right.

It sounds more complicated than it actually is. Once you get the initial level figured out, it's just a quick spot check and small tweaks to adjust the level before a print.

Roger

Re: Levelling the bed nightmares!

Love it Roger. Thank you!

Will definitely print that tool and follow your steps. 😀