Parts coming up short

[nfratianni 1]

Hi I've been printing with the Ultimaker 3 for quite some time now and only recently been running into a few issues. Currently I'm trying to print a simple cylinder with 20 mm height and 20 mm diameter. Each print comes out to be around 0.3 mm short. I've already tried releveling the z-axis and checked the g-code for the final z height which comes up at 20.07. I am printing with Ultimaker brand ABS and am aware that ABS does shrink, however my x and y dimensions are both over the 20 mm mark by about 0.3 mm. Any help would be greatly appreciated.

-Nick

[gr5 2,167]

Cura intersects planes with your model. if your layer height is .2 and the top most plane that intersects with your model is .1999 below the top it will skip the last layer so part of your error is probably this intersection issue. So height error can be almost as large as layer height.

Also click on the part in normal view and click the "move" icon on the edge and make sure Z=0.

Also it's good to level the nozzle a bit close to the glass to squish the first layer well but this can add about another .2mm of error (shorter). Add those 2 errors and you can easily get .3mm. I recommend you just make your model taller by .3mm but in theory you could twist the 3 leveling screws a bit to get .1 or .2mm of correction (but then your parts may come free from the glass during a print) and lower the layer height a bit (but then your print will take longer).

[nfratianni 1]

Thanks for the quick response! I know the model is flush at z=0.

Cura intersects planes with your model. if your layer height is .2 and the top most plane that intersects with your model is .1999 below the top it will skip the last layer so part of your error is probably this intersection issue. So height error can be almost as large as layer height.

This did give me an idea on what my possible issue could be. I do have the initial layer height set at 0.27 mm as per the defaults. Maybe this is causing my issue where at 0.2 mm layer height I'll end up with one layer left at 0.13 mm so Cura then ignores that layer? I'll try setting the initial layer height down to 0.2 mm and see how it affects the dimensions.

[nfratianni 1]

After doing more testing I eliminated the above idea. I even enlarged the model from 20 mm to 20.09 mm to see if it was cutting off the top layer with no luck. Still stuck at a height 0.3-0.4 mm short. I also tried printing just the bottom layer and got the proper first layer height of what I had set at 0.2 mm. The x and y axis are also still consistent at 0.3 mm too big. Finally I know I can modify this part to be 0.3 mm taller but this won't be the case with all the models I'll be printing. I'm just about out of ideas at this point and don't know what else could be the issue. If anyone else has any ideas at this point I'd be willing to give it a try!

[fbrc8-erin 272]

Are you using the active leveling? It can add a little height to the Z axis because it does corrections on the first 10mm for leveling, and then phases out the corrections over the second 10mm.

[nfratianni 1]

I know that it sometimes automatically does the auto leveling. Is there a way to turn it on or off all the time? I haven't noticed it do an active leveling procedure in a few prints now that you mention it.

[fbrc8-erin 272]

I know that it sometimes automatically does the auto leveling. Is there a way to turn it on or off all the time? I haven't noticed it do an active leveling procedure in a few prints now that you mention it.

 

In the menu, you can choose how often the active leveling occurs. It's recommended to leave it on Always/Every print.

I don't have a printer in front of me right now but I believe this is how you choose the settings: System --> Maintenance --> Build Plate --> Leveling Frequency.

[nfratianni 1]

I know that it sometimes automatically does the auto leveling. Is there a way to turn it on or off all the time? I haven't noticed it do an active leveling procedure in a few prints now that you mention it.

In the menu, you can choose how often the active leveling occurs. It's recommended to leave it on Always/Every print.

I don't have a printer in front of me right now but I believe this is how you choose the settings: System --> Maintenance --> Build Plate --> Leveling Frequency.

I just gave that a try and it did help a bit, thanks! Now the model is only 0.2 mm short as opposed to the 0.3 mm before which is better, but I need to get it to be at least 0.1 mm or less.

[gr5 2,167]

Well one thing I didn't mention last time is to calibrate the Z axis. You can put the um3 into developer mode and then use ssh to connect to your printer's IP address. username/password are ultimaker/ultimaker. This puts you into a powerful utility.

Try homing the Z axis:

G28 Z0

Try moving the Z axis to position 10 (10mm from nozzle to glass):

G0 Z10

Now move the Z axis to another position far away - say maybe 160mm from nozzle to glass:

G0 Z160

Measure how far the Z axis moved. You need to measure this quite accurately. If you were getting .2mm error on a 20mm print that is only 1%. 1% at 160mm is now 1.6mm - a bit easier to measure but still.

If it is off then you need to adjust the steps/mm setting. That *might* be somewhere in the menu system on the front of the printer - not sure - but it would be nice to eliminate this.

I seriously doubt it's out by as much as 1%. The parts involved tend to be more accurate than that.

[gr5 2,167]

So if your part is EXACTLY 20mm tall. And each layer is exactly .2mm tall including the bottom layer. Your result should be 100 layers, right? Is it exactly 100 layers in cura? Or is it 99? I'm guessing 99.

[nfratianni 1]

So if your part is EXACTLY 20mm tall.  And each layer is exactly .2mm tall including the bottom layer.  Your result should be 100 layers, right?  Is it exactly 100 layers in cura?  Or is it 99?  I'm guessing 99.

It does show 100 layers in Cura. I'll give the Z-axis calibration a try from developer mode and report back with the results.

[nfratianni 1]

So the strangest thing happened. Friday I was working on trying a second manual leveling as I felt like this was my issue. After doing that I got an error message saying that the offset was an unreasonable amount. I noticed that the nozzles pushed down too far during the automatic leveling and could see them being pushed up into the enclosure. A bit frustrated I let it sit over the weekend and when I went back and correctly redid the manual level, the offset is perfect and my part came out to 20 mm on the dot. I'll be continuing some prints with it and if I run into the issue again I'll try out the method gr5 had mentioned. But for now it seems to be okay *fingers crossed*. Thanks everyone for all your help!