How can Cura print the right height?

[David Andersen 0]

How can Cura print the right height if it doesn't know the distance between the nozzle and bed? Is it assumed there is a .1mm z offset for the sheet of paper?

[Nicolinux 288]

Hi,

 

which printer are you talking about? Depending on the machine you have added to Cura, through the machine definition, Cura knows the distance between nozzle and bed. Also depending on the layer height, there are different settings for the first layer height and the following layers.

 

[David Andersen 0]

I'm using a CR-10 S4. I didn't see a place to enter .1mm for the distance between the nozzle and bed in the machine settings, but I'll look again tonight.

[David Andersen 0]

Also, to be clear, I'm not only talking about producing the correct height of the initial layer, but also the overall size of the object. If the nozzle is .1mm above the bed it seems to me that all objects printed would be .1mm too high.

[Nicolinux 288]

I don't know the Cr-10 printer, but what do you need the 0.1mm offset for?

But even if the printer would print at z+0.1mm the object would still have the correct height since you are talking about an offset. So for example if your object is 5mm high, and you'd start printing at z+0.1mm, the print would finish at z 5.1mm.

[David Andersen 0]

With a .1mm gap between nozzle and bed Cura should end at 4.9mm, producing a print exactly 5mm tall (4.9mm + .1mm). If it stops at 5mm the object would be 5.1mm high.

 

What I want to know is does Cura already compensate for this somehow? Or is .1mm too small to worry about?

Edited March 5, 2018 by David Andersen

[David Andersen 0]

Maybe I can use M290 before printing to raise the bed a little.

[yellowshark 153]

OK, I wish we knew where people lived on this forum, like we did on the old forum. How about it @SandervG !  Several points

 

1. Where you live dictates the thickness of your piece of paper! Have you measured yours? In England our normal sheets are 0.15mm. How we got that one past Brussels God only knows.

 

2. Think about how often you need a part with the printed z-xis to be more accurate than 100 microns; not often I bet. If you do then one answer may be to rotate the part 90 degrees. through the vertical.

 

3. Most fabrications will have a tolerance of at least 100 microns if not more. In most cases 100 microns is not going to bring the house down; I guess I should admit that we do guarantee 50 microns accuracy for our engineering work if necessary.

 

4. That 100 microns is only theoretical, depending on how much you squish the first layer in to get good adhesion. 

 

5. If that dimensional accuracy is really important to you then the only thing to do is to test your printer with your filament at the settings you will use. Print a 10mm cube and measure it. Do it again. Do it again maybe on another area of the bed. Repeat the aforesaid. Repeat the aforesaid again with a different dimension so you can assess whether the difference is an absolute value or a %. Assess your results; are they good enough, say within 50 microns; if not is there a consistent value of error. If not try an work out why that is. Assuming yes then modify your model dimension accordingly; and presumably modify all future models by the same amount/%

 

6. Do not forget that shrinkage may come into the mix too.

 

7. Yes, I use a Custom printer definition and there is nowhere to record the nozzle to bed distance.

 

8. Do not forget layer height. If you have a model that is 10mm high and you print with a layer height of .300 I have no idea what Cura does when it has printed the layer at 9.9mm