nanoDLP

Mazz

Member

Registered: 2020-12-08

Posts: 1

Burn in and Lift Distance Layer Height Influence on Total Print Height

Hi Guys!

Got a question regarding burn in layers and ZLiftDistance. Are they accounted for in the total height of the print?

I am dry running my printer, but set the layer height to 5mm so that I can see exaggerated movements with 3 burn in layers set to 60micron. I have my ZLiftDistance at 1mm, so that it is exaggerated as well.
I am running a simple cube that is 25mm x 25mm x 25mm. After slicing, the total number of layers is at 5 for this entire print according to the slicer.

When running the print, I can see in my RAMPS terminal that the commanded Z-Axis movements are in accordance to the burn in layer heights (first layer @0.06mm, second @0.12mm and third @0.18mm).
After these three burn in layers, it then commands my normal layer height of 5mm: Fourth layer @5.18mm, Fifth layer @11.18mm (5mm layer height PLUS 1mm lift distance)

In the end, the total Z-axis travel of my printer is 11.18mm, not 25mm. It seems that nanodlp does not account for the differences in height between normal layers and burn in, as well as leaving the lift distance in on the final layer.

What also weird is that the main page, the height of the print is all "normal" at 5mm increments according to layer. The final layer is at 25mm.


Here's the output from my terminal:

G90;
G28;
ok
G92 X0 Y0 Z0;
;
G1 X0.06 F400 ; Move to layer position

X:0.00 Y:0.00 Z:0.00 E:0.00 Count X:0 Y:0 Z:0
ok
X:0.00 Y:0.00 Z:0.00 E:0.00 Count X:0 Y:0 Z:0
ok
 ; Save layer position as the current position
ok
G1 X1.0600 F400 ; Lift to wait position
ok
 ; Again update position
ok
G1 X0.12 F400 ; Move to layer position
ok
 ; Save layer position as the current position
ok
G1 X1.1200 F400 ; Lift to wait position
ok
 ; Again update position
ok
G1 X0.18 F400 ; Move to layer position
ok
 ; Save layer position as the current position
ok
G1 X1.1800 F400 ; Lift to wait position
ok
 ; Again update position
ok
G1 X5.18 F400 ; Move to layer position
ok
 ; Save layer position as the current position
ok
G1 X6.1800 F400 ; Lift to wait position
ok
 ; Again update position
ok
G1 X10.18 F400 ; Move to layer position
ok
 ; Save layer position as the current position
ok
G1 X11.1800 F400 ; Lift to wait position
ok
 ; Again update position
ok

Here's the code running, seems like standard fare: (Note: dont mind the X instead of Z, have the Z axis plugged into the X axis of my RAMPS board)
START

G90;
G28;
[[Delay 10]] ; 
G92 X0 Y0 Z0;
[[PositionSet 0]];

----------------------
BEFORE

G1 X[[LayerPosition]] F400 ; Move to layer position
[[Delay 2]] ;
[[PositionSet [[LayerPosition]]]] ; Save layer position as the current position

----------------------
AFTER:

G1 X{[[LayerPosition]]+[[ZLiftDistance]]} F400 ; Lift to wait position
[[Delay 2]]
[[PositionChange [[ZLiftDistance]]]] ; Again update position

Shahin

Administrator

Registered: 2016-02-17

Posts: 3,546

Re: Burn in and Lift Distance Layer Height Influence on Total Print Height

You are exactly right, burn-in layers thickness calculation is based on normal layer. It is working this way to cover difference in height which happens with PDMS floor.
About the second point based on the shared gcode is correct. It move to the last layer position, do cure and lift to wait position, I assume it goes to STOP position if you put proper code in stop code box.
G1 X10.18 F400 ; Move to layer position

By the way thank you for the detailed description.