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#1 2020-05-18 09:24:23

DenTarr
Member
Registered: 2017-06-09
Posts: 9

Periodically wrong G code for lift

In my DIY DLP printer I encountered a very strange bug in Nanodlp:

I have strange layer banding in my prints. Normally, I would think "Z-wobble" or something. However, this banding is depending on the layer-thickness I use.
After some work with microscope and caliper I found out it is exactly every 7th layer that appears "thicker". Like in a filament printer if the extruder is feeding too much.

Now I took a look at the Nanodlp logs and the RAMPS terminal. And look what I found in the Terminal:


G1 Z1.6500 F60
G1 Z0.7 F60
Z_move_comp
ok
Z_move_comp
ok
G1 Z0.8500 F60
Z_move_comp
ok
G1 Z0.75 F60
Z_move_comp
ok
G1 Z1.7500 F60
G1 Z0.8 F60
Z_move_comp
ok
Z_move_comp
ok



That is clearly wrong: the "G1 Z0.8500 F60" should be a "G1 Z1.7000 F60".

In my profile I have 1mm lift height (which is enough for my resin). But here it only lifts 0.1mm instead of 1mm. And it does that exactly every 7th layer.

I am running the latest version of Nanodlp. But I had the same problem with the previous build. It just took me so long to find the bug. I always thought something is wrong with my machine.

I would be immensely grateful if you could take a look at this problem since I invested countless hours building my machine and now I am stuck and cant do much more.

If you need any more debug info please let me know I am happy to provide them. However AFAIK everything else is ok. Just the wrong lift height every 7 layers.

I tried different lift height, layer thickness... I changed the RAMPS board (GEN_L v2 with marlin compiled for NanoDLP right now). Was about to change the stepper but that is pretty pointless as it is to my eye a Bug in NanoDLP.

Here a pic of my prints (with 50u layer - cubes are 5mm)
https://imgur.com/lLcYquQ

Last edited by DenTarr (2020-05-18 09:50:33)

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#2 2020-05-18 12:45:37

DenTarr
Member
Registered: 2017-06-09
Posts: 9

Re: Periodically wrong G code for lift

Well, after writing this I had a burst of inspiration: Relative Positioning.

So I switched my RAMPS to relative positioning and just send a dumb +1 and -0.95 movement every layer. This works now and my layer lines are gone. So yeah.. workaround but finally prints come out fine.

Bug still warrants investigation Id think.

For those in similar straits:

Start of Print code:
G91

Code before each layer:

;

Code after each Layer:

G1 Z[[ZLiftDistance]] F60
G1 Z-{[[ZLiftDistance]]-[[LayerThickness]]} F60



I dont use the [[WaitForDoneMessage]] to eliminate a possible source of error. With F60 culculating wait times is easy.

Anyway.. off to printing

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#3 2020-05-19 04:20:33

Shahin
Administrator
Registered: 2016-02-17
Posts: 3,510

Re: Periodically wrong G code for lift

My guess is jump layer feature got enabled for every 7 layers. You can find it on profile settings.

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#4 2020-05-19 07:31:18

DenTarr
Member
Registered: 2017-06-09
Posts: 9

Re: Periodically wrong G code for lift

Shahin wrote:

My guess is jump layer feature got enabled for every 7 layers. You can find it on profile settings.

Damn, you are right. I totally overlooked that part all the time.

So setting this to "0" disables those jump layers?

And a huge "Thanks!" for your work on NanoDLP! Its a great piece of Software! smile

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