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#1 2018-12-28 21:15:30

macdarren
Member
Registered: 2017-03-20
Posts: 411

Elephant Foot perimeter reductions

As it happens many of my prints work best or would be far quicker if printed directly on the print platform (no underlying support)

Doing this presents a small issue that I think nanoDLP could help remedy with a minor feature addition.

Basically to get the print to stick to the platform the initial cure layers have to be somewhat long to get good cure strength.
by careful tuning of those burnin layer(s) i can get almost what I need but they still, by necessity, have a tendency to over
cure as the light bleeds into nearby resin.

FDM printers have a similar issue as plastic spreads on the first layer and have taken to calling this elephant foot.
Some slicers have a feature to reduce this by shrinking the first layers.

I would suggest that nanoDLP could use something similar by removing inner and outer permitters (lines).
I would do this in pixel increments so 1 pixel removed all the way around all permitters (inner and outer)
would then reduce the light bleed a bit and thus elephant foot...putting zero would of course give the current behavior,
where no change of the geometry is made to the burn layers.

I think this would be buildable on the code used for hollowing which already allows a wall thickness setting.

Anyway however implemented I think it would be a nice add to nanoDLP for those of us that often prefer no underlying support.

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#2 2018-12-29 18:59:08

Shahin
Administrator
Registered: 2016-02-17
Posts: 3,429

Re: Elephant Foot perimeter reductions

Have you tested dimming?

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#3 2018-12-29 20:02:56

macdarren
Member
Registered: 2017-03-20
Posts: 411

Re: Elephant Foot perimeter reductions

yes I have tried dimming...in fact that is where I got the perimeter line idea...no hollowing as I mentioned above.

Dimming works and I used it for my supported models and get good results.
And it does help on the unsupported models but it has only one setting, well two if you count skipping.
Perhaps a second burnin dim stage would be just as effective but might also reduce plate adhesion.

If I normally print with 20% Dim and a 7 second cure time if I could say go with a 60 second cure time and 80% dim on burnin layers
that might eliminate the burn layer bleed....not sure but not option right now....the trick is to get the burnin cure required for adhesion
to have similar overall bleed as the subsequent regular layers that have shorter exposure and may include dimming.


I am testing some other ideas right now to see how close I can get with the current setup.

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#4 2018-12-30 06:35:06

Shahin
Administrator
Registered: 2016-02-17
Posts: 3,429

Re: Elephant Foot perimeter reductions

Issue with shrinking fill areas that it require lots of post processing. Let me know if the other ways you are trying does not yield result

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#5 2019-01-02 07:47:13

TomTuko
Member
Registered: 2018-09-20
Posts: 15

Re: Elephant Foot perimeter reductions

Shahin wrote:

Issue with shrinking fill areas that it require lots of post processing. Let me know if the other ways you are trying does not yield result

I also print several types of models that do better printed vertically without supports.


I think your suggestion of dimming to solve this is a great place to start.


If I understand the dimming option correctly the outer perimeters are fully exposed and the inner part of any contiguous area is dimmed similar to how a mask works.

If that is correct then reversing things and dimming the outer perimeters and fully exposing the inner bits during the burn in layers should help eliminate elephant foot without having to change the slicing process at all.

What do you think Shahin?

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#6 2019-01-02 14:24:58

Shahin
Administrator
Registered: 2016-02-17
Posts: 3,429

Re: Elephant Foot perimeter reductions

I do not think dimmed outline could withstand vacuum force on first layers.

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#7 2019-01-04 01:26:24

TomTuko
Member
Registered: 2018-09-20
Posts: 15

Re: Elephant Foot perimeter reductions

Shahin wrote:

I do not think dimmed outline could withstand vacuum force on first layers.

Perhaps on normal layers the outline would not adhere but the bottom layers are over cured a lot. In my case the burn in layers usually extend out nearly a mm from the object. Dimming the outer pixels should only reduce the distance the over cure extends out from the layers image.

Just a thought.

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#8 2019-01-05 16:54:37

macdarren
Member
Registered: 2017-03-20
Posts: 411

Re: Elephant Foot perimeter reductions

@TomTuko:  my thoughts exactly

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#9 2021-02-26 19:59:29

Shahin
Administrator
Registered: 2016-02-17
Posts: 3,429

Re: Elephant Foot perimeter reductions

Added on the latest beta.

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