1 Topic by ZADNKOMAD

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Topic: DIY High-end DLP 3D printer, inconsistant cured layers

Hello everyone!

In the recent free time, I've managed to finish my DIY 4k DLP printer. This is a big machine (x,y,z=480x260x700mm), intended to produce large parts, but at the moment I'm just pulling my hair out, not getting good results, maybe I'm missing something.

Please take a moment and look at photos: https://imgur.com/a/dQoUj3n

I'm currently printing with 230x120mm build platform for testing purpuses. The VAT is glued Acrylic + applied PDMS (Sylgard, about 2mm).

I've chosen good parts for the build, but when I try to print it just fails to give good results,

Parts used:

- 2x 15mm linear rail guide, The Z axis is very rigid (checked with dial indicator)
-4x rail slider block,
-SFU1605 ballscrew
-closed loop nema23 motor with clutch
-NanoDLP, RPI 4, Ramps 1.4
-Benq TK800M 4k DLP projector
-VAT with PDMS installed


It seems like there are always some sort of Z lines present + some sort oz Z ragging (inconsistant layer outer surface ).
I'm guessing my problem is in the separation force when peeling cured layer, since Z axis does not bend at all, so I'm trying to separate the cured layer by only pulling upwards.
But Z lines also appear on smaller surfaces (where separation force should be lower?). I've attached some photos to better showcase the problems I'm having.


Things I've tried:

-Different resin brands (Photocentric3D, ABS-like resin),
-different exposure times (on photocentirc hard resin, about 12s for 100um at display size 480x260mm),
-different lift distances between layers (from lifting 2mm inbetween layers, than 1mm, than 0.7, 0,5mm, 0.2mm....),
- different lift speeds (from 50mm/min to 20mm/min, 15, 10, 5, 3, 2, 1mm/min)
-Different burn in layers, (typically 3 layers of 30um, 60s exposure, up-to 100 second exposure)
-layer heights of 50-100um.
-Tried really curing a solid foundation for the model, but did not improve..
-Whole Z axis is only made out of aluminum. I use 3mm perforated aluminum flat bed (ground flat).
-I tried implementing tilt mechanism into the VAT, but the mechanism itself had so much play, that VAT was not stable (But I could feel seperation forces with my hand on the other side of the VAT, when The Z axis started raising, and It was somewhat decent for burn in layer RAFT (30x30mm),, than came test cube (13x13mm hollow), and the force was much lower..)


I'm struggling/failing to get stable and good result. I noticed that when I lowered the Z axis feedrate in-between layers, the results got better, so I'm currently lifting with a feedrate of 1mm/min, and problem is still present, but less noticeable on small models, on big models it becomes more noticable..

IMAGES CAN BE FOUND HERE: https://imgur.com/a/dQoUj3n

I will order some aluminum and try to manuafacture aluminum VAT for FEP foil, and test that, as it seems all big scale SLA/DLP printers use teflon instead of PDMS (for example, peopoly)..

Does anyone have any further idea? I'm loosing my mind here..


I print on the following procedure (typically):

G code BEFORE layer:
G1 Z[[Layer position]]
[[WaitForDoneMessage]]
[[Delay 1.5]]


G code AFTER layer:
[[Delay 3]]
G1 Z{[[Layer position]]-0.5} F1
[[WaitForDoneMessage]]


I do not know what else to do?

-maybe move projector closer?

Sincerely,
Komad

2 Reply by carl_m1968

  • carl_m1968
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Re: DIY High-end DLP 3D printer, inconsistant cured layers

Have you laid a piece of paper in place of the resin and vat and tried running a few layers to see if they are in focus and clear? The test grid may look better that an actual slice as it is much more simple.

Printing since 2009 and still love it!
Anycubic 4MAX best $225 ever invested.
Voxelabs Proxima SLA. 6 inch 2k Mono LCD.
Anycubic Predator, massive Delta machine. 450 x 370 print envelope.

3 Reply by ZADNKOMAD

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Re: DIY High-end DLP 3D printer, inconsistant cured layers

Ah, I've always try to find focus point of projector, with test grid and simple microscope... I tried some times to just eyeball the focus on the bottom of the VAT, seem to work..

I will try microscope + actual slice, next..

Thank you for advice!

4 Reply by ZADNKOMAD

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Re: DIY High-end DLP 3D printer, inconsistant cured layers

Focus seems to be on point..

What's weird is, when I only use 1MM/MIN to peel the cured layer, the surface finish seems pretty good, almost acceptable, but when I want to use regular lift speed during layer of like 5-40 mm/min, I get terrible surface finish..

I will try FEP foil next, but in the meantime any advice is apprechiated!

-Komad

5 Reply by pirvan

  • pirvan
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Re: DIY High-end DLP 3D printer, inconsistant cured layers

Here are my $0.02 on the subject.

The PDMS surface is great but it requires a tilt or slide type peel action.  Pulling straight up on it will create layer separation problems, and eventually PDMS tears.

If you look at printer that use PDMS like the FormLabs or or Moai, they all have some sort of peel action.

On the other hand most DLP or direct mSLA printers use FEP film for the separation surface.  The reason for it is because it's flexible.  When the build platform pulls up, the FEP film travels with it a little, then starts to flex, which separates the film from the resin, and the film then returns to its flat state.

If you plan on using the a static vat, without peel motors, change the PDMS to FEP.  You'll have to redesign you vat to have a clamping system that allows you to stretch and tighten the FEP film, and either put a clear glass at the bottom of the VAT, or better yet the glass should be part of the table surface opening, this way when you remove the vat, the frame only holds the FEP film, and it's easier to verify the tightness of the FEP surface.

The surface size you chose for your build, 480 x 260 is very ambitious.  Maybe too much so.  Being able to control the exposure across such a large surface is going to be tough.  Also getting FEP film evenly stretched and tight on such a large surface is not going to be easy unless you design some clever adjustments that can be done on multiple discrete areas of the frame.

I have a Form 1+, and a Photon.  On the Photon there's only the FEP vat.  Small simple, no problems keeping the FEP tight.  Works 100% of the time.  On the Form 1+, I've tried FEP film, and my problem was always keeping the film tight.  It does work, but when you get it wrong, you end up with layer separations or warped parts.  So on the Form 1+ I went back to PDMS.  The printer was designed for it, ot has a Peel action vat and just works.

To print or, 3D print, that is the question...
SD3 printer w/too many mods,  Printrbot Simple Maker Ed.,  FormLabs Form 1+
AnyCubic Photon, Shining 3D EinScan-S & Atlas 3D scanners...
...and too much time on my hands.