nanoDLP

janzobanzo

Member

Registered: 2020-04-15

Posts: 12

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

janzobanzo

Member

Registered: 2020-04-15

Posts: 12

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

Also 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

Sint

Member

Registered: 2018-06-06

Posts: 25

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

Hello fellow 4K DLP builder

Check if the resin can achieve the XY resolution. Otherwise you get XY bleeding.

You need to try 10mm lift. And some wait time after lift. Like 1 second so the resin can flow back. You need to be sure parts have peeled from the Vat floor.

Fep is better/easier than having to apply the PDMS. Instead of Fep you can also try POF film. Much cheaper and will also work. Maybe even better than FEP. POF is Polyolefin.

Overcure can also cause deformed parts. In XY direction like you have. Try to move the projector closer and have a fine XY resolution. Try 50micron XY resolution.

Shake resin bottle before using. Also room temperature is important 20Celcius or higher. To cold and cure reaction will become harder. Because it inhibits the chemical process started by the UV.

What projector are you using? I use Acer H7850.

EDIT:

Try also my Gcodes Check if you are using Absolute or Relative. Then you must change my gcode to fit your machine.
BEFORE

G90
G1 Z[[LayerPosition]]
[[WaitForDoneMessage]]
[[PositionSet [[LayerPosition]]]]

----
AFTER

G90
G1 Z{[[LayerPosition]]+[[ZLiftDistance]]}
[[WaitForDoneMessage]]
[[PositionChange [[ZLiftDistance]]]]

Last edited by Sint (2020-04-25 19:14:44)