Poor print quality

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Bergko
Posts: 2
Joined: Sun Aug 02, 2015 6:36 pm

Poor print quality

Postby Bergko » Sun Aug 02, 2015 8:38 pm

Hello guys!
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I have had a problem with my freshly developed Sla printer. Everything seems to be normal half way through the print and then it won't handle the the remaining half. The printer is simple, only a moving z axis with no tilt or slide option for the VAT.
You can see that the first half of the hole/circe on the cube(10x10x10mm) is fine, then it starts to become a mess.
I have an Optoma Hd65 DLP projector with no colorwheel. There seems to be no problem with the anti-stick coating.The VAT is coated with sylgard 184.
The resin level reaches 3mm in the VAT. Bought resin from makerjuice. Standard sub g+ with no pigment. 8 months old

Gcode seems alright all the way. The print height(z axis) corresponds to the 3d models size and its proportional to the x and y axis. The focus from the projector has been adjusted several times, with different focal lengths but no success. I have tried a number between 1-5 mm in lift height between layers for 5 test cubes. Lead screw is really solid and the nut is anti-backlash.
Motor and driver never gets hot. No missing steps or unusual sounds. Layer slices are timed evenly through the print.
I have tried all different types of exposure times but the same problem remain. I cant go lower than 3600ms or the layers wont cure properly. haven't tried anything over 7500ms. Buttom layers are 4 x 20000ms
Same thing goes for the lift speed, tried many options.
The only thing that has been constant through all tests is the retract speed which is at 100mm/m. But I dont see why that
would make any difference. The resin get at least 1 sec to cool down its movement before the layer exposure.
I get the feeling that the resin cures to thick at the end and the only reason it doesn't show before the second half is because each layer becomes increasingly larger at that point and allows the uv light to cure resin through a level it isn't supposed to.


I would really appreciate some help from an expert because I cant find someone else with this problem anywhere, right now I am running out of ideas and I have no clue what to do next : (

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James
Posts: 136
Joined: Mon Dec 02, 2013 1:56 am
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Re: Poor print quality

Postby James » Mon Aug 03, 2015 4:40 am

I agree with your assumption. I would think that there is stray light coming from the projector in between exposures. A way to prove this would be to stop the print just before the halfway mark and then empty out the build tray and then replace with fresh resin and continue the printing. If it then prints the rest of the print without issue then it's most likely the resin is getting overexposed gradually.

A mechanical shutter can be used to stop light from exposing the resin in between exposures. Also, look to see if light is escaping from the projector anywhere like through seems or air vents and such. One other thing you might consider too is some types of florescent shop lights can cure some types of resins. Sunlight too will cure all types of photocurable resins.

To the best of my knowledge I don't think heat would be an issue. Photocurable resins can be heated and also cooled without effecting solidification.
I prefer to know nothing about everything rather than everything about nothing. :)

Bergko
Posts: 2
Joined: Sun Aug 02, 2015 6:36 pm

Re: Poor print quality

Postby Bergko » Wed Aug 05, 2015 6:34 pm

Great input James. But it turned out to be light scattering. I added some pigment and it solved pretty much everything.
thank you

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James
Posts: 136
Joined: Mon Dec 02, 2013 1:56 am
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Re: Poor print quality

Postby James » Wed Aug 05, 2015 7:13 pm

AH HA! The old light scattering gotcha! That completely escaped my mind. Good to have a refreshing of the memory.

Glad you got it running well. :D
I prefer to know nothing about everything rather than everything about nothing. :)


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