multi-layered VAT caused too many reflections

Various topics related to Vat design, construction and coatings.
g4uts
Posts: 4
Joined: Wed Oct 22, 2014 8:13 am

multi-layered VAT caused too many reflections

Postby g4uts » Tue Oct 28, 2014 12:00 am

Hello guys, I've been reading and learning alot from this society, very appreciate Pacman's great work. Little by little i completed my own DLP.
The VAT is built with borosilicate glass covered with unsticky .05 FEP membrane and the rest of basin is built with PMMA. DLP is H6510BD, ECO mode on to reduce the brightness, and during first loop of test , I tried curing a layer for 2-4 seconds.

Because I am based in Hongkong now, there are no easy access to resin suppliers like FTD, therefor I sourced different resin from China for test, which is very painful. and you know what, they are not cheaper.

1. The first resin I tested is yellowish transparent resin, it bleeds alot even if I set cure time to 1000ms. After I clean the basin, I found the resin around the edge are cured as you may see in the photo. I have no clue what cured these area. Did this happen to any one?

2. Take a close look at the VAT, I can see many layers of reflections of the image projected, particularly a strong projection on top layer, which I guess is FEP. is this normal? or is it because membrane or glass isn't transparent enough? will this cause bleeding to the rest of resin?

3. and in the end I did a test, I expose resin under dlp in blank, and there are still light leaks on in blank which as a result slightly cured the resin in 10-20 minutes. Is it because the resin is too sensitive? and will adding pigment help?

I wish i could understand more of these before I start another loop of tests, there are so many concepts missing in my knowledge, and I appreciate any advice or suggestion. Thank you guys in advance,


1028_1.jpg

Glacian22
Posts: 63
Joined: Wed Feb 19, 2014 4:23 am

Re: multi-layered VAT caused too many reflections

Postby Glacian22 » Tue Oct 28, 2014 1:23 am

The vat reflection issue could be sidestepped entirely with a flexible tensioned vat; there are some examples of this floating around the forum. If you're sticking with your current design, then the borosilicate glass may be the culprit behind all of those reflections, I'd try more acrylic (PMMA) instead, as acrylic is extremely clear and transmissive. Your weird curing around the edge of the vat sounds reflection related too, the sheet of glass may be internally reflecting some light out toward the sides. If the blank image is curing resin, I'd turn down the projector's brightness, which usually helps make the contrast better...on the projector I'm using, 60% brightness will make the black areas bright enough to cure, but at 50% it all works nicely. Adding pigment to the resin won't help the blank-curing issue, but it will give your prints better detail. :)

oliveenchine
Posts: 30
Joined: Tue Feb 04, 2014 9:57 am

Re: multi-layered VAT caused too many reflections

Postby oliveenchine » Tue Oct 28, 2014 2:11 am

Hi g4uts,

I'm also in China , Shenzhen , I have no clue for the UV resin too ( expensive, no data sheet ... ), would you mind sharing your suppliers ?

You could maybe add a shutter to cut the light between each layer ?

android78
Posts: 41
Joined: Sun May 18, 2014 10:33 pm

Re: multi-layered VAT caused too many reflections

Postby android78 » Thu Oct 30, 2014 7:39 pm

Looking in the picture, it looks like you are also using a 45 degree mirror. Are you using a first surface mirror? If not, you will also get terrible double reflections similar to what's pictured.

g4uts
Posts: 4
Joined: Wed Oct 22, 2014 8:13 am

Re: multi-layered VAT caused too many reflections

Postby g4uts » Wed Nov 05, 2014 12:37 pm

androi78: yes, it is a special mirror with reflection in first surface. the Reflection is actually caused by two sides of surfaces of vat glass.
to oliyeen: giving up testing resin from ebay/taobao, we are working with a friend's company now, it is based in Shenzhen called feiyang. Are you making any progress?
glacian22: thx for replying, i will test PMMA when I have time. interestingly, my projector doesn't have option to adjust brightness, the most i could do is turn on eco mode.