Sorry for my long time silence - was kind of busy before New Year and after got some break
Quick results so far - I'm still printing good, no visible problems to prints nor projector. Robert Howle mentioned that "somebody got cracked filter". That's me
But actually not filter, but glass replacement. I opened up the lamp bay and looked closely at the glass that I installed in place of UV filter. My worse suspicions confirmed - it got cracked in the very middle when I heard that cracking sound. But somehow it still prints fine!
So I'll leave it as it is for now. Maybe crack line is under/over the main light stream.
One more thing - I'm thinking about a way to remove the color wheel. Theoretically it should give another boost of 3-5x decrease in cure time. But I'm kinda afraid to break the glass part of it (one will need for sure the motor of the color wheel to stay in place
in order for projector to work properly). I heard the best way is just to MOVE it away from the "light duct" somewhere aside. But looking closely I was not able to find a place in the housing to make such a maneuver. At least with housing closed. Maybe when leave it open it is possible. Maybe someday...
Next thing - during holidays I was able to finally assemble my HMS FS-1 (stands for Humble self-Made Spectrometer From Scrap)
Here it is in the attachment. You can find more at http://publiclab.org/wiki/dsk
So I measured the absorption of this UV filter with CFL lamp as a source of calibrated measured spectrum. Basically I captured spectra with CFL lamp in front of spectrometer and then with UV filter between lamp and spectrometer with few seconds interval, so error should be minimal. As I can conclude from the spectral graphs (in the attachment) calculated by the awesome on-line software http://spectralworkbench.org
our UV filter is strongly absorbing UV AND EVEN PART of BLUE light UP to 420-430 nm. Unfortunately I haven't effort to mod my spectrometer further removing internal UV-IR filter to drastically widen measurable limits, but it is still very informative as it's (uv-filter) highest absorption border lies just in measurable part.
Also I do measured (now with more suitable tungsten lamp as a sourse of light) acrylic window, NuVat window, and PDMS and I haven't noticed ANY absorption peaks across all measurable (380-650nm) region
. General absorption spectrum-wide was extremely little, compared to the error level. Thus making conclusion that using any special glass is not needed
. Theoretically (you could google it) acrylic should "eat" all UV down to 330-360 nm. That's normal for us. ANY glass should absorb no more than up to 320-360 nm, so the same here.
Combining all this points:
1) Measured spectrum of absorption of UV filter
2) Knowing that B9R resin should work with UV-VIS light up to 500-550 nm
3) Experiment on removing that UV-filer with decreasing in cure time 3-8x times (for me it was closely to 7.5x - I had previously to print at 20-25 sec/layer with bad results. Now 3-3.8 with GOOD results).
4) Talks with B9 friends and observation on forum of people who had the "sudden death" effect. When you are not using your B9 for prolonged period like month or more, and then (with all the previously successful settings) try to print something - and it prints nothing, or prints suddenly bad. Examples - me, Robert Howle who stopped to use his v1.1 machine in favor of v1.2, my Bulgarian friend who got the same effect on v1.1 after prolonged holidays and many others. Moreover, when Robert Howle changed back to his little used old lamp, all went back to normal. Well, not that normal, but kind of.
So combining all that points I got suspicion of the problem. Here is my theory
It's likely dust. Yes our ordinary household dust that likes so much to settle on our TV's and computers. Some has more of it floating around, some got less, but it is always there. And I'm talking not about dust collected on top of the lens. That's still flowers (local idiom
). Roots are way deeper. I think that dust, which enters the lamp assembly, insides of housing, could be ejected with frequent use of B9 for printing - when it starts frequently, dust just can't settle a lot and are blown off with fans and hot air. And yes - here it is - hot air. When printer is not used for a long period, nobody will argue, dust will be collecting more. And possibly somehow are compacted, pressed. And suddenly when fellow B9'er starts to print after prolonged break, lamp gets very hot in seconds. That caused my glass (UV-filter replacement) to crack almost immediately after placing. And that could lead to not all dust to be blown by the fans or hot air. Sudden heat blast could just melt or burn some dust remnants. And they will become... what brothers-jewelers? Yes, right - ASH
. And what color is ash? Black, right? But why it is black? As we all know here (with our previous works on pigments) black is black because... it absorbs all other colors, including green and blue! But that's not always true to UV-IR regions. Something that is opaque in VIS light could be easily translucent in UV or IR. Just google "infra red light cola" (https://www.google.com/search?q=infra+r ... a&tbm=isch
). So I expect that ash to be comparably translucent in UV region. That could explain why with lamp giving FULL broad spectrum I got 20-25 seconds to cure WIDEBAND absorbing resin, and after only small region of spectrum unleashed (330-350(???)nm - 420 nm) it started to cure 7 time faster. That *should* mean that I got 7 times less energy in 420-550 nm band spectrum. Also I do noticed that some users after UV filter removing got cure times about 1-1.7 seconds. I still got 3-3.8. That's likely due to me having extremely "dirty" lamp with 420-550 nm region being very weak. That corresponds well to our previous observation and conclusion.
I expect that ash to be located at the lamp reflector, or other optical elements of the lamp. But strangely there was no ash imprint on UV filter - it is very transparent in 430-650 nm region. But still it SHOULD be on the lamp, coz a lot of users who changed lamp noticed absence of this effect (like in the Robert Howle case). Also I have small suspicion that some exotic chemical reactions (or above-mentioned dust-ash transition) could take place with dust and color wheel (or some other internal optical component). Once again - more pause to the printing - more dust collected.
Also I do noticed that v1.2 machines are less prone to this problem. I'm pretty sure that a lot of users are not using their new v1.2 night and day and still not heard of "sudden death" effect. Likely that home (as do I) B9C users are tend to be in the more risky zone due to more dust is likely in home.
That all is my theory. I haven't measured exact spectra from the projector, nor saw any ash on lamp reflector. Just trying to put all the facts together, thought maybe sometimes with the use of Procrustean bed. But well, we all are human here, huh?
Sorry for possible mistakes and abnormal phrase constructions - non-native English speaker here
If you found a mistake don't hesitate to correct me - that will increase my knowing of language and make text more readable