Author Topic: Sawtoothing  (Read 1431 times)

Offline StuJohnston

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Sawtoothing
« on: May 17, 2012, 10:09:04 AM »
I know that this has been asked before, but I think mine might be related to my exposure unit and I was wondering if anyone had any ideas. I am using an OLEC AL-53 with a bulb of unknown age. The bulb type is the standard one, the one that isn't really suited for diazo and that is what I am using. I know that the exposure time will generally go up as the bulb ages, but I was wondering if it would decrease the quality in such a way that it wouldn't expose properly no matter what.

The recommended time for my emulsion on a 5k light is ~130 seconds, which will expose it well enough that it won't be slimy or anything, but I am getting sawtoothing still. I have tried running it over and under that time and still, sawtoothing. The odd thing though, I don't get sawtoothing on lower mesh screens, like 110s, the ones that are sawtoothing are my 305 and 355 mesh screens. Could this be an EOM issue?

The reason that I think that it might be related to the exposure unit is that I was getting good screens when I was just using a grow light. I am going to try to set that up again to see if it would give me better screens, but it is a pain to use in comparison to the olec.

I know that I should be using a calculator, but I seem to have lost mine. I plan to get another soon. I just had thought thatI had it dialed in so I didn't need it anymore and forgot about looking for it. Also, the filter that went on top of it got messed up from sticking to the screen a few times.

I should mention that I am washing the ink out properly, reclaiming fully and degreasing like I should, so I don't think that is it. I also dry them in a box, so I shouldn't be getting any contamination there either.


Offline Zelko-4-EVA

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Re: Sawtoothing
« Reply #1 on: May 17, 2012, 10:32:03 AM »
vacuum blanket suction maybe?




Offline IntegrityShirts

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Re: Sawtoothing
« Reply #2 on: May 17, 2012, 10:43:49 AM »
Are you lower mesh screens white?  The difference between yellow and white mesh on a dual cure exposure time could be the culprit.  Try increasing the yellow mesh exposure time by 75% and see if it helps.

On my AL53 with the photopolymer bulb I have to push times up into the 200+ ltu range to get a decent exposure on a 305 yellow frame.  I'm shopping for the L1250 bulb to lower those times on my unit.

Offline Frog

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Re: Sawtoothing
« Reply #3 on: May 17, 2012, 11:02:46 AM »
It certainly can be EOM.
The article by Douglas Grigar on our home page has photographs, a couple I put here, that show how stencil edges can be affected by the mesh itself when there is insufficient EOM as in the top example



That rug really tied the room together, did it not?