Sawtoothing on lower mesh counts...

[dirkdiggler]

Never had this happen before, but started about a month ago. Same procedures, same everything, don't know where it came from or how to get rid of it.  Only on lower mesh counts, 110, 156.  At a loss.  Anyone?

[Homer]

Light source getting weaker? films not as dense?

[Printficient]

How hard is it to develop?

[dirkdiggler]

Sonny, you and I already tried to remedy this with no luck.  I am thinking its the bulb, as I have ruled out or tried almost everything else. Develops with ease, just sawtoothed.

[Frog]

The two obvious things that come to my mind;
no real EOM, and the mesh itself is really interfering with edges, especially diagonals
or
this will sound silly, but have you examined the films to make sure that you aren't actually just resolving something that's there already?

[mk162]

frog might be on to something...a clogged nozzle or two can cause edges to lose sharpness.

i actually lowered my eom to below what is recommended and I have much less sawtoothing...on 100's i have a little bit, but it's not noticeable unless it's under a loupe.

[Underbase37]

Did someone new start coating screens? Or printing/doing art?

Murphy37

[Evo]

Stencil wall is not high and sharp enough, ie not enough EOM and/or the exposure is weak, or the emulsion is a bad batch.


I'd suggest:

Get a quart of new emulsion (same stuff) and coat up a few screens and test along side the current batch of emulsion.

Check the age of your exposure lamp.

Do a thorough step wedge test for each mesh count.

Check your screen room humidity.

Check the films in a loupe. Check old films vs freshly printed ones.

Check your coating technique. If you aren't the one doing the coating, make sure whoever is is doing it consistently.

[Printficient]

Two questions.
1. Can you see the sawtoothing on the shirt.
2. Is the art on straight.

[dirkdiggler]

yes, yes, yes, and yes, to everything.  Got to be the bulb, gonna change it tomorrow.  NOTHING else has changed.

[Dottonedan]

As you have indicated, everyone has suggested everything "typical" and you've checked that.

Now look at something that only fluctuates like the weather. Litterally.

Considering this is March, temps and humidity are changing from winter to spring. Rain storms and unusual weather.  Imagine a bowl of jello setting out for a few hours. Its got a lot of water in it so it can hold its shape for a long time. Lear it there long enough, and the water eventually evaporates and it draws in to a shriveled up shape.

Let's say that you typically don't see your emulsion drying up so much (a true 100% dried screen) all too often because (maybe), like many shops you need to get it on press fast.  This might " be typical" and you may normally see and use a 110 mesh that is more swollen with moisture (than it really should be).  Now, here is where one might say "Nawh, that's not it, I never have problems with my screen".  That's more than possible...if you are not doing large order that give you the chance to see breakdown. Many shops use unproperly dried screens in production every day on orders of 24-72-114-288 shirts, so you may never "recognize" there is a slight problem.

Now bounce back to the weather. It might be, that the temp/humidity and overall daily envirobnment of your screen room has shifted to be drawing out (more water) faster, causing you to have a more properly dried mesh. This of course draws in closer to the threads and creates thirst curved shaped edges of your stencil.  You may have always really needed (another slow coat with the full edge...or even a face coat all along, but have never seen the need until now.

Just another guess, but it sounds feasible.  The last poster includeed "humidity" as something to check. I agree. I have recently seen some extreme differences in print quality as a result of humidity alone.

[dirkdiggler]

Sonny and I actually blamed it on the weather when he came by, so many changes here in GA, 70 degrees one day 25 the next.  It very well could be weather related, we haven't ruled that out.  A rep from Nazdar and Ulano are coming to my shop this week to finally pinpoint this.

[Printficient]

How about vacuum?

[mimosatexas]

i'm convinced the weather fluctuations killed my exposure unit (broken glass) and knocked out a tub of ink and one or two other things in my shop.  Here in Austin we had the same, freezing one day, 80 the next for about 3 weeks.  So many things act weird when that happens.  I actually had a coated screen of HVP sort of crack/fracture all up one side of my stencil.  Never seen that before, or since.  Was just a weird combination of factors.

[dirkdiggler]

How about vacuum?

NOPE!