Moire?

[lrsbranding]

I have spent the last 3 days trying to get a good print. I keep getting what I guess is moire in straight lines. What is the major cause of that? I have tried round dots, elliptical, 45,50,55lpi, 22.5, 23, 24, 25 and 26 degrees. Tried on 230-45, 280-40 and 280-34S mesh and every time the black prints with zebra stripes. The image in the screen doesn't show any and the films don't either. If you lay the film positive on the shirt it looks good. If you slowly rotate it they show up but not close to the print angle. The only constant is the artwork itself. Can a really bad photo cause funky things to happen when its ripped and printed? I'm printing on a manual press and can't change the results with different pressure or squeegee angles. 

[Dottonedan]

Since you've tried various variables, it could be miss aligned mesh.  Your dots, films, angles, stencil thickness, all can be good and still show (what looks like) moire. In this case, it would be mesh tension interference. A mesh that is tensioned unevenly will show slight patterns in the print (more noticeably in lighter percentages.


A way to tell, is to take a freshly sharpened pencil, and test your un coated mesh. Start at the corner about 4" from the frame in, then holding the pencil on the eraser end, angle the pencil so that it will run in the trough of the two mesh threads.  Lightly run the pencil down the length of the mesh. It will darken enough for you to see a line. Repeat this about every 3" and you may start to see what way it's warping (if any).  This should start to show any patterns matching what you see in the print.

[lrsbranding]

OMG...!!! If that wasn't nerve racking.... Taking a sharp pencil and dragging it down the mesh. Once I got past the shakes and the sound it worked purty good. I presume I'm allowed some deviation towards the top and bottom due to the corner softening? The center of the mesh wasn't too bad but this was a screen that I hadn't tried printing on. I recoated the ones I was using a couple of hours ago so they will need to wait. How would someone get the mesh in perfectly straight. I was taught to tear the mesh since that creates a straight line and insert using that as the guide. But from there it wasn't too high tech. Just taking the locking strip and your fingers to measure the excess. I don't see how, especially on the higher mesh, to be on the same thread all the way down with the locking strip. 

[Dottonedan]

From what I've seen it was only noticeable (or enough of a problem) when tension was grossly inconsistent (in one area or more).
We used to have a person stretching that had a tendency to pull one area more than another.  As an extreme example, imagine using the old hand clamps to (pull) and staple. THAT was inconsistent. LOL.


I don't think there is a way to get the same thread lined up all along the length of the warp or weft with the frame. Kinda not expected, but an ideal goal (if that's possible).  I imagine the best tensions or (most consistent) tensions are pulled by pneumatic and with hold bards running all along the warp and weft. The wider, the better. If it's manually done, oh sheeesh. I don't think straight tension is going to be achieved unless you get lucky.


Again, it's going to be most noticeable in the small dots. The open areas may be getting pinched or torqued into a diamond rather than a square, therefore, blocking off a portion off some of those small dots.

[Dottonedan]

OMG...!!! If that wasn't nerve racking....

LOL.  Yea, I know. The idea of a sharp thing running down your mesh is nerve racking but after you do it, you find it's not that hard or dangerous.

[lrsbranding]

I can see where it's most noticeable in the small dots. I had another print that did the same thing but the halftone area was small and the problem seemed to go away with more squeegee pressure. I need to figure it out. Since I got the LED I have dots where I never had dots before. I kinda got accustomed to the fluorescent unit fading and blending the small dots away into the background.  Now their everywhere.