What causes sawtooth when printing fine lines?
The main reason saw tooth occurs when printing fine lines, is primarily due to the mesh and artwork relationship. In most instances, the artwork on the screen is very close to the angle of the mesh. Most printers will see saw tooth problems when printing artwork close to 0° or 90° to the mesh/thread angle.
Artwork that is exposed close to 0° or 90° to the mesh/thread angle often will not make a smooth transition with the mesh. Every few threads the image makes a thread jump (saw tooth or stair step type pattern). The picture below displays saw tooth on a screen under 50-power magnification using SEFAR® PET 1500 305-34 PW mesh.
Saw tooth effect on the screen caused by similar mesh to film angle:
Two ways to minimize this effect are to:
1) Angle the artwork to the mesh
2) Angle the mesh on the frame.
The proper angle to use depends on the artwork being printed. Ideally, a printer wants to angle the mesh and artwork as far away from each other as possible. In the instance where 0° and 90° lines are predominant in the artwork, the best mesh/film angle is 45° (90°/2). In instances where there are predominantly 0°, 45°, and 90° lines, 22.5° is ideal (45°/2=22.5°). See photos on the next page. The print result will minimize the saw tooth effect and provide a better overall line transition.
Angling the artwork on the mesh is not always practical and many times the process requires the artwork to be printed straight with the frame. In this instance, angling the mesh on the frame may be preferred. Sometimes printers are limited with the angle they can use due to mesh width and/or stretching system constraints. The farther the mesh angle is from the artwork angle, the lower the changes for a saw tooth pattern.
Angled film on the mesh that results in minimizing a saw tooth pattern on the screen:
Approximately 67° from the horizontal axis (or 23° from vertical axis)
Approximately 45° from the horizontal axis
Approximately 23° from the horizontal axis (or 67° from horizontal axis)