Uncontrollable shifts occur during the printing process as the paper travels through the machine and this is a restriction for all printing methods.
For example, if you approve an online PDF proof with an image centred on the page, there is a chance for the paper to shift in any direction causing the image to look off-centre in the end product. The standard tolerance that is deemed acceptable is 1/16", although some specific stocks will have larger shift tolerances of up to 1/8".
Considerations
Digital Output vs Offset
Digital machines use rollers to move and align paper during the printing process, and it naturally has a higher tolerance for shifts than that of offset printing.
Paper Stocks
The degree of shifts depend on the printing method, and the thickness and make of the stock - the thicker the paper, the higher risk of shifting.
Our exclusive line of stocks such as wood, pulp, and thicker stocks (20pt+) are more prone to shifting as they are more rigid compared to standard papers.
Design
Although shifts are minimal, they are more visible with designs that have borders as they may be uneven all around after trimming or to designs that have artwork bleeding over the edge.
Registration
Custom products that require additional production processes after printing (such as applying spot UV, foil or emboss) may appear misregistered (misaligned) due to uncontrollable shifts in the previous production stages. In other words, registration of multiple printing techniques cannot be guaranteed - shifting of up to 1mm in any direction may occur.
For example, if "Jukebox" from "Jukebox Print" needed to be foiled, we would print the word "Print" first, and then foil "Jukebox" after. The two words may not perfectly register (align) because the paper may shift during printing and foiling, which causes the position of the words to vary on the paper.
Registering printed artwork to a score line may also cause the artwork to appear misregistered (the artwork may shift slightly onto the next panel). This is due to unavoidable shifts between the trimming and folding processes. We recommend a safety margin of at least 0.125" from the folded edge.
See: Shifting Along Folded Lines Warning