By R. O. Vandercook, Printing Equipment Engineer, December 1936
Wrinkles do not occur on proof presses when the form is level and no part of it is over or under 0.918 in. high and when the gripper edge (if a cylinder press is used) is perfectly flat and the tympan ts not too soft.
Wrinkles may occur when some part of the form is over type high. The high part of the form may cause the sheet to draw in because of the extra indentation and rules or type are so placed in the form that the sheet is held in the drawn-in position and therefore cannot straighten out without wrinkling.
Wrinkles may occur when there are low spots in the form requiring an extra amount of overlay or a heavy soft tympan is used to make the low spots show up. The sheet is then forced down and wrinkles may result. The more the indentation of the sheet caused by a too soft and overpacked cylinder the more is the liability of wrinkling. A hard tympan is less liable to produce wrinkles than a soft tympan.
For printing page proofs in many of the larger newspaper offices, some presses are so equipped that proofs can be taken when the form is locked in type-high chases. If these chases are bent and battered or any part of the frame is over type-high, the chases may be the cause of wrinkles. It is better to have the stereotyping chases a few thousandths lower than type high.