When performing the lay-up, the peel ply should be larger than your part but should not exceed what measurement?

The correct measurement for the peel ply to extend beyond the part during lay-up is typically 2 inches larger on all sides. This dimension is chosen for several reasons.

Firstly, a peel ply that extends beyond the edge of the part ensures that any excess material can be easily handled and trimmed away after curing, while still allowing for a sufficient margin to accommodate inconsistencies or variations in the edge of the part itself. This helps to ensure that the resin does not continue to flow significantly beyond the intended edges, which might lead to excess waste of material or complicate the finishing process.

Additionally, a 2-inch margin is manageable, providing enough surface area to establish a good bond and facilitate proper debulking and vacuum bagging processes without overextending the peel ply, which can lead to difficulties in achieving a uniform surface finish or alignment.

Having margins that are too large, such as 3 or 4 inches, could complicate handling and may contribute to difficulties in achieving a clean edge and proper adhesion where the peel ply overlaps. Therefore, while the peel ply needs to be larger than the part for practical reasons, sticking to a 2-inch measure provides the best balance between coverage and ease of use in aerospace composite lay-up applications.