TRIMMING A BOARD TO SIZE & SLIP SHEETS
In picture framing, trimming a board to the size needed for matting or backing is called "blanking" the board. Board pieces need to be cut as accurately as possible, paying attention to both size and squareness. Squared corners and straight sides are especially important when blanking boards for mats, because blanks that are grossly "out of square" will result in very obvious problems with the squareness of the mat opening. Typically a mat blank with only a slight un-square corner will cause no problems. Blanking can be done using a straight line or hand-held mat cutter, a Logan #500 Mat Knife or utility blade guided by a sturdy straight edge or T-Square.
In picture framing, a slip sheet is the underlayment material placed under the mat you are bevel cutting. A slip sheet is only needed when bevel cutting as it supports the face paper of the mat being cut. When straight cutting, remove the slip sheet as a straight cutting is cutting clear across from edge to edge and does not need to support the face paper of the mat you are cutting.
Slip sheet material should only be scrap mat board. Never use self-healing vinyl cutting mats as they are dense rubber and will damage the blade and hinder performance of the cut. The slip sheet must be gradually moved around, turned over or flipped the other direction so as not to cut too many times over the same area. Otherwise the blade may drag into previous cuts and produce a curve.
It is very important to adjust the bevel blade depth so that it barely passes through the mat board and only scores slightly into the slip sheet. Save your scraps and drop outs as they can often times be used as a slip sheet.