Glue line edge is a term used to describe the edge surface in which two pieces of wood can be bonded together by a combination of glue and pressure. The solid wood panels produced are used mainly in cabinet, furniture and millwork market segments. The panels produced must have undetectable joints free of open areas or visible glue build-up pockets. Typically, the edges for glue-up are prepared in one of the four ways described below. When comparing the various methods, it is clear that the Diehl rip saw provides the best solution for producing the best quality panels with the least amount of defect and effort.
The table saw/jointer method requires multiple machines and is slow production. The jointed edge does straighten the stock and provides a smooth edge. However, by using a cutterhead, it closes the edge grain, limiting the glue penetration into the wood, reducing panel strength. Both the table saw and jointer require the operator to hold the stock as it is fed past the blade or through the cutterhead.
Over cutting rip saws (typically imported models) produce a marginal edge. The best possible cut this type of saw can produce is a cross hatch mark which is caused by the leading and trailing edge of the blade both cutting the stock. The cross hatch mark can leave glue build-up pockets. The limited saw blade gullet clearance does create some blade deflection affecting the perpendicular edge to face accuracy. Consequently, the best clamping method is by pipe clamps or clamp carrier where excess force can be applied to close the edge gaps. The over cutting saw by its design will have a significant amount of stock kickbacks.
Gang rip saws provide the most productive method of ripping lumber. Like the over cutting rip saws, the best possible edge you can produce will have a cross hatch mark. While ripping multiple pieces may be productive, the stress released when ripping boards is difficult, if not impossible, to control on the leading and trailing edge with the dip chain design. Consequently, the best clamping method is by a clamp carrier where excess force can be applied to close the edge gaps.
Diehl straight line rip saws utilize an under cutting design. They are capable of producing a straight or hollow cut on the edge. By design, the Diehl straight line rip saws cut with only the leading edge of the blade, eliminating any cross hatch marks or visible saw kerf marks. The unique capability of producing either a straight or hollow cut makes the Diehl saw the most practical choice for RF (radio frequency) or clamp glue-up. Producers of high-end panels use the hollow-cut joint to assure there is minimal stress in the panel on glue-up and it eliminates open end defects from occurring. The undercutting design also provides greater control of the stock while ripping, reducing stock kickbacks from occurring.
Typical hollow cut will produce a slight concave cut approximately .002” – .004” over a 4’ long board. This is shown with paper in the hollow. Both ends of board are tight.