The special grade of lumber used for glulam, lamstock, is received and stored at the laminating plant under controlled conditions (see Figure 3.7 below).
Prior to glulam fabrication, all lumber is visually graded for strength properties and mechanically evaluated to determine the modulus of elasticity (E). These two assessments of strength and stiffness are used to determine where a given piece will be situated in a beam or column.
For example, high strength pieces are placed in the outermost laminations of a beam where the bending stresses are the greatest. This blending of strength characteristics is known as grade combination and ensures consistent performance of the finished product.
Figure 3.7: Manufacture of Glulam
Once graded, the individual pieces of lamstock are end joined into full length laminations of constant grade and each endjoint is proof tested. Then, the laminated lengths are arranged according to the required grade combination for the product being manufactured.
Each lamination then moves through a glue applicator and the pieces are reassembled into the desired configuration at the clamping area. Hydraulic or manually activated clamps are placed around the member, and are brought into contact with steel jigs which have been pre-anchored to the floor to provide the desired curvature or pattern.
As pressure is applied, the laminations are adjusted for proper alignment in a level plane to minimize the amount of stock which will be lost when the member is surface planed to a smooth finish. Once full clamping pressure is reached, the member is stored at a controlled temperature until the glue is fully cured.
When glue curing is complete, the members are moved to the finishing area where basic surface planing, patching, and end trimming is done. Depending on what the client has ordered, drilling and notching for connections, sanding, and staining and varnishing may also be done. Because of specialized equipment and mass production, these functions can usually be performed in the shop cheaper than at the building site.
As a final step, glulam members are wrapped in readiness for shipping.