Glulam Building: Start to Finish – Part Six B

 Welcome to our “Glulam Building: Start to Finish” series. Our goal is to provide an overview – from idea to completion – of a glulam building, from the perspective of a glulam manufacturer and designer.

Part 6B: Templates and Plylists

For curved and shaped glulam parts, a glulam schedule alone is insufficient to produce the part. Additional information is needed:

Straight Tapered Beams

Length of plies: In a typical beam all plies have the same length. The simplest example where this is not the case is a straight tapered beam. To minimize waste we will vary the ply length, while making sure that there is sufficient length in each ply to get proper clamping and bond along all ply lines of the finished part. We create a Plylist for the part, indicating the grade and length of each individual ply, as well as information necessary to align the plies properly (typically picking one or more “mark” locations on each ply that can be aligned during gluing). 

Curved Template with set form

Shape of curved part: To create the shape of curved glulam parts the plies need to be glued together on a curved form. The form shape is set using a plywood Template. We program and cut these plywood Templates using a CNC router. However, it’s never quite as easy as simply copying the profile from our shop drawings. Due to variability in wood, curved parts will never match their intended geometry perfectly, but we can minimize this error. Based on the number of plies, each radius of the Template is slightly reduced to account for Springback. The edge of the Template is also offset to account for the cull board (placed between the finished plies and the steel form for protection). Finally, check dimensions and straight reference lines are added to account for the flexibility and dimensional stability of the Template plywood and joints.

Templates and Plylists can get even more complicated for 3D curved and spirals, or curved and shaped parts made with manufactured plies.

Spiral Glulam Beam