Fabrication of Floor Trusses
Building floor trusses requires specialized equipment, notably some kind of a press to embed the nail plates (and posi webs, if used) into the lumber completely. A fairly "low cost" method would involved building the floor truss on a table, embedding the plates partially on both sides, and then transfer it to a finish roller for the final press.
The preferred method is to use a dedicated floor truss fabrication table, as seen here. The truss is plated on one side, a rolling gantry head moves over the truss, embedding the plates, the truss is flipped to the other side of the table to expose the other side, plates are added to that side, and the head makes other pass to embed those plates. The truss is then removed from the table.
The configuration shown here is typical and enables the "first pass" of the gantry head to also complete the "second pass" of the truss that came before.
Pre-splicing of Chords
Floor trusses over 16' usually require the chords to be make from two pieces of lumber, which are spliced together with nail plates on the 3 1/2" side. Since this operation is not on the same surface as other plates pressing the splicing operation is either carried out as a separate manufacturing process, or done on the floor truss production table using specialized modifications to accommodate it. A "floor truss splice machine" is shown above.
Plate Storage
Where to put the plates prior to and during production? Many floor truss gantries come with an optional overhead rack to store boxes of plates, although many end up being used for other purposes (such as storing standard-length verticals.) Pre-splicing on the table takes a lot of the table surface, so some fabricators prefer to pre-splice at another station and use the extra surface to store plates being used for production.
More on Floor Gantries
Trusses built with most newer floor truss gantry tables do not require a pass through a finish roller, as roll-pressed roof trusses built on a gantry do. Newer gantries also come with options that help the workers by ejecting the trusses from the jig and flipping the trusses to the other side of the table. These options greatly enhance the endurance of workers, and take the stress out of the most difficult parts of the fabrication process.