(Editor’s note: The following is an excerpt from the North American Insulation Manufacturers Association’s Fibrous Glass Duct Construction Standards, Fourth Edition, 2001.)
Machine fabrication is fast, accurate, repeatable, and usually more productive than hand fabrication. _ Grooving machines can cut all of the corner fold cuts for a one-piece straight module of fibrous glass duct board, plus cutting to correct stretch-out dimensions and finishing the longitudinal seam edges with staple flap, all in one pass. Two-piece “L”, two-piece “U”, and four-piece duct components can also be cut on grooving machines.
The modified shiplap method is recommended for machine fabrication of straight modules of fibrous glass duct board, although V-groove tools for both 1” (25mm) and 11⁄2-in. (38mm) duct board are available for most grooving machines.
Machine grooving tools have numbered or lettered tabs corresponding to the location and width of the cutting portion. To set up the machine, the interior dimensions of the duct are measured between the tabs on the tools; the tabs represent the necessary add-on allowances.
There are three methods for setting up the cutting tools in the grooving machine: Preferred, Reverse, and Standard.
Closure machines: these provide tightly sealed longitudinal seams at high production rates. When using approved heat activated tape on closure machines, it is not necessary to staple the longitudinal flap.
The Preferred tooling set-up for one-piece straight duct produces the closure flap at the left hand side of the duct board as it passes through the grooving machine.
The Reverse tooling set-up produces results which are identical to those of the Preferred set-up. The only difference is that the tools are identified by numbers.
Preferred and Reverse tooling set-ups both offer the advantage of cutting the closure flap by the blade nearest the side frame of the machine where the tool roller is supported. This contributes to the formation of a cleaner staple flap requiring less hand labor to remove the remaining insulation.
When longitudinal closures are produced by machine, the Preferred or Reverse tooling set-up must be used.
The Standard tooling set-up for one-piece straight duct produces the closure flap at the right hand side of the duct board as it passes through the grooving machine.
(Contact NAIMA at 44 Canal Center Plaza, Suite 310, Alexandria, Va. 22314; 703-684-0084; fax 703-684-0427; e-mail: firstname.lastname@example.org; www.naima.org.)