PG40 80×40 mm Six Slot Super Light Aluminium Strut Profile for Enclosures

What was kept and what was given up

The design of a super light section is deliberately conservative in one respect and aggressive in another. The external geometry is untouched, so the section is a drop-in replacement for the standard beam and no bracket has to be redesigned. The walls, however, are reduced, and that is where all the saving comes from.

Limit one: you cannot tap it

A thread in aluminium needs about one diameter of engagement as an absolute minimum and one and a half diameters for full strength. An M8 thread therefore needs 8 to 12 mm of material. On a super light section the flange is well under half of that, so a tapped hole in the flange is not available at all — not marginal, but impossible.

The consequence is that every connection on a super light section has to go through a slot with a nut. That is a perfectly good method and it is how the whole system is designed to work, but it changes the design: you cannot bolt something to the end face of the beam, you cannot use an end face connector, and you cannot use a self-tapping screw connector. The connection vocabulary shrinks to brackets and slot nuts.

Limit two: the slot lip deforms

The slot mouth is an undercut — 8 mm wide against a 10.2 mm groove. The lip above that undercut is part of the flange, and on a super light section the flange is thin. When a nut is tightened, the load path goes from the nut, into the lip, and into the flange. If the lip deforms, the nut no longer sits square in the groove, the contact area drops, and the joint loosens under vibration.

In practice that means keeping the tightening torque down. A standard wall 40 series section will take about 15 N m on an M8 nut; on a super light section, stay around 8 to 10 N m. The rule that follows is worth writing into the assembly instructions: use more fixings rather than tighter ones.

The load ceiling

With the section mounted the sensible way — the 80 mm dimension vertical, which gives about 43 cm4 — the deflection limits work out as follows for a simply supported beam at an L/500 limit.

Those figures look generous until you put them next to the fixing limits. At a 1.2 m span the beam will carry 2 kN on paper, but the joints that hold it will have been torqued to 8 N m into a thin lip, and that is the real ceiling. On a super light frame the connections are almost always the limiting factor, not the section.

Building a super light frame

1. Design every joint as a bracket and slot nut joint No end face connectors, no self-tapping connectors, no tapped holes. Decide this at the drawing stage, not on the bench.
2. Keep the torque at 8 to 10 N m The slot lip is the limit. A torque wrench is worth having on a super light frame more than on a heavy one.
3. Use more fixings, closer together A 40 mm pitch gives you plenty of positions. Six lightly loaded joints outperform two heavily loaded ones on a thin section.
4. Mount the 80 mm dimension vertical It gives about four times the stiffness of the flat orientation. On a section this light the orientation is the difference between usable and unusable.
5. Add a mid support rather than a heavier section if it sags On a cover or a guard a support is cheap; on a super light section it is usually the right answer anyway.

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