TECHNICAL 17 · QUALITY

Tolerances we hold, and the ones you should inspect.

A frame that is 10 mm out over a 40 m gutter will not assemble. Tolerances are cheap to hold at the mill and expensive to fix on site, which is why we publish them rather than argue about them later.

Covering film, UV-stabilised — XinYonSen

Typical fabrication tolerances
Feature	Tolerance	Why it matters
Cut length	± 2 mm	Accumulated error in a run
Hole position	± 1.5 mm	Clamp fit and pattern alignment
Hole diameter	± 0.5 mm	Bolt fit, no slotting on site
Bend radius (arch)	± 5 mm over the arc	Roof line and cover tension
Squareness of frame	± 3 mm per metre	Racking and door fit
Straightness of purlin	± 3 mm per 3 m	Visible sag between arches
Coating thickness	per standard, min at any point	Inspection failure

Values are our workshop practice; a project drawing may specify tighter and we will quote to it.

The accumulated error problem

A 2 mm error per member is nothing. Two hundred members at 2 mm in one direction is 400 mm, which is why frames are made in repeating sets and why the punching pattern is fixed at the start. If a drawing changes after punching, the change is expensive — that is the real cost of a late design revision.

What to inspect on arrival

Bundle count against the packing list.
Member marks against the drawing set (A/B/C, bay numbers).
One arch against the drawing: span, rise, hole positions.
One gutter length against the drawing: brackets, outlets, fall.
Coating: gauge readings at a weld and a cut end.

One habit that avoids claims

Photograph the first arch assembled on site and send it to us before erecting the rest. If something is out, it is one arch, not a house.

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Turn this into a quoted frame list

If this page answered the technical question, the next step is a number. Send the parameters and we will price the tube, profiles, gutters and fittings as one package.

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