Custom FRP Grating Fabrication — Tolerances & Precision Control

FRP grating arrives as standard 1.22 × 3.66 m panels; real jobs need cut-outs for columns, pipes and equipment, stair treads to stringer width, and custom colours. Custom fabrication is routine — but only if the tolerance on both sides (factory and site) is agreed up front. Misunderstood tolerances are the single most common cause of "the panel doesn't fit" disputes. This article sets the factory tolerance, the site-fit expectation and the drawing rules.

1. Standard Fabrication Tolerances (indicative)

Indicative factory tolerances; confirm against the confirmed fabrication drawing. These are looser than precision-machined metal but tighter than "roughly cut on site".

2. Why Cut-Outs Must Be Sized, Not Eyeballed

A cut-out around a column needs clearance for thermal movement (see thermal expansion), not a tight fit — a column hole that touches in summer will buckle the panel. Size the opening with a 6–8 mm clearance ring, and seal with flexible trim, not mortar. Where the cut-out interrupts a bearing bar, specify reinforcement (edge banding or a bolted angle frame) at the cut; never leave a severed bar unbanded. See cutting and cut-outs.

3. The Confirmed-Drawing Workflow

1. Customer sends a dimensioned drawing (DXF/PDF): panel thickness, resin, surface, cut-out sizes and positions, clip locations, edge banding.
2. Factory returns a confirmed fabrication drawing with tolerances and a quote before production begins.
3. Customer signs the drawing; production cuts to the signed dimensions only — verbal changes do not travel to the saw.
4. Factory ships with a cut-out schedule matching the drawing number.

This one loopback — sign the drawing before the cut — eliminates most fit disputes.

4. Site vs. Factory Cutting

Factory-cut pieces fit first time and arrive banded and sealed. Site cutting is a fallback, not a plan: it needs carbide tools, dust PPE, and the cut edge must be banded or sealed immediately (every cut is a new wicking path). Where site cutting is unavoidable, oversize the cut slightly and trim to fit — never cut a panel smaller than the opening. See installation guide.

5. Colour and Matching Tolerance

Custom/Pantone colours are matched within a typical ΔE tolerance for the grade; batches can vary slightly, so order all panels for one visible run from a single production batch where appearance matters. A replacement panel ordered a year later may not match exactly — another reason to order 5–10% spares with the original shipment.

6. Precision Checklist

• Agree tolerances in writing on the confirmed drawing.
• Cut-outs oversized with thermal clearance; severed bars reinforced and banded.
• Holes +1.5–2 mm over bolt for sliding support.
• Single-batch colour for visible runs; order spares now.
• Factory-cut preferred; band and seal any site cut.

ZeAllgrate cuts, drills, notches and bands FRP grating to your signed drawings with the tolerance table above; send the dimensioned file and we return a confirmed drawing and quote before cutting.

7. The Drawing That Prevents the Call-Back

Almost every "panel doesn't fit" call traces back to a drawing that was spoken, not signed. A workable fabrication drawing carries five things: the datum every cut-out is measured from (never a sketched centre), the over-size rule (cut-outs +3 mm so thermal movement and site error trim, never under), the reinforcement at every severed bar, the clip positions, and a signature date. Verbal changes do not reach the saw — only a re-issued, signed drawing does. The same discipline applies to colour: if the deck is visible, order the whole run from one production batch, because two batches of "green" can differ just enough to show in a strong light. Where site cutting is unavoidable, over-size and trim, and band the cut edge the same shift — an unbanded cut is a wicking path that the next rain starts. A factory that returns a confirmed DXF before cutting is the sign of a process, not a promise; insist on that loopback before the deposit is wired.

Bottom line: sign the fabrication drawing before cutting. Dimension every cut-out to a datum, over-size it, reinforce severed bars, order visible runs from one batch, and band every cut edge. A confirmed DXF is the difference between a panel that fits and a call-back on site.