How do you specify hole patterns on a sign blank?
Clearance diameters, slot widths, the ±0.5 mm / ±0.2 mm tolerance grades and the approval sequence — so the pattern you draw is the pattern you get.
How do you specify hole patterns on a sign blank? (quick answer)
Put the hole pattern on the drawing with three numbers: diameter (or slot width), position from the datum edges, and the positional tolerance you actually need. The default here is ±0.5 mm on hole position — enough for normal bolt fixing — and ±0.2 mm as an optional tighter grade for jigs and repeat orders. Clearance holes Ø6–12 mm cover the common fixing hardware; slots are dimensioned the same way. Nothing is punched until the drawing is approved, so a wrong hole on the drawing becomes a wrong hole on every panel.
Hole punching is a CNC programme, not handwork: the corner radii, round holes and slots come out of one programmed pass on the disc presses. That means the pattern costs you nothing extra to repeat — but it also means an error in the approved drawing is repeated on every blank in the order. The discipline that matters is therefore in how the drawing is written, not in the punching itself.
What hole and slot diameters match which fixing hardware?
Clearance holes are sized to the bolt plus a small clearance so the panel can be nudged square on the post before torquing. Slots do the same job when the panel must slide — most often on overhead or back-to-back installations where two faces share the same post line.
| Hardware | Typical hole | Typical slot | Where it is used |
|---|---|---|---|
| M6 bolt | Ø7 mm | 7 × 14 mm | Small regulatory panels, edge fixing |
| M8 bolt | Ø9 mm | 9 × 18 mm | Standard panels on sign channel |
| M10 bolt | Ø12 mm | 12 × 20 mm | Large panels, banding or U-bolt points |
| Banding strap | — | strap pass-through | Round posts, pole-mounted signs |
Clearance = bolt nominal size + about 1 mm; slot length adds travel for squaring the panel. These are working dimensions, not a hardware standard — always check the fixing hardware against your own installation drawing.
Which tolerance should you write on the drawing?
Two grades exist. ±0.5 mm positional tolerance is the standard grade and suits every normal bolt fixing: the bolt has its own clearance, so the pattern does not need toolroom accuracy. ±0.2 mm is the optional grade — worth specifying when the panel bolts into a prefabricated frame, when two panels must align bolt-for-bolt, or when the blank feeds a customer's own jig. Ask for the tighter grade only where you need it; it is a genuine option but it adds checking effort.
| Feature | Standard grade | Optional grade | Verification |
|---|---|---|---|
| Hole position | ±0.5 mm | ±0.2 mm | CNC programme check + gauge sampling |
| Hole / slot width | ±0.5 mm | ±0.2 mm | Gauge sampling per batch |
| Blank outline (sheared) | ±0.5 mm | ±0.2 mm (laser) | First article + sampling |
First article is confirmed with the buyer before the batch runs; production is then checked by sample against the approved programme.
What is the first-article and approval workflow?
The sequence is deliberate and short. One: you send the drawing — DXF/PDF or a marked panel drawing — and it is reviewed for the pattern against the panel size and the fixing hardware. Two: any change you request after quotation is re-priced before it enters the programme, because a pattern change can move a panel to a different blank size. Three: the programme is written and verified, a first article is produced, and only after the pattern is confirmed does the batch run. Four: production is checked by sample with gauges built from the same data. This is why we ask for the drawing to be approved before production starts — it is the cheapest place in the whole chain to fix an error.
What should the drawing carry so nothing is ambiguous?
Four things, and none of them need CAD mastery:
A datum. Dimension the pattern from two panel edges (say, the bottom edge and the left edge), not from the panel centre. Centre dimensions force the punch operator to derive positions, and a derived number is where errors breed.
Face side marked. A hole pattern is usually symmetrical, but if it is not — for example one slotted corner for a tensioned banding route — mark which face is the sign face. The punch programme is mirrored if the marking is wrong.
Both sides of the joint. If the panel must align with holes on the post, the channel or a second panel, put those holes on the same drawing. The pattern is one coordinate system; splitting it across drawings is how bolt-for-bolt alignment fails.
The tolerance grade. Write ±0.5 or ±0.2 per the table above. If the drawing is silent, the standard grade applies.
Approved drawing → verified programme → first article → batch → gauge sampling. Each step exists because it is cheaper than re-punching a batch. Send your hole pattern with the enquiry and the price you receive already includes it.
General rules for dimensional and geometric tolerances on parts without individual tolerance indications — the framework hole-pattern tolerances are read against — are set out in ISO 2768, "General tolerances", published by ISO (International Organization for Standardization). Sheet thickness and width tolerances for the delivered aluminium panel itself follow EN 485-3 (CEN) or ASTM B209 from ASTM International.
Sources: ISO, Geneva · ASTM International, West Conshohocken, PA. Cited 31 October 2026.
Questions on this note
What positional tolerance do I need for normal sign fixing bolts?
±0.5 mm. Standard clearance holes give the panel room to be squared before torquing, so the tighter ±0.2 mm grade only pays off when panels must align with a prefabricated frame or with each other.
Can you punch slots as well as round holes?
Yes — slots are part of the same CNC punching pass as the corner radii and round holes. Dimension the slot width and length from the same datum edges and mark the face side if the pattern is not symmetrical.
What happens if I change the hole pattern after the order is placed?
The change is reviewed and re-quoted before it enters production, because a pattern change can affect the blank size and the punching programme. Once approved, the new first article is confirmed before the batch runs.
How do you check that the holes are in the right place?
The programme is verified before cutting, a first article is confirmed with the buyer, and production panels are sampled with gauges made from the same approved data. Every panel in the batch therefore traces back to one verified pattern.
Related
Send the drawing, get a written answer
Specification questions are answered by the same person who quotes the job.