How to Export Gerber and NC Drill Files from Altium Designer
By INDiPCB ·
Altium gives you two routes to fabrication data: generate it directly from the PCB document, or define it once in an Output Job file. Both produce the same files. The direct route is quicker for a one-off; the Output Job is worth it the moment you expect to build the board more than once.
The direct route
With the PCB document open, use File → Fabrication Outputs → Gerber Files. That opens the Gerber Setup dialog.
On the General tab, set your units. Millimetres are the sensible default for anything being made today. Then pick the format — 2:3, 2:4 or 2:5. This is the number of digits before and after the decimal point, so it sets the resolution of every coordinate in the file. For modern work, 2:4 or 2:5.
On the Layers tab, select the copper, soldermask and silkscreen layers you use, plus the mechanical layer carrying your board outline. Altium will happily plot every mechanical layer you have ever created, so be deliberate here — extra mechanical layers are a common source of confusion at the fabricator.
The mistake that moves every hole
Generate the drill data with File → Fabrication Outputs → NC Drill Files. This opens a separate dialog with its own units and format settings.
Those settings must match what you chose for the Gerbers exactly. If your Gerbers are metric at 2:5 and your drill file is imperial at 2:4, both files are individually valid and the holes sit in the wrong place relative to the copper.
This is the single most common Altium fabrication error, and it is hard to spot precisely because nothing errors. The files open, the board looks right in isolation, and the mismatch only shows when the two are overlaid. Set them the same, then check them overlaid in a viewer.
When an Output Job is worth it
An Output Job file stores the whole configuration — Gerbers, NC drill, and anything else you generate — in a reusable document that lives with the project and goes into version control with it.
Add one by right-clicking the project in the Projects panel and choosing Add New to Project → Output Job File, then add Gerber Files and NC Drill Files under Fabrication Outputs.
The value is not the first export, it is the fifth. The settings above stop being something you re-enter and possibly get wrong, and a colleague building the board gets your configuration rather than their own guess at it.
About the file names
Altium names its output with your board name and a distinct extension per layer — Board.GTL for top copper, Board.GBL for bottom, Board.GTS for top soldermask, and so on. Every file shares the same stem.
That is normal and expected; the extension carries the layer meaning. Do not rename them to something more descriptive, and do not send a hand-picked subset. A partial set does not fail loudly — it renders as a plausible but wrong board, which is considerably worse than an error.
Package and check
Outputs land in the project output folder, typically named for the project. Zip the whole folder.
Before sending, open the Gerbers and the drill file together in a viewer. Overlaying them is what catches the units mismatch above, and it takes a minute.
Uploading the ZIP on our order page renders and measures the board from the actual files, so you see the real dimensions and a design check alongside the price.