What this drill auditor checks
The Excellon parser reads the M48 header (METRIC/INCH, LZ/TZ, digit format and ;FILE_FORMAT comments), tool definitions, drill hits, G85 slots and M15/M16 routed slots, incremental moves and plating hints from X2 attributes, comments or file names. The Gerber parser reads RS-274X units, format, standard apertures, flashes, draws, arcs, regions, polarity and step-repeat to find the board outline and outer-copper pads.
Catching origin, unit and format mistakes
When holes miss their pads, the cause is almost always the drill export, not the copper. The auditor scores how many plated holes land on a flashed pad as parsed, then tries translating by bounding boxes, mirroring, and—for drill files written without decimal points—every common combination of units, zero suppression and integer.decimal digits. If an alternative fits much better, the finding names it, so you can re-export with matching settings instead of guessing.
Annular ring, edges, spacing and aspect ratio
For each plated hole the nearest pad gives an annular ring—the narrowest copper left around the drill, including any offset—computed for round, rectangular, obround and polygon pads. Holes are checked for edge clearance and containment against the profile, for stacked duplicates and thin webs between holes, and each plated tool for board-thickness-to-diameter aspect ratio against your fabricator’s limits.
Validation boundary
This is a preflight aid, not CAM or a fabricator’s DFM review. Pads defined by aperture macros, regions or drawn copper are not matched; inner layers, solder mask, back-drills, blind and buried vias, drill tolerances, plating allowance (finished vs. drilled size), tool rounding, panel rails and Excellon extensions such as repeat codes and canned cycles are outside the model. Arcs in routed slots are approximated by chords. Confirm every file in your fabricator’s viewer and follow their DFM report.
Frequently asked questions
Why are my drill holes offset from the Gerber pads?
Usually the drill file uses a different origin (absolute vs. auxiliary/drill origin), different units, or the wrong integer digit format or zero suppression. The auditor tests these interpretations and reports which one makes the holes land on the copper pads.
What is a good drill aspect ratio?
Aspect ratio is board thickness divided by the smallest plated hole. Many standard processes plate up to about 8:1; higher ratios often need an advanced process. Set your fabricator’s limits in the options.
Should drill sizes be finished or drilled sizes?
Most CAD tools export finished hole sizes and the fabricator adds plating allowance. The auditor reports the sizes as written; check your fabricator’s convention.
Are my Gerber and drill files uploaded?
No. All files are parsed in your browser and nothing is sent to a server.
Authoritative references
Ucamco publishes the Gerber Layer Format Specification and the XNC drill format, a well-defined Excellon subset. KiCad documents its drill-file export options, including origin, units and zero format.
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