How to check a mechanical drawing: what you need, the checklist and the system

1. What you need before you start

You can't check a drawing in a vacuum. A print looked at on its own will tell you whether it's tidy. It won't tell you whether it's right. Before you start, collect four things.

The drawing and the model

Get the drawing as it will be released, ideally a vector PDF, plus the 3D model it came from (native CAD or STEP). Comparing the two is how you catch dimensions someone typed over by hand, views that weren't updated after a model change, and features that exist in the model but never made it onto the sheet.

The records around it

The part number, description and revision have to agree with what's in PDM and in the bill of materials, and the revision should point to an approved change order (ECO or DCN). An in-house checker can pull these up directly. An outside checker usually can't, so the drawing has to carry them clearly enough to be compared later.

The standards and specs it cites

Know which edition of ASME Y14.5 (or ISO 1101) the drawing claims to follow, because the rules differ between editions. Have the material, heat-treat and finish specs handy too, the ASTM, AMS or MIL documents the notes refer to. A callout can look complete and still cite a spec that's been superseded.

The context

How is the part made: machined, sheet metal, cast, welded? What does it bolt to, and how will it be inspected? You don't need the whole design story. You need enough to know which faces matter, so you can tell whether the datums and the critical tolerances sit in the right places.

2. Do you need a checklist?

Yes. Even if you've checked drawings for twenty years.

Experienced checkers don't miss the hard stuff. They miss the routine stuff, because it's routine: the projection symbol, the thread class on a tapped hole, a blank tolerance block, a finish note that doesn't say whether dimensions apply before or after plating. A checklist puts those in front of you every time, whether it's 9 a.m. or the end of a long Friday.

It does two more jobs. Everyone on the team checks to the same baseline instead of their own habits, which makes results comparable from one reviewer to the next. And a signed checklist is a record that the check happened before anyone ordered tooling or raw stock.

Ours has 150 questions, grouped by topic, each with a short answer on what to look for and how to fix it: the mechanical drawing review checklist. There's a printable PDF and a Spanish version.

3. Do you need a system?

Also yes. A checklist tells you what to look at. A system tells you how to use it so you get the same quality every time. Three parts make it work.

Check in passes, not all at once

Try to check title blocks, views, GD&T, threads and the parts list in one read and you'll find the problems that jump out and miss the quiet ones. Split the work into passes, one topic each, across every sheet in the set:

1. Title block and records. Part numbers, revisions, sign-offs, units, the standard and edition.
2. Views. Projection, view alignment, section and detail labels, hidden lines.
3. Dimensions. Is every feature sized and located? Anything given twice? Reference values marked?
4. GD&T and datums. A complete datum reference frame, correct feature control frames, basic dimensions, modifiers used legally.
5. Notes and finishes. Hole and thread callouts, surface finish, plating, edge breaks, and the parts list against the balloons.

It feels slower. It isn't, because you stop re-reading the same sheet hoping to spot what you missed.

Someone other than the author checks it

The person who drew the part knows what they meant, so that's what they see on the sheet. Self-checks miss the same mistakes the drafter made in the first place. The checker should be someone else: a lead designer, a peer, a quality engineer, or an outside checker. They read only what's on the paper, which is exactly what the shop will do.

Let software do the first read

PDM rules and AI-based tools can now do a first pass: compare title block data, flag empty fields, spot missing callouts and some dimensioning problems. Use them. They're quick and they don't get tired. But they still miss things a trained checker catches, and they flag things that aren't errors. Treat their output as a list of leads, and have a person confirm every finding before it goes back to the drafter. That frees your engineers for the questions no drawing check can answer, like whether the part will actually fit and work.

A simple routine for a small team

No formal checking department? This is enough to start:

1. The drafter self-checks against the checklist and fixes what they find. That clears the easy items.
2. A second person checks the PDF in five passes, marking findings by sheet and zone.
3. The drafter fixes, and the checker confirms each fix against the marked copy.
4. Both sign the title block. The marked copy and the checklist get filed with the release.

If there's no second person, or the second person is the one who's always too busy, that's the gap we fill.