What happens if I leave tolerances off a drawing?

The shop falls back to its standard block tolerance, often around plus or minus 0.1 to 0.5 mm depending on the process. That may be fine, or it may be tighter and pricier than your part needs, so you are leaving the decision to them.

Do I need to tolerance every dimension?

No. Put a specific tolerance only on features that have to mate or fit. A single general note in the title block handles every other dimension.

What is a sensible default tolerance?

A general note of plus or minus 0.1 mm on machined parts and plus or minus 0.2 to 0.5 mm on laser-cut or sheet parts is a safe starting point for most jobs.

Do I need to put tolerances on a technical drawing?

A drawing with no tolerances still gets made

A tolerance is the amount a dimension is allowed to vary and still be acceptable, for example a 20 mm slot specified as 20 ±0.1 mm is fine anywhere from 19.9 to 20.1 mm. Leaving tolerances off does not stop a shop from quoting your part. It just means they fall back to their own general block tolerance, a default that applies to every unmarked dimension. Many shops base that default on a published standard such as ISO 2768, which defines tolerance classes (fine, medium, coarse) for linear and angular dimensions that are not individually marked. The catch is that you no longer control which class they pick. On a precision shop the default might be plus or minus 0.05 mm, which is more accuracy (and more cost) than a bracket needs. On a sheet shop it might be plus or minus 0.5 mm, which is too loose for a bore that has to take a bearing.

So the real question is not whether tolerances are mandatory. It is whether you want to make the call, or hand it to the machinist.

Which dimensions actually need a tolerance

Most dimensions on a part do not matter much. The outer length of a plate, the position of a cosmetic chamfer, the overall height: these can sit on a general note and nobody will ever notice. The few that do matter are the ones where two parts meet.

Feature	Tolerance it usually needs
Hole for a press-fit bearing or dowel	Tight: plus or minus 0.01 to 0.02 mm
Clearance hole for a bolt	Loose: plus or minus 0.1 to 0.25 mm
Mating face that bolts to another part	Moderate: plus or minus 0.05 mm
Overall outline, cosmetic edges	General note is fine

Every tight tolerance you add costs money, because it forces slower cuts, more measuring, and more scrap. Tolerance the three features that have to fit, and deliberately leave everything else loose.

The easy way: one note plus a few callouts

You do not need full GD&T to make a clean, manufacturable sheet. Put a single general tolerance in or near the title block, for example UNLESS NOTED: ±0.1 mm, then add a specific number only on the handful of dimensions that have to fit. That is how most working shop drawings are toleranced, and it is enough for the large majority of machined and fabricated parts.

If you want the deeper version, our guide to engineering drawing symbols and GD&T walks through the symbols, and how to dimension a technical drawing covers where the numbers go. When you generate a drawing from a photo, the AI lays out the dimension lines and you decide which ones get a tolerance, which is the same human-confirms-the-numbers step behind making a drawing for CNC machining.