Overly Tight Tolerances on a Drawing: What to Do

Overly tight tolerances show up on drawings every week, and most of them were never meant.

What Should You Do When a Part Drawing Calls Out a Tolerance Far Tighter Than the Feature Actually Needs?

Ask before you quote it. Overly tight tolerances are often a title-block default or a typo, so confirm what the feature has to do, then quote the drawing as written next to a version with a sensible tolerance and let the customer pick.

Where the question came from

A machinist on r/Machinists vented about a print calling ±.0002 on a cosmetic knurl, and said he was tempted to call the customer and tell them they were getting five thou. The replies were more practical than angry. Several said to call and explain the cost, or just ask "is this tolerance correct?" with a screenshot of the callout. Others pointed out it could be a default left in the title block. One shop described quoting both: the tolerances on the print and their normal ±.005, priced side by side. Another reply noted that a knurl is sometimes turned back to size afterward for a press fit, so the callout may be real.

That last point is why you ask instead of guessing.

Why overly tight tolerances cost so much

Tight tolerances change how a part gets made. Slower finishing passes, more inspection, maybe a different machine or a ground finish. Our post on what drives the cost of a CNC quote covers that in more detail.

Sheet metal has its own version of the problem. Approved Sheet Metal notes that holding ±.005 across multiple bends goes past their recommended default tolerances; a dimension across two bends is typically ±.015. Bends stack, as we covered in how tolerances stack up on a laser-cut and bent part.

Fixing it at the source

If you're the one drawing the part, tolerance the features that mate, seal, locate or slide, and leave everything else on the general tolerance block. Put a short note on the drawing saying which features are critical. Hole patterns are a common trap; see how tight a tapped hole position tolerance needs to be.

If you're the shop, the two-quote approach does the arguing for you. The customer sees what the tight number costs and usually picks the normal one.

At DigiForge

Our capabilities page lists ISO 2768-m as the CNC standard, with tighter work down to ±0.01 mm where a feature needs it. For sheet metal it's ±0.13 mm on cut features and ±0.5° on bend angles. Quotes are indicative and subject to engineering review. If a callout looks tighter than the part needs, flag it, or ask us when you quote.