Guides / Process
Common Mistakes in 5-Axis Machining Drawings
September 26, 2026
A drawing mistake rarely stops a part from being made. It usually just adds a round of questions, a delay, or in the worst case a part that comes back technically in spec but functionally wrong. These are the mistakes that show up most often on 5-axis RFQs.
No general tolerance stated
A drawing with tolerances on a few critical dimensions but nothing stated for the rest leaves the shop to guess your default. Some assume a loose commercial tolerance, others assume tighter, and the two assumptions price very differently. State a general tolerance, for example “unless noted, ±0.1 mm,” even if most dimensions do not carry an individual callout.
Tolerance applied uniformly out of habit
The opposite problem: every dimension carries the same tight tolerance, whether or not it matters. This usually happens when a drawing gets copied from a previous part without revisiting which features actually need to be tight. It raises the quote across the whole part for a benefit that exists on only a few features.
Missing material temper or grade
“Aluminum” or “stainless steel” without a specific alloy and temper leaves the shop choosing for you, and 6061 versus 7075, or 304 versus 316, cut and cost differently. State the exact grade and temper, or note that you are open to the shop’s recommendation.
Ambiguous datum structure
A part with features toed to more than one implied reference point, without a clear GD&T datum structure, makes it hard for a shop to know which features actually need to line up with each other. This shows up most on parts with mating features on multiple faces, exactly the kind of part that goes to a 5-axis shop.
No note on what the feature is for
A bore with a tight tolerance and no context leaves the shop guessing whether it locates a bearing, seals against a gasket, or is tight for no functional reason. A short note prevents both underbuilding a critical feature and overbuilding one that does not need it.
Surface finish specified without a unit
Ra 32 written without a unit could mean 32 micrometers or 32 microinches, a difference of roughly 25 times. Always state the unit, µm or µin, on any surface finish callout.
Assuming certification or inspection is included
A material certificate, first article inspection report, or specific standard compliance is a separate scope from machining the part. If your project needs one, state it explicitly rather than assuming every shop provides it by default.
Specifying the machining method instead of the requirement
Calling out “5-axis simultaneous” on a drawing when only one curved surface needs it can force a more expensive process on the whole part. Describe the geometry and the surfaces that matter, and let the shop choose the cheapest method that meets the drawing.
The short version
Most drawing mistakes are gaps, not errors: a tolerance left unstated, a grade left generic, a unit left off a finish callout. Each one is a five minute fix that saves a round of questions and gets you a faster, more accurate 5-axis quote.
Our guide to 5 axis machining quality control shows where each fix fits in the specify, inspect, accept path.
Frequently asked questions
What is the most common drawing mistake on a 5-axis RFQ?
A missing or ambiguous general tolerance. Without one, shops either guess or ask, and both cost you a day or more before quoting starts.
Can a shop just ask me about a missing detail instead of guessing?
A good one will. But every question adds a round trip. Catching the gap yourself before sending the RFQ gets you a faster, more accurate quote.
Does a 3D model fix these mistakes automatically?
No. A 3D model carries geometry, not tolerance, finish or GD&T intent. Those still need a drawing or model-based annotations.
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