Mastering Tolerances - Xometry on demand manufacturing
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WHERE BIG IDEAS ARE BUILT Mastering Tolerances for Machined Parts General machining tolerances and specific tolerances guidelines xometry.eu

4 Xometry Partner Network 7 When to Use Specific Tolerances 8 General Machining Tolerances 9 Tolerance Standards Used in Europe
 10 ISO 2768 - Linear Dimensions
 11 Basic Tolerances 13 Geometric Dimensioning & Tolerance (GD&T) 16 GD&T Flatness, Parallelism, & Perpendicularity 18 Warning: Avoid Over-Tolerancing 23 Inspection Methods Matter

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WHEN TO USE SPECIFIC TOLERANCES There will be variation between parts Tolerances help identify what range of variation is acceptable for the purpose. Tolerances that have a lower range than General Tolerances should be called out in a drawing.

GENERAL MACHINING TOLERANCES Bilateral Tolerances (inches) For features of size (L, W, H, Ø) and location (position, concentricity, symmetry): ± 0.127 mm. Sharp edges will be broken and deburred by default. Critical edges that must be left sharp should be noted or specified on a print. For features of orientation (parallelism || and perpendicularity ) and form (cylindrical, flatness ⏥, circularity ○, and straightness ⏤) apply tolerances as follows: Distance Length (inches) Bilateral Tolerances (inches) Angularity degrees

GENERAL MACHINING TOLERANCES Tolerance Standards Used in Europe The most common tolerance standards that are used by engineers in Europe for subtractive manufacturing (e.g. CNC machining) are defined by ISO 2768 and ISO 286. Tolerance Standard General Linear Tolerances General Tolerances for External Radius and Chamfer Heights Angular Dimensions ±0.1-2 mm depending on the nominal length from 0.5 to over 4000 mm ±0.2-1 mm depending on the nominal length from 0.5 to over 6 mm ±1°-0°5’ depending on the nominal length from up to 10 to over 400 mm ±0.05-5 mm depending on the nominal length from...

GENERAL MACHINING TOLERANCES ISO 2768 - Linear Dimensions ISO 2768 and the derived geometrical tolerance standards are mainly employed for parts that are manufactured by machining or other material removing processes. Nominal Length (mm) Tolerance Class Values (mm)

BASIC TOLERANCES Bilateral, Unilateral, and Limit What’s the difference? Bilateral is designer-focused Limit is inspector-focused.

CLEARANCE AND INTERFERENCE FITS Clearance 9 Clearance fits need to be toleranced so: Any condition of A is less than any condition of B 9 Interference fits need to be toleranced so: Any condition of A is more than any condition of B6 9 This should not require tools to install (loose to tight) 9 This requires tools to install (press fit, shrink fits, etc.) 12 | xometry.eu

GEOMETRIC DIMENSIONING & TOLERANCE D GD&T is a symbol-based system of communicating feature-based tolerances
 V D GD&T uses setU D DATUMS as references for definining feature tolerancee D Datums are typically planes, axes, or cylinders Datums become a “universal reference” between designers, machinists, and quality assurance GD&T can call out the counterbore dimensions, location, and tolerances by using the DATUM references.

GD&T GLOSSARY Symbol Description ○ Profile (line) Profile (surface) Run-out (total) Run-out (circular)

GD&T: TRUE POSITION True Position ⌖ is used typically for hole locations:
 w c It determines how much variance a feature can have from CAD before it is out-of-spec by referencing datum5 c True position is usually used for sets of hole5 c Features are machined in the same setup These measurements typically require equipment like comparators or CMM.

P Flatness ⏥: non-datum call out for the acceptable variation on a planeh P Parallelism ||: call out to reference the acceptable variation of a surface from a parallel datum planeh P Perpendicularity ⟂ : call out to reference the acceptable variation of a surface from a perpendicular datum plane These can typically be measured with hand tools and gauges.