Reading technical drawings
Example drawing of a shaft - click any numbered element and the explanation appears alongside. Below: the glossary of the key terms, grouped by standards.
EXPLANATION - CLICK AN ELEMENT
Welcome
Click one of the orange numbers in the drawing - this is where you see what the element means, which standard it is drawn to and what you have to watch out for when machining it.
Glossary - Lines & views (ISO 128)
Wide continuous line
Visible edges and outlines - the contour you machine.
Visible edges and outlines - the contour you machine.
Narrow continuous line
Dimension lines, extension lines, hatching, thread root.
Dimension lines, extension lines, hatching, thread root.
Dashed line
Hidden edges - lies behind material (e.g. cross hole).
Hidden edges - lies behind material (e.g. cross hole).
Dash-dot line
Center and symmetry lines, pitch circles, datum axes.
Center and symmetry lines, pitch circles, datum axes.
Projection method 1 (ISO E)
European arrangement: top view BELOW the front view. Symbol: truncated cone with circle on the left. US drawings (method 3) are mirrored - check the symbol in the title block!
European arrangement: top view BELOW the front view. Symbol: truncated cone with circle on the left. US drawings (method 3) are mirrored - check the symbol in the title block!
Section A-A
Part imagined as cut open; cut material is hatched (45°). Cutting plane trace: dash-dot line with arrows and letters.
Part imagined as cut open; cut material is hatched (45°). Cutting plane trace: dash-dot line with arrows and letters.
Detail X
Enlarged detail view (own scale, e.g. 5:1) for small features such as undercuts.
Enlarged detail view (own scale, e.g. 5:1) for small features such as undercuts.
Half section
For symmetrical parts: one half as a section, one as a view.
For symmetrical parts: one half as a section, one as a view.
Glossary - Dimensioning & tolerances (ISO 129 / ISO 286 / ISO 2768)
Nominal size
The entered numeric value (e.g. 25). Without an addition, the general tolerance from the title block applies.
The entered numeric value (e.g. 25). Without an addition, the general tolerance from the title block applies.
Limit deviations
Directly specified tolerance: 25 +0,1/−0,05 → dimension must lie between 24,95 and 25,10.
Directly specified tolerance: 25 +0,1/−0,05 → dimension must lie between 24,95 and 25,10.
Fit designation
Ø25 h7: letter = position of the tolerance zone, number = grade (smaller = tighter). Lowercase = shaft, uppercase = hole (h7 shaft in H7 bore = clearance fit). → Calculator: Fits
Ø25 h7: letter = position of the tolerance zone, number = grade (smaller = tighter). Lowercase = shaft, uppercase = hole (h7 shaft in H7 bore = clearance fit). → Calculator: Fits
General tolerance ISO 2768-mK
Applies to ALL dimensions without an individual tolerance. First letter (f/m/c/v) = linear dimensions, second (H/K/L) = form/position. “m”: e.g. 6–30 mm → ±0,2.
Applies to ALL dimensions without an individual tolerance. First letter (f/m/c/v) = linear dimensions, second (H/K/L) = form/position. “m”: e.g. 6–30 mm → ±0,2.
Theoretically exact dimension
Number in a rectangular frame: NO tolerance - the position is checked via the associated position tolerance.
Number in a rectangular frame: NO tolerance - the position is checked via the associated position tolerance.
Reference/auxiliary dimension
Number in parentheses: for information only, not inspected (derived from other dimensions).
Number in parentheses: for information only, not inspected (derived from other dimensions).
Ø / R / SW / □
Diameter / radius / wrench size / square - before the dimension value.
Diameter / radius / wrench size / square - before the dimension value.
Cone / taper
Symbol ⊳ with ratio (e.g. 1:5) - reference: Ø difference per length. → Calculator: Turned taper
Symbol ⊳ with ratio (e.g. 1:5) - reference: Ø difference per length. → Calculator: Turned taper
Glossary - Form & position tolerances (ISO 1101, “GD&T”)
Reading the tolerance frame: [symbol | tolerance value | datum]. The datum (A, B, C) is the reference surface - marked on the drawing as a triangle with a box.
- Straightness · ▱ Flatness
Form tolerances without a datum: how straight/flat does the surface itself have to be?
Form tolerances without a datum: how straight/flat does the surface itself have to be?
○ Roundness · ⌭ Cylindricity
For turned parts: deviation from the ideal circle/cylinder - independent of the diameter dimension!
For turned parts: deviation from the ideal circle/cylinder - independent of the diameter dimension!
∥ Parallelism · ⊥ Perpendicularity · ∠ Angularity
Orientation tolerances relative to the datum.
Orientation tolerances relative to the datum.
⌖ Position · ◎ Coaxiality · ⌯ Symmetry
Location tolerances: where may the axis/centre lie?
Location tolerances: where may the axis/centre lie?
↗ Circular runout · ↗↗ Total runout
The turned-part classic: part rotates about datum axis A, dial indicator on the surface - deflection ≤ tolerance value. Checks roundness AND coaxiality together.
The turned-part classic: part rotates about datum axis A, dial indicator on the surface - deflection ≤ tolerance value. Checks roundness AND coaxiality together.
Ⓜ Maximum material condition
Tolerance may increase when the dimension deviates from the maximum material size - gauge inspection. → Details: GD&T page
Tolerance may increase when the dimension deviates from the maximum material size - gauge inspection. → Details: GD&T page
Glossary - Surface & edges (ISO 21920 / ISO 13715)
Ra
Arithmetic mean roughness - average of the profile deviation. Typical: roughed Ra 12,5 · finished Ra 3,2 · fine Ra 0,8 · ground Ra 0,4.
Arithmetic mean roughness - average of the profile deviation. Typical: roughed Ra 12,5 · finished Ra 3,2 · fine Ra 0,8 · ground Ra 0,4.
Rz
Mean roughness depth (peak-to-valley) - more common in German-speaking countries than Ra. Rule of thumb: Rz ≈ 4–7 × Ra. → Calculator: Surface finish
Mean roughness depth (peak-to-valley) - more common in German-speaking countries than Ra. Rule of thumb: Rz ≈ 4–7 × Ra. → Calculator: Surface finish
Surface finish symbol
Tick √ = basic symbol · with bar = produced by material removal (machined) · with circle = material removal not permitted (e.g. left as rolled).
Tick √ = basic symbol · with bar = produced by material removal (machined) · with circle = material removal not permitted (e.g. left as rolled).
Edge condition ISO 13715
+0,3 = burr/transition permitted up to 0,3 · −0,3 = edge broken up to 0,3 · ±0,3 = both. Otherwise "deburr sharp edges" appears as text.
+0,3 = burr/transition permitted up to 0,3 · −0,3 = edge broken up to 0,3 · ±0,3 = both. Otherwise "deburr sharp edges" appears as text.
Glossary - Symbols that constantly appear on turned-part drawings
DIN 76
Thread run-out/undercut - space so the threading tool can run out.
Thread run-out/undercut - space so the threading tool can run out.
DIN 509 (form E/F)
Undercut at the shaft shoulder - grinding wheel run-out; E = for the cylindrical face, F = additionally the flat face. Specified e.g. as E 0,6×0,3.
Undercut at the shaft shoulder - grinding wheel run-out; E = for the cylindrical face, F = additionally the flat face. Specified e.g. as E 0,6×0,3.
DIN 332 (form A/B/R)
Center hole for machining between centers; B = with protective chamfer. → Calculator: Center drill
Center hole for machining between centers; B = with protective chamfer. → Calculator: Center drill
DIN 6885
Keyway - note width P9/N9. → Calculator: Keyway
Keyway - note width P9/N9. → Calculator: Keyway
M12 / M12×1,25
Metric thread coarse/fine pitch. Tr = trapezoidal, G = pipe. → Calculator: Threads
Metric thread coarse/fine pitch. Tr = trapezoidal, G = pipe. → Calculator: Threads
Heat treatment
“hardened 58+2 HRC” · “quenched and tempered” · “case-hardened CHD 0,6+0,2” - clarify BEFORE finishing: distortion + hardness spec!
“hardened 58+2 HRC” · “quenched and tempered” · “case-hardened CHD 0,6+0,2” - clarify BEFORE finishing: distortion + hardness spec!
1.7225 / 42CrMo4
Material number and short name designate the same steel - both notations are common. → Material database
Material number and short name designate the same steel - both notations are common. → Material database
Ra/Rz only where needed
Fine surface = expensive surface. Whatever the designer tolerances too finely costs you lead time - it's fine to ask.
Fine surface = expensive surface. Whatever the designer tolerances too finely costs you lead time - it's fine to ask.
Note: all cutting and material values are guide values. The tool or machine manufacturer's recommendations are decisive.
The calculator also runs in the workshop without a connection: app and desktop version