Spur gears, 12 diametral pitch (DP): 12 to 60 teeth, 14.5° and 20° involute, pitch / outside / root diameter and STEP/STL

sizes

13 in table

Notes

• 12 diametral pitch (DP) means 12 teeth per inch of pitch diameter: pitch diameter = N / 12 in, outside diameter = (N + 2) / 12 in, circular pitch = π / 12 = 0.2618 in (6.650 mm), addendum 1 / 12 = 0.0833 in (2.117 mm), tooth thickness on the pitch circle π / (2 × 12) = 0.1309 in. Centre distance of two gears = (N1 + N2) / (2 × 12) in = 1.058 (N1 + N2) mm. Module equivalent: 2.1167. A 12 DP gear does not mesh with a metric module gear unless the two are within rounding of each other; use the module pages for metric gears.
• Below 20 DP the coarse-pitch proportions apply: 20° (ANSI B6.1) dedendum 1.25 / P, whole depth 2.25 / P; 14.5° dedendum 1.157 / P, whole depth 2.157 / P (all minimum values), so the 14.5° root circle is a little larger. The table lists root and base diameters for both pressure angles so a hob or a CAD mate can be checked. 14.5° and 20° gears do not mesh: the pair must have the same DP and the same pressure angle. 14.5° is the older Brown & Sharpe / Boston Gear stock form (undercut below 32 teeth), 20° the current standard (undercut below 18 teeth).
• Files: 26 gears, a 14.5° and a 20° gear for each of the 13 tooth counts, as one extruded solid with a plain bore. Flanks are the true involute of the base circle, tooth thickness on the pitch circle half the circular pitch (no backlash), outside and root diameters as in the table, the root circle held at the root diameter for every tooth count (the flank is carried down to it; the real root fillet and trochoid are not modelled). Example choices (not published values): face width 11/16 in (17.46 mm), which is 8 / DP rounded to 1/16 in, and a bore of about a third of the root diameter picked from 1/16, 1/8, 3/16, 1/4, 5/16, 3/8, 1/2, 5/8, 3/4, 1 in. Hubs, keyways and set-screw holes are not drawn. Teeth below 32 (14.5°) and 18 (20°) are drawn without profile shift, so they are undercut-prone as real unshifted gears are.
• Stock tooth counts: the 12 to 60 range covers common stock gears (Boston Gear lists 16 DP 14.5° 14-tooth with 0.875 in pitch diameter, 1 in outside diameter, 0.5 in face, 0.375 in bore, which the formulas above reproduce; SDP/SI lists 48 DP gears from 14 to 108 teeth). Face widths and bores of stock gears vary by maker and series; those are not a standard.
• Left out: the 25° pressure angle, stub and profile-shifted teeth, tolerances (AGMA quality numbers), backlash allowances, helical and bevel forms, and hub dimensions. Maker CAD: SDP/SI publishes inch-pitch spur gears with per-part CAD; linked, not copied.

Spur gears, 12 diametral pitch (DP): 12 to 60 teeth, 14.5° and 20°… size chart

Mating features

Drawn at the exact size. Open press, slide, run and socket features by your process's clearance (tolerances by process); leave designed gaps and clamp fits as drawn.

Where the files are

Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.

Free files

★ Free files 26 parts. Generated by Xem Studio from the standard; threads are plain cylinders at major diameter. CC BY 4.0. index.json

Plain text: sheet.txt · JSON: /api/geometry?object=spur-gears-dp-12

Fits with

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