Select a gear pair from ratio and center distance, then deliver nominal DXF

Write constraints before choosing teeth

For an illustrative external parallel-axis pair near 3:1, document the center-distance target and tolerance, envelope, candidate modules, tooth-count range, and minimum contact ratio. Choose permitted spur or helical strategies. Record power and life requirements separately: fitting the housing and meeting the ratio does not establish load capacity or manufacturability.

Retain the selection rationale

1. Enter ratio, center distance, and envelope constraints in Gear Design Master, checking units and angle conventions.
2. Review candidates and score explanations for the permitted strategies.
3. Compare actual ratio error, working center distance, contact ratios, and rejection reasons.
4. Check profile shifts, thickness, backlash, and theoretical undercut. Use preliminary strength screening when the required load inputs exist.
5. Save complete inputs and the selected candidate before manufacturing preparation and export.

Check the order of magnitude

For an unshifted standard spur example, m = 2 mm, z₁ = 20, and z₂ = 60 give ratio 3 and reference center distance a = m(z₁ + z₂)/2 = 80 mm. This is an illustrative check, not a universal formula for shifted or helical working geometry. Investigate normal-module, angle, and constraint conventions if candidates appear unexpected.

Review the delivery files

The release includes span and pin measurements plus millimetre-based ASCII R12 DXF, CSV, and Markdown export. Open the DXF in independent CAD and check units, closed profiles, tooth counts, and key dimensions against the selected report. Deliver inputs, selection rationale, nominal profiles, and unresolved manufacturing checks.

Nominal geometry is not production approval

Published version 1.1 supports solving, checking, and export. Strength is preliminary screening; final release needs load spectrum, life, reliability, lubrication, modifications, and tolerances. Before CAM, verify the cutter-generated root and manufacturing requirements. A successful export does not certify a manufacturable gear.

Source: Apple App Store: Gear Design Master 1.1.