Holes, fasteners, pockets and spur gears: reference values

This skill holds data, not a procedure. The checks that use it live in solidcraft-requirements-and-sanity (before building) and solidcraft-delivery-gate (before delivering).

(Idea source: wzyn20051216/solidworks-automation-skill, MIT. Process values there are initial suggestions for CNC, sheet metal and plastic parts; restated here, not copied. Confirm against the real process, supplier and load.)

1. Decide the hole type before modelling

"An M5 screw hole" is ambiguous. State or ask which one it is, and never default it to a tapped hole:

• Clearance (through, screw passes freely)
• Counterbore or countersink (head sits below the surface)
• Tapped (the thread is cut in the part)

Starting diameters, mm:

Other pitches, plastics or soft metals need the tap chart for that case; do not assume the table holds.

Tapped holes:

• The drilled hole must be smaller than the nominal thread; a counterbore must be wider than its through hole.
• Starting thread depth about 2 x the nominal diameter; check that thread engagement is at least 1.5 x the nominal diameter. A blind drill must be deeper than the thread depth.
• A small mouth chamfer (about 0.3 mm for M3 up to 1.2 mm for M12) helps the tap start.
• Find out how SolidCraft represents threads (list_commands with a filter such as thread). If only the tap-drill hole is modelled, write that in the notes: the model carries the tap drill, not the thread.
• A flat-bottom blind hole has no drill point, no incomplete thread zone and no tap run-out or chip room. It is a good model of the hole, not a finished tapping design.

2. Starting values to confirm per process

Hole edge distance is measured from the hole edge to the part edge. State whether a ratio multiplies the hole diameter or its radius.

Other starting values:

• Machined mounting plate: at least 4 thick (8 as a default), pocket side wall at least 3, pocket floor at least 2, slot end radius at least 1.5.
• Holes under 3 mm in machined parts: warn (drill stiffness, chips). Holes under 1.5 mm in moulded parts: warn (fragile core pin).
• Where a sibling skill gives its own numbers (solidcraft-3d-print-dfm, solidcraft-sheet-metal, solidcraft-sheet-metal-flatpack), use the stricter value and say which one you used.

3. Spur gears

Ask for module, number of teeth, pressure angle, face width and bore. For a part that will be made, do not invent them; for a visual demo, defaults are fine if the reply says so.

Standard full-depth external spur gear:

• pitch diameter d = m x z
• base diameter db = d x cos(alpha)
• tip diameter da = d + 2m
• root diameter df = d - 2.5m
• tooth thickness on the pitch circle = pi x m / 2
• centre distance of a mating pair = m x (z1 + z2) / 2

Check undercut risk when the root circle falls below the base circle; at 20 degrees that starts at roughly 17 teeth or fewer.

Not covered without a specialist route or an engineer: helical, bevel, internal, rack, worm, profile-shifted gears, backlash, tolerance grades, strength, and a true hobbed root shape. A gear that measures right (single solid, tip diameter, bore, face width, volume) is not production ready.

4. Report

List the hole types chosen and which values are starting values still to confirm.

5. Related skills (fill gaps, do not duplicate)

• FDM walls, overhang, bridges, clearances: solidcraft-3d-print-dfm (this skill has no printed-part row).
• Bend radius, relief, flat size: solidcraft-sheet-metal; tabs, slits, perforation: solidcraft-sheet-metal-flatpack.
• Manufacturability of holes in sheet-metal or CNC parts, and shop limits: solidcraft-dfm-review. Where its numbers differ from the table above, use the stricter one and name both.
• Real screw, nut and insert geometry instead of the nominal sizes: solidcraft-step-parts.
• Clearance across moving or mating parts: solidcraft-assemblies.
• The checks that read this data: solidcraft-requirements-and-sanity (before building) and solidcraft-delivery-gate (before delivering).