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Just Do It 🫵🏾

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Format: Position tolerance with projected height symbol and dimension. Example: Position 0.2 (P) 20 means tolerance zone projects 20mm above surface. Pro tip: Projection height equals fastener engagement length plus 2-3mm.

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Why project: Position tolerance controls hole axis. For deep holes, axis deviation accumulates. Projected zone ensures fastener clears over engagement length.

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When to use: Threaded holes deeper than 1.5x nominal diameter, dowel pins, any fixed fastener with significant length.

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HOW AI BUILDS feature control frames:

1. Identifies geometric tolerance type needed
2. Calculates appropriate tolerance value
3. Selects datum references based on function
4. Orders datums by precedence (primary, secondary, tertiary)
5. Applies material condition modifiers when beneficial

Onshape AI follows ASME Y14.5 rules automatically.

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Your design looks great but the tool can't reach it. Here's how to prompt AI for manufacturability checks on CNC tool access:

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Reference dimensions in AI outputs need parentheses. Type 'Show reference dimensions in parentheses, not for inspection.' These are calculated values for information only. Prevents machinists from measuring non-critical features.

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Complex contoured surfaces (cams, airfoils, organic shapes) need profile tolerance. AI can model them but not tolerance them. Use profile of a surface with bilateral tolerance zone (plus/minus 0.2mm typical). Reference datums. Alternative: Provide coordinate table with X, Y, Z points and tolerances.

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Before releasing any AI-assisted drawing: verify every dimension has a tolerance, every hole has a size, every thread has a specification, every surface has a finish, every material is specified, datums are logical, and notes are complete. AI assists, you verify, shop makes it right.

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AI-generated notes section? List all general requirements. Prompt: 'Notes section includes deburr and break sharp edges, part marking location, heat treatment requirements, and special inspection requirements.' Comprehensive notes prevent assumptions.

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Create precision rules for your AI prompts: Critical mating dimensions get 3 decimals. General machined surfaces get 2 decimals. Rough dimensions get 1 decimal. Reference dimensions match their source. Consistent precision prevents over-machining and unnecessary costs.

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AI models don't automatically match precision to function. A bearing bore needs 3-4 decimals: Ø25.000. A rough cutoff length needs 0-1 decimals: 150. Tell the AI which features are critical and require tighter precision in the dimension callout.

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Pro tip: Your AI drafting assistant gets smarter with use. Feed it approved drawings from your shop >> AI learns your dimensioning style, preferred tolerances, standard notes. After 50 drawings, Fusion 360 AI matches your company standards 95% automatically. Training investment pays off in months.

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Game-changer for AI part documentation: Prompt with 'include parts list for assembly drawings with item numbers, quantities, and material specs.' AI creates geometry easily. Complete documentation requires explicit instruction. Assembly without parts list = chaos.

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Your bolt heads need spotface callouts. Type 'SF Ø18 depth 2mm' or 'Add spotface Ø18x2 deep on 4x holes'. Spotfaces provide flat seating for bolt heads on curved or angled surfaces. Include diameter and depth. Different from counterbore, spotface is minimum depth for flat surface only.

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Heat treatment callouts AI must include:

Harden to Rc 58-62
Carburize 0.5-0.8mm deep
Stress relieve after rough machining
Anodize Type II Class 2 per MIL-A-8625

Place in notes section. Heat treat happens between rough and finish machining. CNC shops need to know the sequence.

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Cylindricity = circularity plus straightness in one callout.

Use for precision CNC turned parts:
- Hydraulic cylinders
- Bearing bores
- Seal surfaces

No datum needed. Controls entire cylindrical surface.

Pro tip: Expensive to inspect. Only specify when function demands it. Otherwise use separate circularity and straightness.

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Coordinate dimensioning table for complex CNC hole patterns:

Create table with columns:
- Hole ID (A, B, C)
- X coordinate
- Y coordinate
- Diameter
- Depth

Reference datum origin on drawing. Game-changer for parts with 20 plus holes. CNC programmers love this format.

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Maximum material condition vs least material condition in AI prompts. MMC WINS for fastener holes and assembly clearances. LMC WINS for minimum wall thickness. Your prompt specifies which modifier based on functional requirement.

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Pro tip: Basic dimensions always pair with geometric tolerance. If you see basic dimension without position or profile control, something's wrong. Train your AI to catch this.

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Basic dimensions define theoretically exact locations. No tolerance. Used with geometric controls. Prompt: 'Show hole pattern locations as basic dimensions, position tolerance controls actual location.'

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Your AI needs to know which type for each dimension. Basic dimensions appear in feature control frame chains. Reference dimensions stand alone for convenience.