Turn a simple gift into a clever surprise.

The Logical CashLock Case transforms an ordinary cash envelope into an interactive puzzle box with a 4-digit programmable mechanical lock — printed almost entirely in one piece!

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🔒 Key Features

• 100% 3D Printed – no screws, pins, or metal parts
• Print-in-Place Mechanism – works right off the print bed
• Programmable 4-Digit Lock – set your own combination
• Snap-Together Design – easy to assemble, no glue required
• Compliant Mechanisms – printed springs, flexible detents, and tumblers
• AMS & Non-AMS Versions Included – choose between a clear-bottom or solid single-color case
• Super fun to print, assemble, and give!

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⚙️ How It Works

The CashLock Case uses a unique compliant tumbler system:

• Four Dials and control Gears, each with one missing tooth defining its unlock position.
• When the correct combination is set, notches align with the Tumblers, releasing the Latch Bar.
• The 4-point locking system disengages, allowing the case to open.
• To lock again, simply scramble the dials.

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🧩 Assembly Highlights

1. Snap each Gear into place (the large inner fillet faces up).
2. Align gear notches with their matching tumblers.
3. Insert and snap in the Dials, setting your preferred combination.
4. Angle the Latch Bar into position until it clicks.
5. Install the False Bottom insert.
6. Verify the lock slides freely when the correct code is entered.

No glue, no hardware — just geometry doing all the work.

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✅ Prints fully functional off the bed — all compliant components and hinges are active immediately after printing.

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🎁 Perfect For

• Gifting cash in a creative and interactive way
• Teaching compliant mechanism principles
• Showcasing multi-material AMS printing
• Makers who love functional prints and puzzles

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🧠 Behind the Design

This design continues the LogicalPlanet tradition of functional, educational, and fun printable mechanisms.
It’s an evolution of my earlier puzzle-based projects — this time, combining mechanical logic, compliant geometry, and elegant form.

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🧩 Maker Notes

• Use a clear AMS bottom to watch the gears move.

🔧 Changing the Combination

Each gear’s missing tooth defines its unlock position.
To change your lock code:

1. Open the case and remove the False Bottom.
2. Set the dials to the current open position.
3. Lift each gear slightly and rotate it to a new position.
4. Reinstall and verify that the latch bar slides freely.

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Related Links

3-digit Logical CardLock Case - The Programmable Gift Card Case with a Twist

PuzzleLock Box — Lock and Puzzle in a Box

BinaryBin – 16-Digit Binary Coded Lockable Container

Programmable Combination Lock Gift Box

StashCan 2.1 - 3D Printed Secret Safe with Programmable Lock

Sequential Discovery Puzzle Gift Box #1 (GBS1)

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Please join the LogicalPlanet Discord community via my linktree to discuss this and any other LogicalPlanet projects, upcoming projects, ideas and anything else related to LogicalPlanet.

https://www.logicalplanet.com/ email me at logicalplanet3d@gmail.com

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Revisions and Updates I occasionally update and revise my designs. When I do, I’ll document the changes here. Check back periodically for the latest revision notes or if you’re experiencing any issues with a model.