MODULE M4 · 15.0 HOURS

3D Printing and Part Machining

0% complete

Prototype safety boundary

Low-voltage educational prototype, not a certified machine safety system
Do not use stop circuits created by learners as safety functions or emergency stops
Perform normal stops by software torque release; after planned stops, physically disconnect the 3 insulated power adapters and verify the de-energized state by measurement before maintenance or access
Do not place hands in the operating range while power is applied; test from no-load in a fixture
Wear impact-resistant work goggles during cutting, drilling, and tendon tension testing
In case of abnormal heat, odor, or smoke, do not approach; cut the power supply to the 3 adapters via a pre-designated building panel breaker outside the hazard zone or a certified upstream master disconnect and evacuate. If no upstream disconnect is available outside the hazard zone, do not energize the system. Torque release is not a substitute for power disconnection
Before introducing to environments with human access, a dual-channel, manual reset, EDM, feedback-capable dual contactor must be separately designed and verified under the review of a qualified safety expert

LEARNING OBJECTIVES

Module objectives

Understand part fabrication using carbon-fiber-reinforced PC filament (PC-CF) and optimization of printing settings
Acquire precision assembly tolerance management for heat-set inserts and sleeve bearings
Understand handling of Dyneema lines and capstan design structure for tendon-driven mechanisms
Master machining and fastening techniques to ensure dimensional stability and rigidity of robotic structures

3D Printing and Part Machining Theory

Carbon Fiber Reinforced Engineering Material (PC-CF)

PC (Polycarbonate) has excellent rigidity and heat resistance, and PC-CF filament added with carbon fiber maximizes rigidity, making it suitable for structural parts [S19]. However, due to the abrasiveness of carbon fiber, a hardened steel nozzle must be used [S19], and high-temperature printing of around 285°C is required [S19].

Inserts and Fastening for Precision Assembly

Heat-set threaded inserts are used to allow repetitive assembly/disassembly in plastic prints [S21]. For M3 inserts, a 4.0mm diameter pilot hole must be pre-placed in CAD design to ensure accurate seating [S21]. Also, maintenance-free polymer sleeve bearings (iglide J) are designed to have optimal clearance after being press-fitted when assembled with 8mm aluminum shafts [S17], and tolerance management with the 8mm shaft diameter is essential [S17, S18].

Tendon Driving Structure

Dyneema SK78 fiber shows a high breaking load of 230 daN and elongation of less than 1% at a 1.5mm diameter [S16], making it an excellent alternative to steel cables. Since the tendon is repeatedly bent at the rotation axis, structural design that rounds capstan corners to prevent breakage due to friction is important.

WORKED EXAMPLES

Worked examples

Example 1: PC-CF filament nozzle selection - Considering the high abrasiveness of carbon fiber, confirm that a Brass nozzle must be avoided as it wears quickly, causing printing quality degradation and nozzle clogging, and a Hardened steel nozzle must be selected [S19].
Example 2: Insert hole design - Since the outer diameter of the Accu HTBI-M3-BR insert is 4.4mm but the official recommended hole diameter is 4.0mm [S21], fix the hole diameter to 4.0mm in CAD design so that plastic sufficiently penetrates between insert knurling during heat-setting [S21].

LAB PROTOCOL

Finger Structure Fabrication and Assembly Practice

1
Configure FDM 3D printing environment for carbon-fiber PC filament with a hardened steel nozzle [S19].
2
Remove supports and finish surfaces after printing finger links and palm frame.
3
Vertically seat heat-set inserts into 4.0mm pilot holes using a hot tool [S21].
4
Cut IGUS precision aluminum shafts according to bearing specifications and deburr the ends [S18].
5
Press-fit sleeve bearings into housing, insert shafts, and check clearance [S17].
6
Fasten structure and sensor brackets with M3 cap screws [S20].

Safety check

Beware of burns from high-temperature nozzles (285°C) and beds (110°C) [S19].
Always wear goggles when finishing and deburring prints.
Operate ventilation facilities as smoke may be generated during insert heating.
Check all mechanical fastening states before applying power.

Lab deliverables

Fabricated 5-finger robotic hand structure (links, palm).
Records of heat-set insert perpendicularity and bearing clearance measurements.
Final fastening visual inspection completion report.

ASSIGNMENT

Robotic Hand Fabrication Precision Verification

Deliverables

Comparison table of CAD data and actual dimensional measurements of completed structuresAssembly tolerance management planManual for friction-reducing design of tendon routing structure

Rubric

Vertical seating of heat-set inserts (High/Medium/Low)
Smooth rotational movement after shaft-bearing assembly (Pass/Fail)
Compliance with part ratings and model specifications specified in BOM [B10, B11, B12, B13, B14]

KNOWLEDGE CHECK

Knowledge check

1What is the main reason for using a hardened steel nozzle when using PC-CF filament?Prevent rapid wear of brass nozzles due to carbon fiber abrasivenessFilament melting point is too low for ordinary nozzlesIncrease surface gloss of printsIncrease extrusion speed

2What is the recommended pilot hole diameter when using M3 heat-set inserts (Accu HTBI-M3-BR)?3.0mm4.0mm4.4mm5.0mm

FIELD CHECK

Completion criteria

All structural parts fabricated with FDM 3D printer [B10]
Heat-set inserts seated accurately in all designated holes [B14]
Assembly clearance of aluminum shaft and sleeve bearing satisfies standard [B11, B12]
M3 spec cap screws correctly used when fastening [B13]

MODULE SOURCES

Module sources

Prusament PC Blend Carbon Fiberprusa3d.com · technical_documentation
M3 Heat-Fix Threaded Inserts HTBI-M3-BRaccu-components.com · datasheet
iglide J JSM-0810-10 Sleeve Bearingigus.com · technical_documentation
drylin R Metric Aluminum Precision Shaft AWMPigus.com · technical_documentation
D-Pro 1.5 mmliros.com · technical_documentation
Socket Head Cap Screws Technical Datain.misumi-ec.com · technical_documentation