Kwawu 3.0 Prosthetic Hand Stringing Tutorial and Assembly Guide

This video demonstrates essential tools and techniques for cleaning up 3D printed objects, including using a heat gun to remove stringing by heating and retracting strings, manually removing rafts and supports by bending or cutting, and employing a temperature-controlled hot knife (set to 220-250°C) with flat or ironing tips to slice off stubborn strings and smooth surfaces. The presenter emphasizes that 3D printed objects require post-processing similar to other manufacturing processes, with the first level focusing on removing supports, brims, rafts, and strings while preserving the original material.

This segment covers the critical post-processing phase of 3D printing. The creator demonstrates how to remove support structures and assess print quality, revealing both successes and failures. The Ferox print showed issues with support material causing deformation, while the Parassauro demonstrated successful detail reproduction. The creator explains the relationship between layer count, detail resolution, and printing challenges. They discuss the importance of proper support placement and how excessive support can damage delicate features. The segment emphasizes that 3D printing is an iterative learning process where failures provide valuable insights for improvement.

The complete workflow for post-processing 3D printed parts involves multiple sequential steps: (1) Removing excess resin from the build plate using a plastic spatula, (2) Cleaning the part in a solvent bath (alcohol) with automatic washing cycles, (3) Manually rinsing with a brush for thorough cleaning, (4) Removing support structures while the part is still soft, (5) UV curing to achieve full hardness, and (6) Touch-up work including cleaning contact points and optional sanding. This systematic approach ensures printed parts are clean, properly cured, and ready for assembly or further machining.

This segment covers comprehensive post-processing techniques for achieving professional 3D print finishes. The process begins with single extruder multi-pass printing to create multicolor waveforms. Post-processing involves progressive sanding: starting with 120 grit to remove deep scratches, then moving to 320 grit for a smoother surface. Polyurethane clear coat (Minwax) is applied to enhance shine, though it may increase scratchiness. For superior results, Zona polishing paper (30 micron to 1 micron) is used with circular motions on a wet surface. The final result produces a surface where the 3D printed nature is barely visible, though some imperfections may remain.

Successful 3D printing of detailed figures requires careful parameter selection. Printing speed should be reduced to 30-40 mm/s for pieces with facial features and fine details, as higher speeds sacrifice detail quality. Layer height should be set between 0.14-0.16mm for PLA material, with 0.08mm being the minimum supported height. For post-processing, use sandpaper with grain numbers 150, 360, and 400, starting with the coarsest and progressing to finer grits. Always sand in the direction of the layer lines, never against them. A Dremel tool can be useful for difficult areas but should be used at reduced speed to prevent melting the PLA.

The hand's complex functional anatomy involves coordinated action of multiple muscle groups and nerves: the median nerve innervates thenar muscles (abductor pollicis brevis, opponens pollicis, and superficial head of flexor pollicis brevis) and first two lumbricals, enabling thumb positioning for pulp-to-pulp opposition; the ulnar nerve innervates hypothenar muscles, adductor pollicis, and intrinsic muscles (dorsal and palmar interossei, lumbricals 3-4), controlling fine finger movements; the radial nerve innervates supinator, brachioradialis, and extensor muscles; and the flexor and extensor tendon systems work together through the digital fibrous sheath and dorsal aponeurosis to achieve coordinated hand function, with loss of intrinsic muscles causing claw deformity.

The fingers have three joint types: hinge joints (IP joints) with one plane of motion (flexion/extension); ellipsoid joints (MCP joints) with two axes allowing flexion/extension plus abduction/adduction; and saddle joints (CMC joints) with similar two-axis movement. The extensor mechanism comprises four key components: the extensor hood over the proximal phalanx, the central slip inserting into the middle phalanx to extend the PIP joint, and the lateral bands inserting into the distal phalanx to extend the DIP joint. Sagittal bands serve as locators keeping the mechanism in place during flexion. Three retinacular ligaments stabilize the system: triangular (prevents volar subluxation, injured in boutonniere), transverse (prevents dorsal subluxation, injured in swan neck), and oblique (communicates PIP-DIP motion). The volar plate prevents hyperextension of MCP and PIP joints. The flexor mechanism involves FDS and FDP tendons. At the proximal phalanx, FDS splits to form the Cambridge chiasm through which FDP passes. FDS inserts into the middle phalanx to flex it, while FDP inserts into the distal phalanx to flex the DIP joint. FDP to digits 3-5 acts as a mass action muscle—one tendon controls multiple digits together. If repaired too short, all three digits lose excursion (quadriga effect). Lumbricals originate from FDP and insert into extensor hood, functioning as guy ropes to fine-tune movements. They flex MCP and extend IP joints. Interossei also flex MCP and extend IP but are weaker extensors due to shorter lever arms. The lumbricals have greater mechanical advantage because their center of rotation is further from the joint axis.

The hand's functional movement relies on a complex muscular and tendinous system. The flexor system includes the long flexors (flexor digitorum superficialis and profundus) and lumbrical muscles working together for finger flexion. The extensor mechanism involves the extensor digitorum tendon splitting into separate slips for each finger, with contributions from the extensor indicis proprius and extensor digiti minimi. The interossei muscles, divided into palmar and dorsal groups, produce finger abduction and adduction. The digital margin (collateral ligaments) and volar plate stabilize finger joints and prevent hyperextension. Together, these structures enable precise finger movements essential for fine motor control and gripping activities.

The flexor retinaculum is a strong fibrous band that bridges the anterior concavity of carpal bones, converting the space into an osteo-fibrous tunnel called the carpal tunnel, through which the median nerve and tendons of flexor digitorum superficialis, flexor digitorum profundus, and flexor pollicis longus pass; it attaches medially to the pisiform and hook of hamate, and laterally to the scaphoid and trapezium. The extensor retinaculum, also known as the dorsal carpal ligament, is a modification of deep fascia on the dorsal wrist that divides the space into six compartments containing extensor tendons: compartment 1 contains abductor pollicis longus and extensor pollicis brevis, compartment 2 contains extensor carpi radialis longus and brevis, compartment 3 contains extensor pollicis longus, compartment 4 contains extensor digitorum, extensor indicis, anterior interosseous artery, and posterior interosseous nerve, compartment 5 contains extensor digiti minimi, and compartment 6 contains extensor carpi ulnaris.

Extensor tendons are organized into six compartments: 1st (abductor pollicis longus), 2nd (extensor pollicis brevis and longus), 3rd (extensor pollicis longus), 4th (extensor digitorum communis), 5th (extensor digiti minimi), and 6th (extensor carpi ulnaris). The abductor pollicis longus can have anatomical variants including complete or partial septation within the first compartment. Flexor tendons are housed within the carpal tunnel with four superficial and four deep tendons. The flexor pollicis longus has its own tendon sheath.

To tie fluorocarbon to spectra backing on a fishing reel, hold the fluorocarbon in your right hand and spectra in your left, tie a double uni knot around the spectra by wrapping 11-12 times in each direction, then tighten carefully while avoiding cuts from the lighter line, and finally trim the excess ends for a clean splice.

Two primary knots are used for connecting fluorocarbon to Spectra fishing line: the FG knot and the RP knot. The FG knot is preferred for heavy line (60-100+ lb) and is known for its strength and slim profile, though it is easy to tie incorrectly. The RP knot is better for lighter line (30-50 lb) and is easier to tie quickly. To ensure the FG knot holds properly, it must be cinched down thoroughly before finishing and tested under pressure. The FG knot's design involves pinching onto a single piece of line rather than wrapping around multiple strands, which is why it feels like it should slip through but actually holds extremely well when tied correctly.

This comprehensive technique creates a durable, smooth connection between fly line and backing. Required materials include thin braided Spectra line (6-10 lb), splicable backing (Micron, Dacron, or holo core), size 100-130 needle, UV glue, UV light, and scissors. The process involves loading the fly line into the needle's hollow side, feeding backing through to create the Chinese finger trap effect, and attaching Spectra line with a uni knot to prevent sliding. Apply UV glue to create a smooth transition, then cure with UV light. This splice provides zero friction through guides and has proven durable when tested with big fish.

Successful dacron netting requires proficiency in knot tying since dacron knots stay tight and can take 10-20 minutes to untie. Use fingers instead of needles to avoid fraying. For the last row, double the 30-pound test dacron line rather than using heavier line, which is expensive and creates larger knots. Optional upgrade to 50-pound test for added strength. To create double cord, fill a needle half full, spread the line on a flat surface, then pick up the remaining line and fill the needle again with equal portions from spool and spread line.

This comprehensive tutorial covers two methods for attaching fishing lines to the AMS Ever Glide Safety Slide used in bowfishing. The first method uses 200-pound Dacron line (available in orange, yellow, and pink), while the second uses 350-pound braided spectra line. Both techniques involve threading the line through the slide's two openings, creating loops, and positioning the knot behind the nock for optimal arrow flight. The Dacron method involves feeding the line through both openings, creating a finger loop, and walking it over the arrow point and behind the nock. The braided spectra method uses a loop knot technique where you create a large loop, feed it through the slide, and walk it over the nock and point. Both knots are strong and allow for quick arrow changes without cutting the line by simply repositioning the loop.