Flexy Index

thingiverse

SUMMARY This is a remix of a remix of the Kinetic Hand. It is a prosthetic index finger for a child (age 3) which now only shares with the Kinetic Hand the profile of the finger tip and the principal of a flex material spring. The parent design (Aline's Index) uses the distal finger section, flex hinge and grip pad from the Kinetic Hand and has a hard (PET-G) palm piece. This version is printed as one piece in flex material - but with a PET-G ring or tab to move the prosthetic index with the middle finger. Although more challenging to print, this provides a softer interface against the users hand and assembly is limited to attaching the PET-G ring or tab with a single M2 screw. DESIGN COMMENTS The recipient's hand was modelled using 'makehuman' http://www.makehumancommunity.org/), adjusted to match photos provided. The hand model was imported into Fusion 360 and the external surface profile of the makehuman model was used as the internal surface of the palm piece. The STL files attached are sized as suitable for the 3 year recipient, and the internal diameter of the middle finger ring attachment is 14.5 mm. 2 options are provided for linking to the middle finger - a full ring and a tab. The flex hinge will cause the index finger to return, so a full ring is not essential, but users might find that it provides more control of the index finger position. The filament used was Recreus Filaflex TPE, Shore hardness 82A. With a harder TPU or TPE filament (Shore 95A) the finger hinge as the STL supplied was too stiff - but detail changes to the hinge design could reduce the stiffness. The Velcro palm strap is actually a cable tie (eg https://uk.rs-online.com/web/p/hook-loop-fasteners/0219465/). The Fusion 360 file includes the hand model and there are a small number of variable parameters: an overall scale factor, key dimensions of the M2 retaining screw and the finger ring diameter. This was to easily scale up the design as the young recipient grows. Fusion 360 file and a STEP files attached. ADDITIONAL MATERIALS NEEDED 1 each M2 x 12 screw and nut.