One of the biggest challenges in low-cost 3D printed prosthetic devices is achieving the proper fit. If the loads on the device are not properly distributed across the skin and underlying tissue, it can lead to irritation, bruising, or rashes. In the case of the body-driven prosthetic devices that the e-NABLE community designs, there are two body-interfacing components: the palm and the gauntlet. The palm serves as a "pocket" into which the user slips their residual hand and the gauntlet anchors the device to the forearm. When it comes to fitting, one solution is to 3D scan the residual limb to which the device will be fitted and model the gauntlet in software to conform to the surface of the scan. When printing, the resulting geometry often requires significant support material and has weak regions due to the poor matching of the slicing plane to the planes of action in the geometry.
A more analog solution to the fit problem is thermoforming. Similar to the process by which mouth guards are formed, PLA thermoforming allows for custom-fitting directly to the body. Additionally, the fit can be adjusted as needed after the initial forming.gauntlet.stl
Step 1: Print the flat gauntlet
Print the flat gauntlet in PLA on a FFF/FDM machine of your choice. It's important to use PLA for two reasons:
Print with 2-4 shells to ensure that the resulting object is water-tight.
Step 2: Step 2: Heat and Form the Gauntlet
Once you have printed the flat gauntlet form, you will need to heat it to soften the material. I have tested the following methods and have ranked them in order of preference:
The PLA will gradually stiffen over the course of a minute or so after it has been removed from its heat source, so you will have a reasonable window in which to form the gauntlet. And the gauntlet can be re-formed at any time by repeating the heating steps. Prepare the arm by draping a piece of cloth over the area to which the gauntlet is to be fitted. Quickly remove the gauntlet from the heat source and drape over the arm and apply pressure to form the gauntlet to the arm. Check that the wrist pin hole are parallel and are at a comfortable location. You can either continue to hold the gauntlet in position until the PLA firms up, or you can hold the arm and gauntlet in place in a sink and run cold water over both to set the form of the gauntlet.
Step 3: Step 3: Integrate the Gauntlet into the Rest of the Device
With the gauntlet finished, add padding, tensioners, and attach it to a palm of your choice. Sources of hardware and padding can be found on the e-NABLE resources page.