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Hello, this is my first post on the forum and I thought I would ask around to know if anyone has any information about the production process for mechanical undershells in regards to make up effects. I have scoured all the lessons and while the lessons on how to create fiberglass shells for animatronic characters, animatronic heads and character mechanisms all gave me the laydown on the basics, no lesson seems to cover this branch of make up effects with elaborate mechanisms working underneath the prosthetic appliance, at least so closely to a performer's face like in these images I obtained from a few blog posts here aside from bladder work which is not what I am looking for. If anyone has any reading, video guides, or documentation on the process to create something like this it would be greatly appreciated.

For the project I plan to do something like this with it involving a small mechanized piece, think a small mandible or antenna that would be a simple joint attached to a servo with a limited range of motion, and I just can't imagine how to attach a moving mechanized piece so closely to an actor's face without the use of an undershell or harness. For what I have in mind, a larger helmet-like harness would not work as the actor's face would need to be visible. Are these undershells simply strapped tight to the actor's heads using something as simple as an elastic strap or are they glued down? How do I ensure the excess weight of the mechanics don't cause the appliances to warp or buckle after being adhered to the skin? Would I simply mount the finished mechanism on top of the shell which is then adhered to the actors face or do I create the shell with space for the mechanism to fit through? Questions like these are what is bounding around in my mind for weeks and I am just not sure how to find information on it, as google searches fail to provide anything of substance or even relevance. Honestly any information would be a blessing. I appreciate anyone going out of their way to reply to me, even if info is scarce.