Here's how I made this work on this dummy - it's essentially a mouth hole with a fixed upper lip and a hinged lower lip. There's an operating lever attached to the lower lip
Here it is in action...
Cutting out the mouth openingThe dummy head was originally carved as a solid head from wood with the mouth carved into the solid wood of the face.
To make the dummy head animatable, the removable face of the dummy needed a mechanism to be attached inside it, but before that could be done, the solid mouth needed to be cut out to produce a mouth hole.
This was done crudely with a saw attachment on a multi-tool.
The multi-tool saw gives a pretty accurate cut for the basic mouth hole. I then needed to emlarge the hole to fit the moving lower lip. Because this lip would be hinged, the lower half of the hole needed straight edges to allow free rotation.
I enlarge the hole with a tungsten carbide cutter burr in the die grinder
Until it was gaping nice and vacuously.
Creating the moving lower lipThere is no jaw movement at the chin for the mouth. The face has a fixed upper lip and the lower lip is separate and hinged.
This was carved by eye from an oak offcut. Here it is being sized after some initial rough carving.
After some more shaping with the grinder and sanders it started to look like this...
Adding the hinge
Fine tuning the fit
But, I realised that the first go at carving the shape by hand had misjudged the size of the back of the lip. To make this better, I use my old friend Plasticine. Here's the original lip and a roll of it.
I judged the required shape by shoving a blob of Plasticine into the mouth and shaping it a bit with sculpting tools and fingers...
And then shaped it down with the filing sander locked in the vice.
As well as the main cut for the hinge plunge saw, I used a drill bit in the Dremel to cut an extra narrower slot for the control lever.