Expansible rigging w/o scale

I’m trying to help somebody rig up an hand mesh for use in XR applications. The input data come from hand tracking as oriented points – and the points reflect the size of the wearer’s hand. This means that the hand skeleton joints will translate to accommodate different size hands… but not scale. For some bones this creates odd effects, because there’s not easy way to smooth out the juncture of two bones that have been moved relative to each other but not scaled… the artist painting the weights is kinda confused.

Anyone have some quick pointers I could pass along?

To have joints fake scale with position, you need to skin a section of stretching mesh across two joints, one at the top and one at the end. So for sections that would have been skinned to one joint in a normal rig, you need double joints skinned across the section you expect to change proportions.
The blend between the two will define how the mesh stretches when the joints change proportions and if done right will mimic non-uniform scale.
It may help to think of it like adding twist bones to the hands/fingers, to help distribute the deformation of the mesh.

Here is a badly drawn diagram to illustrate what I mean:

1 Like