Remove unused bones from a Skin Mod


Hello maxscript masters,
This is probably a simple script but after a few hours and with my very weak programming skills I was unable to make anything working. My project needs a script that will find all unused bones (without weights) in a skin mod and remove them (from the mod only!).
I tried to find a function that will get all weights per bone, and than use a cycle to check if there is an empty one, but it seams it’s not that simple. Any help is welcome.
Thanks in advance for spending time reading this!


Delete Bones when they are not weighted?

Yes this function is useful and I’ve been using it for years

	local weightThresh = 0.0001
	local objs = selection as array
	for obj in objs do (
		select obj
		for m in obj.modifiers where classof m == Skin do (
			modPanel.setCurrentObject m
			local vertCount = skinOps.GetNumberVertices m
			local bonesCount = skinOps.GetNumberBones m
			local unusedBones = #{1..bonesCount}
			for v = 1 to vertCount do (
				local vertWeightCount = skinOps.GetVertexWeightCount m v
				for i = 1 to vertWeightCount do (
					local weight = skinOps.GetVertexWeight m v i
					if weight >= weightThresh then (
						local boneID = skinOps.GetVertexWeightBoneID m v i
						unusedBones[boneID] = false
			for i = bonesCount to 1 by -1 where unusedBones[i] do (
				skinOps.SelectBone m i
				skinOps.RemoveBone m
			format "% Bones where removed from %.%
" unusedBones.numberSet


Holy cow, so it’s not 3-4 lines like I thought :slight_smile: You RULE, MatanH! Thank you very much and wish you all best!



just curious… what is a practical use of removing bones from a skin by weight threshold?


@denis Optimization of course.


for optimization you need a ZERO influence but not an absence. any other reason?


Hello again :slight_smile:
Let me explain my case: we create add-ons for characters (clothes, armor etc). In order to copy the weights we use Skin Wrap and than fix the problematic areas. Then we use a plugin that extra polishes and smooths the skin and this plugin really hates bones that are there but not in use (they mess up the calculations) It can be done on hand of course but sometimes they are just too many. This script is a huge help :slight_smile:


I also use this usually after converting skin wrap to skin. You could set weights to zero but I like to clean up useless thinds when I rig. I find it easier to work like this. You can call it OCD if you want :sweat_smile:


my OCD has left further… i prefer to initialize a skin without bones i will never need


but… in many cases i prefer to add bones with no influence to have the right (continuous) hierarchy for example .

how the ‘optimized’ skin bones list will look like if a hand-bone doesn’t have an influence instead of lower-arm and fingers?