Any chance you could extract the parts that cause problems for CSG operations and send them to us? Thanks a lot for the feedback. 
Sure, here’s a place with some of the models I had most issues with… UnionPlace.rbxl (219.4 KB)
(BTW In folder number 4 there’s unions that were made with the older engine…)
Does that only happen with CSG v3? If so, could you provide a place we can use to investigate? Thanks!
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Hi yes - one of the major goals of V3 is speed improvement over V2 for the purpose of having a much faster in-game CSG. CSG V3 will eventually be enabled in-game, once we work out all the issues. Studio V3 beta is sort of testing ground for that.
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Supporting meshes in CSG is one of our future goals.
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In terms of robustness/accuracy, V3 should be as good or better than V2, but the major drive of the project is to make it way faster than V2. Some of the perceived V2 accuracy issues are UI related - V2 engine is actually waaay more accurate than V1.
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UI related? I’m confused, when I separate v1 unions in v2 it can not only offset parts, but rotate them wrong. I have cylinders on a model I made, and separating with V2 caused it to rotate the cylinders into a different position.
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Hi! Not sure if this is a CSG issue. It looks like the multi-colored picture at the bottom shows convex decomposition (collision geometry) for this object (Default setting, I think). Can you please confirm and/or, if possible send me the place or model file in a DM.
Hi - would you be able to share the place or model file in a DM, so we can take a look at the issue. Thanks!
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I should have been more specific! By UI, I meant how the frames (position/orientation) of the objects are handled on the level above the CSG engine. When you work down on the low level a lot, you tend to think of everything higher up as “UI” 
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Oh, noted. Thank you for clarifying.
Yep - definitely a bug! Thank you for reporting it. Would you be able to share the model file in a DM?
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Hi! Thank you for reporting this. If possible can you share the part of the model that is creating issues in a DM. We are eager to look at this issue!
Thanks for the feedback thus far! This is a case where we wanted to release a beta early to get feedback/catch issues in the wide ways folks use the system so that we can iterate fast/release fixes each week and get it to an awesome place. We’re going to disable this beta for a couple weeks to address the blocking issues that have arisen (and we also have reviewed why we didn’t catch them before release). When we re-enable CSG v3, we’ll be doing continuous bug fixes and let you know with each Studio release what’s been improved.
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This explains some of the odd behavior surrounding unions and meshes. Even if v3 doesn’t support them, the crash that occurs when trying to union meshes is still an issue.
Here are meshes that cause problems in our game (in both beta and current CSG):
https://www.roblox.com/library/5003092686/RenderMesh
https://www.roblox.com/library/5002670651/RenderMesh
Those are simple colliders for roads. We have hundreds of different collider meshes, but only some are causing this issue - car gets really bumpy, no axle or suspension settings can help that. With Hull CF you can even see wheels sinking into the mesh. With Default, it’s better, but still bumpy. I can share video of this issue with you, if you are interested.
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Oh neat! Will we also eventually be able to use CSG on the client? I would really like this for local/client-side and quickly responsive destruction physics.
It’s nearly the sole reason I use it for since I can just make all of my meshes and models in Blender and optimize their triangle counts, etc.
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Absolutely, this will be available in-game.
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When do you think we will be able to separate unions in-game? This would be a very useful feature and it’s a bit odd that it’s missing.
Also, how far off do you think Roblox’s CSG is from being able to construct meshes at a comparable speed to other game engines (at least a few times per frame), and from a set of vertices rather than parts?
Any plans to clean up useless or unseen vertices made by unions?
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