WeldConstraint changes CFrame of parts randomly

when applying WeldConstraints to parts in Studio, the parts being welded will sometimes, but not always have the CFrame property changed. This doesnt happen every time and sometimes when I simply reposition the parts and redo the same steps, the CFrame will not change. The Undo action will not Undo the CFrame property change so this is doubly frustrating.

We had found a work around where we were doing the weld while the parts were parented to ReplicatedStorage instead of Workspace and we had a model fully working and the welds were good, parts were in the right place. We published the game and tested it an everything was good for 2 days. Then this morning we went to play the game, and the CFrames had been moved again. See screenshot.


the model on the left has no welds. The model on the right is welded together with WeldConstraints (this model was perfectly fine yesterday).

This seems completely contrary to the point of WeldConstraint. Parts should not move at all, ever.

So to recap we have two issues here. Simply welding parts in Studipo is a complete pain because applying the WeldConstraint instantly moves the parts, undo doesnt work, and they have to be repositioned. Sometimes we have to repeat the steps as many as 5 times before the part will not move. Second issue is that once successful and working, the parts will still randomly move their CFrame relationships WHILE WELDED , days later!

I don’t remember this happening to me before, but for the last 2 weeks or so I have had various issue like this. Its not just me, but other devs workign on the same game with me experience the issue as well.

very strange indeed.


Are you using Team Create?

It is extremely critical that you provide reproduction steps like how the bug report requirements explain, or nobody will be able to replicate this issue to fix it.

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This has also happened to me sometimes.

Yes, we are using Team Create.

This happened to a game I’m working on yesterday, which completely broke vehicles ([NEW🏁] Driving Empire - Roblox)

It would probably be best and most reliable to just switch to standard welds. Completely destroyed our game at random and risking something like this happening again is not a risk we’re willing to take.

I have had this happen to me as well, entire creations destroyed, very frustrating. The only fix I have found for this bug is to use standard welds. Standard welds do not have this issue as far as I know, and are simpler than weld constraints.

This could be because the CFrame of WeldConstraints becomes less and less percise the CFrame gets from the original.

Anyways WeldConstraints seem to have a lot of buggy behavior.