Yes now I see.
I have already get similar gab with the joint, but currently only when I connect 2 joints acting on the same body.
Edited: Video showing the gab problem when two joints acting on the same body, Maybe it can help a other user with similar problem.
https://www.youtube.com/watch?v=qQJ6R9Nk8Bg
In the video the left gear with the long shaft in the middle is one compound construction.
The right gear is a other compound construction without shaft.
The left gear is linked with a hinge on the H base, And the right gear is linked by a hinge to the left gear with the shaft.
This situation cause gaps on the two gear body linked with the two hinges.
For fix this problem I have remove the hinge on the right gear.
I have add the right gear objects inside the left gear compound construction.
On this way the left gear the shaft and the right gear become only one object with only one hinge.
This have fix the gabs problem with my demo and my wrong construction method.
Sorry about my english.