Hi Michael...

> One other thing you can try with join is to scale your objects down in size by 1/10 or 1/100 and then try to join them,
> that may shrink the gaps between pieces to within the join tolerance.

Thanks, its much better.
I scale it down 1/100 and now the total number of surfaces = 30.
Looks like there are some bad geometry like overlapping each other.
Should edit the surface manually...

Thanks