I need help placing a prefab

[Tahaan]

I have managed with the help of some Youtube tutorials to export a base I built and then place it in another world.

However I have two problems.

Problem #1. When any block is changed, the entire thing falls appart.  I think this has something to do with "recalc stability" which I probably am just not doing at the right time.

I tried a few different combinations

Debug Mode, Start selection, K, Prefabs, Select my building, then K, Prefabs, Apply BB positions.

Then ESC, Recalc stability, then K, prefabs, Save all locations.  Exit and come back in - it stands, but when any block is changed, it all falls appart spectacularly.  (Who knew concrete could explode and fly upward)

Problem #2.  The prefab had an underground part so when I exported it, I extended the selection down.  Placing the prefab causes it to create a raised area about 7 blocks high - clearly it is putting the lowest part of the original selection on the ground level.

I tried to "lower" it by adding an extra step to the process above.  After I start the selection, I use Shift-G to extend it down 7 blocks.  This appears to have no effect on where the prefab is placed.  So how do I get it to have the point 7 blocks up to be level with the ground?

Thank you!

 

[Laz Man]

https://youtu.be/BqQtvsjfok0

 

[Tahaan]

Yeah, a long video that ends with "Well if you figure out how todo it tell me also".

The video "shows" that stability is OK but he doesn't actually try to add onto those or destroy a block on those placed prefabs.

Mostr frustrating thing is when you focus superhard trying to remember th steps the guy takes in the video and he goes "oops, seems that doesn't work, uhm,lets try this.  Nope, ok,well let me try that! And then he cuts out of the video and back in and says OK, now it works...

That's not a tutorial.  That is a recording of someone trying to figure things out.  Which sadly appears to be about the best we have at this point.

Why doesn't the devs answer these kind of questions to explain the placement of prefabs and such?

------------- FFS STOP MERGING MY REPLIES ----------------
Now that I'm done ranting....

I figured out how to  move the prefab down.

If in stead of exending the selection down, you MOVE the extention down, it works.  I assume what happens is that the placement process uses the FIRST point of the selection, not the lowest.

This does not make complete sense because what if I extend a selection first UP and then DOWN?

------ AND ANOTHER SEPARATE MESSAGE ------

I have also managed to get a placed prefab to .... remain stable.

But I can not tell what I'm doing differently, only that it works now.