Problem:

After a 3D drawing has crashed, the *.bak file was renamed in Explorer to *.dwg. 

The *.dwg file for the actual drawing had already been copied "elsewhere".

The back-up drawing status now corresponds to the state of the actual drawing several hours before, even though the "Save" button had been used to save the file several times in the interim period.

It appears that AutoCAD only updates the *.bak file if the user saves the file twice in succession, since only doing this updates the file time for the *.bak file.

 

Solution:

Concerning the saving behavior of AutoCAD, we can tell you the following:

• The *.bak file is updated each time it is saved, but not the current state, rather the state when the save action was last performed on your *.dwg file (not the automatic save action – the manual save action).
• If the Save automatically option is set in AutoCAD, the *.dwg file is saved at set intervals, but not to the current *.dwg file. Instead it is saved to your temporary folder.

 

The following is an excerpt from AutoCAD help:

If you activate the automatic save function, drawings are saved at regular intervals. By default the automatically saved files are allocated a temporary file name filename_a_b_nnnn.sv$. Filename is the name of the current drawing, a specifies the number of opened instances of this drawing file in the single AutoCAD session, b specifies the number of opened instances of the drawing in other AutoCAD sessions and nnnn is a random number generated by AutoCAD. 

These temporary files are deleted automatically when the drawing is closed normally. In the case of a program crash or power cut, however, these files remain. To recreate the previous version of your drawing using the automatically saved file, rename your file by changing the extension .sv$ to .dwg.

 

Notes:

In the case of a crash causing a corrupt *.dwg file, the .sv$ file should be restored from the temporary folder, not the *.bak file.