nanoCAD DWG File Recovery: Fixing Corrupted Drawings and Recovering Lost Data

nanoCAD DWG File Recovery: Fixing Corrupted Drawings and Recovering Lost Data

DWG file corruption is every CAD user's nightmare. Files can become corrupted from power failures, network disconnections, application crashes, or simply from accumulated drawing database errors over many editing sessions. nanoCAD provides several recovery tools, and understanding how to use them — and when to use manual techniques — can mean the difference between recovering hours of work and starting from scratch.

Understanding DWG Corruption

A DWG file is a binary database with indexed pointers between entities, symbol tables, and object definitions. Corruption occurs when these pointers become invalid or when the file structure is incomplete. Common causes:

• Power failure during save — the file is partially written, leaving an incomplete database
• Network disconnection — saving to a network drive that drops mid-write
• Application crash — nanoCAD crashes while holding the file open, leaving lock files
• Disk errors — bad sectors on the storage device corrupt the file
• Version conversion — saving through multiple DWG versions can accumulate errors
• Overly complex drawings — files exceeding 500MB with thousands of blocks can develop index errors

Automatic Backup Files

nanoCAD creates several backup files automatically. Knowing where to find them is the first step in recovery.

.bak Files

Every time you save a DWG file, nanoCAD renames the previous version to .bak:

• drawing.dwg → current version
• drawing.bak → previous saved version

To restore from a .bak file:

1. Close nanoCAD
2. Rename drawing.bak to drawing_recovered.dwg (do not overwrite the current file yet)
3. Open drawing_recovered.dwg in nanoCAD
4. Verify the content is intact
5. If good, replace the corrupted file

Automatic Save Files (.sv$)

nanoCAD creates automatic save files at a configurable interval:

1. Check SAVEFILEPATH system variable for the save location (typically C:\Users\<username>\AppData\Local\Temp\)
2. Check SAVETIME for the interval (default is 10 minutes)
3. Look for .sv$ files with timestamps matching your editing session

To restore from a .sv$ file:

1. Copy the .sv$ file to your working directory
2. Rename the extension from .sv$ to .dwg
3. Open in nanoCAD and verify content

Lock Files (.dwk)

When nanoCAD opens a DWG file, it creates a .dwk lock file. If nanoCAD crashes, the lock file remains and prevents reopening:

Error: Drawing is locked by another user

To fix:

1. Close nanoCAD
2. Delete the .dwk file in the same directory as the DWG
3. Reopen the DWG file

Using the RECOVER Command

The RECOVER command is nanoCAD's primary file repair tool. It performs a deep scan of the drawing database and attempts to fix structural errors.

Basic Recovery

1. Type RECOVER
2. Select the corrupted DWG file
3. nanoCAD scans the file and displays a recovery log:
   • Number of errors found
   • Number of errors fixed
   • Number of objects recovered
   • Number of objects lost
4. If recovery succeeds, the drawing opens with repaired data
5. Immediately save the recovered file with a new name: File > Save As > drawing_recovered.dwg

Recovery Results Interpretation

• 0 errors, 0 objects lost: The file was not actually corrupted — the issue may be elsewhere
• Errors found and fixed, 0 objects lost: Good recovery — all data preserved
• Errors found, some objects lost: Partial recovery — check the drawing for missing geometry
• Recovery failed: The file is severely corrupted — try manual techniques below

Manual Recovery Techniques

Technique 1: Insert into a New Drawing

When RECOVER fails, try inserting the corrupted file into a blank drawing:

1. Create a new drawing (NEW)
2. Type INSERT
3. Browse to the corrupted DWG file
4. If the insert succeeds, the geometry is brought in as a block
5. Explode the block (EXPLODE) to restore individual entities
6. Save the new drawing

This works because the insert operation reads the file differently than the open operation — it skips some header data that may be corrupted.

Technique 2: WBLOCK Recovery

If the file opens but some entities are inaccessible:

1. Open the corrupted file (if it opens at all)
2. Type WBLOCK
3. Select "Objects" mode
4. Select all entities (ALL)
5. Specify a new file name
6. The WBLOCK operation writes a clean database with only the selected entities

Technique 3: Partial Open

If the file is large and only certain areas are needed:

1. Type PARTIALOPEN
2. Select the DWG file
3. Choose which layers to load
4. Only the selected layers' geometry is loaded, bypassing corrupted data on other layers

Technique 4: DXF Export/Import

DXF is a text-based format that can bypass binary corruption:

1. Open the file in nanoCAD (if possible)
2. Type DXFOUT and save as .dxf
3. Create a new drawing
4. Type DXFIN and select the .dxf file
5. The geometry is rebuilt from the text representation
6. Save as a new .dwg file

Note: DXF export/import may lose some entity types (complex hatches, custom objects) but preserves core geometry.

Preventing DWG Corruption

Set Automatic Save Interval

SAVETIME
5

Set to 5 minutes (or shorter for critical work). This ensures .sv$ files are created frequently.

Set Backup File Count

nanoCAD can keep multiple backup versions:

1. Tools > Options > Open and Save
2. Set "Create backup copy with each save" = Yes
3. Set "Maximum number of backup copies" = 3

Save to Local Drive First

When working on network files:

1. Copy the DWG to your local drive
2. Edit locally
3. Save locally
4. Copy back to the network drive

This eliminates network-related corruption from interrupted saves.

Regular AUDIT

Run AUDIT with Y (fix errors) at least once per day on active drawings. This catches and repairs minor database errors before they accumulate into corruption.

Avoid Exceeding File Size Limits

Files over 500MB are prone to corruption. If a file is growing large:

1. Split into multiple drawings using WBLOCK
2. Use XREFs to reference split drawings
3. Purge unused objects regularly with PURGE

Recovery Workflow Summary

When you discover a corrupted DWG file, follow this sequence:

1. Check for .bak file — rename to .dwg and open
2. Check for .sv$ file — rename to .dwg and open
3. Run RECOVER — use the built-in repair command
4. Insert into new drawing — use INSERT to bypass header corruption
5. WBLOCK — extract entities to a clean file
6. DXF round-trip — export to DXF and reimport
7. Contact support — if all else fails, send the file to Nanosoft support

Each step is less likely to succeed than the previous one, so always start at step 1.

Conclusion

DWG corruption is recoverable in most cases if you know where to look. The .bak and .sv$ backup files are your first line of defense — configure them to save frequently and to a known location. The RECOVER command handles most structural corruption, while manual techniques (insert, WBLOCK, DXF round-trip) cover severe cases. Prevention is always better than recovery: set short auto-save intervals, work on local copies of network files, and run AUDIT regularly. By following this guide, you can minimize data loss and recover corrupted drawings with confidence.