Engineering drawing OCR is not really an OCR problem
People often assume engineering drawing extraction means running OCR and cleaning up the text.
That works reasonably well for title blocks. Part numbers, revisions, and drawing numbers are usually in predictable places.
The harder part is the drawing area itself. Dimension callouts often sit on top of extension lines, center lines, hatching, and other geometry. A standard OCR tool can mistake those lines for noise or formatting and misread the actual callout.
There is also a separate issue: sometimes the information is missing from the drawing entirely. If the scale or general tolerance field is blank, OCR cannot fix that. It needs to be flagged as a drawing issue, not a reading issue.
So the pipeline needs more than text recognition. It needs to separate geometry from annotations and check whether the required fields are present.
Title block OCR may look good early on, but that does not mean the full extraction is reliable.