During the life of a product, parts that are used for many years, may be revised several times to improve performance or reduce cost. After a drawing change request is made, the drawing is modified. Any change to a drawing after release, shall be recorded in the Revision History Block.
When a drawing is first issued, it is called revision zero or dash (-), and the revision block is empty. As each revision is made to the drawing, an entry is placed in the revision block. This entry will provide the revision number, a summary of the revision, the date of the revision, and approver name.
As the component is modified, and the drawing is updated to reflect the changes, the revision number is increased by one, and the revision number in the revision block is changed to indicate the new revision number. For example, if a Revision 2 drawing is modified, the new drawing showing the latest modifications will have the same drawing number, but its revision level will be increased to 3. The old Revision 2 drawing will be maintained in the filing system for historical purposes.
ASME Y14.35M Standard for the Revision of Engineering Drawings
ASME Y14.35M Updated on September 2015, has issued standards for the proper documentation of drawing revisions.
ASME Y14.35M allows for changes to be made to drawings by adding and crossing out information on a drawing or by creating a new drawing revision.
The ASME drawing standards state that new drawings can be recorded as a new revision letter or as a new drawing number that supersedes the old one. The replaced drawing will be modified to note “replaced with change by drawing 1234567”. This ensures configuration management and product verification is handled correctly.
The first version of a drawing is identified by a revision dash “-“. After that, revision letters are used. Revision letters can be a single letter up to multiple letters
All letters can be used as revision letters except I, O, Q, S, X and Z. These letters are not allowed because they can be mistaken for numbers or for other letters. For example, a revision letter I can be mistaken for a 1 while an S can be mistaken for a 5. Revision letters must also be uppercase, to minimize confusion between a lowercase "l" and "1" and "I".
After the end of the revision letter sequence is used up, the next letter is added to the end. Revision letter Y is followed by revision AA. Revision AY is followed by BA. Revision DY is followed EA.
However, revision letters are not allowed to exceed two characters, so there is no revision greater than YY. At this point, you should issue a new drawing number
Revision columns are located in the upper right corner or next to drawing the title block. Revision columns include the revision letter of the drawing, a short description of the changes made between this revision and the prior one, and the date the revision was made or the revised drawing was approved. Revision columns frequently include the drafter who made the latest revisions.