Drawing
Drawing and model say something different.
The model was changed, the drawing was not. Or the drawing was updated and the BOM on it was not. The dimension on the drawing, the material in the title block and the quantity at the position must all three match the model.
Published 21 September 2026
01 What it is
Drawing against model, briefly explained.
The drawing is derived from the model. When the model changes, the geometry on the drawing usually changes along, but the texts do not: material, comments, quantities and sometimes the main dimensions.
That produces a drawing that looks right and yet says something different from what is in the model.
How you notice it
- A material in the title block that does not occur in the model
- A main dimension that deviates from the size of the model
- Quantities at the positions that do not match the BOM
- A note about a part that is no longer there
In a check
This shows up as error in the check of the drawing. You judge what has to be done about it.
02 Example
What it looks like.
Example drawing GRP-2210 (demo)
- Title block, material
- S235JR
- Model, material
- 1.4301
- Main dimension drawing
- 1200 mm
- Model, size
- 1180 mm
The frame was made in stainless steel and became twenty millimetres shorter. The drawing still shows the old version, and that goes to the supplier.
How it comes about
- Material and quantities put on the drawing by hand instead of linked
- A drawing that was not updated after a change in the model
- A main dimension put down as text instead of as a dimension
- An old PDF that was sent again
03 Approach
Find, fix, prevent.
How to find it
You put the text of the drawing next to the data from the model: materials, main dimensions and the quantities per position. That can be done by hand, but it is work that comes back every revision.
- 1 Read the title block and the notes of the drawing.
- 2 Put the materials that are in the model next to it.
- 3 Compare the main dimensions on the drawing with the sizes of the model.
- 4 Check the quantities at the positions against the BOM and the model.
Fix
- Link material and quantities on the drawing to properties of the model, so they follow along.
- Update the drawing after every change in the model and plot the PDF again.
- Put main dimensions down as real dimensions, not as text.
Prevent
- Everything that is on the drawing and also in the model should be linked.
- At release, check model, drawing and BOM against each other in one go.
- Have someone other than the drafter go through the drawing, or have it done automatically.
With BOMproof
Every release, without having to think about it.
BOMproof puts your STEP model, your PDF drawings and your Excel BOM side by side and points out every deviation: with a pin in the 3D model and a balloon on the drawing. You tick off what is correct.
04 Frequently asked questions
Drawing against model.
01 Which differences are the most dangerous?
Material and quantities, because purchasing is based on those. A deviating main dimension usually still stands out in the workshop; a wrong material does not.
02 Can a check read the drawing?
The text from a vector PDF, yes, including title block, notes and the BOM on the drawing. That is put next to the model and the Excel BOM, and every comment gets a balloon at the spot on the drawing.
03 And if several drawings belong to one design?
Then they are all read and also compared with each other, because contradictions between two drawings are just as annoying as a difference with the model.
05 Often seen together
Other errors from the same corner.
You never want to hunt for this error by hand again.
Upload your model, your drawings and your BOM and let BOMproof check them against each other. Book a demo with your own design.