Step by step
A file opened at the wrong size
A drawing at the size it was drawn, and a way to tell before you cut.
Before you start
Anybody who has imported a DXF and got something 25 times too big.
- The file, and one known dimension from whoever drew it.
Know why it happens
A DXF can carry no unit at all. A drawing made in millimetres and one made in inches look identical to whatever opens them, and 25.4 is the number you see when the two are confused.
It is not a broken file and it is not a broken importer. There is genuinely nothing in the file that says which one it is.
Check one dimension you know
Before anything else, measure one thing in the drawing that you know the real size of: a hole for an M3 bolt, the width of a shelf, anything.
The import tells you what it found rather than silently picking, so this is usually a five second check rather than an investigation.
Scale it once, by a number rather than by eye
If it is out by 25.4 it was inches read as millimetres, or the other way round. Set the size exactly rather than dragging a corner: dragging gets you close, and close is a part that does not fit.
Set one known dimension to its real value and the rest follows.
Every setting, and what it does
5In the order you meet them. The second line on each is what goes wrong when it is set badly, which is usually the more useful half.
Left edge (mm)
Starts at 0
Top edge (mm)
Starts at 0
Width (mm)
Starts at 100
Height (mm)
Starts at 100
Keep width and height in proportion
Starts off
How to know it worked
- The dimension you know reads its real value.
- The whole drawing fits the material it is meant for.
When it goes wrong
3It is out by 25.4, or by 0.039.
Inches and millimetres. Scale by that number and check your known dimension.
It is out by 10 or 1000.
Centimetres or metres read as millimetres. Same fix, different number.
Some parts are right and others are not.
That is not units. It is a drawing assembled from two sources at different scales, and it has to be fixed per part.