problem printing to scale

[mrzog]

Hi folks,
I need to print mechanical CAD drawing to scale.
I'm trying to assess if QCAD is OK for my task...
I have a simple benchmark to test this: I use a dxf with a rectangle of 200mmx280mm and I try to print it on A4 paper.
When I print throught QCAD, result are wrong: my rectangle is printed with a size of 198mmx279mm which is unacceptable.
I mesure it with multiple rulers and print it on multiple printers so I guess the problem is really QCAD related...

Any idea?
Thank you in advance,
Zog

FYI, I'm using
- qcad_2_2_2_0_demo_win32.exe
- Windows 7 64bits professional
- samsung CL320 printer
- Xerox WorkCentre 5645 PS printer

[andrew]

Thanks for trying QCAD.

QCAD should indeed print 1:1 if that is the scale factor configured in the print preview (I assume so). Don't use the auto fit function, it will scale your drawing down to fit on paper.

I've tried to reproduce this with my HP LaserJet P2055dn under Mac OS X:
- The result is a rectangle that is about 200.1mm x 280.25mm as far I can measure it on paper.
- Both QCAD 2.2 and QCAD 3.0 yield the same result.

I will try to reproduce this also under Windows to see if that makes any difference.

Working solution:
If you are willing to download QCAD 3 (currently release candidate 5, reported to run stable) and to make a simple adjustment to a script source file, you can adjust the printer factor to create an immediate working solution:
- Download and install QCAD 3 RC5
- Open file scripts/File/Print/Print.js with a plain text editor
- Look for this code (around line 157):

Code: Select all

    var printerFactor = new RVector(
        printer.paperRect().width() / widthInMM,
        printer.paperRect().height() / heightInMM
    );

- After this, add your correction. In my case that is:

Code: Select all

    printerFactor.x *= 200/200.1;
    printerFactor.y *= 280/280.25;

- After two more test prints, I had to finally correct this to 200/200.05 and 280/280.3 to produce the best result.
- Be sure to restart QCAD after changing any script code.

A proper printer calibration feature (printer based additional X/Y scale factor) is planned for a future release.

Remaining problems:
- How to accurately measure a distance on paper (required for a calibration feature)?
- Paper size changes depending on air humidity and temperature.

[mrzog]

Thank you Andrew, it effectivelly solve my problem.
Have a nice day
zog