Thanks Michael,
Yes, sorry, I only want to print one of the orthographic view (Top, Front, right) with a scale 1:1 ie a 1" model is 1" on the paper.
What I did so far, and it seem to work, is:
1. Maximize the model;
2. Ctrl-P;
3. Measure the width of the viewport with Alt-D script

then open IrfanView

4. Paste the image already in the clipboard from 2:
5. Select Print ;
6. Set radio button Custom in Print size;
7. Change Width with the value measured is 3 with Aspect ratio ticked;
8. Press Print

That prints a 1:1 drawing of the viewport.

My question is for an easier way to do step 3. Could I add a line Viewport size under X;, Y:, Z: in the Alt-D script popup ? If yes what should it read? That would be perfect.

Gaston