Hello...
I do use compensation (ie image scalling to 99.8%) as in that case I got
best result.
The anyoning part is that error is not constant. It's varies from sheet
to sheet. And error seems to be sum of paper stretching (humidity and
temperature change) slipping in printer and optics difference. I found
that lines (width in paper) is far more consistent than height. So
scanning mirror in laser doesn't make big error, but paper transport
mechanism does.
Year's ago I try with pen in CNC but all pen's tested doesn't have
precission I wanted. The consistent width of line is problem. As I want
line in range of 8 - 10 mils I can't find the such pen.. For lines over
1mm there are no problem...
On 09/17/2013 06:57 AM, Mark Harrison wrote:
> Hi Slavko,
>
> It is very common for laser printers to have errors in vertical and horizontal dimensions. It's probably the same for Inkjet printers and plotters.
> Laser printers can also have some distortion across the width of the page because of errors in the lenses and mirrors.
> As you mention, the feed mechanisms may slip a little, or the rollers may change dimensions due to temperature or accumulation of dirt, or rubber rollers may shrink.
>
> Good PCB editing software tools should allow you to adjust the X and Y scales to compensate for errors in the printer.
> Some laser printer drivers also allow for fine adjustment in scale, although normally apply an equal scale factor to both height and width.
> Some Gerber tools also allow you to expand or contract the X & Y scales to compensate for different output devices.
> If you don't have tools to do this, you may be able to manually add a few extra commands to the start of the PCB Gerber file using a text editor as I seem to recall there are scale factor commands in the Gerber standard (???).
>
> Using a CNC machine for photo plotting sounds like a good idea if it's fast enough. Have you tried using a ink pen in place of the milling bit? I have been tempted to try this but I haven't found a good ink that will stick to copper and is waterproof, and doesn't run.
> It may be easier than photo resist and would work on plain PCB.
>
> Cheers,
> Mark
>