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
-----Original Message-----
From:
Homebrew_PCBs@yahoogroups.com [mailto:
Homebrew_PCBs@yahoogroups.com] On Behalf Of Slavko Kocjancic
Sent: Tuesday, 17 September 2013 06:15 AM
To:
Homebrew_PCBs@yahoogroups.comSubject: Re: [Homebrew_PCBs] Re: Imaging PCB with LED
...so to clean up the problem, and not to argue...
I can make small board with toner transfer metod. Fine traces aren't
problem.
I can make small board with sensitived board and printed transparency on
laser Fine traces aren't problem.
... But I have problem with accuarcy. If I draw rectangle 200mm x 200mm
and then print that and then measure that, the dimennsion is not right.
With few prints made with same settings I measure the side from 199.5mm
up to 201.3mm. I tested 3 printers I own, and LaserJet 1018 and 1020
works identicaly. The Brother HL2030 is little better (from 200mm to 201.1)
So If I pick some big SOIC or TQFP with side of 20mm the error is aprox
aprox 0.1mm. It's bare visible with naked eye. So no problem with that.
Then I pick some chip in DIL40. The last pin is aprox 0.4mm off the
hole. If holes are drilled oversized then package should fit, else wil NOT.
Now I have terminal blocks on the edge of board. I have 20 pins stacked
(200 mils) and in last pin the difference can be 1mm and it's not
possible to fit that component.
And other thing is that I drill with CNC. And of course if one side of
board is ok the other is not.
Why the print's isnt consistent I don't know.
For toner transfer (printing on paper) It can be humidity, but when
printing on plastic transparency I think the humidity can't be problem.
As image is more distorted in height I assume that it's printer
mechanics problem.
As I know that my CNC is way under 0.1mm precission It's logical for me
to try to use it as photoploter.
The process is slower but got accuracy. So If I need accuracy (large
board) I should go with photoploter style, for small board's the toner
transfer is better choice...
I know that my english isn't perfect, but think that majority of people
will understand me. ...ker ne govorim kitajsko.
Slavko.
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