Although a cheap S.O.H.O laser printer, retailing at £79 or £45 on sale, the ML-2165 / Dell 1160 has a good toner composition conducive with good toner transfer. There is one however a downside, which does not affect the usefulness of the printer under normal circumstances, but does when used to make homebrew PCB's,
Repeatability due to alignment issues when performing multiple passes!
When making homebrew PCB's one of the most important features of a laser printer when using it for toner transfer, is repeatability, due to the fact the media has to be passed through at least twice to get a good transfer. The first print is merely a sub-straight for the next overlay.
If your not familiar with the function or purpose of toner transfer it relates to the fabrication of D.I.Y circuit boards or PCB's. The toner is transferred onto a bare copper clad sheet by way of pressure and heat. The toner layer acts as a mask to an etching solution. The process may be more easily explained by watching the following video showing one of the various methods.
Here we can see the single roller which feeds the paper to the upper pinch rollers.
This is the position when the roller is engaged with the paper.
This shows the back of the paper feed pressure plate. There is a rubber pad which applies grip in conjunction with the spring on the rear.Initially I assumed that this was spring loaded to aid releasing the paper in the event of a paper jam, by pulling the plate back to release the paper. After looking through the manual I could find no mention of it.
I experimented with releasing some of the pressure the plate apply's by using some card to pack the plate.
Due to the fact there is only one initial feed roller in the middle, too much pressure at this point seemed to affect the consistency of the feeds. This resulted in misalignment when the second print was fed into the paper tray.
After some promising results I found some wedge packers in the workshop used for shimming gaps, such as those used in door frame packing.
Here you can see the cut down shim inserted between the case and the pressure plate.
The second part of the fix is to make a card tray to ensure a level and consistent position for subsequent feeds.You could say to make a "home" position.
The tray is held simply with BluTac (poster putty)
After the fixes, the below transparency film was ran through the printer 3 times to apply a nice thick layer of toner.
It has to be noted, the fix only applies to the Samsung ML-21XX range. My preferred media is OHP transparency laser printer film. It will give much more consistent results due to is rigidity compared with paper.