Homebrew PCBs

I'll answer some of these questions now, but followup with pictures 
and a detailed description when I have time.

In measuring the voltage from the internal power supply (IPS) to the 
transfer roller (TR), I found that the voltage starts at about -400 
vdc when the printer prepares to print, then changes to +1400 vdc 
(approx) when printing, then reverts back to the negative voltage 
after the image is printed. If you just apply a positive external 
voltage to the TR, it works, but the drum never really gets cleaned 
off between runs. You can connect the IPS, run a dummy print (a 
period on a blank sheet) to clean the drum, then disconnect the IPS 
and attach the external power supply (XPS), and it works ok. I found 
(ebay) a hv relay that I programmed to use the IPS till the actual 
printing is about to start, then switches to the XPS for printing, 
then back to the IPS to clean up the drum.

The IPS is attached to the TR via a spring under the left (as you 
face it) TR bushing. I need to do more experimentation as to what's 
optimal, but for now I removed the TR, cut away the rubber roller on 
each end, leaving about 4 inches of rubber in the middle. This allows 
a 4" wide board to be printed, which is fine for me, but I'm sure it 
can be much wider. I then soldered some high voltage wire to 2 
bushings and put them on the bare steel rod on both sides to the 
rubber roller. This is where I charge the board.

I should mention that the voltage required seems to change depending 
on things like humidity and temperature, but once you get familiar 
with the system you can zero in on the correct voltage in a few quick 
runs. Since a run takes only a few seconds, this isn't much of a 
problem. One of the things I want to do is measure the humidity and 
temperature and see if there is a consistent relationship.

I am currently using a garolite (FR4 is garolite??) carrier 6 inches 
wide with a 5 inch wide opening to carry the board. The board is 
suspended by masking tape in the cutout so that when the carrier runs 
through the TR, only the board hits the TR.

To feed the board I removed a lot of the stuff at the front of the 
printer and added a spring loaded roller so that the carrier is 
pushed through the printing area. This is MUCH easier than you might 
think because there is a slot on each side of the printer that is 
perfect for the purpose. I am reusing the centering mechanism, so the 
board does feed right up the middle. Again, I'm not sure what is 
optimum but I can run .062 board through , though I usually use .032 
board. The .062 is too thick for the gear on the TR to mesh with the 
drum gear, but it doesn't seem to matter because the board is being 
pushed through via the front rollers and there is enough friction via 
the drum to push the carrier out the back. I have experimented with 
pulling the board through using the drum/TR vs pushing it through 
from the rear, but have reached no firm conclusion as to which is better.

Right now I am timing the whole thing from when the solenoid pulls 
in, but a better way is to use an optical sensor to start the timing 
when the board reaches a fixed position. In theory you can use the 
centering mechanism to set the X axis and the sensor to set the Y 
axis, enabling registration for double sided boards.

Mark







At 11:00 AM 4/28/2010, you wrote:
>I was thinking the same as everyone the charge that will conduct on the
>metal part of the board and have no electrostatic difference for the powder
>to stick to the board but when I saw the 3kv power supply I think you are on
>to something unique and that will work. Please post more details on how you
>charge the board, is the powersupply on all the time and connected between
>the drum and the board? how are making contact to the board and hv when it
>is moving...  lots of questions. please post  details. I think this could be
>the coolest breakthrough for direct printing, for all of us who have been
>trying to do this for years.
>Kim
>----- Original Message -----
>From: "Mark Lerman" <mlerman@...>
>To: <Homebrew_PCBs@yahoogroups.com>
>Sent: Wednesday, April 28, 2010 4:14 AM
>Subject: Re: [Homebrew_PCBs] direct laser PCB
>
>
> >
> > A subject dear to my heart!
> >
> > I have spent the last six months experimenting with direct laser
> > printing of PCBs, and I am now able to (fairly) reliably produce
> > boards using this method. If anyone is interested I can share a LOT
> > of details, but the Brother is NOT the way to go. I spent a month or
> > so working with the HL-2170, as well as a few other false starts
> > before settling on the Lexmark E260 as the printer of choice. The
> > "straightness" of the path is relative, and all of the laser printers
> > have to be modified to pass pcbs, although you can run the thin,
> > somewhat flexible (eg 8 mil) boards through some of them. You cannot
> > use the internal fuser.
> >
> > When I described some of my earlier efforts at direct laser pcb,
> > there was some concern that the drum is too easily damaged. In the
> > past months I have made several hundred "runs" through my modified
> > printer, many of which were experimental, without proper smoothing
> > and protecting of edges, and I am still using the same drum. I am
> > still not sure of the limits of the process, but I have produced 5
> > mil traces without problems.
> >
> > The steps are:
> > 1 - Produce the artwork - I use Eagle.
> > 2 - Print the pcb.
> > 3 - Place board in oven to "fuse".
> > 4 - Etch.
> >
> > One real advantage of direct laser pcb is that you can see the
> > results instantly, and if the "image" is not perfect, you can just
> > brush the toner off, wipe the board with acetone, and do another run!
> >
> > I was waiting till I had the process perfected before "publishing" on
> > this forum, but if anyone is interested, I can provide details. You will
> > need:
> >
> > 1 - A Laser Printer - I strongly recommend the Lexmark E260, on sale
> > at Staples for $169 (?) with an additional $50 off if you bring in
> > any dead printer for "recycling".
> > 2 - A high voltage power supply to provide a variable Transfer
> > Voltage. A 3KV (variable) at 100 microamps will do - Ebay is your friend.
> > 3 - A high voltage relay to switch between the internal transfer
> > voltage and the external supply is useful but not strictly necessary.
> > 4 - A simple microprocessor board to spoof the sensors that need to
> > be emulated and control the printer solenoids and such.
> >
> > Mark
> >
> >
> >
> >
> >
> >
> > ------------------------------------
> >
> > Be sure to visit the group home and check for new Links, Files, and
> > Photos:
> > http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
> >
> >
> >
>
>
>
>------------------------------------
>
>Be sure to visit the group home and check for new Links, Files, and Photos:
>http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
>
>
>