Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

Hello all,
I am a new member here and just starting over after many years.

I like to make things fool proof so that even I can use them.

For a resist mask I will be using an Epson Stylus C90 in a similar way to
what others here have. Please let me know if this model is a poor choice. It
seems that Magenta is the best choice of ink?

I will be doing some things differently however -
(you can skip to info on the drilling machine below)

1) The whole printer carriage assembly will move along the Y axis so that it
is a true flat bed printer.
2) The paper sensor will be changed to a precision opto sensor that senses a
fixed guide on the bed.
3) Bearings on an extended Y axis guide will keep the printer parallel.
4) Fixed alignment pins will be placed into the bed so that the PCB clips
into the correct place.
5) Adding a paper feed drive release lever so that the drive can be
decoupled and the printer manually returned past the Y axis home position
after each PCB is printed. This same lever will be operated automatically at
the far end of the Y axis so that the Y axis does not continue to run as the
printer normally does the extra feed motor running after the end of the
page.
6) Y axis motion will be accomplished by a simple fixed wire cable that runs
around a normal paper feed roller outside of the printable area.

The driller.....

The idea of the pins is that the driller will also have the same alignment
pins. This way both sides of the board can printed and then the board can
later be drilled with no manual alignment. Just clipping it into place.

I am confident with the flat bed modification. The driller hardware will
take time to make and the electronics (small computer) is easy to design but
will take time to write the software in machine code.

What I need help with is file formats for drilling files. I don't want to
write (driller)printer drivers for windows. I want to send files to the
driller via floppy or USB.

I previously have used Protel AutoTrax and it is easy to extract the drill
information (x,y,hole size) directly out of the .pcb file.

I am trying new software but I am not familiar with it yet.

I am wondering what PCBCAD others are using and what file formats are common
to many or all.

If you can suggest a format that is broadly used by members here then I will
write the machine code for the driller to accept this format. This may be of
great use to you if I publish the full mechanical specs along for the CPU
PCB and source code.

Mechanics....

I am a hobbyist working on a budget so you can expect the drilling machine
to be as inexpensive as practical. I have already hunted down cheep
suppliers of common parts that will be used.

The machine itself will have the bed move on both the X and Y axis. Motion
will be via thread rod directly coupled to stepper motors. This simplifies
most of the mechanics and reduces the cost and work to create it.

I could alternatively use a cable setup for the X and Y axis. Although this
alternative is even cheaper it will mean the machine is much slower in
movement to compensate for the looser mechanics. It will also need periodic
re-calibration.

The drills (4 to 6 of) will be in a fixed line in the X and Y plane with
only Z movement. They will be bearing mounted chucks that can slide in the Z
axis. They will be connected to flexible cables similar to those used on
model aircraft. These cables will then go to a drill control unit on the
non-movable part of the bed. The drill control unit will select which drill
is moved in the Z axis via the cable. One motor will drive all drills and
one (stepper) motor will move the Z axis via moving the outer sheath of the
cable. The drill selection will be via cheep solenoids.

The drill assembly will be electrically isolated from the bed so that the
computer can wind the Z axis to the bed outside the PCB area to recalibrate
drilling dept when I bit is replaced.

I have priced around and I can get most of the mechanical materials from a
hardware store. The bed substrate will be compressed cardboard, the
framework will be extruded aluminium and the drive will be high mesh
threadrod and nuts.

The steppers are AUD$6 the spindle motor is the same. The solenoids ate
about AUD$2. The bearings can be bought in packs of 10 for AUD$12 for a
pack. The couplings for stepper to threadrod will be thick rubber tube and
hose clamps. The drill cables can come from a hobby model store.

I haven't found where to get the chucks but I see hobby drills in shops for
about AUD$10 so they can't be too expensive.

Suggestions....

Any ideas on how to make this even cheaper or any features you think it
should have would be most appreciated.

If someone knows of a freeware and simple mechanical CAD package then I will
get so draft plans up onto the groups site.

Thanks, Robert.

PS: This is not my first driller. The last one was big, cumbersome,
expensive and was difficult to make. I was software driven from windows and
had no independent operation.