--- In
Homebrew_PCBs@yahoogroups.com, Stefan Trethan
<stefan_trethan@g...> wrote:
> thanks Dave.....
>
> i don't like the "couple of weeks" part,
> an the "fast programmer".
Compare to a newbie making a PCB with plated thru holes.....
> i could of course edit the librarys so that there is a short line
on the
> place
> where the paste has to go.
If you can add a goto line then that is half the battle.
With the X/Y location, your table moves to those coordinates and
stops. The goto command would send the software to the paste
dispensing section.
Of the top of my head, I see it as
state a rapid to some 20 mills above the PCB.
slow feed to close to the part while also slow feeding a drop.
then slow retracting to allow the drop to remain on the board.
then a fast retract to normal Z height
(then retrun to g-code for move to next posisiton.)
Of course, if one were to have 5 drops along a SOIC pad, either the X
or Y would have to move while dispensing, OR each of the 5
coordinates would be needed to be a place the machine stopped and
called the paste function.
Since there are only so many specific pad sizes, it is quite possible
to make a routine that would so a whole 8 pin SOIC chip or a routine
that would do specific pad sizes.
I have a variable for feed rate so that I can change that one point
at the beginning of the program and run the part with that value.
Basically on my machine tool, it is for drill depth as I change
drills and find it is easier to measure the new tool and put in an
offset than to try to get a tool to go back into exactly the same
height as the last tool.
Dave
> Is there a really simple solution to modify these "z axis" action
to get a
> dispenser
> to "mill the paste above the pad"?
> I mean imagine you have a 2d drawing of a part you want to mill,
how do
> you add the
> z axis? how do you tell how fast the dispenser goes down, and how
far it
> moves?
YES.
as I laid out above, a simple goto in the existing files can send the
software off to a sub-routine that handles the feed and dispense
section. That leaves your drill file very readable and puts all of
the feed/dispense stuff into one small section.
>
> Maybe the "pump paste now" could be hardware engaged - whenever the
nozzle
> is down fire up..
> one could use adjustable delays and "suck back" as soon as the
nozzle is
> raised.
I would look at a CNC stepper motor with a leadscrew. imagine a 20
turn per inch leadscrew and a 400 step per inch motor. and a quarter
step motor driver circuit.
that is 20x400x4 or 32,000 steps per inch. each step is 0.00003125
inces per step. If there are 40 mils per mm, then add a zero for
steps per mm.
As you can see, a very tiny step will push on the syringe a very tiny
amount. As I said a long time ago in this thread, accuracy will go
way up with doing CNC.
Also, if you wanted, you can get an 8 step driver that will multiply
motor steps by 8. or a 10 step driver. I have seen one that had up
to 250 microsteps per motor step.
Bottom line on the dispenser it that it is the easy part.
the CNC is the easy part.
the file handling between generating your Gerber files to getting the
paster file is (currently) the hard part.
Dave
>
> ST