it's usually the CAM software not the hardware when it comes to macros, I
think one would need 4 axis hardware though, with the forth being the
specialty drive for the dispenser, you could use G81 to position, and place
a M code between each G81 entry, have the M call the 4th axis movement sub
routine. You use the Z and R variables to control depth of plunge, and safe
height with G81.
This could all be done easily and freely using Eagle lite, and Mach2 demo
(although I highly advise actually buying the software in the long run- then
you can actually have enough room to mill stuff, but the demo allows plenty
of room for canned cycles. , at least for the boards that fit in eagle lite
: )
I really think this topic probably would be better suited to the cnc group,
but since the people involved with this subject frequent the same places,
the topics blur the lines.
JT
----- Original Message -----
From: "ballendo" <ballendo@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Sunday, April 25, 2004 7:07 AM
Subject: [Homebrew_PCBs] Re: solder paste - cnc dispenser
> Stefan,
>
> If your cnc machine was set up as Dave suggests, you'd use a couple
> of its "normal" features to make this easy:
>
> 1)Incremental motion, which is G91 (considers previous/starting point
> as zero each time)
>
> 2)Canned cycles for "drilling" G81 (this makes your cnc file just a
> set of locations, as each time the G81 is called, a series of moves--
> designed for drilling-- are made. We wouldn't be drilling, but with
> some creative use of the canned cycle parameters, we would achieve
> the desired motion--as Dave already described.
>
> If you add the ability to use Macros--which my cheap cnc machines DO
> have--then it gets even easier. A macro is just a set of instructions
> that YOU (or anyone) creates and holds "together" under one code,
> like M345.
>
> Now the dispensing can be done using either of these methods; you
> will just have more control if Macros can be created and used. Not
> all cnc machines have them...
>
> So you would set up the canned cycle drill params for different
> sized "dots"--same with macros--. The difference is that with macros
> you'd have a DIFFERENT macro for each line, dot or even entire SMD
> package that you want to "lay down" paste for. With the drill cycle
> (s), you'd have to change the parameters for each set of dots of a
> given size. Then do the next size, and so on...
>
> Dave left out one critical part, which is that the stepper driving
> the paste plunger needs to reverse a bit after each dot is placed.
> This keeps a "string" from hanging between dot placements. (Any one
> who's ever used a caulking gun knows what I'm talking about<G>) The
> drill cycle "retract" does this for us.
>
> Hope this helps,
>
> Ballendo
>
> PS. You will actually be using TWO drill cycles per dot. One for the
> paste syringe, and one for the z axis movement. With macros these two
> can be combined into ONE macro call. And the rest of the file, as
> written above, is just the xy coords of your dots. (The canned cycles
> are "persistant" until something else is called, so the desired
> action takes place at each defined XY location.) My machines will do
> this.
>
> PPS. For this "screw drive" method of dispensing to work well, you
> need a stiff syringe, and a SOLID mount for it. Because "flex" plays
> havoc with dot size, as the syringe pluger moves downward. At the
> top, the entire syringe tube can flex to absorb some of the downward
> movement without dispensing; so as you get lower the dot size can
> increase. Fortunately we have another couple "normal" cnc functions
> which we can use to deal with this, which are tool offsets, and tool
> wear offsets. Creative use of these will acount for the problem
> mentioned.
>
> And the "other" choice is to use a dispenser from (or modeled after)
> those industrial units sold by EFD, and others...
>
>
>
>
>
>
>
>
> --- In Homebrew_PCBs@yahoogroups.com, Stefan Trethan
> <stefan_trethan@g...> wrote:
> >
> > >
> > >
> > > This is one of those things you find out about machine control.
> > >
> > > with some practice, you find that by being 0.5mm from the pcb, and
> > > starting the paste to flow and presising the syringe 0.1mm, that
> some
> > > exact amount is dispensed.
> > >
> > > this will be repeated on every occurance.
> > >
> > > One thing that comes to mind is the surface adhesion. If the
> paste
> > > does not adhere to the surface, it will not stick and the next pad
> > > will get double.
> > >
> > > But, each of these things are things you can control.
> > >
> > > Dave
> > >
> > >
> >
> > You basically say whatever the machine does wrong, it does it wrong
> the
> > same way every time, right?
> >
> > What about the software, how do i get the file i need to feed the
> cnc?
> > No point in building a expensive cnc machine and then it is
> impossible to
> > get the right file.
> >
> > I reckon the "generating the file" thing would be even harder if
> one
> > thinks of pick and place?
> >
> >
> > ST
>
>
>
>
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