Hi, Roman

> Looks like i've decided to go the opposite way to your
> machine (in the picture) and keep the travel distances
> short and build a small, very light machine to try to
> keep speeds high, instead of a big sturdy mill.
>
> Imagine something NOT like a gantry mill, but more
> like a box on a rail. 300mm travel. The box has a short,
> light unsupported arm out one side, with a head travel
> of about 140mm. The arm is light and the head is lighter.
> I've been toying with the idea of using long bent tubes,
> one for the paste applicator tip, and a rotateable one
> for the vacuum tweezer. These have small lightweight
> stepper motors, (from disk drives maybe?), to lower and
> lift the tubes. Have you ever seen inside a pen/chart
> plotter machine? The long thin pen arms can move very
> fast, and no real strength is needed for PNP, only speed
> and accuracy. :o)

    I already tried to work that idea out and all the mechanical guys that I
consulted told me to forget about it !!!! The long arm will always flex and
shake a lot unless it is very sturdy and then it gets to be too heavy for
the other driving axes ! I quoted some strong driving system to use just 2
arms, one mounted over the other and the pickup head on the end of the top
arm and the mechanical system would cost over us$ 3000 !!! The idea is great
but maybe harder to implement then it seems. I decided to go with the gantry
style because the parts are cheap and readily available and everyone knows
how to workout the design. I will spend about us$ 300 to us$ 400 in parts
that are ready available, except for the motors that I already have scrapped
from old printers. I will send you in a private msg some pictures of a very
interesting design with just 2 arms. If anyone else want's it drop me a note
and I will send the pictures. They are small and should be about 100k.

    The long bent tubes will flex and shake all over, unless they are very
strong and them they get to be too heavy. Be carefull there. A tube with 150
mm that flexes 0,5 % will put the component in the wrong position.

> So I get only 300 x 140mm work area, maybe less, but
> the work area is on the corner and can fit large boards
> if they are partially hanging out. The advantage is
> a fast action, i'm hoping for 1 to 2 PNP's per second,
> from a machine basically built from junk but with
> good microstep motor drivers. I don't see the small
> work area as much of a sacrifice to get a fast and
> portable sized machine. Something you could put on
> the back seat of a car and take to a friends place,
> plug it into their PC and it's running.

    The 300 x 140 mm work area should be enough for most applications. You
may not need all the speed you are running for. It is nice to have a fast
machine but remember that if the machine is cheap enough you can just make
one more when you need more production. I prefer slow, cheap and reliable.
Working with the mechanics people for a while I lost some of my urge for
doing the best all the time, sometimes the best is the worst enemy of the
good. In the electronics we can usually make it cheaper, faster and more
reliable. On the mechanics we have to settle for one of the goals and try to
work the others out the best we can.

    You can put the gantry on the car and show friends :-) It would be
somewhat like a square 400 mm by 400 mmm. That fits my car ;-)

best regards,
Alexandre Guimaraes

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