Re: [CAD_CAM_EDM_DRO] Re: Machine construction.

I'm not too sure about them having rigidity problems...
http://www.ferret.com.au/articles/images/c3/24002dc3.jpg

They are often used to machine core materials like balsa, sytrofoam,
expanded foam, nomex honeycomb and aluminium honeycomb due to their
theoretically limitless travel. Which makes them particularly useful for
cutting out long objects.

Very light weight, easy to machine, soft core materials are used extensively
in resin based composite construction.

First, the multimillionaire decides on the profile of his new babe magnet
yacht. Next, the portal machine cuts a big styrofoam model of the yacht out.

Dry carbon fibre, kevlar, fibreglass or a hybrid of the three is laid out
all over the styrofoam model.

Then the entire model is enclosed in an air tight plastic bag. The air is
sucked out of the bag. Matrix resin, or a two part epoxy glue to you and I,
is fed in through a number of lines connected to the bag, along the length
of the model. The vacuum pulls the matrix through the lines, infuses the
fabric and pulls the whole thing tightly together to get rid of any air
pockets.

A few days later, you unwrap the plastic bag, and you have yourself a near
bullet proof shell of a multimillion dollar yacht.

That's something that just wouldn't be possible on a standard VMC, which is
why you often see these machines designed specifically for cutting out
sytrofoam and balsa - with rigid ways being replaced with higher speeds.

Accuracy is not the first priority in building something like a yacht. A few
mm off here and there isn't too bad. But it is important that the core is
reasonably accurate, otherwise the boat will need corrective weighting and
it will waste even more power trying to push it's self along. So, you want a
machine with moderate accuracy, and high speeds to cover the entire length
of the hull in less than a day or two.

Best wishes,
John

> Most of us don't plan on turning our workspace into a
> mill, but by the looks of this link, we could.
>
> http://www.scaled.com/services/cms_mill.html
>
> Moving gantry benefits;
>
> Good physical space to work area ratio. (the travels
> can be very close to the physical machine dimensions.)
>
> A know mass to move with the drives. The only real
> variable is the tool weight.
> Low cost to travels ratio.
>
> The hang up is they are not rigid. (software can
> compensate for this, but surface finishes, tool wear,
> and rates of removal suffer)
>
> In the larger dual drive gantry machines (and even
> some overhead cranes) the skew of the gantry is
> compensated for with software. Feedback from each
> side is monitored and the side that is lagging gets
> more force.
>
> Rob
>
>
>
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