Re: Machine construction.

How are these 'portal' mills driven? By two screws or one? I am
planning on a similar design, but I only have one ballscrew for
the "wall" axis, so I'm wondering how robust this configuration is.
Using linear rails, will there be a problem with the axis getting
skewed under cutting loads?



--- In CAD_CAM_EDM_DRO@yahoogroups.com, "John Heritage"
<john.heritage@v...> wrote:

> > One way to maintain accuracy using a gantry might be
> > to raise the table/frame sides high and securely (since you are
> > talking 12" z-axis movement, and glide the basic horizontal

gantry

> > over these so the gantry's "arms" are as short as possible.
>
> This is in fact the way almost all new gantry machines are built.

They are

> often referred to as 'portal' mills, as the structure ressembles

and

> archway, which is also termed, a portal. The machine is

essentially sitting

> on top of a pair of walls.
>
> With big machines, you can literally work around in the work area.

But I

> thought that things might get a bit squashed if you want to scale

it down to

> a desktop sized area, as the walls would block your access to the

table

> quite a lot.
>
> I have seen numerous portal mills specified for a positional

accuracy of

> 0.001mm. The design offers excellent access to the work piece for

the work

> it's self and can be built to be just as strong, if not more so,

than a

> standard VMC - I have seen two manufacturers offering the design

right up to

> the point of machining solid titanium.
>
> Best wishes,
> John