Re: [CAD_CAM_EDM_DRO] One side gantry drive

Doug,

All of my designs are for moving tables. I have built a gantry machine, but
was never able to totally eliminate racking of the gantry.

At least I am now aware of what it causes the problem.

Bob Campbell

----- Original Message -----
From: "Doug Harrison" <prototype@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Wednesday, October 23, 2002 8:04 AM
Subject: Re: [CAD_CAM_EDM_DRO] One side gantry drive


> For the purposes of this discussion I will declare the length of the table
> as X and the length of the gantry as Y.
>
> To make the single side drive work we must abandon the idea of a gantry as
a
> beam and think of it as a truss (triangle). Think of it as a right
triangle
> where the long leg is the Y axis and the short leg is the X axis.
>
> The short leg if the triangle is roughly 50% of the long leg. Thus, for a
> 60X120 table the distance between trucks that run the X axis rail is about
> 30-36 inches. As such, the in-plane force (neglecting acceleration) on
the
> X axis trucks is about twice the tool load - not much.
>
> The principle advantage of this method lies in the rigidity of the truss.
> Bending is no longer an issue. Deflection in the XY plane is avoided
without
> resorting to adding bulk. Les Watts' router base is built this way. It
> seems incredibly stiff though it is only 2X2 box tubing.
>
> The one sided approach allows you to invest your ballscrew budget in one
> good piece instead of two lesser units. The drive side rail should be
> beefier than the opposite rail. No problem. A disadvantage is that the
> drive side rail must be about three feet longer than the intended travel -
> still better than with a moving table though.
>
> One of our list members (was it Bob Campbell?) has built a few tables this
> way and was happy with the results.
>
> Doug