Re: [CAD_CAM_EDM_DRO] RE:rE:re:Re: not stiff enough! (machine design considerations)

Smoke,

I don't know why you need a sketch. A bridge design like the one on my web
page is where the X axis table moves in and out along the X axis and the Y
axis is fixed on a bridge. A gantry system is where the table does not move
and the gantry that supports the Y axis moves along the X axis.

Bob Campbell

----- Original Message -----
From: Smoke <gordonr@...>
To: <CAD_CAM_EDM_DRO@egroups.com>
Sent: Tuesday, January 23, 2001 4:30 PM
Subject: Re: [CAD_CAM_EDM_DRO] RE:rE:re:Re: not stiff enough! (machine
design considerations)


> I sure would like to know (via a sketch) what you call a gantry design and
> what you call a bridge design.
>
> I might want to build one of these CNC routers one of these days and I'm
> just wondering what (all you experts) would call the one I've got
designed.
>
> Smoke
>
> >Some thoughts on machine design:
> >One of the MAJOR disadvantages of a 'gantry' style machine (like you
> >have) is "axis error buildup". What this means is that ANY 'flex-
> >ability' in X WILL BE ADDED to Y, and whatever 'flex-ability' is in Y
> >(which now includes the X problems) WILL BE ADDED to Z! Finally,
> >whatever Z has on its' own will be added...
> >
> >A bridge design "solves" this problem by NOT connecting Y support to
> >the X axis. But at the cost of larger footprint, longer slide
> >travels, etc.
> >
> >The reason I'm saying all this to you is your statement re: changing
> >the Z axis shafts... This is like putting a solid performer (think
> >circus acrobats) on the shoulders of two wobbly, 'supporters'!
> >
> >In a gantry design, the X axis (being 'lowest' in the stack) needs to
> >be STIFF!!!
> >
> >Keep in mind that any mass you add at
> >"the top" of the stack is like putting the fat man on the shoulders
> >of the child... (circus again)
> >
> >It may even be worth making the X travel shorter, and "picking it up"
> >by making the Y travel greater... When using unsupported shafts this
> >will definitely increase overall machine stiffness (all else being
> >equal).
> >
> >Hope this helps.
> >
> >Ballendo
> >
> >>Thanks all those who responded to my stiffness quiestions.
> >>
> >>Taking cuts no more than 1/2" the bit diameter, and running the
> >>routine twice has solved 90% of the problems.
> >>Still get some flex when the 1/4" router bit plunges in. I'm putting
> >>the 3/4" rails on Z, and trying different bits.
> >>Richard S
> >
> >
> >
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