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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