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

Richard,

Good to know our suggestions are helping!

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