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

Gary,

On some bridge and gantry type mills I am sure that your observation
is true, however on the MiniRobo, facing the front of the machine the
X axis is from left to right and the Y axis is the in-out motion. I
have studied the MiniRobo drawings extensively and I am currently
building my own version of this type of machine. I need a small bench
top / table top milling machine which is significantly stiffer than
the currently available machines such as Sherline and Taig. I have a
Sherline 5400 which I really like, but I need 12 inches of X travel
and that is just not available on a table top machine for a price I am
willing to pay.

It really should not make any difference whether X or Y is the in-out
motion or the left to right motion. As long as the part is properly
placed on the machine and the controller is connected to the proper
axis is should work. That is to say, X is the long axis and that
motor is connected to the X axis controller, the program doesn't care
whether that motion is in-out, right-left or up-down as long as the
part is positioned properly and the appropriate axis is connected to
the correct port on the controller it should work fine.

Look at milling on a lathe, X is the cross slide, Y is the milling
adaper up and down motion and Z is the carriage travel along the lathe
bed. Perfectly satisfactory parts can be made this way either by hand
or CNC control as long and you or the controll are moving the correct
axis.

John Guenther

--- In CAD_CAM_EDM_DRO@egroups.com, "Rose, Gary" <Gary.Rose@c...>
wrote:

> Ballendo,
>
> With regard to gantry and bridge style machines, I am a little

confused. In

> a "normal" mill (like a Bridgeport or whatever), the operator is in

front of

> the machine and the X-axis is right-left. The Y-axis is in-out.
>
> Your description below seems to indicate that the X and Y of the
> gantry/bridge machines is opposite to that of the conventional

machines,

> with the in-out motion being the X-axis. Is this true?
>
> If so, I could see a real problem arise if you used the same g-code

program

> to make parts on a MaxNC and, say, a Minirobo. They'd be flipped

around!

>
> Any thoughts?
>
> Gary
>
>
> > Date: Tue, 23 Jan 2001 21:41:26 -0000
> > From: ballendo@y...
> > Subject: 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