Steel Framed Router

[JAZZCNC]

Rick (anyone), A silly question perhaps... most of the utube vids I've looked at seem to position the work at 0,0 giving the forces you describe in the pic 2. Would I be right in thinking that if the work was positioned mid Y (above the ball screws) with x=0 or where ever, it wouldn't be so so much of a problem? And, would that imply that best accuracy / precision would be in the centre of the table rather than at the edges??

Ok understand better now.! If using just a single centrally placed screw then yes the most accurate position is in the centre of the machine and as you approch the outer edges the gantry will flex and twist~(racking) reducing precision.
How much racking depends on several factors but obviously the wider the machine the worse it gets, wide gantry or wide placement of the bearings the gantry sits on helps reduce this to a degree.
Basicly if you have central screw on narrow machine with wide bearing placement then the racking affect can be controlled to acceptable levels. Wide machines are better suited driven from both sides of the gantry using 2 screws.

Regards work positioning I think you'll find when you see a referanceto 0,0 position it will often relate to work coordinates which are often differant to Machine coordinates.

Excuse if you know this.! . . . Machine coordinates define the overall cutting area of the machine. .Work coordinates define a referance point on your material that you want to start work cutting from.
So say you have 400mm * 400mm cutting area with machine coordinate 0,0 defined in the lower left corner (looking down from the top) and place 100mm x 100mm material in the centre with the cutting start point in the lower left corner of the material.
Then the work coordinate is at 0,0 but it's actual position on the machine is at 150,150. Where you position the work 0,0 coordinate will be determined by where abouts you position the 0,0 in you cad program and the part your drawing.
Often Machine coordinates are positioned in the lower left corner so you'll never have negative machine coordinates, so If your work as negative coordinates IE Circle with centre defined as 0,0 work coordinate then you need to offset the 0,0 work coordinate far enough away from 0,0 machine coordinates other wise the machine will crash into the limits.

Hope this helps if i'm teachng dad to suck eggs then i'm sorry.!