Quote Originally Posted by JRoque View Post
Hello all,

I'm looking to build a new CNC/manual mill. I have a ~1,000 pound (450 kg) table that has been ground flat, with a surface area of 42" x 36" x 1" thick (106 x 91 x 2.5cm).

The build criteria is simple: be as rigid as possible, within limits.

To that end, I'm leaning towards a fixed bridge design using heavy wall square tubing, 35 - 45mm guide rails, and as big a diameter ballscrew as I can practically fit under the axes.

Here's a scratch design I've been noodling with while contemplating ideas. This is not a final design and I'm not really looking for feedback on it, just to serve as a conversation starter:



Soooo... if you were building a mill from scratch that can hog through steel and not break a sweat (or end mills), what would you design? Is a fixed gantry a better design (within its compromises) than column? The commercial machines I've seen on YouTube easily cutting steel have all been column types... hmmm.

Thanks!
JR

PS: good to be back. Looks like I've been bitten by the CNC bug again ;-)
For a table that width size you will have to have a bridge mill design.....a single column will not support the over hang for the Z axis to reach over the full width of the table you plan have but a double column or bridge will enable it to do so......but you could make the Y axis (under the bridge) the short size and the X axis (across the bridge) the longer size as the bridge can cover the long size easier as it's more supported.

Column mills normally have a long narrow table because of that reason.

BTW, the length of the mill base between the columns (Y axis) is usually twice the width of the table (X axis) to enable the full length of the table Y axis to move under the bridge. and to prevent too much overhang by the spindle (Z axis) from the face of the bridge

Bridge mills also have less Z axis travel due to the height restrictions of the columns which can be massive to make them less liable to back and forth movement due to cutter torque forces.

Attached is a pic of my favorite bridge or gantry type mill design.
Ian.