various thoughts on home-built CNCs

[Doug4d3s]

spring tension must overcome cutter forces.

If you are cutting plastic, it isn't much.

If you are cutting steel with a 2" cutter - forget the sprung nuts, nobody uses them, since they can vibrate and cause real problems.

Well I already said, the cutter size would likely be limited to 1/4-dia.

And if you are using ballscrews, you are probably already using spring nuts,,,,,, every internal-view of preloaded ballnuts I have found shows TWO ballnuts either separated by a spring, or screwed apart against the screw threads & epoxied. MOST of them use a spring to leave the preload user-adjustable.
One example-
http://rockfordballscrew.com/ball-screws.htm
The above page says that if the preloaded nut is adjusted for minimum turning stiffness then it may have up to .015" of backlash.

[Doug4d3s]

Can g-code describe two entities simultaneously?
That is, if both the tool and the workpiece can move separately of each other but both have 5-axis of freedom, then the positions and orientations of both always have to be specified separately.
Is there a way to do this?

[oldvan]

Can g-code describe two entities simultaneously? ...
Is there a way to do this?

Here is a wonderful tutorial that can help you to understand what G Code is and what it isn't: TUTORIAL

[Doug4d3s]

Can g-code describe two entities simultaneously? ...
Is there a way to do this?

Here is a wonderful tutorial that can help you to understand what G Code is and what it isn't: TUTORIAL

It doesn't really say. Nothing I've found so far says.

Wikipedia mentions machine and work coordinates, but says that the work coordinates are offset from the machine coordinates... so those wouldn't really be separate.

[Bill Shields]

The answer to this question is yes, a single G-code with associated address values can move both work and tool.

The g-code tutorials are very limited in their description / understanding of advanced machines.