Friday, 21 November 2008

The many steps to 4 axis machining

I'd like to run some "all round" machining jobs on my router. To do that, I need a rotary axis. I intend to convert a rotary milling table into a CNC rotary axis by fitting it with a servo (more on that later).

To do that, I need to do some 3 axis machining, but there are a few obstacles that I'd like to get out of the way first.

At the moment it takes me annoyingly long to set up my CNC router after I change the stock or tool, and even then the results are often compromised by poor calibration of tool length and stock position. The next few posts will explore faster and more accurate ways to do this calibration. At some point I'll have to find out how the pros do fixturing, too.

The old way (if you care)

To measure tool length I fit the tool, and then jog it down close to some datum (such as the router bed or the top surface of a flat piece of stock). Then I use a feeler gauge to measure the offset and setting that to be Z=n with:

G92 Zm

with m=n + measured offset, in the MDI window of AXIS (the tab that's in the background in

I'm using oversize stock, positioning it by eye, fixing it down, and then jogging the router until the spindle is in approximately the right place above the stock and setting that to be X0 Y0 with:

G92 X0 Y0

in the MDI window of AXIS.

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