On 16 April 2013 01:17, Gene Heskett <ghesk...@wdtv.com> wrote:

> Ooookkaaaaayyy.  Now, what is the diff between probing for a switch closing
> where the switch may be mounted on the ways, and my probing for a ground
> contact where the contact just happens to be removable because otherwise it
> would get in the way of doing any work?

Because the thing you are probing with is of variable length. (the
tool). You would have exactly the same problems as you report if,
instead, mischievous elves were to randomly move your conventional
homing switches around.
The issue is that the INI file contains _axis_ home positions, and you
are homing with a sensor on the tool-point.

Your way will work as long as you never use any touch-off or offsets,
but if you do have offsets then the code compensates for them, but the
physical world is _also_ compensating for them.

> But on my small lathe, how would one go about putting tool offsets into the
> tool.tbl that mean something when in changing a tool, the stickout its
> clamped up at is effectively completely random give or take 1 cm or so?

You can only use a tool table if you have reproducible tool lengths.
The solution that people with collet-routers have to use is to do a
length-probe after any tool change. Your situation is exactly the
same. The difference is that the router folk are not trying to use the
length-probe as a home switch too.

> To me, it makes 100x as much sense to mount the tool such that it can reach
> its cuts ok, drop the gauge on the ways and simply re-home the machine.

And I think that you would do better to home to physical marks on the
axes (if you lack the IO for switches) and then _probe_ the tool
length when you change tools.

-- 
atp
If you can't fix it, you don't own it.
http://www.ifixit.com/Manifesto

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