Re: [CAD_CAM_EDM_DRO] Shoptask Z-axis - quadralift?

jmkasunich wrote:

>This is addressed to those who have CNC'd Shoptask machines.
>
>Do you have the quadralift or equivalent on your machines,
>or do you make do with the 3" or so of Z travel that the
>quill provides?
>
>If you have a lift of some type, how does the CNC control
>know when you move it? For instance, suppose you start with
>a short end mill in a collet. The head is fairly low. Then
>you change to a 17/32 drill bit in a jacobs chuck, and need
>to raise the head by 6" to make the tool change. Do you have
>to touch off each tool after the change, or is there some
>way that the control can do it automagically?
>
>I am considering a lift for my machine. I want to mount an
>encoder on the lift axis so the control knows how high the
>head is. The lift will NOT be under CNC control, it will
>either be hand-cranked, or motor operated with a simple
>up/down switch. It will NOT move while cutting. I know
>that the mechanical and electronic aspects of this are
>doable. Will the software (EMC) be able to make use of
>the encoder data?
>
>

I don't think it will be able to directly use this information. One
easy hack that
comes to mind is have the extra encoder (I guess it would be called a W
axis, while
the quill would be the Z axis) read in, and subtracted (added?) from the
tool
length offset. As long as you moved it only while the interpreter was
NOT in
tool length offset mode, it should work correctly when the offset is
engaged.
If you moved it while the offset was engaged, the quill would move in the
opposite direction to remain at the correct Z axis height. If this
drove the
quill into the limit, it would cause a fault.

A very simple hack would be to have the two axes summed every time the servo
routines read the position. This would have the undesirable effect of
the quill
ALWAYS moving opposite the head movement, but would be a 5-minute
hack to test the concept. It would require you to jog the quill to keep
it from hitting
the limits.

Jon