lathe in cx machining polor coordinate need help

[northernmach]

Hi, I am hoping someone may have a simple solution to try for getting our 1997 Eurotech lathe, with a Fanuc 0t control machining correctly in the CX motion. We do not have a "Y" axis, so to do a flat across a diameter the machine is switched from the machine coordinate over to a G112 which is poloar coordinate. This make the c-axis act as a y-axis as it is rotating the spindle.

What I am having trouble with is this, say for example I am machining a square boss on the very end of a diameter. Here is what my code looks like in a generic maner:


T???? (end mill)
>
> M10
>
> G28 C0
>
> G0 C0
>
> G97 S???? M73
>
> G112
>
> -----------
>
> -----------
>
> -----------
>
> -----------
>
> G113
>
> M11(C AXIS OFF)
>

So as you can see before I do any milling and switch to G112 I make sure to reference the spindle G28 C0. Then do a rotational move to G0 C0 (realizing this may be overkill but safer). Then I switch to G112 (polar coordinate). Make all my linear moves to cut the four flats of the square which looks just fine when done machining. Switch off polar coordinate with the G113 and shut the c axis off.

Everything looks fine until I turn on m10 (c axis on) and then MDI the machine to C0. Place an indicator on the turret and move the x axis to check for one flat being parrallel with the axis of the machine and it is out alot.

I noticed this by trying to cross drill a hole through a flat. The hole is actually out at least 4 degrees. At a loss as to why this is happening. Checked with the machine manufacturer and they are unsure why it is happening.

As another note I can call the program back up and run it again and it will just spring cut so, that tells me that it is running consistant but not retaining the same zero in polar coordinate and the normal machine coordinate.

Could this be a parameter and if so does anyone know what one to look at? Any help would be much appreciated.

Chad

[CNCRim]

You should try return it to machine zero that is G28 H0., and move G0 C0. after G112. Try that.

[northernmach]

Thanks for the info, but I did get more info from the manufacturer that said that most likely it has something to do with cutter compensation in the program. So he recommended just doing a c work shift to get it rotated correctly when back in machine coordinate. Have yet had time to test it. Sounds like that should do it though.

Chad