On Wed, Oct 15, 2008 at 03:13:53AM +0000, acondit wrote:
> I am trying to wrap my head around lathe tool offsets.
> 
> Say I have a reference tool with both X and Y offsets of zero.
> 
> Now I have a threading tool and it sticks out 0.252" farther in the X 
> direction
> than the reference tool.  Is that a 0.252 positive X offset?

No, it's -0.252 if you mean it sticks out toward +x

> It sticks out 0.176" farther towards the spindle nose than the reference tool.
> Is that also a positive Z offset?

Yes it is positive since it points toward -z

> What if I have a smaller tool can I use a negative offset for Z and/or X 
> offsets?
> 

Yes you can use positive and negative numbers.

> If I back off my toolpost to change tools (part of the gcode) and follow the
> tool change code with a G43, will my tool move into the proper position when I
> make the next move if all my moves are setup based on the reference tool? In
> particular, if I put on a cutoff tool, an move a cut off position based on the
> front corner of my reference tool (and have my tool offsets for the cutoff 
> tool
> set correctly) will my cutoff tool be in the correct position for parting off?

Yes.  You'd want to issue two moves to get there

G0 X[radius plus a little bit]
G0 Z[-desired part length]

then part, something like this:
G96 D2000 S50 M3 (constant surface speed 50 SFM, up to max RPM 2000)
G1 X0 G95 F.001 (part with 0.001 inch feed per revolution)

**note** for CSS to work, your reference tool's tip must be at the
spindle centerline when machine coordinate X is zero (G0 G53 X0)

Chris


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