threading tool Z offset question
I tried to find this in forum history but no joy and the books I have don't say ... probably a dumb question ...
My question is this: what is the convention, if there is one, for setting the Z offset for a single point threading tool be it indexable or solid? Is the Z offset set to the end of the tool or to the actual threading point. If it's set to the point, how is that accomplished?
I've been successfully threading using the tool end to set the Z offset but depending on the size of the tool, especially the solid type, I have to compensate in the program the Z end point for the length of thread by at least 1/2 pitch. In other words if I want a .500 length of thread from zero I have to command the tool to go to -.500 plus some (that would be negative "plus") to get the threading point to .500
I have no problem dealing with the "plus some" but what is the practice out there with the offsets?
I know I still need to know the full length of the tool so I don't run into anything.
Hope my question is clear - no biggee, just curious.
(Fanuc 0i TB gang tool lathe)
I use the side of the insert for z-zero, or whatever would crash into a shoulder. I mostly use top-lock inserts, where the tip is located at 1/2 the width. If I need a certain length of thread I add 1/2 width to the depth and check it with a ring gauge, I find this easier to remember than to subtract some from the z depth when threading close to a shoulder.
We always program from the side of the insert. Programs need to be modified if not threading into an under-cut, and our guesses aren't close enough. No big deal. I do program for a family of lathes that require a bit more trouble if the thread has to go close to a shoulder. I have to go to a G32 and the last 3-4 passes add an empty block between the end of the thread and the pullout. This keeps the tool at the root diameter until it reaches the final Z-position. Otherwise it pulls out too soon regardless of RPM.
Same here set to the edge of the tool and add the amount from the edge to the point. After all you only have to alter your program once. Then you are not crashing your machine because somebody forgets to account for the difference later.
Thanks again, folks.
Sounds like the vote so far is to offset to the end (edge) of the tool and compensate for the desired point position within the program.
I ALWAYS use the end too, I often have to thread up to within .03 of a shoulder on some small parts and this way it never crashes.