Developments on my Home built 5C CNC Lathe - Polar interp. and Live tooling

besriworld wrote:

At a later stage, I plan to add an additional 1kW servo motor, which will operate in torque mode to act as a dynamic load on the main 7kW motor. This will increase the system's rigidity. Currently, I'm using the encoder from the main motor
 

That sounds interesting.  How are you planning to couple the secondary motor to the spindle?

I’ve bought a hydraulic chuck closer for the lathe chuck, but in order to mount it onto the spindle shaft, I need to cut a thread on the spindle. After that, I’ll add an additional gear on the spindle, which will be connected by a belt to a second servo motor with a 1:2 gear ratio. The motor will be mounted on top of the spindle housing

andypugh wrote:

Yes, it's probably best to turn off CSS when threading. 

Andy,

I wasn't using CSS when threading.  Multiple attempts at tapping the same thread at different speeds resulted in different start points.

What I discovered (through @Aciera's help) was that caxis.comp interfered with threading/tapping, and that LCNC has a bug in G33.1 and G76.

forum.linuxcnc.org/38-general-linuxcnc-q...peed?start=30#317931

Yes, this definitely seems like a bug.

I can see the cut starting at a different place at different spindle
speeds due to the time needed to get synched to the spindle
varying at different spindle speeds, _but_ once synced and cutting,
the threads should be identical regardless of spindle speed...

(as they are in a normal manual lathe than maintains strict gearing
between the spindle angular position and Z offset)