Dynomotion Forum

Greetings,

I have a lathe controlled by KMotionCNC, and am wondering how to set up up the spindle with live tooling. Imagine cutting an arc with an end mill on the face of the spindle (C-Axis). How do you set up the feed rate for cutting that arc? Obviously the larger the radius the farther a given movement will rotate the work. Does the KFlop have any way of knowing the radius and coordinating the C-Axis speed correctly to maintain a constant feed rate?

Thanks,

Scott

Hi Scott,

I'm not sure I understand the scenario. But sounds like an interesting question. I suppose this would be the same as a Trunnion table RTCP configuration. So for example to mill a small groove around a 1 inch radius rod you would specify the XY tool tip move around a 1 inch circle radius at some feed rate while rotating C 360 degrees. Or to mill a small groove around a 2 inch radius rod you would specify the XY tool tip move around a 2 inch circle radius at some feed rate while rotating C 360 degrees. When executed the xy axes wouldn't move, only C would rotate and tool tip would move at the specified feed rate.

The other option would be to have the CAD calculate the feedrate based on geometry and specify the rate using inverse time G93 mode.

Thanks Tom,

I have a part chucked up in a lathe, with the spindle configured as the "C" axis where I can control the rotary position. I have an end mill on the X/Z saddle of the lathe so I can plunge it in and cut arcs in the face.

I am not particularly familiar with lathes, I know G96 will keep the spindle at constant surface speed changing the RPM based off of the X radius position. I was wondering if a similar command would work with feed to rotate the "C" axis at a feed rate "F" based off of whatever the X position is.

I guess I need to fundamentally understand how this works better. Lets assume I put the following code into the lathe:

G01 F10 C90 - The "C" axis is set up with the "Degrees" box checked. Would KMotionCNC interpret this to be degrees/min instead of IN/min? A feed move on X or Z is IN/Min, and on C it is Degrees/Min?

This is something I need to research soon, as the first parts for my new lathe build have arrived, although getting as far as live tooling is probably going to take me at least a couple months.

It's probably worth having a look at some of the Haas programming guides, to understand how they achieve it.
A quick google has thrown up the Helman guides - http://www.helmancnc.com/cnc-lathe-live ... c-m-codes/

My initial task with live tooling, will be to mill some flats, so will require interpolation between the spindle and X axis.

Thanks Moray, some of the challenges I have faced is changing the spindle back and forth between running as a spindle and a C axis. Optimally the C axis would be very stiff with zero backlash. When running as a spindle the high high RPM is the target. I have been looking for a company that makes two stage gearboxes to change back and forth between these modes. Unfortunately most of the lathes I have built are not optimized for either condition.

I am hoping Tom can provide insight on the units when an axis has the "Degrees" box checked in KMotionCNC. I am assuming units for feed rate "F" is in degrees/min. Even more confusing is how the G code interpreter would handle mixed units. For example a fed movement on X and C where X is in moving in/min and C us degrees/min?

Hi Scott,

Yes when the Degrees is checked then the resolution is in counts/degree and the C angle would be in degrees.

If radius is 0 then the axis is treated as a angular axis. In this case if there is a mix of X or Y or Z motion with A or B or C motion then the feedrate is based on only the XYZ motion as if there was no angular motion and is in units of distance/minute. The angular motion will complete in the same time as the XYZ motion. This assumes there are no limitations on any of the 6 axes moving at the required speed or accelerations, otherwise the motion will be proportionally slowed down. If there is no XYZ motion and only ABC angular motion then the feedrate is based on the ABC motion and the feedrate is in degrees/minute.

HTH