Simon:
 
    I cant tell exactly whats wrong. The numbers dont look particularly bad. They show a slowdown of about 20% during the cut. 
   Its been awhile since Ive odne any threading work, couple years anyway, so Im not fully up to snuff of the readings. 
   I dont like that the adder value is always zero, but that may be normal in that driver. The adder controls the speed. The error
   controls the adder. Mach3 purposely increases planned speed by 20% so the thread shoudl immediately drop that speed by 20% when the thread starts, thus 
   giving the right speed, and allowing it to speed up by at most 20% if the spindle speed should increase. ( yours doesnt increase so thats not an issue).
   
    The reading of pitch of 40 is simply the G1 or G0 at th end of the thread and as a result shows no threading run vaues after the report. ( Thats normal
    in other words..). 
    
Thu - 11:07:22 ---Spindle Lock: 5220 , Total Ints: 0, Total Spindle Ints: 0, Error: 811, Adder: 0 LastRot: 6489
Thu - 11:07:22 ---Spindle Lock: 5220 , Total Ints: 5765, Total Spindle Ints: 5220, Error: 545, Adder: 0 LastRot: 6587
Thu - 11:07:22 ---Spindle Lock: 5220 , Total Ints: 11711, Total Spindle Ints: 10440, Error: 1271, Adder: 0 LastRot: 6481
Thu - 11:07:22 ---Spindle Lock: 5220 , Total Ints: 16977, Total Spindle Ints: 15660, Error: 1317, Adder: 0 LastRot: 6549
Thu - 11:07:22 ---Spindle Lock: 5220 , Total Ints: 22206, Total Spindle Ints: 20880, Error: 1326, Adder: 0 LastRot: 6544
  The spindle Lock is the spindle speed in interrupts just before the threading begins. The error is the difference it saw
  in the last rotation.  The resport of a large pitch you can ignore, its just a false report based on the G1 motions post 
  threading. The Adder is the only value I dont like, but I cant recall if thats normal or not. 
  
 Be nice to know if anyone using threading  gets an adder value in that test, I simply cant recall. The readings other than
   that though, show no failure at all. They seem to track, the errors are what Id expect from a proper thread and they dont 
   seem to grow meaning the variations appear to be properly dealt with. 
   
    Im assuming you have "Use Actual Spindle Speed" checked in the config?  
    
    Art