That is what I would have though too regarding the initial pass. I am not sure if it actually slows because the toolpath on the rod is very symetrical. It just seems to sound that way. Since there are so many variables in my set up, loose gibs and screws I will spend an hour or so adjusting before my next real passes. Also I will check all of my settings and possibly record it. I have been thinking about another youtube account for these videos. I know how much I enjoy other videos when I need to see new set ups or ideas. Of course mine would be more the crash and burn type but maybe someone could learn from my mistakes! I learn better by making my own mistakes, seems like I must verify the results for myself. Somebody elses testing procedure could have been different or flawed. Btw I start the thread .1 away from the piece. I do notice in the turn mode my accel is different and I really havent had the time to sort those issues out yet. I have played with the PID settings in an attempt to change it. In my mill profile the accel on the spindle is quick but not on the lathe. Much more of an incremental accel, same motor just different profiles so I am guessing it is a settings change. I dont get much over run either direction regarding rpms. Seems to stay within 3-4 rpms while cutting and 1-2 if no load.  

Rich, I always just thought averaging was used only for the display in Mach so that you dont see that jumping about if you have variations such as you may get with a vee belt that is unevenly worn but maybe not.
Hood

Interesting, so maybe averaging helps quell the erratic rpms I see occasionally? Btw the first pass segmenting I was referring to even occurs with an air cut. I sometimes turn off my controller to reset my tool by manually turning the stepper when it is off (could be the problem why I have issues at startup LOL). I have read there are ways to reset the code or tool offset instead of the way I am doing it. I just havent learned them yet. Btw did I tell you how much abuse a little Sherline can take waiting for an idiot to hit the Estop? What an excellent learning tool.  

Hood,
I may be confused with something else.....that's why i need to go back and look through the testing information.
It's one of those "the light bulb comes on but it's kind of dim". 
RICH

 "I must verify the results for myself. Somebody elses testing procedure could have been different or flawed."
Convince yourself and if you come up with an easier or  better one than is in the write-up let me know.

"Btw I start the thread .1 away from the piece."
3 to 5 pitch diameters away is a general rule of thumb, but, it depends on your system.

"in the turn mode my accel is different"
The accel will vary and is dependant on how far you are away from the start point to the thread and how fast the spindle is turning. Make note of the accel required for a particular threading operation in the wzard.

"Seems to stay within 3-4 rpms while cutting and 1-2 if no load"
Waite until you try doing larger threads, or threading material other than Al.
That's were experimenting helps. Also consider doing flank cutting.


 "Btw did I tell you how much abuse a little Sherline can take waiting for an idiot to hit the Estop? What an excellent learning tool. "
I sure had fun with mine and at least it will stop if there is a problem. You get a bigger lathe / horsepower it will do damage. 
RICH

Fastest
 It is often the case that wee machines can take more abuse than bigger machines. This is because they dont have much weight or power behind the tools so damage is less. My lathe is big and heavy and fairly fast, the saddle, crosslide and turret/toolpost probably weigh in excess of 400KG (880lbs approx) so if they smash into something at 10m/min the something has to be fairly solid to withstand it. Then the problem would be all that force has to go somewhere so my turret would take the brunt of it. Fortunately I have only had minor crashes during the learning curve of CNC lathes and just smashed up a few tools, the worst was the threading tool that is an upside down type and costs about £120 thankfully I only did that once

Tool offsets and work offsets are all dependant on how you have things set up and how repeatable your replacing of tools can be. With a toolchanger you can set upp the tools to have the correct offsets in relation to your master tool, then all you need to do is find where that tool is in relation to your stock. Zero position on the X is always the centre line of the bed and Z is usually the end of the stock or at least the part you are making if the stock will need facing. With accurate homing you can have all your tools set up so that if you command a 20mm dia move it will go there no matter which tool you have in the slot but obviously that needs a means of placing the tools in the slot accurately and be repeatable.

Now bacjk to your first pass, is the spindle stable when the first pass is happening? if not then it is likely the axis is reacting to the varying spindle.

Hood

Rich and Hood thank you for helping in my understanding of this topic. I have truly enjoyed the thread. I was very aware that I would try to learn as much as I could on a machine that wasnt so destructive to itself before going bigger. I also could have bought a plug and play system but what would I have learned? This is fun, challenges the brain and isnt filled with groupies like GOLF. Rich I definitely wouldnt even want to tackle such a technical topic, nor could I. If I ever do have a suggestion that I think would help, I will definitely throw it out there. So far your doing great.  "I must verify the results for myself. Somebody elses testing procedure could have been different or flawed." this comment was a statement on my stubborness/ignorance at others peoples experiences applying to my life. Been a problem since birth, I am 48 now and just beginning to realize it! I guess that might be better than never realizing it. Does age make you give in and conform? or make you realize you werent as smart as you think you were?

Ok my bad,
Spindle speed averaging was for use when timing was available. It would average the speed of multiple slotted discs
as compared to a single index over a few rpm. Now multi slotted discs are not provided for in the latest version of threading / MACH3 Turn. Timing should  be disabled in configuration. Amazing what you find in the manuals. 
 
BUT......I still need to look in the volume of info on threading as that dim light bulb above my head is still flickering for some reason.  Maybe it's an indication that the brain is still active! 
RICH

Maybe it's an indication that the brain is still active! 
RICH

No probs with that Rich, easy enough to fix,  go to the Operator menu then down to Brain Control and you can switch it off totally

Hood

I switch it off in a different way but requires an additonal  knowlegable control person.      
Timing is everything when threading. 
RICH