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Lathe question
« on: February 03, 2017, 11:14:32 AM »

I was looking at Soctt's threading wizard since I now have a need to do a ½-13 left handed internal thread.  Seems like it is what I am looking for, but, as I was reading the readme file he made the comment that If you swapped the start and end points you could do reverse threading.  Not being an experienced machinist I somehow imagined that this produces the same result as left handed threading.  What/is there a difference between reverse and left hand threading?


Ralph Tuttle

Offline RICH

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Re: Lathe question
« Reply #1 on: February 06, 2017, 08:08:28 AM »
More than a simple answer but figured the additional comments would be appropriate.

- Reverse threading - The term has no meaning at all to me.
- Could not find the read me file that you mention here.

- Just some basic things to consider in threading
  - Spindle rotation direction for the lathe is defined by looking  from the headstock towards the tailstock, thus you have CW which
    would use an M3 and CCW which would use an M4, else, you need to mannualy set  the turning direction of the spindle.

- Left or right hand threading in CNC
  - depends on the direction of the tool Z movement which can be plus or  minus as input into a wizard from a start point.
  - depends also on the spindle rotation direction

The spindle rotation and Z movement along with the following also come into play in defining how the thread that will be cut:
 - type tool left or right and how mounted in the tool holder
 - configuration such as front or rear toolpost / lathe
 - external or internal thread
 - M3 or M4 rotation and Z axis movement
Thus you have a number of combinations, 16 total ( I think  :o ) , depending configuration to be used such as front post, rear post, external, internal.

Three wizards available to do threading are:
Simple Threading - Brian Barker
Quick Threads    - Scott Shafer
Complex Threading- Brian Barker / Rudy

You will notice that in both the Simple Threading and Quick Threads the left hand threads are done with the M4 to set the spindle rotation for CCW rotation and they assume a front tool post. With a front tool post orient the actual thread tool appropriately in the holder to cut using CCW towards the chuck.

Have fun......, ;)

Hmm.....maybe above should be added to Threading on the Lathe write up in Member Doc's!
« Last Edit: February 06, 2017, 08:17:34 AM by RICH »
Re: Lathe question
« Reply #2 on: February 06, 2017, 11:11:27 AM »
Rich, thanks for taking the time to put this write up together.

I am not one to wait around very long so I made a threading tool and made the 1/2-13 internal thread using the wizard in a standard fashion.  Just for giggles and grins I also tried using the wizard with reversed starting point, left to right, threading tool on the near side of the bore and the threads came out the same as the first.

When I first downloaded Scott's wizard there were several entry boxes with no labels.  After scouring the support site I found an updated version and reinstalled it.  The missing bitmaps were there and made sense of the entry boxes.  It also had a word document "Read Me 1st.doc" that in item 12 he made the reverse comment.

Thanks again for the write up, your posts have been most helpful to read.