I need to cut a slot / thread for a new spindle mount that is 1" pitch, but two start.  Each start is 180 degrees apart.  I figured out how to cut the feed slot using the threading wizard, but I see no way to turn the job 180 degrees.  I do not want to rotate the part.  I took a great deal of care to true it up and have several other MOPs to follow that while not critical position is important. 

Go to Members Doc's and you will find a write up called Threading on the Lathe ( See page 13 / section 3.6.3 )
Also see section 8.0 starting at page 48.

RICH

This a a thread milling operation.  Nopt a lathe operation.  Spinning this part on my lathe even if possible would probably be dangerous.  I am threading a 3.5" minor diameter hole to 3.7" major thread diameter.  Its a loose fit application.  I suppose I could do it all after the part is completely finished at the sacrifice of my thread placement, and just over cut them slightly. 

I do not want to rotate the part.

No need to....... instead the start point of the thread cycle is changed in the code.
It would have been better if you tried multiple threading in advance of actually doing it the first time.

If you removed the stock or have already done one thread you can always pick up the thread and adjust for the second.
Be meticulous.

RICH

That I can't help you with.
RICH

I am threading a 3.5" minor diameter hole to 3.7" major thread diameter.

You could always use alternate flank cutting and a few fine spring passes on the lathe.
Would be fine for a single thread but never attempted the combo for a multiple thread.

That's a deep thread and also fast z axis move on a lathe.

Wish ya luck,
RICH
 

I don't think doing this on my lathe is really an option.  I don't think I have gears that fast, and even if I did this is an irregular shaped part and I need to thread through.

I can do one thread easy enough on the mill using the mill threading Wizard in NFS Wizards.  I just need to figure out how to rotate it 180 degrees for the second thread.  I actually need to check the geometry of that wizard, because some of the results don't look right. 

Not really appropriate now since this is an NFS forum, but I think I found a solution using ViaCad 2d/3d and Cambam.

Ok, how is this.  In this case it seems simple because the larger threaded hole happens to be at the origin of the machine. 

I have ViaCad 2d/3d which has a helix tool.  I make a helix of the correct pitch, and the diameter of (Major diameter - cutter diameter) and then do an engrave MOP at a depth of .000001".  I can copy and rotate the helix 180 degrees and then duplicate the mop using the second rotated primitive. 

Seems relatively straight forward.  What obvious fubar am I am missing?

If the hole were at a different location I should be able to do the work at the origin for the simplicty of the rotation, and then move it to where ever my hole is. 

What obvious fubar am I am missing?

I am thinking that the gotcha will be timing even if you rotated the part 180 degrees.
I will admit that i never did any thread milling.

For the lathe, the G32 threading cycle index triggers the movement of the Z and feed rate is sampled and adjusted so that
the entry point would be exactly the same based on rpm of the rotating stock.......in the case of a 2 starts, Z is adjusted to offset the thread start by 180 degrees,but you still have the monitoring of movement from the new start point. For the mill you have no way of having the mills z travel monitored to make sure  the 2nd thread pass enters the piece 180 degrees from the first pass.
Any small difference in total Z travel timing (distance relative to acceleration and feedrate  and also start point) will affect the entry point of the cutter and it doesn't take much to throw it off by some amount of degrees. So the distance between pitches will not be correct. I am guessing that one could do some testing and see the how it goes but the outcome will be hit or miss.
FWIW
RICH

 

  

You calculate the thread height for 1/2 rev then add that to the starting point. Have done it several times for large threads. It will put the second start 180 deg out from the first.

Justa thought, (;-)TP