Threads - "Spring pass" wipes out threads

[ThickChips]

Hello,

I am attempting to thread 3.75 - 12 UN 2A on some cold rolled low carb.

I have 2 separate ops for this. First is the thread cycle. Then the second is a spring pass (see screen shots and output code) to work in the thread.

When running the first cycle, the cut is smooth but the crest of the thread is very flat and wide. Clearly and unusable thread not to size. This makes no sense to me.

Finally  when i run the spring pass op, the thread is cut heavy and produces a chattered thread that now looks more like the form of the thread im cutting.

 

Both posted ops are almost identical with exception of first pass depth (or whatever D value is). Its deeper in the spring pass because its going to full depth which makes sense to me.

 

Control is a Haas NGC. 

 

Any ideas whats going wrong?

Thanks a lot!

 

 

 

[AHarrison1]

Change the NC code format from canned to longhand, re-post then compare the values of the last pass to the spring pass. 

They should be the same. I think the issue lies in the canned cycle... just guessing here.

[DC CNC]

Looks like you are starting your thread with two different Z values Z.3214 and Z.3

[AHarrison1]

5 minutes ago, DC CNC said:

Looks like you are starting your thread with two different Z values Z.3214 and Z.3

This is normal with the 29 deg lead in angle. If posted out longhand the Z value changes with each pass.

Most of the cutting is done with the leading edge of the insert.

[ThickChips]

Hi all, thanks for helping with this.

 

Update, on a fresh piece i just ran the roughing cycle and the thread was as expected, too big, large crests.

 

I comped the tool about ten thousandths and made a perfect thread (according to pitch mics and gage)

I will test after lunch and run the spring cycle and see if it wipes the threads out.

 

I did notice there is a varying Z start position and wondered if there isnt mismatched threads

[Leon82]

It sounds like the spring pass is removing lots of spring

[ThickChips]

UPDATE

 

The discrepancy from the start Z value was 100% the culrpit! 

Is this a mastercam issue or post?

[AHarrison1]

One thing I have noticed is your A value being different to mine.

Your A value is pulled from the lead in angle of 29 deg, mine is pulled from the included angle of 60 deg.

As for which one is right I don't know.

[cruzila]

20 hours ago, ThickChips said:

UPDATE

 

The discrepancy from the start Z value was 100% the culrpit! 

Is this a mastercam issue or post?

Operator error.......