Left hand thread - FADE IN to avoid machined groove?

[thomas-buchan]

Hello 

I am designing a turnbuckle with a right hand thread on one side and a left hand thread on the other side. 

When i simulate the left hand thread i can see in the simulation where it machines a groove with the threading insert before it picks up on the thread, is there a way to stop this? i know there is a fade out option which works great with chamfers and the like when cutting right hand threads but the machined groove on the left hand side does not look very good on the radiused corner. 

Any advice is appreciated. 

 

[seth.madore]

This is actually a graphical error. The simulation doesn't recognize that the insert is being pulled away from the part at the same rate of travel as the pitch requires, and thus, creates a false "groove"

[thomas-buchan]

Hi Seth 

I know this was a little while ago but i've had a chance to start test machining some of these now and the simulation is correct, it cuts a groove first and then pulls away. (Please see attached photo)

That is problematic as that is the worst possible place you would want a groove to focus all the stress into. 

I could have a larger uncut to get under this "groove" but it's only a LH m6 thread, there's not a lot of material there already and i need as much there as possible. 

Thanks 

Tom 

[seth.madore]

Hmm. Could you share your Fusion file?

File > Export > Save to local folder, return to thread and attach the .f3d file in your reply

[thomas-buchan]

No problem, please find attached. 

Let me know if you find anything odd going on. 

When watching it machine in the lathe, it'll drop down to depth, pause for a split second (this is what causes the groove) and then it'll pick up on the thread and move away from the chuck creating the LH thread. 

Realistically you want it to descend and then pick up on the start of the thread so the thread is feathered in nicely so you don't have this groove for the stresses to concentrate on.

I've noticed when cutting a Right hand thread the "Fade thread END" option works perfectly well and it feathers the thread out nicely every time but when you are cutting a left hand thread you want a  "Fade thead IN" to stop this grooving. 

Thank you for taking the time to look at it

(Also ignore the setup named "Ignore", that's just some testing i'm doing to avoid deflection) 

[seth.madore]

Hmm.

Does your machine have a Y axis, or can you flip a LH tool upside down and adjust the centerline with shims? If you have either, you could use a LH tool upside down and program it as a RH thread, but edit the g-code to be an M4 instead. This would get you the "Fade" that you need 🤔
I have created a task for "Fade In" for LH threads; CAM-45852

[thomas-buchan]

Hi Seth 

Is there any timeline on when this will be implemented in? It would save so much time doing work arounds. 

This still isn't a usable feed in for left hand threads.

thanks

Tom