Multiple spring passes on a thread?

[thomas-buchan]

Hello 

I have a M6 thread that is 20mm long, the thread cuts nice, lovely finish but as expected the thread is over sized at the start due to the part deflecting being furthest away from the chuck (and being aluminium). I am already using the "Spring pass" selection but the thread needs an additional spring pass at final depth to bring the thread into tolerance, how do i do that? I can't see an option to choose more than the one spring pass when really it needs 2. 

I cant just add on more depth of cut as the section of the thread closer to the chuck will then be under size as the deflection reduces. 

Many thanks,

Tom 

[aliobidi]

Hi , 

attach your file with some "PIC"

[thomas-buchan]

Thank you for getting back to me, i've attached the file. I'm even doing the undercut last to keep the material as thick as possible during the screw cutting but the start is still a little over sized and needs a second spring pass. 

If you look at the thread, it's slightly not fully formed at the start but is at the back, if i just add on more depth of cut, the start would most likely be fine but the section near the under cut would then be under. I need a second spring pass but i can't see that option in the CAM.

 

[HughesTooling]

Don't think there's anyway to make Fusion do more than one pass. My post has an option for number of spring passes not sure if I added this or if other post have this option.

[thomas-buchan]

Thanks for posting that, i'll take a look and see.

Could i copy the block of G code that does the spring pass and add it below effectively duplicating the final spring pass? 

Can i suggest multiple spring passes to the development team? it's pretty standard thing to take additional spring passes on thin parts, i'm surprised Fusion doesn't have this as standard. 

[HughesTooling]

What threading cycle are you using? is it a simple G32/G33 or a full cycle like G76?

Mark

[thomas-buchan]

Hi Mark 

I've attached the portion of the G-code that does the threading. I'm not even going at it aggressively, taking 0.8mm off over 8 passes (7 step down + spring pass).

Cheers,

Tom

[HughesTooling · Accepted solution]

You want to duplicate the first of the finish cuts, the last one goes to the home position.

So from your example file you'd copy from N106 to N110. Then you need to renumber, if you don't have a NC editor give NC Corrector a try. It doesn't back plot lathe toolpaths but you can use to view and renumber.

[HughesTooling · Accepted solution]

@thomas-buchan  You could also try reduced in feed instead of constant and even an angled in feed might help.

[thomas-buchan]

Hi Mark

I really appreciate you taking the time to work through this with me, super helpful. 

This is a Centroid retro fitted machine so the compiler will renumber, i'll duplicate that block and change the infeed and report back. 

Been a good lesson to learn. 

[thomas-buchan]

So with reduced in-feed and copying the spring pass block of G-code, we have a nice thread. 

 

Thanks for your help Mark.