external thread problem

[strof]

hi.
after indpection of my m20 x1.5 mm pitch threads with our new thread comparitor.iam finding that my first thread drpth is always around .06mm shallow and sightly out of tolerance.
we do a lot of back turning and externsl threading toward tsilstock and use a part off tool to chsmfer the thread which eorks fine one one machine but not the other 3
anybody have sny suggestions ot solutions
thanks
paul

 

[Ox]

Am I to decipher from your writ that this is a back thread app?

Are you using G32, 76 or other?

Feeding in Z+ or Z-?

First guess is that you are threading in Z- up to the cut-off, and the "first thread" that you mention is actually the last thread - on the cut-off end?

If so - edit your "pull-out" chamfer on your threading cycle, or add more Z depth.



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I am Ox and I approve this h'yah post!

 

[strof]

cheers ox
moving in z+ direction dropping into an undercut and screwing toward
a mating face

 

[strof]

ive tried pulling back in z- thread g76 starts 3 mm shy of undercut and at x 23.0

 

[Ox]

Could you post your code?


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I am Ox and I approve this h'yah post!

 

[strof]

just off the top of my head mate
x 23 z -39 start point.
g76 p000000 q0500 r0.05
g76 x18.16 z-22 p9230 q0500f1.5

i slowed the speed right down to 800 it was 1300.its just the first couple of threads arent in tolerance.material is 314 stainless

 

[WILLEO6709]

why no spring passes?

 

[strof]

sometimes use them but not always

 

[strof]

the program works fine on one of the machines.maybe i need a spring cut on the others i am open to suggestions to solve this annoying problem

 

[Ox]

just off the top of my head mate
x 23 z -39 start point.
g76 p000000 q0500 r0.05
g76 x18.16 z-22 p9230 q0500f1.5

i slowed the speed right down to 800 it was 1300.its just the first couple of threads arent in tolerance.material is 314 stainless

Well, off the top of my head /= exactly what it is, but ....

Is this a square buttress thread or what?
Zero* infeed angle?


OK - so where is your cut-off length?


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I am Ox and I approve this h'yah post!

 

[strof]

m20 x 1.5 cut off is z-36.i could try putting in an in feed

 

[Ox]

With an OA part length of 36, and you are starting at 39 is only 3mm length for the Z axis to get up to speed.
Depending on your RPM, that may or may not be enough. Add to that the fact that the C/L of your threading tip is likely less than your 39 as well.

Could you start at 41 or so and see what'chew get?
Or - slow the RPM down.

The infeed angle is not going to help your issue here, but it will likely give you a better finish on your thread.
P010160


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I am Ox and I approve this h'yah post!

 

[strof]

thsnks for taking time out again ox

i did chop out a bigger groove and moved the tool further back.also slowed rpm to no effect.
i will try spring passes.
have you any thoughts on my using the part off to clip the thread as it parts off.could this be creating a burr.the part looks and feels great just this bloody comparitor is showing me the thread is .06 high first 2 threads

 

[Gobo]

If this an old machine, it may be unable to cut a "perfect" thread at the beginning or the end of that thread. Newer machines usually do not have that issue. We see it on some of our older lathes where the very start or the very end of the thread is less than perfect. With the newer machines and their better technologies, that is pretty much a thing of the past. If this is the case, giving it more room to "catch up with itself" will help. Your above post does seem to be working in that direction.

 

[strof]

yes gobo the other 3 are older machines.im going to have to be gentler with them maybe

 

[Ox]

thsnks for taking time out again ox

i did chop out a bigger groove and moved the tool further back.also slowed rpm to no effect.
i will try spring passes.
have you any thoughts on my using the part off to clip the thread as it parts off.could this be creating a burr.the part looks and feels great just this bloody comparitor is showing me the thread is .06 high first 2 threads

Cycle your cut-off tool to form your thread relief and place the chamfer before running the threading tool.


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I am Ox and I approve this h'yah post!

 

[Gobo]

Is this on a flat bed lathe or slant bed?

 

[strof]

slant bed cmz lathe

 

[strof]

thanks to all for the advice.i dropped the speeed on the threading cycle by a 1/3 .no high spot on the first 2 threads now

 

[Ox]

thsnks for taking time out again ox

i did chop out a bigger groove and moved the tool further back.also slowed rpm to no effect.

thanks to all for the advice.i dropped the speeed on the threading cycle by a 1/3 .no high spot on the first 2 threads now

OK, so what changed?



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I am Ox and I approve this h'yah post!