[gibsoni]

Hi Guys,


Can someone please help me understand how the threading terms tie together in a G71 threading cycle?

I thought from my manual that:

L was a fixed value of 1x lead in the absence of M23 and designating your own.

Does the machine specific delta value apply after the thread chamfering occurs (time to decelerate the axis)?

I understand its also needed as time to accelerate the axis and synchronise with the spindle.


I have recently cut a 16TPI 3 start thread and the chamfer/lead out length in the Z is very close to the pitch, NOT the lead. Can anyone confirm this is reliable? i.e. its the pitch not the lead.

So, 2 Questions -
1. How does the L and delta value work together at the end of a thread
2. Is the L distance actually the pitch not the lead (in the absence of M23 and prescribing your own L)

Thanks everyone.

Stay safe!

Iain.

[deadlykitten]

How does the L and delta value work together at the end of a thread

hy gibsoni please, what do you mean by delta ? do you reffer to the distance required for the axis ( S and Z ) to get in sync ( thus Z axis acceleration distance ) ?

Is the L distance actually the pitch not the lead (in the absence of M23 and prescribing your own L)

according to manuals, L = pitch

also, manuals do not clearly specify what happens when you use L and M22 ( absence of M23 means that M22 is active; if you don't specify M22, it will be active by default, since it is modal @ cnc start-up, power-on, etc )

do you need to generate a specific taper ? pls share your drawing and i will give you code and how to create the taper drawing for machining

it is possible to test what happens when you use L M22, by messing with machine parameters, etc, but this is only for fun

so, do you need help with a real thread, or are you intersted into how it works ? or both ? kindly

[kurmay]

Hi deadly

delta is

[deadlykitten]

How does the L and delta value work together at the end of a thread

hello again, that delta explained in the manual is specific to z axis motion : if you thread from z5 to z-50, then travel will be 55, but desired feed will be available only for 55-2*delta (*1)

when "z estimated position" will be -55+L, X axis will start to raise up (*2) using a feed value calculated with the formula from image 01, explained by kurmay and me

however, is pretty time consuming to set "X axis retract feed" by using a parameter and doing some math in order to compute the angle of the composed movement; just imagine, if you will change the rpm then it will be needed to start all over again, in order to keep the retract vector orientation constant ... also, in the end, it may not work

so, if you wish to control the final taper, like among a single pitch/lead, or to obtain a vanish thread, i recomand you to use G34 (attached *.pdf); if you share a drawing, i will share how to create the code ( hope g34 is working on your machine )

Is the L distance actually the pitch not the lead (in the absence of M23 and prescribing your own L)

i strongly recomand you to use M23 L each time you need to obtain a vanished thread, and, if it does not work, then you will need to mess with a parameter inside your machine ( it may work after a few trials ), or switch to g34 ( this will work as expected, but coding requires much more time ) / kindly

---

(*1) if you need to deliver an od thread with low left and/or right clearances, then deliver the diameter before threading as low as possible, and use the threading insert as deep as possible, thus craft it with maximum material removal, just a bit over the no-go gauges ... like this, even if the cnc won't be able to sync it's movement, you should still have room for errors; is all about tolerances ...

(*2) more precisely, X will begin to raise when" z estimated position" is -55+L+ipw_for_feeding

"z estimate position" <> " z real position ", and their difference is equal to diff
... if diff = 0 then z axis is moving as it "should"
... if diff > 0 then z axis is a bit behind, mostly because of the cutting force, or acceleration slower then expected ( a heavy turret behaves <> empty turret )
... if diff < 0 then z axis is ahead, mostly because of inertia during acceleration / breaking, and/or backlash swipping sides even if axis direction did not reversed

also "z estimate position" <> "z comanded position", and their difference is always positive, thus the control always has to be in front of the estimated position; check attached 02

[gibsoni]

Thanks for the replies.

I didn't get any email alerts informing me that someone had replied so I assumed no one had. Sorry for the delay.

So, When we call the Z value as the finish point of the thread, this INCLUDES the 'L' distance, and, after this there is still the delta value required?

Thanks for the clarification.

(As a side note - L on this job certainly seems to be the pitch, not the lead)

[deadlykitten]

So, When we call the Z value as the finish point of the thread, this INCLUDES the 'L' distance ?

hy gibsoni, yes, finish Z includes the L distance; please consider this simple code :
G00 Z+ 5 ...
G71 Z-50 ...

when z will be -50+L, X axis will start to raise up ( check also attached 01.png )

travel will be 55, but desired feed will be available only for 55-2*delta ( check also attached 02.png )

and, after this there is still the delta value required?

delta is a machine specific, you can't provide it inside your code

delta is the length of the deceleration/acceleration sector :
... deceleration occurs before final Z
... acceleration occurs after initial Z

is it ok ? should i explain more ? kindly

[gibsoni]

Thanks DeadyKitten,

I think I disagree or don't understand your comment about delta.
I have calculated it per the manual for my machine so know what it is for this machine,rpm and lead.

However, I don't think it makes sense when you say that deceleration occurs before final Z. If this was the case you would have incorrect and changing lead WITHIN the L value as the tool retracts. Hence, I assume the delta value is after the final Z.

[deadlykitten]

hy gibsoni in this case, i believe that is a good moment to run some trials, in order to decide if delta is before, or after, final Z

what do you say ?

if you wish, i can suggest you a nice test, but i need to know the constant for your machine, that one that you use to calculate delta / kindly

ps : if delta is located after final z, then it would be impossible to cut a thread close to a shoulder obviously, i can help you to test this behaviour without crashing ... but more important, if you wish, i can help you to crash your machine just kidding

ps2 : please excuse me, i don't wanna be impolite, but you should 1st understand how delta works, and only after that you should start to think of L; so, let's run some real trials that will convince you, then we should move to L; also, don't worry, even when everything with delta will be clear, you will see that using L is a tiny mess, so is better to use G34 ... i have been there, i have done that