G76 Confused. com

[TechnoSpanner]

I appreciate this forum and many others have discussed the g76 threading cycle. Some of you will find this topic annoying. I am interested in particular the chamfering amount at the end of a thread. Will someone please explain to me in detail how to work it out. I understand it’s a chamfer. Is it a percentage. If so a percentage of what. I would like to understand how it works.

G76 P010060 Q00500 R.001 (chamfer Amount At End Of Thread)

A picture will paint a thousand words.

Thank You.

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[deadlykitten]

hy techno spanner, i am sorry, i can't explain the G76, but if you wish i can explain the code syntax for Okuma code is a bit different, but same stuff happens : pls check attached image

however, main problem is not understanding the code, but machine cinematics, because it is possible that the cnc won't perform as you expect

near a thread end, all cncs are losing syncronization between Z and S

similar, near a thread start, all cncs are building the syncronization between Z and S

there is a certain portion, in between, where the quality of the syncro is at its best

fact is that a portion of the back chamfer is executed among the desincronization palier, and the controller will put accent on the deceleration, and not on the back chamfer

this does not mean that the back chamfer is not executed; it is executed, but not at the best sync quality ( it is not prioritized ) : one consequence is that "good code" may lead to signifiant downtime

the back chamfer ( or the pull-out movement ), may be executed :
... accordingly to specific code, that has "back chamfer" parameters
... even if the code does not have "back chamfer" parameters : for example, it may happen, as default, during the last spindle revolution

on quick servos, inertia has a very important role, and may lead to negative diff, thus the "detected value" will go in front of the "calculated value" : in that moment, the Z servo will break even harder, and the "pull out movement" will be out of sync aggressive threading will increase backlash, especially when high Z feeds are used on heavy turrets for short threads + fast rapids, with quick accel/decel


- is hard to measure the back chamfer, but not impossible
- is possible to log cinematic data, so to have an idea about the numbers, but this is not common


a good alternative, when there is no undercut, would be feeding each pass at a shorter Z, so to reduce stress on the insert near the thread end

kindly

[deadlykitten]

pls check #27 in here : https://www.cnczone.com/forums/gener...20i-fanuc.html

Pxx00yy may not mean that there is no pull-out, but that "default" pull-out is executed

if you are curious about it, run some trials, and check if the thread vanishes



ooookey / i hope there was something usefull ... kindly !

[sinha_nsit]

The middle two digits of P, divided by 10 and multiplied by the lead, is the chamfer distance (00 to 99 allowed).
Chamfer distance is the distance L in the figure posted by Deadlykitten.
Chamfer angle is 45 degree. It can be changed by a parameter.

For more information, refer to this.

[sinha_nsit]

This figure explains chamfer distance in case of taper threads.
(copied from the same eBook)

[TechnoSpanner]

deadly kitten, Thank you for answering my thread.

[TechnoSpanner]

Sinha_nsit, Thank you for answering my thread.