Re: Understanding the TXXXX offset function on a Fanuc
hy stoty, i will make a bit of general explanations, with examples for different machines
background can be particularized, to fit whatever machine/lathe/mill you wish
explanations will go the other way arround, ending with T, and not begining with it
for a general/simple operation, such things must be known :
... what post to index to ( will be refered as atc-pos, thus position of the tool magazine )
... where is the tool cutting edge tip ( will be refered as tool-xoy; thus coordinate for cutting edge )
for a compensation operation, is also required to know the radius ( will be refered as rad ); how turning do not use revolution tools, but asymetrical ones, it is required to know also the position of the tool nose arch in respect to arch center ( will be refered as quad;similar to trigonometric quadrants)
thus is needed for the operator ( and/or for an automatic initialization mode ) to input data for:
... atc-pos : in most cases, this field is not initialized in a virtual manner, but only a real tool mounting inside a phisical pot/post occurs
... tool-xoy : there has to be a table for tool corection, that can be offset, offset+wear, offset+wear1+wear2, etc
... rad : there has to be a table for radius, radius+radius wear, etc
... quad : there has to be a table for P
futher more, previous data, has to be referenced inside the program; please notice that reference is not always directly to [ atc-pos. tool-xoy, rad, p ], but may be indirect; difference is simple :
... direct reference means that each item of this set [ atc-pos. tool-xoy, rad, p ] is being linked, thus ratio between input data field and reference fields is 4:4
... indirect reference ocurs when ratio is not 4:4
for example, on :
... lathes, rad & P are most times referenced both, toghether, thus ratio becomes 3:4
... lathes with pivot, mill-turn centers, rad & P & tool-xoy can be referenced all toghether, ratio is 2:4
so far, conclusion is that :
... input data ( during machine setup ) is a set of 4 items [ atc-pos. tool-xoy, rad, p ]
... reference data ( used in automatic mode ) is a set of 2 3 or 4 items; it can be also 1 item, but this is a particular case; more on this later, below the line below
reference data is being activated through g-code, and depending on machine type, g-code defaults can vary; examples :
... okuma mill with side magazine :
...... atc-pos is used T syntax
...... tool-xoy and rad is used G56 H* D* syntax
... okuma turret lathe :
...... atc-pos, tool-xoy , rad & P is used T syntax
on most machine T involves mainly a magazine/tool index reference, thus it will index the magazine ( side magazine or turret, etc ); thus atc-pos is nailed to T, while tool-xoy and rad is not always nailed to T
after the magazine is inposition, next thing to do is to use that tool :
... on side magazines(mills, multitask lathes) , is needed a comand to take the tool from the magazine and put it into tool-chuck/spindle
... on turret lathes, turret will revolve, and it itseld is the tool-chuck
*many have doubts on the difference between T on mils and T on lathes; but to put it into the backgournd explained so far, T is always referencing the magazine/atc-pos, while tool-xoy rad & p may or may not be referenced also by T
those g-codes examples show how to enable the references to input data
initial reference is milestions/critical, always done in a single manner, and requires the use of a wcs
those [ atc-pos. tool-xoy, rad, p ] are related to tool, while wcs is related to material
after this initialization occured, is possible to talk about optional/partial references
an options/partial reference will not go to the full set of [ atc-pos. tool-xoy, rad, p ], but to a subset, including single items, for example :
... is possible to change from left to right side of a grooving insert, by changing only tool-xoy;same technique can be used for drills with chamfer adapters, or to autoinitialize a corection to counter tool wear, like raise X after 5 parts ?!
... not so coomon, but is possible to change rad, from some particular reason
... is possible to reference only atc-pos, when sending turret away ( offset is no longer needed to reach a consistent home position )
*and examples can continue
as a conclusion, partial/optional refrences, thus a call to a subset of [ atc-pos. tool-xoy, rad, p ] can not occur unless the full set was previously iniitalized
for specific fanuc examples, i am sure that a fanuc person will elnghten you
please, so far, if you have questions, feel free to ask
in other words, a T comand is folowed by an argument, which is longer or shorter, depending on how many items of set [ atc-pos. tool-xoy, rad, p ] are being referenced
that argument, varies with cnc brand, for example Txxyyzz and Taabbb, etc may reference the full set[ atc-pos. tool-xoy, rad, p ], but 1st ones uses a ratio of 3:4 while the second uses a ratio of 2:4, even more :
... Txxyyzz :
...... xx reference to rad & P
...... yy rererence to atc-pos
...... zz reference to tool-xoy
... Taabbb :
...... aa rererence to atc-pos
...... bbb reference to rad P offset
what makes it a bit tricky is that most times, ratio is not 4:4 and is even far far away from that, when it comes to subsets; for example :
... Txxyyzz may have subsets Txxyy and Tzz
... Taabbb may not have subsets, or may have ?!
is important to undersatnd that T argument is calling initial data through a ratio that is not 4:4, and it varies with cnc brand
if it matters, is possible to program a machine without using Ts, and still make it take corections, etc
an useful aproach, is to use a custom syntax that pleases you, like you wish, then leave the particularities, for each machine, to the postprocessor / kindly
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