Offset vs. Compensation

[sinha_nsit]

This is not a serious discussion. In fact, many of you may not agree with me. But, here it goes:

A few years back, when I was new to CNC area, these two terms used to confuse me a lot. I often wondered what the difference is between the two. I now believe that the term offset should be used only for work offsets (External offsets, G54 offsets etc). For other offsets, the term compensation should be used. In fact, this is the practice on a milling machine where we talk about length compensation and radius compensation. But, on a lathe, following similar logic, we do not talk about radial/axial shape compensation. These are referred to as X/Z axis geometry/wear offsets.

In my opinion, the term work offset should be used for offset distances of an imaginary tool, to establish a work coordinate system. Since the actual tool would have a different shape, we can use the term shape compensation to take the differences into account, which would have both geometry (meaning, difference due to difference in geometry) and wear (meaning, difference due to tool wear) values. And the term offset numbers be replaced with compensation numbers.

There is a lack of consistency in Fanuc manuals. To confuse/clarify further, 0i TC Operator's Manual says at one place (section 14.1.5, P.191), "Compensation is the same as offset vector". I believe, we should either use a single term for everything, or use the two terms for two different purposes.

[dcoupar]

I don't know about you, but on a lathe I use Geometry Offsets, Wear Offsets, AND Tip Nose Radius compensation. However, I store the radius compensation values in the same place I store the Geometry offsets.

Fanuc manuals have always been confusing, and they always will be. That's what keeps this forum so busy.

[sinha_nsit]

I also use the same terms because these are what people have accepted. But I do feel that "offset" and "compensation" should be used for different purposes.

Regarding Fanuc manuals, not just ambiguity, there are several typographical mistakes also. Even some of the figures are not correctly made. Till a few years back, I used to believe that Fanuc manuals are "Bible" which can never be wrong. But when I detected several illogical things, I sent a mail to Fanuc, Japan. They accepted nearly all the mistakes pointed out by me, even apologized for causing confusion, and assured that these would be corrected in a future edition. Incidently, before writing to Fanuc Japan, I exchanged a few mails with Fanuc India. And very soon I realized that even though they are good at machine maintenance, they do not know enough about part programming. I do not know how the Fanuc branches in other countries doing.

[tobyaxis]

To add a little more confusion to your thread.

On a Lathe you set a Work Shift, and Tool Geometry (Machine Position, TNR and Tool Tip Designation).

An offset is made to change a specific size of the Part being Machined. This is usually caused from tool wear.

More confused??

[sinha_nsit]

I am not really confused because I am well familiar with these terms, but, of course, I do not find these things too logical.

I would have used the term "offset" for "work offset", "offset shift" for "work shift", and "compensation" for all other offsets. On lathe, there could have been radial, axial, radius and tip-direction compensation. On milling, we already use the terms length and radius compensation. And all the compensation values would have both geometry and wear components.

"An offset is made to change a specific size of the Part being Machined"

There is no harm in using the word "offset" with its literal meaning, as long as it does not confuse the reader. In fact, this applies to the term "parameter" also. We sometimes talk about parameters of a macro (referring to its argument list), parameters of a pocket (referring to its geometrical features), cutting parameters (referring to rpm, feed and depth of cut) etc.

[Geof]

sinha; I think you are a voice in the wilderness exhorting people to be more precise in their use of language and technical terms.

You can go beyond offset and compensation to things like; DNC for Direct Numerical Control and DNC for Distributed Numerical Control; High Speed Machining used in the Haas context where it means looking ahead in the program and using algorithms to slow the feed down approaching an abrupt direction change allowing faster feeds to be used for straight cuts without overshooting corners and High Speed Machining in the context of running very high rpm, high feeds with small depth of cut and stepover.

I sometimes wonder if some of this ambiguity arises because english is such a versatile language with different words meaning the same thing and the same word often meaning different things depending on context.

[tobyaxis]

Originally Posted by Geof I sometimes wonder if some of this ambiguity arises because english is such a versatile language with different words meaning the same thing and the same word often meaning different things depending on context.

This is why English is taught from Grade School through High School, LOL. I must agree that the English Language can be confusing to say the least. It is pretty amazing that anyone can understand each other.

BTW: I have found the Fanuc Books to be confusing in the past too.

[gbowne1]

I have the FANUC Series 0/00/0-Mate manuals and they are not always very easy to understand. Thankfully I learned the 6M and the other controls before I learned this one.

I'm still learning how to use the button labeled [4th] among some others that are on my CRT/MDI and operator panel. (As Shown on my FANUC Manual post).

Greg

[John_B]

Originally Posted by dcoupar Fanuc manuals have always been confusing, and they always will be. That's what keeps this forum so busy.

Good one! Shame it's so true.

Originally Posted by dcoupar I don't know about you, but on a lathe I use Geometry Offsets, Wear Offsets, AND Tip Nose Radius compensation. However, I store the radius compensation values in the same place I store the Geometry offsets.

I was taught since I first was introduced to NC technology that the baseline setting for workshift and tool length/diameter were to be considered offsets - them adjustments off baseline were compensation. This is especially evident on lathes with Geometry and Wear data tables for the tools. This is how I have taught all of my people to keep the concept straight as they move between different machines and controls.

Rgds,
John B

[gbowne1]

In the 0M-C, since I use Kurt D675 vises on the machining center I have. I set my work area to be well within the limits of the opening of the vise jaws, even when I have two vises side by side, but also ofen I use vise fixtures.

Then again sometimes I play around with teach mode. Hi-Hi!

Greg

[sinha_nsit]

Originally Posted by John_B I was taught since I first was introduced to NC technology that the baseline setting for workshift and tool length/diameter were to be considered offsets - them adjustments off baseline were compensation. Rgds, John B

This is exactly what I am suggesting: "offset" for baseline setting, and "compensation" for adjustment due to differences in tool geometry (I often use the term "standard tool", referring to the baseline settings). This is so logical. So, on a lathe, we should use, for example, the term "X compensation geometry/wear" instead of "X offset geometry/wear", and "compensation numbers" in place of "offset numbers". Similarly, on a milling machine, instead of "H offset geometry/wear" we should use "H compensation geometry/wear". We can imagine as if the "standard tool" on a milling machine has zero length and zero radius. And, your machine does not have 400 offsets; it rather has 400 compensations!

These two terms should not be used interchangeably. These are not plain English terms; these are technical terms. There has to be some discipline in using technical terms. Perhaps, Japanese to English translation created this problem.

Finally, I am happy that none of you felt that I was talking absurd!
Thanks to everybody for sharing your views.

[Geof]

Originally Posted by sinha_nsit .....There has to be some discipline in using technical terms. Perhaps, Japanese to English translation created this problem......

No, I think we english speakers are capable of screwing up our own language without assistance.

I agree with your viewpoint whole-heartedly. I get very frustrated when people use ft-lbs as a unit of torque when it should be lb-ft, and call themselves newbies when they are novices, and refer to transparent plastic as 'see-through'; I think discipline is needed in all terms otherwise we degenerate into the situation of Alice and the White Rabbit who said "words mean what I want them to mean". The words someone uses to explain something to me should be assigned the meanings which I expect otherwise how can I be expected to understand?