Reporting BASIC Dims

[[To...]]

I'm curious as to how many of you are required to show actuals of BASIC dimensions on your inspection reports. What excuses do you get for why?

[[Ma...]]

We are not reporting those values.

I would say they are theoretical values, which are controling another evaluation. For example you have to report line profile on specific place, so used basic dimension is useless to report.

But since we are using Inspect now it can make a sense to report it due possible usage of RPS.

[[Cr...]]

Funny you ask this. I just got done adding actuals for basics on a program. I'm starting to see more customers demand them. One of our customers stated they caught a company manipulating true position values, so they now require the actuals for basics to see if the math lines up. I also have encountered people at companies that don't understand what a basic dimension is. 

[[Ma...]]

Like Craig, I see people demanding them but I don’t think those people understand blueprint reading or GD&T. I’m dealing with right now where a radius is defined by a X location (basic) and a size (basic) but both are controlled by a profile callout. They want the basics reported to +/- 0.50 but the profile to 0.400. 
 

They don’t understand it.

[[Ja...]]

I don't mean to ruffle any feathers - This is just my point of view. I can understand the hesitation to supply the basics if you're dealing with people who don't understand how GD&T works. It forces you to take time to explain to them how it does and like most everybody, we're probably all pretty busy and it slows us down. It can be a pain, but it is an opportunity for us to help people learn something new. For me personally, I love doing that.

When I first came here, all programs that were written by my predecessors didn't report the basics. The machinists are really happy that I include them on the reports now. They have more confidence in the results because it's easier for them to verify that what's on the report is accurate. Almost none of the machinists question the findings now. It also helps them tweak their machines to get the process closer to nominal. Most people (some could care less) have a natural desire to make good product.

We are a global OEM, but we still do get audited (by companies/agencies I can't mention) and they like seeing the basics reported as well because then they know we're being straight with them, not trying to pull something over.

It's so easy to report. Just go to "Resources/Characteristics Settings Editor/Additional Report" and turn it on for the characteristics you desire. Then go to  "Resources/Characteristics Settings Editor/Transfer Tolerances From The Enhanced Report Option To PiWeb" and turn it off for the ones you don't want tolerances assigned to. Other than that, there's no extra programming involved.

Edited October 23

[[Ri...]]

I report them and the vast majority of our aerospace partners want them reported for the last 30 years of my career.

My argument for basics, as an example I will use a true position (TP).

If you report a TP value, whether accepted or OOT, you have no data to determine what to do. (Unless you report coordinates of the TP and in many cases differ due to the construct of a TP).

The majority of our partners (partners I have worked with) want the Basics for stack up analysis.

I can calculate any TP with accuracy from Basic value analysis and provide direct feedback for engineering departments.

It's a Win-Win.

[[Ch...]]

ok I'll chime in - how about the people that want the basics reported out separately, even thought they are clear and exact in the position results already ??

 

I'm willing to do it usually if the person is not that knowledgeable about GDT etc.

 

 

[[Ze...]]

The problem with reporting basic dims is what tolerance do you apply? They have none. Another problem is that depending on how the basics are applied to the drawing, they may or may not represent an actual value related to a datum. People will daisy chain basics hole to hole, etc. that don't represent the actual value to the datums called out. 

[[Lu...]]

What I typically do is put the basic dimensions on the report, but remove the tolerance and put a comment on there for what dimension that basic dimension is referencing, I believe this not only makes it easier on me in the long run (before people would often ask me why I'm leaving dimensions that are "easy to get" off the report) and it also will explain that these dimensions are references for a different dimension which can help in teaching people what a basic dimension is. Typically I put something like "REF for TP DIM XX"  (which means "Reference for True position Dimension XX", in the "XX" I would put the dimension number it goes to) It also helps the programmers to know which way to adjust.

Though, before I knew anything about GD&T I was told to follow the tolerance block for what tolerance to put on basic dimensions. Makes me facepalm every time I open an old program lol

[[Ja...]]

I typically have the basics reported as well. The actual data may not be transferred to our final inspection sheets that we supply to our customers but we do have the data saved in case we or they need to review something in more detail. It's also been said in this thread already but I find it really valuable to record basic dimensions on features for our in-process programs for our machinists on the floor so they can dial their programs in and make as good of parts as possible, it's easy enough to add them in and they are useful for making adjustments and proving CMM accuracy and repeatability to the occasional skeptic. Sometimes it isn't super clear what basics should be toleranced as but usually you can find constraints on the print through profile callouts, positional callouts, etc. that get you close to what the intent should be.

Where I have had some pushback on whether to report basics or not is when I am performing full first article inspections. One of our customers is kind of old school and doesn't like basic dimensions reported and I was told in more delicate terms that reporting them showed my ignorance of what a basic is when it comes to GD&T. Okay, that's fine and the customer is king (even when they are more of a court jester) and we make the parts to their print so I have no problem not providing that info to them per their preference, but I do keep it for my own records. 

[[Lu...]]

I report TED/BASIC actuals to:

1) show in which direction and how much injection mold needs to be tuned or

2) let statistics (Cmk, Cpk etc) to be monitored

[[Ro...]]

We have a few customers that require basics to be reported.  We argued with them that they are not needed as the GD&T covers them, but they still refused to budge and demanded basics being reported.

 

[[Jo...]]

ASME Y14.45-2021 

Mandatory appendix

Characteristic Identifiers(bubble) shall not be applied to basic dimensions for the following reasons:

 

and goes on for the rest of the page. I would start there

[[Jo...]]

The way to defend it is that there cannot be any actionable output from attempting to "measure a basic".  If you cant do anything if its out, what are you measuring it for?

 

 

[[Pa...]]

Please sign in to view this quote.

YES!!!

Because most folks I work with cannot deal with me quoting specifications, I've come up with a two-sentence answer for this request:

Basic dimensions are where you measure deviation FROM.  I can report basics if you'd like but they will be the exact same numbers you see in those pretty rectangles on the drawing.

🙂

[[Lu...]]

Please sign in to view this quote.

The way I understand it is the reason reporting basic dimensions can be useful is to show them what needs to be moved in what direction. Say you have a square part with a hole in the middle, and that hole has a true position attached. If that true position were to show out, it wouldn't tell the operator if it is too far up, down, left, or right, it would just tell them how far away it is from being in the center. If you report the basic dimensions (as in, the distance from 2 of the walls) they can then use those outputs to know which direction the hole is out, and know how to bring it back in the middle. I typically remove the tolerance on the characteristic and then add a comment to let them know that the characteristic I put in the report is just a reference for the true position. It also serves as an easy way to train a new operator so they can have a better understanding that basic dimensions don't have tolerances, they are just references for GD&T.

I am still pretty new to GD&T and CMM programing though, this is just what I have understood to be most helpful to both the setup guys and operators.

[[Ja...]]

Exactly. I’m not understanding peoples’ predilection for not wanting to report basics. It’s not going to hurt anything. In fact it does the opposite. As Luke mentioned, it helps anyone who reads the report. If the basics are showing as being in or out of print, you simply forgot to turn the tolerances off, that’s all. Anyone who is looking for the basics already knows how GD&T works. If they don’t, that’s an opportunity for you to teach them, not argue with them. It makes you and the report look better and also gives both more credibility. I personally have not had one single person, literally, say they don’t like seeing the basics on the reports. I can’t fathom a reason why, but if you don’t want to report the basics, that’s certainly your prerogative but I certainly wouldn’t recommend it. By not reporting, you’re just shooting yourself in the foot.

Sorry. I have a habit of getting up on a soapbox every now and then. Just trying to help.

[[Ma...]]

Please sign in to view this quote.

Basics should only be shown by using Additional Positional Result. The actual values based on the Base Alignment may not be the same when Position is applied, especially if the callout is to several datums and not fully constrained. The ability to have datum shift or datum mobility will alter the result. True it might be slight but when you are chaining a tight tolerance it matters.

Try this, take the actual in the report and calculate the position on a calculator, or app, then take the Additional Position Result actual and calculate the Position are you will see a difference.

[[Ja...]]

Thank-you Mark. I neglected to mention that. It's also a lot easier and faster that way too.

[[Te...]]

If you just turn on additional report they will show up in the report just not in the proper order this works for most GD&T prior to the new GD&T in 2025.  Profile no longer has support data.  I usually use a comment stating that X is Bubble ? and Y is Bubble ?.  Not sure right now how I would report support data for Profile and get it to match the value it is calculating correctly with the new GD&T engine.

Does anyone know if we can use PCM to get those values from the Position or Profile Characteristic it is just Characteristic actual

[[Jo...]]

Please sign in to view this quote.

This is the problem. You and the customer are conflating BASICS with WORST CASE measurements.

Basics are fixed in relation to FCF precedence

Worst case measurements are used to calculate Position,profile etc.

Additional report are the only sure way to get those because:

1. Alignment and Datum discrepancies

2. Depending on software, the measurement i.e  cylinder "position" can be to centroid, or origin . It is not guaranteed to be WORST CASE.

 

 

[[Ch...]]

Although I do agree that reporting the basics can be helpful, Most of the parts we make have hundreds of holes in them, and typically have wide open positional tolerances of like .014. I fall back to this, if the customer model shows all of the basics, then lets report them. If their model only shows the positional tolerance , then that's what we should give them. Unfortunately, our engineering and planning teams want them all included all the time. So, they give me a print with 200 dimensions bubbled that I then have to add the the program I'm writing, when we could have a print with only 35 dimensions to record. typically quadrupling my programming time. 😫