GD&T question: Measuring basic dimensions

S

sept68

#1
There is an on going debate in my company about basic dimensions. Our engineering group has determined basic dimensions alone are not toleranced. Because nothing is theoretically exact, basic dimensions should be treated as reference. Bottom line - if there is a box around the print dimension, ignore it. Is that interpetation correct? ASME Y14.5.1M 994 is not really clear how to treat standalone basic dimensions not linked with GD&T.

I know there is later standard but my company hasn't forked out the bucks for the new one yet.
 
Elsmar Forum Sponsor

Stijloor

Staff member
Super Moderator
#2
There is an on going debate in my company about basic dimensions. Our engineering group has determined basic dimensions alone are not toleranced. Because nothing is theoretically exact, basic dimensions should be treated as reference. Bottom line - if there is a box around the print dimension, ignore it. Is that interpetation correct? ASME Y14.5.1M 1994 is not really clear how to treat standalone basic dimensions not linked with GD&T.

I know there is later standard but my company hasn't forked out the bucks for the new one yet.
I would love to have you guys come to my course! ;)

Basic dimensions are used to specify:
  • Exact location of a feature of size (True position)
  • Exact profile (Profile of a line - Profile of a surface)
  • Location of datum targets (area - line - point)

Because "exact" does not exist, there's always variation in any process, a tolereance will be provided to indicate how much variation is permitted.

For example: The true position of a feature of size, will be specified with basic dimensions (the "Bull's Eye" so to speak). The tolerance of position (see feature control frame - the box with all that fancy stuff in it) will specify how much variation is permitted from true position).

Some basic GD&T training is required.

In the mean time, look here.

Stijloor.

NOTE: I am not associated with this organization. For training, look at my personal profile.
 
Last edited:
A

alspread

#5
Stijloor is right!

Basic dimension do not have any tolerance by themselves.

If you have a basic dimension on your drawing with no accompanying GDT frame then it is likely to be a definition of a datum target (the place your fixture or set locates). Or the drawing is incorrect.
 

Jim Wynne

Staff member
Admin
#6
There is an on going debate in my company about basic dimensions. Our engineering group has determined basic dimensions alone are not toleranced. Because nothing is theoretically exact, basic dimensions should be treated as reference. Bottom line - if there is a box around the print dimension, ignore it. Is that interpetation correct? ASME Y14.5.1M 994 is not really clear how to treat standalone basic dimensions not linked with GD&T.

I know there is later standard but my company hasn't forked out the bucks for the new one yet.
In addition to Stijloor's good advice, it sounds like your engineers are using the "basic" box to create, in effect, reference dimensions. If a rational GD&T scheme is in use, the feature control frame controls the location or form of the feature in question, and it might be necessary to measure the basic dimensions (as in the case of position callouts, e.g.). The block tolerance should never be used to evaluate basic dimensions, and if your engineers are using pseudo-basic dimensions they're being lazy, and the dimensions in question are essentially uncontrolled.
 
D

David DeLong

#7
As mentioned here, basic dimensions are theoretical dimensions with geometrical tolerances shown in the feature control frames. They can also be used for locating datum targets (set up points) and chain lines (exact location of the applied geometrical tolerancing).

I do have the ASME Y14.5 - 2009 standard and it is exactly the same as the 94 and 82 standard relative to basic dimensions.

Here is problem that really blows people away when it comes to basic dimensions. How would one report positional tolerances reflected with basic dimensions? I spent a little time and came up with a web page shown at http://www.qmsi.ca/reportingpositional.html
I think it might help out.
 
S

sept68

#8
Thanks. I appreciate all of the responses. As inspectors we want to measure everything. Its hard to gloss over basic dimension when the actual does not even come close.
 

Proud Liberal

Quite Involved in Discussions
#9
You shouldn't be glossing over anything. Basic dimensions are used to validate part geometry as defined in feature control frames.

If there are features that have basic dimensions defining their location or orientation without an associated feature control frame, then the print IS improperly dimensioned. If, as previous respondents have postulated, the engineer is indicating basic dimensions as meaning reference dimensions, the print IS also improperly dimensioned.

Good luck, though, trying to get engineering to admit when they improperly draft things. "I've always done it that way." is their mantra.
 
P

Phil Fields

#10
Thanks. I appreciate all of the responses. As inspectors we want to measure everything. Its hard to gloss over basic dimension when the actual does not even come close.
Sept68,
Hello, have you, other inspector or the engineering department had training in GD+T? I think this would be a valuable investment for your company.

There are many companies that provide training. I know of company in the Western NY area that does public seminars and in-house training if required.

I organized such training in a previous company that I worked for. The Quality and Engineering departments had the training together, this worked out very well since both departments heard the same message.

I hope this helps,
Phil
 
Thread starter Similar threads Forum Replies Date
R CMM (Coordinate Measuring Machine) Comparison/Verification Question Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
R Machine Stability Question - Machine's measuring performance has tendency to drift Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 5
M Resolution question - Measuring a product on a CMM - the tolerance is .000/.001 Inspection, Prints (Drawings), Testing, Sampling and Related Topics 3
lanley liao Question regarding the calibration of monitoring and measure equipment. Oil and Gas Industry Standards and Regulations 0
C Gauge R&R Question Using Minitab Software 1
J IATF 16949 Internal Audit question - Auditor's responsibility Internal Auditing 6
K Question on MDR classification EU Medical Device Regulations 4
D Question on equipment - when to use reference only or research only stickers ISO 13485:2016 - Medical Device Quality Management Systems 5
D Work Instruction Question ISO 13485:2016 - Medical Device Quality Management Systems 5
M Clinical Decision Support Software Question 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 2
John C. Abnet VDA 6.3 - Question 7.3 - "blocking of parts" VDA Standards - Germany's Automotive Standards 6
D Approved supplier list - Distributors question ISO 13485:2016 - Medical Device Quality Management Systems 6
D Equipment Register and PM question ISO 13485:2016 - Medical Device Quality Management Systems 2
D Question regarding "storage and distribution" ISO 13485:2016 - Medical Device Quality Management Systems 1
D Calibration tolerance question using Pipettes Medical Device and FDA Regulations and Standards News 1
D Question regarding customer feedback process ISO 13485:2016 - Medical Device Quality Management Systems 3
D Equipment Register related question ISO 13485:2016 - Medical Device Quality Management Systems 1
S Study sign off question / responsibilities ISO 13485:2016 - Medical Device Quality Management Systems 3
S Qualification question - ISO 13485 - Setting up a small lab Reliability Analysis - Predictions, Testing and Standards 2
M Question for Auditors - "Off the Record" Conversation? General Auditing Discussions 14
D Question regarding ECO process, specifically for Life Science products and defining form fit and function ISO 13485:2016 - Medical Device Quality Management Systems 1
R Accelerated Aging - Creating test samples - Implantable medical device Question Other Medical Device Related Standards 4
A Question on Authorized Representative in Malaysia Other Medical Device Regulations World-Wide 3
D Limited Scope for second site Question? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 5
I ISO 2233:2000 Question - Medical Device Shipping/Transportation Validation Other ISO and International Standards and European Regulations 1
Anonymous16-2 Labeling Question (Dietary Supplements/Food) Pharmaceuticals (21 CFR Part 210, 21 CFR Part 211 and related Regulations) 1
T Question for: Cg & Cgk calculation General Measurement Device and Calibration Topics 3
N ASL Question for GitHub ISO 13485:2016 - Medical Device Quality Management Systems 6
hogheavenfarm GDT Flatness measurement question Inspection, Prints (Drawings), Testing, Sampling and Related Topics 10
A Question on ISO 14001:2015 - Are annual audits required? ISO 14001:2015 Specific Discussions 11
dinaroxentool Question about FDA Classification of a Device 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 3
J Another DFAR question 252.225-7009 AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 0
F Conflict Mineral Smelter Question RoHS, REACH, ELV, IMDS and Restricted Substances 8
R NRTL - Scope Question - Off-the-Shelf Plug In IEC 60601 - Medical Electrical Equipment Safety Standards Series 0
D API 6A Certification Question Oil and Gas Industry Standards and Regulations 4
dinaroxentool Question about qualification as a medical device or accessory in Europe EU Medical Device Regulations 2
R DHR question: Traceability of components ISO 13485:2016 - Medical Device Quality Management Systems 2
C MDR - Question around software accesories EU Medical Device Regulations 2
K My question is, what/when is a nonconformity? Therefore what requires an NCR? Nonconformance and Corrective Action 9
Watchcat Authoritative References about the Research Question? Quality Tools, Improvement and Analysis 0
T Question about Quality Department employee position titles Quality Manager and Management Related Issues 10
N Question on creepage/clearance requirements for HF Active Accessories for 2nd edition 60601-1 IEC 60601 - Medical Electrical Equipment Safety Standards Series 1
J Question: How to create an IMDS RoHS, REACH, ELV, IMDS and Restricted Substances 3
K Question on whether IEC 60601-2-62 standard is applied IEC 60601 - Medical Electrical Equipment Safety Standards Series 4
B QMS question in regards to multiple medical devices/products and N/A activities Other Medical Device Related Standards 12
C NB approval - Basic question about Notified Bodies and their role EU Medical Device Regulations 10
G Question about Non-conformances during New Product Introduction Nonconformance and Corrective Action 14
F ISO 13485 8.2.3 Reporting to regulatory authorities: Question regarding a procedure for this clause. ISO 13485:2016 - Medical Device Quality Management Systems 4
O Mitutoyo Digital Caliper to PC USB question General Measurement Device and Calibration Topics 2
R Probability - Need a help to solve the below question Statistical Analysis Tools, Techniques and SPC 5

Similar threads

Top Bottom