One of the finest short explanations for using "GD&T" as a product or tool designer. Thanks for the great effort! The standard applied to all as a designer, shop-floor technologist, automation-technician or a user of CAD prints! T J (Tom) Vanderloop, Author, Technology-Instructor; ATEA, AWS, & SME Leader/Memberships
Hello Tushar, Thanks for your comment. We are glad that you like the video explanation! All of the GD&T Symbols are available in our Online GD&T Fundamentals Course. Please feel free to check it out: www.gdandtbasics.com
11:06 mark - typo on the "faster and more CONSISTENTLY inspected"... says "constantly inspected"... Aside from that, a perfect explanation of how true position works and the benefits of using it!
I have a different line of thinking. To start with, the co-ordinate dimensioning and tolerancing system with +/- bilateral tolerances, is not suitable in case of controlling the position of some cylindrical hole or bolt under fitment. It is simply because of the circular cross section of the circular cross section of the parts. At your illustration, if any hole centre gets dislocated to the corner of the square 0.1 × 0.1 mm, then the resultant dislocation becomes 0.707.mm radially. Here, if the corresponding bolt is at true position, it shall result into a guaranteed fouling of 0.207 mm; which will deny the fitment. Modifying such square zone to a superscribing circular zone with 56%more area, is further illogical. In short, at any ID/OD fitment, the tolerance zone has to be circular, of a size equal to the gap between the OD/ID at MMC. Then all fitments shall be assured which can be the principal aim of the designer. Making the production easier and economical can be perhaps the secondary aim. Your comments please.
Thanks for your comments! When designing for fitment between two cylindrical features, both can be designed to allow the virtual condition of the OD to match the virtual condition of the ID. This will ensure fitment. Check out our video on virtual conditions. www.gdandtbasics.com/virtual-condition-mmc-or-rfs/
Perhaps l was not able to clarify my thinking in appropriate manner. We agree to the statement that the +/_ tolerancing system is not suitable to control the position of any hole within a group. My different line of thinking is about the REASON behind the statement. 1. Though not mentioned at the video, the +/_ 0.05 tolerance for the coordinate dimensions like 40, 45 etc; are due to the available clearance between the bolt and hole size. Some +/_ 0.05 tolerance shall be due to the bolt being smaller than the hole nominally by 0.1. The +/_ position tolerance basically depends upon the available nominal gap between the hole and bolt. 2. If the function of fitment of the parts is agreed upon, then it becomes obvious to avoid the fouling between the bolt and hole. This can only be done by allowing the hole to have a max RADIAL dislocation of 0.05 (assuming the bolt at its true location). Crossing the limits means fouling. In my opinion, this is the reason. 3. If the fitment doesn't allow any dislocation beyond 0.05 radially, then all dislocations beyond but within a circular zone of 1.414 diameter automatically get disallowed. Hence modifying disallowed 0.1 × 0.1square zone to a circular zone of 1.414 diameter is, in my opinion, meaningless. Please correct me if I am wrong anywhere.
Thanks for the question! In the earlier part of this video (around 5:30) we explain that the equivalent diametric tolerance to a ±0.005 tolerance is found by using the Pythagorean Theorem. This means the equivalent diametric tolerance is one that is created by a circumscribed circle around the original square tolerance zone.
@@Gdandtbasics Oh, in the video (8:40 min) you say ".05" which means 0.05mm. Which is 0.1/2=0.05. That makes sense. To reiterate, it's the wording that confused me. Because in another printed learning resource someone also gave a value of 0.5 instead of 0.05 as I would expect. So I didn't know whether it was an error or I was just not getting something about the tolerance zones. (The confusion was causing pulling out my hair!) Thank you for your answer. And for the great learning resources!
Hello Cory - Thanks for your question - Sorry for the delay in our reply. To answer your question: No. The reason for this is that coordinate dimensioning leaves “a lot” open to interpretation. Coordinate dimensioning does not use a Datum Reference Frame and therefore, does not explicitly tell Quality how to constrain the part and take measurements. Position tolerancing will ALWAYS give more tolerance over coordinate dimensioning while still maintaining the functional requirement. The features will not get more “sloppy” since we are simply converting from a square tolerance zone to a round tolerance zone. Hope this helps! GD&T Basics Team
Hey Mohamed - Thanks for your question, sorry for the delay in our reply. It really depends on the drawing and the Datum Reference Frame. In most cases, the Primary Datum Reference is establishing orientation only (perpendicularity), so the Secondary datum feature (and Tertiary) are establishing the location of the tolerance zone. If the Primary datum feature is establishing a perpendicularity orientation requirement, the Secondary datum feature can only establish a location requirement and not an orientation requirement. Hope this helps! GD&T Basics Team
Could you explain the bonus tolerance position when the feature is in the maximal condition? I work in an automotive industry and we have a lot of problem to interperate this part. Thank u
Hello Alexis - Thanks for your question, sorry for the delay in our reply! If we see the MMC modifier present after the position tolerance, it means that we will get that position tolerance when the feature is at its MMC size (meaning that we do not get any “bonus” tolerance). However, once we depart from MMC towards LMC, we get that incremental departure (within the size limits) from MMC in the form of “bonus” tolerance. If a size dimension had a tolerance of ±Ø0.5, the maximum “bonus” tolerance available would be Ø1. Hope this helps! GD&T Basics Team
There is no actual "true position formula". It's just the "hypoteneuse" of a triangle with equal legs of the coordinate tolerance. Example: The linear coord tolerance is .005 in both vert and horiz. The true position tolerance = diameter = hyp of triangle with (.005 + .005) leg vert and (.005 + .005) leg horiz. Using pythag theorem: Hyp = .0141 = diameter of the true position tolerance diameter zone. If you're an engr you will get that, if you are machinist use √2 x legs of a 45 degree triangle rule of thumb.
I would dimension the final "correct" example differently - holes should not be measured in chains, in my opinion. I know they are basic, so "perfect", however at some point you would produce a chain of 10 basic dimensions, which are not so round and easy to add for a machinist, so a mistake is possible and it takes more time to produce definietly. Example: [88]+[17]+[22]+[24]. They are all basic, but what's the distance of the last hole from the datum? (imagine you are a production worker). I would use parallel or running, instead.
Thank you for your comment. what you're suggesting would be considered a "bad practice". Having Chain Dimensions that are BASIC does not produce any kind of tolerance stack for the location of the tolerance zone(s). Aside from being an engineer, I am also a machinist. As a machinist, I must know/understand that when it comes to Position tolerancing (regardless of how it is dimensioned on the drawing), all measurements come from the Datums (Datum Simulators). It is a fundamental rule of Position tolerancing. Remember that Position tolerances are for the TOLERANCE ZONES and they are located at TRUE POSITION. TRUE POSITION does not/cannot move. NEVER! Now, the "as is" machined part will have holes/features that do move. This is different. As a machinist, I will measure these "as machined" features and see if they fit within its respective "perfect" cylindrical tolerance zone. I hope this helps clear things up! Thanks
@@Gdandtbasics I understand that chain of basics does not produce tolerance stack ups. my point was quite different. imagine you have to machine a shaft on a lathe. there are basic dimensions in a chain and their values are not so easy to add up (i'm an engineer too, but most of machinist are not) each time you start another cut, you need to add previous dimensions to the current one, i.e. 1st - 88mm, 2nd - 105mm 3rd - 127mm, 4th - 151mm (values as in my first comment). you are wrong by 1mm in the 4th cut and the part is destroyed. now imagine they are like [187.83] + [236.64]. tolerances are not changed, but you have to add those numbers in the process, as the lathe measures your knife's position from the original 0, and i think it may be quite challenging (i use ISO and I don't think that chains of basics are correct there)
Thanks for the question! If it is a pattern of holes being controlled with position that is subsequently used as a datum feature its best to attach the datum feature symbol to the position feature control frame. This indicates the use of the pattern of holes as a datum. If you wish to use a single cylindrical feature as a datum feature you can simply attach the datum feature symbol to either the surface of the cylindrical feature or directly attached to the leader arrow of the size dimension for that feature.
Hello - Thanks for your question, sorry for the delay in our reply! For an external feature we will take the MMC size and add any applicable geometric tolerance at MMC. For an internal feature, we will take the MMC size and subtract any applicable geometric tolerance at MMC. Hope this helps! GD&T Basics Team
How to achieve true position of holes?? if there are 4 holes which are pre casted and there is variation in position of each hole what to do in this case??
Hello Vrushali, Thank you for your question. This should not be an issue. Remember, the tolerance zones for position are perfectly located and oriented to the DRF (Datum Reference Frame). However, the features themselves (the as cast features) will not be perfect, but the respective axis must “fit” within the specified tolerance zones. Hope this helps! GD&T Basics Team
I do apply GD & T on my drawings however isn't GD & T more suitable for mass production OR parts made overseas? This way they will definitely fit or rather few rejects. If they were made in-house or locally then any part/feature discrepancies could be rectified within a few hours - if that time is permissible in a project of course. They've always complained about the time required to apply GD & T and are unable to realise the benefits of the end result.
Once the confusion is overcome and "actual go/no go gauges" are made and sent to the supplier it becomes a no brainer. However, to get to the point could be a headache.
At the end of the day there will be countless visits to the customer while you have to educate them on how gdt works . And you end up losing money . As a rule when you see these call outs make the best part you can. And be afraid.
...and engineers that design parts and see that 'true position' option, and decide 'hey! I'll just use that, so they put my holes where I want them! Let's see... I'm running this part with most dimensions at +/-.01, with a few less important ones set to +/-.03... hmm, I want these holes in a good place, so true position at +/-.01! Perfect! Ok, send this to the machining shop, and I don't want to hear any whining. They should be able to make it just fine!' Pay no attention to the fact that an a/b/c true position callout for the holes often will render their 'easy to make' +/-.03 tolerance dimensions to be forced to a +/-.002(or less) to remain in relation to the called position, because if they are outside that distance, the true position falls out of the +/-.01 callout, when the engineer ACTUALLY only wanted the holes to be +/-.01 from the datum, but now that it reads 'true position', well...MAKE it that way. You called it exactly: Make the best part you can, and be afraid. Because engineer intent means nothing compared to the anal-retentive inclination of their receiving QA department... Gods. I HATE when I see a true position callout...
![[MV] A leap of faith...ความเชื่อใจครั้งสุดท้าย (From "Petrichor the series")](http://i.ytimg.com/vi/U1piZH2CNXA/mqdefault.jpg)
there are many yt vids that failed to explain it. finally, I can sleep peacefully.
One of the finest short explanations for using "GD&T" as a product or tool designer. Thanks for the great effort! The standard applied to all as a designer, shop-floor technologist, automation-technician or a user of CAD prints!
T J (Tom) Vanderloop, Author, Technology-Instructor; ATEA, AWS, & SME Leader/Memberships
Finally the video explaining the GD&T that is worth watching. Thank you.
Thank YOU!
Bloody fantastic. Explains in basic english. Every position and a good example is shown. This channel is so helpful.
after 5 years of development experience today i got know what it is really meant for..thanks for the video guys
Hahaha same here....
Very good explanation.
Please keep uploading videos.
You guys are exceptionally good.
Very very deeply explained... thanks sir.
this video is so informative. It cleared all of my questions about datum setting.
Excellent Video-Thanks!
Thomas J. Vanderloop, CMfgE, LSME & AWS Member
Super clear video, thank you
good concept sir, Thanks
Welcome!
what an excellent video
Thank you for sharing this! It's so clear and explanatory by bar. Saving & getting subscribed.
Excellent video - Explained really well .
Dear sir,
Please upload videos for all gd and t characteristics and concepts like this by your deep knowledge... waiting for it.
Hello Tushar,
Thanks for your comment. We are glad that you like the video explanation! All of the GD&T Symbols are available in our Online GD&T Fundamentals Course. Please feel free to check it out: www.gdandtbasics.com
Thank you! Par exellence video!
11:06 mark - typo on the "faster and more CONSISTENTLY inspected"... says "constantly inspected"... Aside from that, a perfect explanation of how true position works and the benefits of using it!
Dave Perkins hey, do you work at GM?
OmaRi, I do not.
Oh I seem to remember your name on a GM dimentional report with your name.
OmaRi Must be another guy.
more videos like this. they aew very useful for us. if you can add subtitles, it would be great.
thx
Such an amazing explanation
Glad you liked it
THIS MIGHT SAVE ME IN MY 3351 MANUFACTURING CLASS
Very helpful
Great video!
Neat explanation. Thanks!
Thank you for explaining this.
Please make video on symmetry
Thank u very nice video
I have a different line of thinking.
To start with, the co-ordinate dimensioning and tolerancing system with +/- bilateral tolerances, is not suitable in case of controlling the position of some cylindrical hole or bolt under fitment. It is simply because of the circular cross section of the circular cross section of the parts. At your illustration, if any hole centre gets dislocated to the corner of the square 0.1 × 0.1 mm, then the resultant dislocation becomes 0.707.mm radially. Here, if the corresponding bolt is at true position, it shall result into a guaranteed fouling of 0.207 mm; which will deny the fitment. Modifying such square zone to a superscribing circular zone with 56%more area, is further illogical.
In short, at any ID/OD fitment, the tolerance zone has to be circular, of a size equal to the gap between the OD/ID at MMC. Then all fitments shall be assured which can be the principal aim of the designer. Making the production easier and economical can be perhaps the secondary aim.
Your comments please.
Thanks for your comments! When designing for fitment between two cylindrical features, both can be designed to allow the virtual condition of the OD to match the virtual condition of the ID. This will ensure fitment. Check out our video on virtual conditions.
www.gdandtbasics.com/virtual-condition-mmc-or-rfs/
Perhaps l was not able to clarify my thinking in appropriate manner. We agree to the statement that the +/_ tolerancing system is not suitable to control the position of any hole within a group. My different line of thinking is about the REASON behind the statement.
1. Though not mentioned at the video, the +/_ 0.05 tolerance for the coordinate dimensions like 40, 45 etc; are due to the available clearance between the bolt and hole size. Some +/_ 0.05 tolerance shall be due to the bolt being smaller than the hole nominally by 0.1. The +/_ position tolerance basically depends upon the available nominal gap between the hole and bolt.
2. If the function of fitment of the parts is agreed upon, then it becomes obvious to avoid the fouling between the bolt and hole. This can only be done by allowing the hole to have a max RADIAL dislocation of 0.05 (assuming the bolt at its true location). Crossing the limits means fouling. In my opinion, this is the reason.
3. If the fitment doesn't allow any dislocation beyond 0.05 radially, then all dislocations beyond but within a circular zone of 1.414 diameter automatically get disallowed. Hence modifying disallowed 0.1 × 0.1square zone to a circular zone of 1.414 diameter is, in my opinion, meaningless.
Please correct me if I am wrong anywhere.
More lessons pleaseee
In the 8:40 min he says that Ø0.141mm equals to 0.5 tolerance. Where does the 0.5 come from? Can anybody explain this?
Thanks for the question! In the earlier part of this video (around 5:30) we explain that the equivalent diametric tolerance to a ±0.005 tolerance is found by using the Pythagorean Theorem. This means the equivalent diametric tolerance is one that is created by a circumscribed circle around the original square tolerance zone.
@@Gdandtbasics Oh, in the video (8:40 min) you say ".05" which means 0.05mm. Which is 0.1/2=0.05. That makes sense. To reiterate, it's the wording that confused me. Because in another printed learning resource someone also gave a value of 0.5 instead of 0.05 as I would expect. So I didn't know whether it was an error or I was just not getting something about the tolerance zones. (The confusion was causing pulling out my hair!)
Thank you for your answer. And for the great learning resources!
Is there ever a situation in which it would preferred to use coordinate dimensions instead of GD&T position for a tolerance zone?
Hello Cory - Thanks for your question - Sorry for the delay in our reply.
To answer your question: No. The reason for this is that coordinate dimensioning leaves “a lot” open to interpretation. Coordinate dimensioning does not use a Datum Reference Frame and therefore, does not explicitly tell Quality how to constrain the part and take measurements. Position tolerancing will ALWAYS give more tolerance over coordinate dimensioning while still maintaining the functional requirement. The features will not get more “sloppy” since we are simply converting from a square tolerance zone to a round tolerance zone.
Hope this helps!
GD&T Basics Team
Could you please explain, how secondary datum affects in GD&T position tolerance? Thanks in advance.
Hey Mohamed - Thanks for your question, sorry for the delay in our reply.
It really depends on the drawing and the Datum Reference Frame. In most cases, the Primary Datum Reference is establishing orientation only (perpendicularity), so the Secondary datum feature (and Tertiary) are establishing the location of the tolerance zone. If the Primary datum feature is establishing a perpendicularity orientation requirement, the Secondary datum feature can only establish a location requirement and not an orientation requirement.
Hope this helps!
GD&T Basics Team
Waiting for more videos
Keep it up
Could you explain the bonus tolerance position when the feature is in the maximal condition? I work in an automotive industry and we have a lot of problem to interperate this part. Thank u
Hello Alexis - Thanks for your question, sorry for the delay in our reply!
If we see the MMC modifier present after the position tolerance, it means that we will get that position tolerance when the feature is at its MMC size (meaning that we do not get any “bonus” tolerance). However, once we depart from MMC towards LMC, we get that incremental departure (within the size limits) from MMC in the form of “bonus” tolerance. If a size dimension had a tolerance of ±Ø0.5, the maximum “bonus” tolerance available would be Ø1.
Hope this helps!
GD&T Basics Team
What is repeatable measurement
Best
Very informative, but how would I solve something like this using the True Position Formula?
There is no actual "true position formula". It's just the "hypoteneuse" of a triangle with equal legs of the coordinate tolerance. Example: The linear coord tolerance is .005 in both vert and horiz. The true position tolerance = diameter = hyp of triangle with (.005 + .005) leg vert and (.005 + .005) leg horiz. Using pythag theorem: Hyp = .0141 = diameter of the true position tolerance diameter zone. If you're an engr you will get that, if you are machinist use √2 x legs of a 45 degree triangle rule of thumb.
just wow
I would dimension the final "correct" example differently - holes should not be measured in chains, in my opinion. I know they are basic, so "perfect", however at some point you would produce a chain of 10 basic dimensions, which are not so round and easy to add for a machinist, so a mistake is possible and it takes more time to produce definietly. Example: [88]+[17]+[22]+[24]. They are all basic, but what's the distance of the last hole from the datum? (imagine you are a production worker). I would use parallel or running, instead.
Thank you for your comment.
what you're suggesting would be considered a "bad practice". Having Chain Dimensions that are BASIC does not produce any kind of tolerance stack for the location of the tolerance zone(s). Aside from being an engineer, I am also a machinist. As a machinist, I must know/understand that when it comes to Position tolerancing (regardless of how it is dimensioned on the drawing), all measurements come from the Datums (Datum Simulators). It is a fundamental rule of Position tolerancing. Remember that Position tolerances are for the TOLERANCE ZONES and they are located at TRUE POSITION. TRUE POSITION does not/cannot move. NEVER! Now, the "as is" machined part will have holes/features that do move. This is different. As a machinist, I will measure these "as machined" features and see if they fit within its respective "perfect" cylindrical tolerance zone.
I hope this helps clear things up! Thanks
@@Gdandtbasics I understand that chain of basics does not produce tolerance stack ups. my point was quite different. imagine you have to machine a shaft on a lathe. there are basic dimensions in a chain and their values are not so easy to add up (i'm an engineer too, but most of machinist are not) each time you start another cut, you need to add previous dimensions to the current one, i.e. 1st - 88mm, 2nd - 105mm 3rd - 127mm, 4th - 151mm (values as in my first comment). you are wrong by 1mm in the 4th cut and the part is destroyed. now imagine they are like [187.83] + [236.64]. tolerances are not changed, but you have to add those numbers in the process, as the lathe measures your knife's position from the original 0, and i think it may be quite challenging (i use ISO and I don't think that chains of basics are correct there)
Thank you Sir God bless you :)
If you have a cylindric part that has holes on it with position feature, where do you place your datum feature?
Thanks for the question! If it is a pattern of holes being controlled with position that is subsequently used as a datum feature its best to attach the datum feature symbol to the position feature control frame. This indicates the use of the pattern of holes as a datum. If you wish to use a single cylindrical feature as a datum feature you can simply attach the datum feature symbol to either the surface of the cylindrical feature or directly attached to the leader arrow of the size dimension for that feature.
How to calculate pin gauge size from position tolerance
Hello - Thanks for your question, sorry for the delay in our reply!
For an external feature we will take the MMC size and add any applicable geometric tolerance at MMC. For an internal feature, we will take the MMC size and subtract any applicable geometric tolerance at MMC.
Hope this helps!
GD&T Basics Team
It's plain and simple in such a generic example. I'd love to see a similar explanation of some more complicated case :/
How to achieve true position of holes?? if there are 4 holes which are pre casted and there is variation in position of each hole what to do in this case??
Hello Vrushali,
Thank you for your question.
This should not be an issue. Remember, the tolerance zones for position are perfectly located and oriented to the DRF (Datum Reference Frame). However, the features themselves (the as cast features) will not be perfect, but the respective axis must “fit” within the specified tolerance zones.
Hope this helps!
GD&T Basics Team
@@Gdandtbasics Thank you
I do apply GD & T on my drawings however isn't GD & T more suitable for mass production OR parts made overseas? This way they will definitely fit or rather few rejects. If they were made in-house or locally then any part/feature discrepancies could be rectified within a few hours - if that time is permissible in a project of course. They've always complained about the time required to apply GD & T and are unable to realise the benefits of the end result.
Once the confusion is overcome and "actual go/no go gauges" are made and sent to the supplier it becomes a no brainer. However, to get to the point could be a headache.
So how do you persuade designers of low or no volume parts say weldment or some machined parts to use GDT?
Using calipers is not like using a random number generator.
At the end of the day there will be countless visits to the customer while you have to educate them on how gdt works . And you end up losing money . As a rule when you see these call outs make the best part you can. And be afraid.
...and engineers that design parts and see that 'true position' option, and decide 'hey! I'll just use that, so they put my holes where I want them! Let's see... I'm running this part with most dimensions at +/-.01, with a few less important ones set to +/-.03... hmm, I want these holes in a good place, so true position at +/-.01! Perfect! Ok, send this to the machining shop, and I don't want to hear any whining. They should be able to make it just fine!'
Pay no attention to the fact that an a/b/c true position callout for the holes often will render their 'easy to make' +/-.03 tolerance dimensions to be forced to a +/-.002(or less) to remain in relation to the called position, because if they are outside that distance, the true position falls out of the +/-.01 callout, when the engineer ACTUALLY only wanted the holes to be +/-.01 from the datum, but now that it reads 'true position', well...MAKE it that way.
You called it exactly: Make the best part you can, and be afraid. Because engineer intent means nothing compared to the anal-retentive inclination of their receiving QA department... Gods. I HATE when I see a true position callout...
So how do you persuade designers of low or no volume parts say weldment or some machined parts to use GDT?
For those interested in a handheld probe that measures hole location on the shop floor, check out th-cam.com/video/HrooZ1jfkT0/w-d-xo.html
I don't see this type of explanation
more videos like this. they aew very useful for us. if you can add subtitles, it would be great.
thx
Excellent suggestion.