GD&T example: 2 parts with datums, position, and profile tolerance
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- Опубліковано 23 лис 2024
- This is an example clip from our GD&T course called GeoTol Pro 2020 updated to ASME Y14.5-2018. This video shows how to select datum features. The datum features are qualified with flatness and perpendicularity. There is application of position and profile tolerance with basic dimensions.
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Thank you for your videos, I bought the GeoTol Pro fundamentals book and it's very informative.
3:30 When you talk about the counter bore doing the locating, how do you determine the position of the original hole? Would it depend on the application?
Like in the case of the gearbox:
- the 0.550 +/- .005 for size, and .015 for position, then .002 for position tolerance for the bore
- Where in this case the max positional distance would be .034, taking into account position tolerances of both gears and their bores?
- So, the amount that the working depth could change for the gears is .034 inches?
- According to these drawings, this is the design intent that's being communicated?
- In terms of center spacing and tooth interaction distance for the 2 gears?
Awesome, glad to hear. Yes, depends on the application. If it is a clearance thru hole, then the position tolerance is dependent on the clearance between MMC shaft and MMC hole. If there is a seal there, then it may need to be tighter.
Thank for the information on GD&T
Could datum B be a positional tolerance instead of a perpendicular tolerance? what would be the difference between the two?
If Datum B and C are at MMC, would they not also be at MMB when they are called out on feature control frames?
Position and perp would be the same on this example. The hole B is 90 degrees to A so it cannot be located. The position would only control perpendicularity. I'd advise to say-what-you-mean and keep it simple with a perp instead.
The material condition modifier (MMC) on the perp is completely separate from the material boundary modifier on the datum feature reference.
Do you want to allow bonus perp as the hole gets larger? YES (add MMC modifier)
Do you want to allow datum feature shift when evaluating other features? NO (keep it RMB)
@@GeoTolPro thank you, love the channel thanks for all you guys do
Great 👍
If possible,pl make video on datum shift condition MMB,LMB
你好
You explained very well. But why perpendicularity is used at Datum B and C, please explain.
Because datums provide the origin of the other features, they need to be qualified. By that, we mean that we need to quantify their relationships to one another. In this example, [A], as the primary datum, is qualified with a form control (flatness). [B], as the secondary datum, is qualified with respect to [A] with an orientation control (perpendicularity). Finally, [C], as the tertiary datum, is qualified to [A|B] with another perpendicularity GTOL (note: position is used in the first example which controls location and orientation of the slotted feature). Hope this helps.
What would you do if do if datum C was an inch below datum A? Would any variation of the hole in Z be anyway included in the calculation of where the hole is? Or is it just the deviation from the 4.600?
No the Z height doesn't affect the measured value. The tolerance zones must be rotationally aligned to that primary datum A plane. The perpendicularity of the datum feature C axis does affect the measured position tolerance value however.
@@GeoTolPro What if C nominally isn't perpendicular to A?
do we need to put basic (box on) dimensions if we are applying GD&T what is the rule?
Dimensions shall be basic when the features are located with position and profile. A dimension can be made basic with either a box around it or a note. (A note is used in this drawing) See Y14.5-2018 section 5.1.1.2
How can be sure the location of datum C ? If there is any deviation on Datum C according to the horizontal axis , how can we verify other features then?
There is a position tolerance on datum feature C to control it left/right. The datum ref frame origin is not set by C. The datum feature B hole sets the origin. The datum feature C only constrains rotation (clocks it rotationally).
Oh, and the datum feature C can never be "off" in the up/down direction. It sets the datum! The datum planes always pass thru that feature wherever it may be. Therefore can not have a Y deviation (except for perpendicularity).
Good one...
Can we give lose tolrance to datum than position control ?
Usually datum features have the tightest tolerances on the part. (Your leaders should be better qualified than the followers)
why are these not included in the cad design, let us say cad would give a minimum and maximum configuration, andjust check the interference (i am a solidworks user)
Dim Expert and Tol Analyst within Solidworks does a good job of reading your GD&T and looking for stack up issues.