The MMC modifier with Position (Bonus Tolerance)
Вставка
- Опубліковано 28 сер 2024
- This video shows the basics of the MMC modifier with position tolerance in ASME Y14.5-2018. It includes the calculations of bonus tolerance.
This is a sample video from our GeoTol Pro 2020 online course per ASME Y14.5-2018
►► Check out our self-paced online GD&T course→ GeoTol Pro 2020: geotol.com/tra...
GeoTol Inc. is a full-service training and consulting firm on geometric dimensioning and tolerancing. Please visit our website for information regarding onsite training, online training, virtual training, consulting, books, pocket guides, DVD video, leader PowerPoint and model set packages.
www.geotol.com
#position tolerance #asme #asme Y14.5 #Y14.5
#GD&T #geometric tolerance #Y14.5-2018
The only video i watched and made me subscribe. Following to watch all the other videos.
The best explanation I ever seen on UA-cam
Dude you're a life saver
Wow you're the best person ever to have explained bonus tolerance in a short video with graphics and everything!! Finally the first video I understood bonus tolerance on and it stuck with me without confusion. Please keep these videos up!!
Glad you liked it!
Great explanation
I have watched a thousand of videos about MMC. Everytime I asked myself why the hell do we cut material more in maximum material condition. I finally understand it. thx.
This reduced the swelling in my head by 100% thank you 😂
As an engineer, I find it frustrating when GD&T explainers act like it is a good thing, a "bonus" when there is even more tolerance, due to the position /size variation. Sure, this is a good thing for the inspector, who can pass the part, and for the manufacturer, who can sell the part, but for the designer who wants the part to function perfectly, the 'bonus' looks more like a booby trap. I would like to see some teaching on how to devise GD&T specs from the standpoint of the functional designer who wants to hold very tight tolerances that fully function without causing too much expense.
You certainly don't want "bonus tolerance" everywhere. This MMC modifier has two strategic applications: clearance holes and qualifying datum features. Don't apply this modifier to a bearing hole, an alignment hole, or press fit hole.
There are two goals of a design engineer:
1. Make the part function
2. Maximize manufacturing tolerance.
And goal #1 is way more important than goal #2. Applying a position tolerance achieves goal #1. The MMC or LMC modifier is only for #2. (only when it doesn't affect goal #1)
This is only a short video showing the mechanics of the MMC modifier. If you can get more tolerance while not affecting function, then that's amazing (clearance holes for bolts). Look at some of my other videos for practical example parts and when to use this modifier.
Excellent video explaining MMC and Bonus tolerance
Thanks for making this video.. Before watching this video I didn't know where the tolerance (.010") originated from .
Thanks for your explanation. It is clear & your presentation is perfectly & easily to understand.
Thank you so much for your well explanation about MMC it's very easy to understand. God bless you..
Thank you,
Thank you sir❤
Thanks for the informative video!
yes departure from MMC does not sound fun 🤣!! I love your course and book!
I'm a huge fan of your videos, you blend theory and practice so well which makes it very clear at the end.
Also, what stylus and pad are you using?
Thanks for the comment! I use a usb writing tablet called a Wacom Intuos.
Great!!
You stated that LMC is discussed in another video. I can't find it, can you post a link? BTW, thanks for clarifying that MMC is used for assembly clearance *not* for locating the part. I'd love to see a discussion of how to use bonus tolerance to locate a part within certain limits. Thanks!
ahh, this is an excerpt from my online course. I don't have that video here. LMC modifiers are less common. It works the exact opposite--smaller holes are allowed more tolerance. RFS usually gets the job done without extra bonus tolerance.
What if the hole had a countersink. How do you treat the situation.
Countersinks often "self-center " the fastener. MMC modifiers may not be appropriate here.
Is that Bouns TOl Parts Applicable for Process Capability?
Calculating capability with a position tolerance zone and the added bonus tolerance is tricky because the allowed tolerance changes based on the hole size. There is another technique using the calculated virtual condition (MMC hole minus the position). This is a fixed boundary that the hole must not violate. Then measure how close the hole surface gets to the boundary (calculated RAME). Here is a related video for that: ua-cam.com/video/HSx7ofsad1k/v-deo.html
One question: I do not understand why the MMC of the hole cannot be reduced if the position is better than the diameter .01?
Or: What is a functional reason for the specification of a position tolerance bigger than zero?
If the fit function is specified with position tolerance zero, it would be much simpler to use a profile tolerance, isn’t it?
The use of MMC is based on ideas for a manufactoring specification like milling.
But: A specification coming from design shouldn‘t define the manufactoring process. For example: A profile tolerance would match the needs of additive manufacturing…
A MMC-specification can describe „What manufactoring should deliver“. A specification „How is the manufactoring prozess running“ will define the holediamter near at minimum material.
I‘m afraid: It is so difficult to manage the game changer „maximum tolerance at border of function“ instead of the well known manufactoring drawing.
A lot of questions and comments to unpack here.
You are right that any size and position tolerance at MMC could probably be edited to make the MMC equal to the virtual condition and use a zero at MMC. Watch my video on "using zero tolerance at MMC". However, the zero at MMC does not give many benefits for a drilled hole using a standard tool size. Zero at MMC helps manufacturing with turned, milled or additive manufacturing (processes that can easily target a different size). Zero tolerance at MMC allows a greater size tolerance.
Profile requires a basic dimension for the diameter. Then there is one profile tolerance spec for both the size and location. Profile creates 2 boundaries (MMB and LMB). This is not good for a bolt hole because the hole can get too big (the head of the bolt does not get the clamping pressure).
Position tolerance at MMC, on the other hand, creates only one boundary (MMB/ Virtual condition) Then the size tolerance controls the LMC size. This is why position at MMC is better for clearance holes for bolts.
Hope this helps.
Let's take a look at the product development process itself:
The verification of a specification with linear size (and ISO modifier GN or GX) plus position of the derived feature at the MMC provides a result that gives information about the functional gap between this real part and a virtual second part.
With the result of a verification based on a profile specification it is not possible to get an idea of how big the functional gap to this real part might be - only the question: "Is the (hopefully) functional specification fulfilled?" can be answered.
But: What is the required function? It‘s always the same: Without an explicit functional feature specification there are always long discussions while working with a given drawing.
If an initial specification from the development department is based on the "joint fit" function, both specifications are good.
However, in real life, this first specification is used for any later process. My solution for the famous function "joint fit": The geometric specification of the single part feature should be specified with MMS and position tolerance field zero at MMC. This simplifies the calculations for the fit and ISO 286 with „H“ or „h“ is very useful. For manufacturing issues, I offer the service of creating a nominal 3D CAD version with a nominal linear size according to their requirements (typically close to the minimum material size). Nowadays, with 3D CAD, this is not a big task. But when it comes to how the manufacturing process works, using MMC is not recommended.
There are a few more fits: "screw fit", "trunnion fit", "interference fit" ... they all require a suitable initial specification by the design department. For all these a profile tolerance is not suitable.
Sometimes, during long discussions about MMC for a joint fit, I‘m dreaming of profile tolerance. Keep it simple or not simple. And I‘m dreaming every day of a functional feature specification…
does bonus tolerances using the MMC modifier work in the same way when following the ISO/British Standard?
Yes, it works the same way even though ISO explains it differently. ISO 2692-2014 states the feature must not violate the MMVC (virtual condition) when MMR (MMC modifier) is invoked. This has the same effect; as the feature's size departs from MMC, it allows additional geometric tolerance.
I heard that, there's a thumb rule in GD&T that size tolerance should be more than the geometric tolerance. Is it correct?
I don't like that rule. It just depends on the application. Sometimes the size is very important (press fit) but where the feature is on the part is not important (big position tol). On a rotating shaft, sometimes the size does not matter but the coaxiality is very important (for balance).
@@GeoTolPro Thank you for your quick response..
For what reason a designer would want the position tolerance for a hole to apply RFS, why he/she would not want bonus tolerance
Depends on what the hole is used for
Agreed. Alignment holes should not use an MMC modifier. Press fit holes, bearing holes should be kept RFS.
Cast holes that need to be post-machined should not use MMC modifiers either.
do u have an example, at lmc?
I don't have a UA-cam video for it yet. LMC modifiers are not as common. They give bonus tolerance as the hole gets smaller. Its a good modifier for cast holes where a bonus position tolerance could be helpful for manufacturing and the outer boundary still matters.