Flatness Tolerance - How to apply and measure

This video shows everything you need to know about flatness tolerance in ASME Y14.5. It includes proper applications and functional uses. It also has demonstrations on how to inspect. Per unit area flatness is also covered.
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#profile tolerance #datum #datum feature #asme #asme Y14.5 #Y14.5
#GD&T #geometric tolerance #Y14.5-2018

[@nickp4793]

Great overview! Very clear demonstrations. Thanks.

[@ajeshgeorge2202]

Thank you for the video. It's very helpful. Keep posting such contents. Wish you good luck...😉

[@SuperJJ37]

Really good explanation, keep up the excellent work!

[@QwertyCanada]

As always a great video.

[@mscscambodia]

You need to have the part mounted on three points on the surface plate (gauge or 1-2-3 blocks) for flatness as 3 points make a plane, see GD&T Y14.5-2018 setup processes.

[@GeoTolPro]

The video mark 6:06 explains the three gage block method. However, this is a terrible way to check sheet metal or a large heavy part (gravity causes the part to sag). ASME Y14.5-2018 does not define how to measure tolerances! It only defines the theoretical tolerance zone. The part's quality plan defines the inspection method based the situation (risk vs. cost analysis). That's what the video is about.

[@mscscambodia]

Two points is never acceptable, putting on the surface plate is not flatness check, part will be reject by any metrologist if this is how you set it up for flatness. @@GeoTolPro

[@mscscambodia]

The risk is you put a company out of business for what you are showing as a way to check the parts for flatness, not worth it.@@GeoTolPro

[@surendranagdali6788]

Thanku sir

[@kreeskalay7042]

Great video

[@stringmanipulator]

very clear and informative video 😁👍

[@nikhilfci]

Thank you sir

[@ud4458]

It is my goal to learn GD& but so many caveats and definitions and interpretations makes my head spin. Difficult subject, great video!

[@GeoTolPro]

Yes, there is a lot to learn with GD&T. Its just like learning a CAD system. It ranges from casual users of the program who can make a few simple parts all the way to the experts who can model the most complex assemblies. Good luck and keep at it!

[@ganeshshenoy2615]

And just when you think you get it, one query can throw you off.

[@mahanteshhindiholi432]

Great explanation! Could you also explain the difference between regular flatness and a flatness with CZ? How the tolerance zones would be in these two cases?

[@GeoTolPro]

Flatness "combined zone" is an ISO-GPS concept. The CZ modifier locates the flatness tolerance zones together to also control location between the surfaces (usually to control coplanarity). ASME would instead switch to a profile tolerance to control location between multiple surfaces.

[@mahanteshhindiholi432]

@@GeoTolPro Understood. Thank you very much!

[@ashow13]

Seen scenarios where large plates get stacked directly onto one another and slide/shuffle around during shipping and are left with scratches. Usually parts are still functional even though they would fail a flatness check because of a scratch. How would you specify that indented scratches/gouges are allowable on let's say 5% of the surface as long as the other 95% of the surface is flat within the specified tolerance zone? Add a note on the drawing?

[@GeoTolPro]

There is nothing in Y14.5 like that requirement. A note sounds like the best method here.

[@jasperamsing]

Hey thanks for this explanation! Question 0:15: Is there a difference for the manufactured part to inspect if you: 1) Datum A onto the flatness callout itself (like in the video), or if you put: 2) Datum A on directly the surface Does it matter or is it actually the same? Thanks :)

[@GeoTolPro]

No difference there. The surface must be flat. Then it is also named "datum feature A". Personally, I like to have the symbols together.

[@adithyaasrinivaas1445]

in the starting, does flatness of 0.1 means it is controlling Ra(Surface roughness) or Ra is further refinement of flatness. Size->Flatness->Ra ??

[@GeoTolPro]

Surface roughness is a much smaller scale than flatness. It is a localized peak to valley. Surface roughness also applies to curved surfaces where flatness does not. Not sure I would call roughness a refinement, its just a totally different jurisdiction. But geometric tolerances do control "all elements" of the feature.

[@forrestgumpv9049]

Try that on a 2.0 wide flange that is 333.5 diameter.

[@GeoTolPro]

Sounds like a good one for a CMM!

[@ajtroglio5248]

Umm...I don't think adding some random size shim under a side @4:40 gets you to correctly measure flatness. All you're doing is adding another unknown 'parallel' surface to the mix. To measure flatness of that part I was taught to turn the surface to be measured upside down and support the part at tool points spaced as far apart as possible to limit their effects, like shown at 6:15. Showing the method at 4:40 I think is misleading but I'd like to hear the reasons why it's not.

[@GeoTolPro]

There is never a "perfect way" to measure flatness. Instead, there are different levels of risk vs. cost. Feeler gage check for flatness is common for large plates with say a 2mm flatness requirement. Feeler gages are cheap and quick way to verify this. However, feeler gages would be terrible for a machined part with a 0.05 flatness. A more precise (and expensive) measurement with a dial indicator (or CMM) would be needed.

[@GeoTolPro]

Also, supporting off tool points would not be good for a heavy part or sheet metal that sags under its own weight. Again, there is no perfect way to measure flatness. There are different techniques for different scenarios with the need to balance risk vs cost.