Hey Dean, Just wanted to thank you for all the knowledge shared. There aren't much GD&T content creators, let aside quality. But your videos have helped me a lot while learning GD&T. I'm a designer and the part that I like the most is defining my part tolerances, and you've helped me improving on that. So thanks and keep the awesome work!
Thank you so much! I’m working on more content to address design in general. Choosing dimensions and tolerance and why certain decisions get made. I feel like some many textbooks focus on detail drawings, and ignore the importance of parts in an assembly.
Good for you to learn how to apply the correct, effective and only as much as is necessary tolerances. I'm a Senior Aircraft Machinist 45yrs. I have seen very costly tolerances applied unnecessarily and part design that did not consider manufacturing processes. Apply these things and you will at the top of your engineering dept.
@RDeanOdell : Just some constructive criticism, you're not wrong in any of your explanations/inspection-set-ups but theres some assumptions being made that are confusing other people. I feel you need to explain the different inspection methods and why you would use that set-up instead of other methods. Explain the need to take into consideration the maximum deviation tolerance and the accuracy/inaccuracies of the instrumentation being used. For example, as for the profile of a surface with a Basic dimension. If the basic dimension is 2" and the profile max deviation is less than .001", I would use a ten-thousandths indicator and a 2" gauge-block to set the height to reduce the instrumentation error and try to be as close to a 10:1 accuracy ratio as possible. Also, temperature is a big factor for high accuracy set-ups as thermal expansion varies from one material to another (aluminum having twice the rate of linear thermal expansion coefficient as steel). I know a lot of shops that dont have a temperature controlled inspection areas. Per ASME Y14.5, all dimensions need to be refenced back to 20°C(68°F). I hope this helps in future videos.
Hi Dean, I enjoy your GD&T videos very much. For the top flatness checking using HG, it looks like it cant be checked like that. Because you cannot assume the bottom surface is perfectly flat. We should use CMM instead, so that even the bottom surface is slanted by putting a shim under it, the CMM reading will always give us flatness measurement. Using HG to measure like in the video will actually gives us Parrallelism instead. Hope for your comment if I am wrong. Thanks a lot!
Hi, Thanks for leaving a comment. I agree that the check I did with the height gauge was checking for parallelism, but flatness is covered by parallelism. If the part failed that check, I would need to adjust the part to get the correct reading for flatness. With the part I checked, it passed flat on the table so there was no need to shim. I agree the CMM will give the flatness result much easier than on the plate. Thanks for watching. I appreciate your feedback.
If the part permits, I will check parallelism how you checked and then flip it to the other side and check parallelism again. If both side are within the flatness max deviation, then I don't need to go any further. In a fast pace environment, this works and is pretty accurate.
Thanks so much! I actually missed one common method of measuring flatness, which is to place the surface on 3 pins and sweep the surface upside down. This technique is faster, but the location of the pins has to be taken into account because they may lie in low or high points.
Would it be better when checking flatness and parallelism to have a digital device that recorded the dimensions as it is run over the surface… then when you press a button and it gives you the top number and the lowest number and subtracts them so you can easily see if it exceeded the tolerance?
Hi, there is such a device, I explain how it is used in this video: Starrett Height Gage Demonstration ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-hdeF75o0vKg.html
Hi, for parallelism yes. For flatness the part could be shifted to achieve the smallest reading between high and low readings. In either case the high and low readings represent the distance between parallel planes given the indicator runs parallel to the table.
Hi this is Balasubramani, can we apply straightness tolerance to feature of size other than the cylinder is possible? I have doubt in this, kindly answer if possible.
Hi, straightness applied to a feature of size is only explicitly shown for cylindrical features in ASME Y14.5. My interpretation is that it does not prohibit applying straightness of a derived median line to symmetric features other than cylinders.
Mr O dean the first mistake you are not using a proper granite surface plate and that laminated work top could be off by 0.25 mm to 1mm so all readings are off kilter.
Hi, I agree checking a part on a laminated work table is unacceptable. The table I am working on is a large starrett granite surface plate. It’s more clear in this video: GD&T: Inspecting Position Tolerance with Bonus Tolerance Calculation ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-PHrylNNgJb8.html
Hi Dean, Hope you're doing good.. Thanks for the videos. I have a query on the GD&T. Requesting you to clarify on the same please, 1. Is there any difference between the Profile with basic dimension with respect to Datum A and Parallel with basic dimension with respect to Datum A. Best regards, Nakul Shindhe
Hi, great question! Profile can control location as well as orientation form etc.. Orientation tolerances like parallelism do not control location, so specifying parallelism with a basic dimension would result in an incomplete requirement. There should be a plus-minus dimension, or a profile tolerance to control the location of the surface.
Don’t believe that’s how you check flatness. Thought that flatness would be checked by setting the surface on 3 1,2,3 blocks of the same height and run your indicator under the surface sitting on the blocks.
Hi, Thanks for watching. The way you mention is a valid technique. The technique I describe in the video is in accordance with the Handbook of Dimensional Measurement 5th Edition, Page 573 Figure 20-12.
The inside Handbook of Dimensional Measurement #5 has a publication date of September 2013 The industry standards over the past 50+ years have always been to use 3 point Jack's set up to zero, then place in a triangle to measure underneath your work to verify flatness. Then checking top of work to inspect Surface deviations, along with inspection of flatness you will have an idea of the parallelism of the 2 surfaces to help aid in determining the condition of your work you are inspecting. Even though not specified on the blueprint or feature control frame, as a good inspector, it is also wise to check the Engineers for critical errors in their process of Comprehending Blueprint tolerance and inspection techniques. We need to work as one in unison to maintain the integrity of the project.
Question, isn’t that parallelism when sweeping a surface on the granite stone. Wouldn’t this require a flatness plate……place your part on the plate, define 3 points of the inspected item where the 3 points read zero on your indicator…..::when all 3 points read zero then you sweep the component surface.
@mojo_n_sb5483 What you are referring to is a check of the underneath surface of a part. Using 3 jacks in a 🔺️ is the preferred method to sweep underneath your work surface. But after qualifying the bottom of your work piece to be in print, you can sweep the top. But keep in mind the deviations have to be taken into consideration when traveling a long distance of your work surface. The further you move out, the greater the deviations appear. Therefore, you have to take in consideration the feature control frame Material condition modifier to determine you +/- outlined by the engineers.
That procedure is incorrect for evaluating flatness. For the part you have in this example the surface in question needs to be inverted and supported by three pylons, that are identical in height, and resting on the surface plate. The inverted surface is interrogated with an indicator in the manner you described. Your demonstration was a measure of parallelism, not flatness, because the geometry of the opposing surface of that part will influence the reading on the indicator on upper surface. When the part is inverted and supported on pylons the geometry of the opposing surface will have no bearing on the measurement of the surface in question.
