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The original purpose of GD&T was to reflect the features function and relationship to its mating part. Over a period of time that seems to have fallen apart and many designers place GD&T on all features. In your situation, I probably would use co-ordinate tolerances on holes that had no...

First of all, datum A should be shown with a Profile of a Surface tolerance rather than flatness. Flatness is only used on one uninterrupted surface while the Profile of a Surface creates a common plane of which the 3 surfaces share. One would set up on the 3 surfaces with 3 solid jacks and...

I haven't replied for a while but here goes. The simple answer is yes but why isn't the 1.734/1.797 diameter shown as datum B?. The datum targets are great but datum B at a.797 is its maximum material size. Go for it but please show datum B as the diameter. Dave D. www.qmsi.ca

SeasonLee: I agree with your thoughts. We check roughness with a profilometer and flatness with a indicator. Dave D. www.qmsi.ca

Perpendicularity of a plane to a plane can be either all angle or all flatness or a combination of both. I have attached a example on how one should measure this requirement. Dave D...

Hi John (Powerhound) You are correct that a Go/No-go gauge is better but could you imagine, we would need 3 gauges for a tube. Form derived from Rule #1 does not happen yet many Designers here believe so much in Rule #1 that when they really need it confirmed on a feature they feel Rule #1...

Hi Evan: Could you give me an example how you would check form size in my example noted. Use tool room equipment or a CMM with computer control. I would appreciate seeing the difference in our methods. Thanks Dave D. www.qmsi.ca

DaSalo: To describe form size, let's take a 3.000 +/- .010 tube with and and ID. We have 3 features of size, OD, ID and length. You may take many readings on the OD and report that it is 2.996 - 3.002 but this is size. Form size is difficult to check but imagine that the tube has a .013 bend...

Yes, Evan, you are quite correct. Whenever there are sample submissions, a marked up drawing would travel with the samples to the Customer. On the marked up drawing, all dimensions are number for reference. The CMM Operator would have to assign 2 numbers for each dimension relating to a feature...

Designers seem to think that Rule #1 is widely understood in North American but people on the shop floor and most CMM Operators do not understand nor do they confirm form size. Every dimension is numbered on the drawing for referencing. If Rule #1 was understood, then each dimension covering a...

Jim: I agree that slots are clearance and the word "boundary" should apply when using positional. The virtual condition boundary will give us inner boundary shape, location and orientation. Love to see those profile hard gauges for a pattern of holes but I certainly can make a positional gauge...

Don't know why anyone would want to apply a profile (line or surface) on a pattern of slots. At least if you use positional at MMC, one can develop a checking fixture and truly check them simultaneously. Why profile rather than positional?? Dave D. www.qmsi.ca

No CMM? Need data for ISIR? I know that what I say will be tough but you can do it with a height gauge, indicator and great math to figure out the diametrical tolerance zone but it would be at best, provide a 60 - 70% confidence level in the result. Today, there aren't too many people skilled in...

Well, this is a mess. It is too bad that you could not convince the Designer that having positional tolerances at MMC since it will not hurt the integrity of the design. I have just got to see you gauge since it is not practical (nothing is impossible) to use a hard gauge in a positional...

pmarc: Interesting topic. Love to see, in real life, a RMB expanding gauge for 4 holes deemed as secondary datum. I think I know how Evan would set it up on a CMM and I know how I would set it up and it would not include all 4 holes. 2 holes as a secondary datum are OK in RMB but 4 holes - MMB...

Yes, the positional tolerance should reference datum A as shown. The positional tolerance to qualify datum B reflects the positonal of the holes to each other and perpendicularity to datum A. Your drawing, in my opinion, is correct to ASME Y14.5M-94. Dave D. www.qmsi.ca

Yes, CheckerHater, I have had experience in manufacturing and quality includng CMM. I wanted to reflect that something that may be legal may not be practical and it seems I have done so. You used the word "useless" and I agree. Dave D. www.qmsi.ca

CheckerHater: Again, ASME has tried to clarify a feature of size with the "Irregular Feature of Size" 1.3.32.2 but has it muddied the waters rather than clearing it. Using the ISO method and our regular feature of size using opposing elements (caliper mehtod), there is no question of what...

I agree that there is no "caliper rule" but it is a good "rule of thumb" in cases where we may have 1/2 a diameter or more, as an example. The definition of a Regular Feature of Size 1.2.32.1 states "two opposed parallel elements or opposed parallel surfaces" which a vernier caliper is capable...

dgallup: Your R & R study would go wild on most GD&T applications such as the flatness example unless there is a set documented measuring method including set up. If the application is considered "critical" then no more than 10% of the process or tolerance specification is allowed. On other...