Flatness measurement for restrained surface ??

[Madhu454]

Hi All,

I need your help to fix this issue.

Please see the attached drawing (Fig-1), it is a simplified drawing of a flange segment. 4 flanges of similar kind will be assembled to form a complete ring.

The question is , the datum feature C calls for a flatness control.
0.2 mm under restrained condition
10 mm under free state
The part needs to be restrained by a force upto 100N.

To restrain the datum feature C, datum feature C should be mated to a flat surface by a force equal to 100N by bolts or by other means. if we do so how to access the surface for the measurement.

As I know we can indirectly check the flatness of the datum feature C, by restraining the opposite face of the datum feature C, and dialing the datum feature C - if the value is less than the 0.2 then the part is accepted. if it is more than 0.2 then we cant reject the part since we need to consider the parallelism effect as well.

But How to measure the flatness by restraining the same surface??

Can anyone suggest a cost effective method to check this? or is it the drawing is Wrong? Please suggest me to fix this issue.

Supplier says the measurements are not practically possible. Also is it 0.2mm which is too tight for the part ??

Please suggest me.

unfortunately there is a error in uploading the file,

 

[CheckerHater]

Picture please?

 

[pmarc]

Madhu454,
Having a picture would be really great because without it too many assumptions have to be made.

My first very blind guess is that the flatness 0.2 callout could be applied in free-state because during fixation of the ring you are not affecting form of flange bottom surfaces but you are changing their coplanarity which was set to be within 10 in free-state (at least this is IMO the intent of the second callout).

If that was your intention, you have to change the symbol from flatness to profile of surface in the second FCF.

Really sorry in advance if I completely misunderstood the application.

 

[drawoh]

Madhu454,

Your drawing specification is a valid example of ASME Y14.5M-1994, section[ ]6.8.1, or of ASME Y14.5-2009, section[ ]5.5.1. A feature subject to free state variation is being controlled by fixturing.

We cannot comment on your inspection procedure without a picture of your part.

JHG

 

[Madhu454]

Hi,
here is the picture.

 

[MechNorth]

Madhu,
First, the composite flatness control MUST have the larger value on the top, with the smaller value being a refinement.
Next, assuming standard stock (i.e. reasonable quality as opposed to waffly), then you can try using gauge wire of 0.2mm and see if you can pass it under the edges anywhere. If you can, it fails ... not 100% checked, but maybe the best you can do, and it is commonly done with an acceptable risk.
Alternately, move the flatness to the FOS callout and make it at MMC so that you can hard-gauge it. Is the stainless steel magnetic grade? If so, use a magnet of adequate force to hold it down instead of an external clamp.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[Madhu454]

Hi Jim Sykes,

Thanks for the reply.

Sorry I forgot to mention, We use ISO GPS standards which is similar to GD&T. It allows to use the bigger value in the lower frame and smaller value in the upper frame. Please see the attached file.

In this can I use a guage wire of 0.2mm, after restraining the part as you mentioned. We use both magnetic and nom magnetic grade steels based upon the customer request, Drawing says 100N force to be applied to hold the part. can I use a magnetic table to hold the part.

 

[Madhu454]

Also If I use the datum feature C to restain the part, how Do I access the same surface for the dialing. If we want to check the entire surafce flatness.

 

[CheckerHater]

If you are not able to "dial" the surface, your another option is "feeler gage".

Basically you are trying to slide 0.2 mm gage underneath the datum [C]. If you cannot do it - you are good.

 

[dgallup]

Can you use something like the plastigage used to check bearing clearances? Basically you put a piece of the material in the gap, tighten down the bearing caps, unbolt the caps and measure the width of the material from which you can determine the gap.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[MechNorth]

dgallup,
I have had to measure features using a negative in casting compound (essentially what you are getting in your description). Depending on the grade of compound used, you can get significant shrinkage or lack of resolution. Doing non-direct measurement always adds error; how much is the first question, and the second is whether or not it's acceptable.
Madhu,
Tks for the illustration; if you could, please check if that is only applicable for use with a Free-State modifier, or if it is also allowed for a refinement per unit area. Tks.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com