GUAGE DESIGN FOR COMPOSITE POSITION CONTROL

[Madhu454]

Hi All,

I have question on designing a hard gauage to check the composite position called out for a 4 pattern of hole. Please see the attached drawing. For the part drawing dimensioned in left upper corner, I have designed a guage to check the PLTZF and FRTZF.

My question is if I include datum A in the lower frame of the Composite position control how the design of the hard guage will change ? (CASE 2)

If I include the datum A and B in the lower frame of the composite control how the guage design will change? (CASE 3)

If you see the present guage drawing for FRTZF (without any datums in the lower frame of composite position)the gauge pins are perpendicular to the bottom surface and as group the gauge pins are oriented to side faces (datum B and datum C).

Can any one please explain me how the hard guage will change for these two requirements. Please refer to the left bottom corner of the drawing. Really confused.

 

[pmarc]

1. If there is no datum reference in lower segment of the frame, only the spacing between gage pins is fixed. This means that the pins can be inclined at any angle with relation to bottom surface A within upper segment tolerance zone. Putting A in lower segment simply refines perpendicularity.

2.If A and B are in lower segment pattern perpendicularity to A plus pattern parallelism to B are refined. Without B pattern could rotate clockwise or counterclockwise within upper segment tolerance zone.

 

[fsincox]

Or to put it in another way, if no datum is restated in the FRTZF it means you can use a gage like your second gage but the face does not need to touch while ingaging the pins.
Frank

 

[dingy2]

The first gauge is similar in design to the example in ASME Y14.43 but the Operator would be checking datums B and C to the pattern of 4 pins rather than the opposite way as shown in the feature control frame. I would suggest that a part rest on datum A and butts up against datums B & C being held with toggle clamps. We have now set up to the reference datums as shown in the FCF.

On the datum A face of the checking fixture we have 4 pilot holes at true position. We have 4 pins of virtual condition size (9 mm)with a pilot pin attached to the fixture with a wire. All 4 positional pins must inserted in the 10 mm holes using the pilot holes. All positional pins must be inserted all the way into the holes and contact datum A face of the fixture for the part to meet the positional requirement.

I believe that there is an error in the FRTZF as shown in the composite feature control frame. Datum A should be referenced otherwise, it is correct that holes could be on any angle and not necessarily perpendicular to datum A.

I agree with the other comments about the composite feature control frames named case 2 & 3.

Dave D.

http://www.qmsi.ca

 

[SeasonLee]

The lower segment of case 1 does not reference any datums, it means the lower segment controls the spacing within the hole pattern only, the orientation (perpendicularity) is controlled by the upper segment. So case 1 callout (without any datum in the FRTZF) is correct, you may find out the application example and its explanation from Alex’s “Advanced Concepts of GD&T” in Fig.19-6.

If datums are not specified in the lower segment, the pattern (of the hole) is allowed to tilt or rotate within the confines of the upper segment, if the datums are specified in the lower segment, they limit the orientation relative to the specified datums.

As for the case 1 FRTZF gage design, there is no doubt that the gage pins are not fixed relative to the plate as Dave mentioned above, but I think the gage pins are fixed relative to Datum A on case 2 FRTZF, this is the difference between case 1 and case 2 FRTZF gage design.(please correct me if I am wrong here)

You need to pay more attentions on case 3 (references two datums A & B) FRTZF gage design, the basic dimension from datum B no longer applies, this is composite position tolerancing rules, basic dimensions that define location of the features apply to the upper segment only, the gage pins are located relative to each other by the basic dimension, but the gage pins are not fixed relative to datum B, the distance from datum B is not being controlled with the gage, so datum B plate should be designed on a movable slide base.

SeasonLee

 

[dingy2]

The gauge for the FRTZF as shown is valid only for condition #2 since it does reference datum A. Love to see a design for condition #1 for it FRTZF and the practical use of such.

The comment that I made was that I felt that the design of the gauge for the PLTZF is not valid. If we place the part on this gauge, we would end up checking to see if the sides contact datum B & C rather than if the holes are in position.

Dave D.

http://www.qmsi.ca

 

[Belanger]

Dave, if you'd love to see a sample of condition #1 FRTZF and its gage, simply look at any wall in your house!

An electric outlet and the plug that goes into it serves as an example -- we certainly care about the location of the holes to each other (OK, they're not circular holes, but rather the three slots of an outlet). And there is no requirement that they be perpendicular to the face of the outlet...a plug that inserts into the outlet might not be flush with the face of the outlet. The juice can flow even it the body of the plug never touches the outlet. Thus, no datum is needed (although I suppose it would be wise to include one so that the slots aren't at a really crazy angle from the wall).


John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[Madhu454]

Hi All,

If i summerise all of your points

1) If we dont use any datums in the lower frame of a composite control frame, the orientaion of the holes is not controlled. For this case we cannot design a fixed gauge since the holes can be tilted to datum A. I hope FRTZF needs to be checked with the Axis interpretation, surface interpretation is not possible here. The best fit guage pins can be inserted to all the 4 holes and the distance between the axis can be checked to see wheter it is inline with the FRTZF. This is how i understood. Please correct me if I am wrong.

2) If we use only one datum that is datum A in the FRTZF, then the gauge which I have mentioned in the drawing would be applicable since all the pins (dia 9.3) are made perpendicular to datum A. Please see the drawing in the original post.

3) If we use both the datums that is datum A and datum B in the lower frame, as SeasonLee mentioned we need to use some movable arrangement, so that the entire pattern of gauge pin moves in parallel to datum B. But I dont know how to design a movable arrangement here.

This is what i understood from the above discussion, Please can anyone correct me if I am wrong here.

 

[Belanger]

Just to clarify your point #1 ... even if there are no datum references in a FRTZF, we can use a fixed gage. The fixed gage for your example would simply be four pins fixed in location to each other that plug into the holes, without requiring the part to flatten out onto a surface.

Also take a look at Fig. 7-49 of the standard. For that FRTZF, the fixed gage would simply be a single pin of 10 mm. That still considered a fixed, functional gage even though there are no datum references.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[Madhu454]

Hi Belanger.

I was not knowing this.
Thanks for the reply, your are correct. For the example you mentioned Fig 7-49 we can design a fixed gauge as you mentioned.

Also I need a small clarification from you, in the example fig 7-49 all the holes are coaxial, where as in this example it is rectangular pattern of holes, if the holes are oriented in differnt ways, can we still able to pass the patten of holes through the gauge ( as you mentioned we should not see whether the all the surfaces are exactly flattened out with the respective mating surfaces).

Please clarify does this holds good for the 4-rectangular pattern of holes as well?

 

[dingy2]

I agree with J-P on the gauge design for the FRTZF without a datum but you won't anything in the standard reflecting this. The 4 pins must in parallel to each other on this gauge.

Your application where this FCF is applied should not have any fasteners into the holes otherwise the inside of the bolt head or nut face may not butt onto the mating surface.

Dave D.

http://www.qmsi.ca

 

[Belanger]

As Dave mentioned, even with no datum references the orientation of the holes are always controlled to each other (parallel). That is understood anytime a position symbol is used on a pattern. So if the holes are orientated to each other in different ways (beyond the tolerance amount allowed) then the functional gage will reject that, even if no datum references are given.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[SeasonLee]

Madhu454

You may find out a lot of movable slide design examples from ASME Y14.43-2003 (latest version is 2010) Dimensioning and Tolerancing Principles for Gages and Fixtures, please note that the movable slide is datum B I/O the 4 pattern pins.

Attached is an example of the design concept (this is not an example of composite position tolerancing).

SeasonLee

 

[SeasonLee]

Sorry for the typo, ASME Y14.43-2011 is the latest version.

SeasonLee

 

[Madhu454]

Hi SeasonLee,
Thanks a lot for sending the design concept.