TP got any suggestions?

[#2#]

So, I ran across this on a print today. I'm looking for suggestions.

[tking]

1.720 +/- 0.0025 ?

TK

[Matthew D. Hoedeman]

2-D distance, +/-0.0025.

[craiger_ny]

I'd treat it like profile of a surface.

Craig

[#2#]

2-D distance, +/-0.0025.

So if this is true shouldn't 1.720 be a basic dimension?

[tking]

So if this is true shouldn't 1.720 be a basic dimension?

Yup

TK

[Matthew D. Hoedeman]

One thing you have to remember, Goodluck, is that the people who put the GD&T on the prints do NOT have any idea what they are doing. So many times I see a B-Datum hole, with the C-Datum hole dimensioned to the B-Datum hole using TP, but the B-Datum hole is the 4-way locator, the C-Datum hole is the 2-Way locator, so there is 1 and only 1 direction the C-Datum hole can vary, and that is along the axis which is the distance between the two holes. So, if the B & C datum holes are not in a straight line (happens ALL the time) and you do a regular TP dimension for it, it will show 2 axis off 'perfect' if the distance between them isn't perfect (and it never is). So, you will then get some other yahoo come in there, and they will then ASK YOU why, if it is a 2-way locator, are BOTH axis off location? Thus the reason for doing the 2-D distance. I have never had ANYONE question me when dimensioning in this manner.

[tking]

One thing you have to remember, Goodluck, is that the people who put the GD&T on the prints do NOT have any idea what they are doing. So many times I see a B-Datum hole, with the C-Datum hole dimensioned to the B-Datum hole using TP, but the B-Datum hole is the 4-way locator, the C-Datum hole is the 2-Way locator, so there is 1 and only 1 direction the C-Datum hole can vary, and that is along the axis which is the distance between the two holes. So, if the B & C datum holes are not in a straight line (happens ALL the time) and you do a regular TP dimension for it, it will show 2 axis off 'perfect' if the distance between them isn't perfect (and it never is). So, you will then get some other yahoo come in there, and they will then ASK YOU why, if it is a 2-way locator, are BOTH axis off location? Thus the reason for doing the 2-D distance. I have never had ANYONE question me when dimensioning in this manner.

WMS

TK

[CGoode]

1.720 ±0.0025

[#2#]

When I first saw it I said to myself "why". It is understandable that it may have been included in error. What I mind is that it will never be changed! Instead, we will continue to confuse our suppliers with it until the part is no longer produced!

Guys, Thanks for the help and the emotional support.

[VONDY]

With the positioning of the datum -B- directly in line with the 1.720 ( non-basic) dimension. I would consider this as a virtual size datum, meaning I would use both outside edges to square up the part, then place your origin at the center point of these two edges The TP is a bogus call out, the virtual size would be the prints ± standard practice tolerance. I would reject the parts and place then into the holding rack until the print got changed or a 'deviation to print' was signed and dated by the engineer. I see this when they normally want the hole,slot, etc. located from the center of the part instead of an edge. What I don't see on this print are any other features so I'm not sure why he would use this type of feature anyway.
If considering a profile, I would then say that the datum -B- should be moved over, the 1.720 should become basic and a profile leader line should point to the opposite side with its feature frame instead of a TP feature frame.
Either way a print change is required
You all have to learn to strap on a pair, reject the parts and tell them engineers you can't check the part correctly because of his lack of GD&T training. Almost all of our engineers will admit to not knowing a 'hill of beans' about GD&T and most will listen to what I "suggest" they change it to.

[craiger_ny]

......... I would reject the parts and place then into the holding rack until the print got changed or a 'deviation to print' was signed and dated by the engineer......You all have to learn to strap on a pair, reject the parts and tell them engineers you can't check the part correctly because of his lack of GD&T training. Almost all of our engineers will admit to not knowing a 'hill of beans' about GD&T and most will listen to what I "suggest" they change it to.

Ah yes, the old put the onus on engineering by holding up production trick. I've used it many of times and in some cases have found it to be the only thing that works. Like a tourniquet, it is a last resort trick and you must make absolutely sure you are standing on firm ground when you pull it (even better find a manager, preferably quality manager, to back you up). Very sound advice Vondy, probably the best advice in this thread. Hold the parts hostage and make your demands Goodluck.

Craig

[#2#]

I am in no position to hold the parts hostage. They are hot parts that my boss's boss's boss keeps asking when they will be done. I am measuring these so the QE and design "engineer" can review the results and decide whether the supplier can supply these parts to print.

I just decided to say "can't measure" for the true position and put in a note that says "it is unclear as to which features this dimension applies".

They'll probably just disposition it as "Final disposition pending completion of testing" and that is where it will stay forever!

I found one print about a year ago that the 5 notes on the print are numbered 1, 1, 1, 1 and 1! I pointed this out in my report and it is still this way on the print.

[Tested]

With it going back just to -B-, I'd think that they are looking for it to be Parallel to -B-.

[Paul Barriage]

A combo of Matt & Craig would be best for quick decision.

Measure it to exactly what it says. Let them tell you later if their interpretation is different from the expression stated. Good or bad, at least it is interpreted correctly.