Hi, I am a frustrated engineer dealing with a plastic injection moulder. This company is providing an electrical connector to us. During several months the main quality concern is the height of the female connector opening (internal feature) being warped in the that our operators have troubles to fit the male connector in there since the opening is being reduced to be lower than the min limit. The vendor says that they need an extra dimension in the middle in order to justify an extra measurement in their process. According to rule #1 the size limits apply to the whole extent of the feature, so there is no need for other specification. Could someone comment on this, please? I already started to hesitate if I am correct to demand that dimension to be corrected either by process or mold size fixes, or just must give up and sort the incoming inventory with a block gage.
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conflict on limits of size 2
- Thread starter Alberto40
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- #3
Alberto40,
Your diameter dimension and tolerances apply for the entire length of the feature. If you applied a ±[ ]tolerance, you have probably not controlled perpendicularity very well. Could this be the problem?
Your drawing is effectively a clause in a contract. Everything on your drawings must be precisely meaningful. You need a note on your drawing stating that your dimensions and tolerances are as per ASME Y14.5M-1994 or something equivalent. Otherwise, there is no formal standard that explains your dimensions and tolerances.
JHG
Your diameter dimension and tolerances apply for the entire length of the feature. If you applied a ±[ ]tolerance, you have probably not controlled perpendicularity very well. Could this be the problem?
Your drawing is effectively a clause in a contract. Everything on your drawings must be precisely meaningful. You need a note on your drawing stating that your dimensions and tolerances are as per ASME Y14.5M-1994 or something equivalent. Otherwise, there is no formal standard that explains your dimensions and tolerances.
Wrenchbender
Mechanical
As I understood it, the connector hole has a constant crossectional shape which has been properly dimensioned, but the bore resembles a banana and the mating part, which is straight, doesn’t fit. Yes a drawing would be helpful, but I’m pretty sure the above mentioned standard does cover a situation such as this.
I believe your rule #1 about size limits is also in Y14.5, but you may need to add something like ‘perfect form at MMC required’. Check pp. 141-144 of Y14.5, or with a draftman who is up to speed on GD&T. Rather than throw in an extra dimension midway as the vendor suggested, maybe specifying some datums with position feature controls on the hole would allow functional gauging (on the entire depth).
As to the source of the problem, could it be related to shrinkage from non-uniform sections? Maybe that can be fixed as well by a simple mod to the mold.
I believe your rule #1 about size limits is also in Y14.5, but you may need to add something like ‘perfect form at MMC required’. Check pp. 141-144 of Y14.5, or with a draftman who is up to speed on GD&T. Rather than throw in an extra dimension midway as the vendor suggested, maybe specifying some datums with position feature controls on the hole would allow functional gauging (on the entire depth).
As to the source of the problem, could it be related to shrinkage from non-uniform sections? Maybe that can be fixed as well by a simple mod to the mold.
Alberto40,
I am just reading through this thread again. When you refered to Rule[ ]#1, I assumed you had a single dimension, like a diameter. Rule[ ]#1 applies to single dimensions.
If you have a feature that requires more than one dimension, you need more control over your geometry. For example, a rectangular feature controlled by length and width dimesions and tolerances, also is affected by angular allowance, defined by the note on your title block. An error of half a degree can get you in trouble. Rule[ ]#1 does not work. Profile tolerances do work.
JHG
I am just reading through this thread again. When you refered to Rule[ ]#1, I assumed you had a single dimension, like a diameter. Rule[ ]#1 applies to single dimensions.
If you have a feature that requires more than one dimension, you need more control over your geometry. For example, a rectangular feature controlled by length and width dimesions and tolerances, also is affected by angular allowance, defined by the note on your title block. An error of half a degree can get you in trouble. Rule[ ]#1 does not work. Profile tolerances do work.
MikeHalloran
Mechanical
The molder's process should not be your problem.
Surely you can find another molder who is not a weasel.
( Apologies to actual weasels, who just do what they've always done. )
Mike Halloran
Pembroke Pines, FL, USA
Surely you can find another molder who is not a weasel.
( Apologies to actual weasels, who just do what they've always done. )
Mike Halloran
Pembroke Pines, FL, USA
- Thread starter
- #7
Thanks to all of you for the time dedicated to help others. I will try to put a sketch shortly so some of you can visualize easier the situation.
Unfortunately on this drawing there is no direct reference to the ASME GD&T std, neither has the note of perfect form at MMC.
My personal opinion is that this type of response from any supplier is very easy to solve: move the business to a American vendor that cares about education on technical matters.
Perhaps the shape of the connector is not helping with the shrinkage and warpage, this connector is 24x2 pins, very narrow in one side and very long in the other. Wall thickness is even all around the rectangle. Basically the locating datums are the central planes from both the width and length of the cross-section, with a tertiary datum at the bottom end of the connector cavity.
Thanks again for all the comments, once I upload the sketch it will be easier for others to comment, I guess...
Unfortunately on this drawing there is no direct reference to the ASME GD&T std, neither has the note of perfect form at MMC.
My personal opinion is that this type of response from any supplier is very easy to solve: move the business to a American vendor that cares about education on technical matters.
Perhaps the shape of the connector is not helping with the shrinkage and warpage, this connector is 24x2 pins, very narrow in one side and very long in the other. Wall thickness is even all around the rectangle. Basically the locating datums are the central planes from both the width and length of the cross-section, with a tertiary datum at the bottom end of the connector cavity.
Thanks again for all the comments, once I upload the sketch it will be easier for others to comment, I guess...
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- #8
MartinSr00
Mechanical
With proper drawings, the vendor need not concern him or herself with whether or not the part fits. The only concern is whether it conforms to the drawing and the contract.
Often, I find people in the manufacturing world who have trouble creating drawings. So, for example, if your molder needs an extra dimension to direct internal means and methods, he may try to get you to put it on the drawing instead of making an internal print.
Problem is, if you put it on the drawing, it could become a contract element. Once there, the vendor can complain that you dictated means and methods, and therefore are responsible for them in case of a bad outcome. Supplying roughout dimensions, etc. on your drawings puts you in a bind -- you're trying to dictate someones means and methods. That's forbidden in Y14.5's fundamental rules. You can, however, put a nonmandatory processing dimension, however if it is noted as such. That's a suggestion that your molder need not follow. Whether it puts you in a contractural bind or not, you'd have to ask your lawyers.
Also, as a note, to invoke Y14.5, you need to say so either on the drawing or a document referenced on the drawing. That's 1.1.3 on both ASME Y14.5M-1994 and ASME Y14.5-2009. If you don't say, it's not there.
As stated in other posts rule number 1 applies unless otherwise noted. The fundamental rules state that tolerances apply for full depth, length and width of the feature. But remember, rule 1 doesn't cover orientation with other features, it only covers features of size.
Often, I find people in the manufacturing world who have trouble creating drawings. So, for example, if your molder needs an extra dimension to direct internal means and methods, he may try to get you to put it on the drawing instead of making an internal print.
Problem is, if you put it on the drawing, it could become a contract element. Once there, the vendor can complain that you dictated means and methods, and therefore are responsible for them in case of a bad outcome. Supplying roughout dimensions, etc. on your drawings puts you in a bind -- you're trying to dictate someones means and methods. That's forbidden in Y14.5's fundamental rules. You can, however, put a nonmandatory processing dimension, however if it is noted as such. That's a suggestion that your molder need not follow. Whether it puts you in a contractural bind or not, you'd have to ask your lawyers.
Also, as a note, to invoke Y14.5, you need to say so either on the drawing or a document referenced on the drawing. That's 1.1.3 on both ASME Y14.5M-1994 and ASME Y14.5-2009. If you don't say, it's not there.
As stated in other posts rule number 1 applies unless otherwise noted. The fundamental rules state that tolerances apply for full depth, length and width of the feature. But remember, rule 1 doesn't cover orientation with other features, it only covers features of size.
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