I am trying to determine the most commonly accepted way of measuring the depth of a threaded blind hole. The drilled hole is plenty deep to go past what is needed, but our QC is rejecting based on their method of measuring the threaded portion depth. Any ideas would be appreciated.
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thread depth measurment 2
- Thread starter morach
- Start date
ajack1
You may be technically correct, however do you really think the engineer or the draftsman who created this part design actually did a tolerance study and determined that the tolerance must be +/-.005 on the thread depth? What if the part has a thread .001 too deep does your gage tolerance catch the difference. No because first a thread gage is a combination gage covering thread form, pitch diameter, helix angle, and straightness. Secondly a thread gage is made to low limit of a thread PD which I could prove would allow a thread on high limit to be gaged incorrectly just because of the clearance on the threads. How are you going to provide gage repeatability/accuracy. The old 10 to 1 rule applies so is you depth control capable of +/-.0005 accuracy and repeatability? I would also guess the amount of torque applied to the gage would also provide error in reading the depth. I would also contend the gage itself will act as a tap if reseated multiple times in the same hole increasing thread depth with each gaging.
You may be technically correct, however do you really think the engineer or the draftsman who created this part design actually did a tolerance study and determined that the tolerance must be +/-.005 on the thread depth? What if the part has a thread .001 too deep does your gage tolerance catch the difference. No because first a thread gage is a combination gage covering thread form, pitch diameter, helix angle, and straightness. Secondly a thread gage is made to low limit of a thread PD which I could prove would allow a thread on high limit to be gaged incorrectly just because of the clearance on the threads. How are you going to provide gage repeatability/accuracy. The old 10 to 1 rule applies so is you depth control capable of +/-.0005 accuracy and repeatability? I would also guess the amount of torque applied to the gage would also provide error in reading the depth. I would also contend the gage itself will act as a tap if reseated multiple times in the same hole increasing thread depth with each gaging.
On the information given I believe I am correct and so is the inspector for failing the parts, to suggest you fire the inspector is IMO crazy.
Having said that I seriously doubt any true engineer or draftsperson would put a +/- .005 dimension on the depth of a thread, as it is near impossible to achieve or measure.
Again only my opinion but the solution to the problem is to get the drawing changed not buy some expensive gauges that would only prove that the tolerance is stupid, as stated in my original post.
This seems to be a growing problem at least in the UK that we are forced to chase stupid tolerances because no one can find an engineer that will sign off a change, surely the solution to all this should be no more than a phone call and or email?
Even worse than any of this is the attitude that I have a problem I cannot solve so I will fire the inspector who fails the parts given above.
People question why work is sent to the Far East and engineering is struggling in the USA and Europe, this is a perfect example we are handing it them on a plate.
Having said that I seriously doubt any true engineer or draftsperson would put a +/- .005 dimension on the depth of a thread, as it is near impossible to achieve or measure.
Again only my opinion but the solution to the problem is to get the drawing changed not buy some expensive gauges that would only prove that the tolerance is stupid, as stated in my original post.
This seems to be a growing problem at least in the UK that we are forced to chase stupid tolerances because no one can find an engineer that will sign off a change, surely the solution to all this should be no more than a phone call and or email?
Even worse than any of this is the attitude that I have a problem I cannot solve so I will fire the inspector who fails the parts given above.
People question why work is sent to the Far East and engineering is struggling in the USA and Europe, this is a perfect example we are handing it them on a plate.
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