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  Measurement, Test and Calibration
  Accuracy & Explosive Bolts

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Author Topic:   Accuracy & Explosive Bolts
Marc Smith
Cheech Wizard

Posts: 4119
From:West Chester, OH, USA

posted 20 October 1999 05:53 PM     Click Here to See the Profile for Marc Smith   Click Here to Email Marc Smith     Edit/Delete Message   Reply w/Quote
From: Greg Gogates
Sent: Thursday, October 14, 1999 6:21 AM
Subject: Accuracy

> Date: Thu, 14 Oct 1999 05:24:52 EDT
> From:
> To:
> Cc:
> Subject: Accuracy
> To group,
> I have a client who has been using pin gages to measure reamed holes. The
> tolerance of the hole is 20 mil of an inch. The pin gages have been verified
> to an accuracy of 20 mil of an inch. Because the reaming process does not
> guarantee this tolerance, they use the pins as go, no go gages to sort them
> according to size and group the parts. Do the pins need to be verified to a
> tighter tolerance than 20 mils. If so they will have to make a huge
> investment in more accurate pins. Also the holes are reamed into parts of a
> mold cavity which is later verified through measurement on the product
> produced. This is for an ISO 9001 system not guide 25. I am stumped on this
> one and would appreciate any advice.
> Mike Gospodinsky


Date: Fri, 15 Oct 1999 15:23:45 -0700
From: Bruce Mayfield
To: Greg Gogates
Subject: Re: Accuracy

This is an interesting question that I was involved with not long ago. A manufacture who's products go into space satellites had a seminar problem. They used a caliper to check the diameter of a pin gauge. The pin gauge verified a hole that was drilled into am assembly. Into the hole fit an explosive bolt. The bolt was used to separate the stages of a launched booster rocket.

With all of this information, the caliper was not calibrated nor were the pin gauges. An ISO finding was not issued because the hole was tapped at the next stage to fit the bolt. The hole was tested with 15 bolts prior to acceptance. The bolt it self became the means in testing the specification. So there was no purpose in calibrating the caliper or the pin because they were not used to inspect the drilled hole.

I asked why they checked it at all, they stated that the hole had to be slightly under size to properly accept the tap. The check was to determine that the hole was about the right depth and not oversize more than the pin. The pin used was selected to be undersize of the tap requirement. The caliper was to make sure the ware on the pin did not affect the quick check. A log was kept of the caliper and pin verification. All of this was documented.

Bruce Mayfield
RAB-IRC ISO auditor

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Marc Smith
Cheech Wizard

Posts: 4119
From:West Chester, OH, USA

posted 20 October 1999 05:55 PM     Click Here to See the Profile for Marc Smith   Click Here to Email Marc Smith     Edit/Delete Message   Reply w/Quote
Date: Fri, 15 Oct 1999 06:17:28 -0400
From: "Kenneth A. Grams"
To: Greg Gogates
Subject: Re: Accuracy


The practice of measuring a .000020 tolerance hole with a gage pin regardless of the pins accuracy is not usually considered good practice. It is very difficult to put a pin that has a diameter of .0001"-.0002" smaller into a hole. Secondly, reaming does not generate a hole with that tolerance. It usually has to be jig ground and lapped. For example, your typical XX Class ring gages are made to that .000020" tolerance and they are defininately not reamed! The normal practice is using air gages or dial bore gages with the appropriate indicator. The problem you may encounter is that the hole size may not lend itself to this method. When dealing with holes smaller that .25, an air gage is about your only choice. The pins will only get you in the "BALLPARK". Forget the pins!

Ken Grams
CMM Services, Inc.

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Forum Contributor

Posts: 244
Registered: Sep 1999

posted 21 October 1999 09:07 AM     Click Here to See the Profile for Sam   Click Here to Email Sam     Edit/Delete Message   Reply w/Quote
I agree wit Ken G., sounds like they need to do a MSA.
Ref: Bruce M.
"An ISO finding was not issued ......"
IMO a finding should have been issued; IM&TE used to varify quality of the product requires calibration. The tap drill diameter is critical for maintaining proper thread geometry.
Also, if the bolts are being used to test the hole I would suggest that they too should be calibrated.

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