How could this Hole Diameter and True Position problem have been Detected & Prevented

Michael_M

Trusted Information Resource
#11
Re: How could this have been prevented/detected?

I use inspection reports, that basically look like a FAI but I add two columns. I put the low limit tolerance in column G and high tolerance limit in column H. The actual data (dimension) is checked to be between these two numbers. If the value is NOT between the two columns, the actual value cell turns red. This helps find typo's and transposed numbers.

This might help you as well as looking at numbers at high and low limits is different than looking at just a single value.
 
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H

Hodgepodge

#12
Re: How could this have been prevented/detected?

I use inspection reports, that basically look like a FAI but I add two columns. I put the low limit tolerance in column G and high tolerance limit in column H. The actual data (dimension) is checked to be between these two numbers. If the value is NOT between the two columns, the actual value cell turns red. This helps find typo's and transposed numbers.

This might help you as well as looking at numbers at high and low limits is different than looking at just a single value.
Good idea for an inspection report, but it wouldn't keep the first piece from being programmed improperly.
 
H

Hodgepodge

#13
Re: How could this hole diameter and true position problem have been prevented/detect

As long as people are involved, this type of thing is possible. Even if you have someone double check the program or even the inspection report, a mistake like this can slip through the cracks. That doesn’t mean you shouldn’t try.
· You could have every program double checked prior to use.
· You could have the programmer write (with pen and paper) the high of the tolerance and the low of the tolerance for each feature and compare the program to the sizes. When working in more than one medium and thinking the same series of numbers more than once, it is less likely to make a mistake. Of course I don’t have any data to support this, just personal experience.

How often does this happen? If this is an isolated incident, why worry about making changes that will cost more time? What is the risk and what is the reward?

I personally have a problem with inverting digits. Not a good thing for a programmer and inspector. When reading a number, I used to say each digit in my head. Ex: Two point two four four one. After recognizing that I had a problem, I found that if I were to say the number properly in my head, I would not make the inverting error. Now I say Two inches, two hundred forty four thousandths and one tenth. Sometimes something this simple can make a difference.
 

Kingsld1

Involved In Discussions
#14
Re: How could this have been prevented/detected?

Do you have the capability to program to a CAD model? Assuming that your model is correct, the program nominals should be correct as well. In addition, programming to CAD potentially could speed up programming time as well.
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#15
Re: How could this Hole Diameter and True Position problem have been Detected & Preve

FYI, actual requirement is:
0.281" Diameter +/-.010"
True Position to be within 0.005" MMC relative to datum "C" MMC.
True position to MMC is a blessing - it generally means you can use a hard gage for location. Add to that a go/no go gage for the ID tolerance, you should be good to go (unless the cutting method creates a significant taper)
 
F

Frank T.

#16
Re: How could this hole diameter and true position problem have been prevented/detect

How often does this happen? If this is an isolated incident, why worry about making changes that will cost more time? What is the risk and what is the reward?
This is an isolated incident, first time its ever happened in the 10 years I've been here, but like you said as long as humans are involved this type of thing can happen. The reason I asked the question is because my customer wants a response to a corrective action and I don't know how to respond.

Do you have the capability to program to a CAD model? Assuming that your model is correct, the program nominals should be correct as well. In addition, programming to CAD potentially could speed up programming time as well.
Unfortunately we do not. I will see if this is an option, Thanks!

True position to MMC is a blessing - it generally means you can use a hard gage for location. Add to that a go/no go gage for the ID tolerance, you should be good to go (unless the cutting method creates a significant taper)
This is an option I have considered.
 
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B

Bentley

#17
Re: How could this Hole Diameter and True Position problem have been Detected & Preve

I worked with machined parts for many years. I have found that if you have a FAI report you always make sure the report is correct by the drawing specifications before release to inspectors. Calculated electronic spreadsheets are best and will alert the inspector the part is out of tolerance and make someone investigate further. I am not saying that an error will never be made, however, this will make your process more robust.

You say the customer asked for a corrective action? Then the part must have shipped to the customer. Is this how it was found to be incorrect?
 
F

Frank T.

#18
Re: How could this Hole Diameter and True Position problem have been Detected & Preve

You say the customer asked for a corrective action? Then the part must have shipped to the customer. Is this how it was found to be incorrect?
You are correct.
 
J

JLang

#19
Re: How could this Hole Diameter and True Position problem have been Detected & Preve

My gut instinct would be along the first line of respond that sjared shared about the mating part.

If you do not have access to the mating part for assembly would it be possible to manufacture a type of go/no-go gage? Something that has a pin at the required location and if the hole does not line up with the pin there is obviously a problem.

I have done something similar before for a gasket that had multiple holes that needed to be in precise locations. Instead of making a gage though, we made a layover for our optical comparator. If all of the holes did not line up with the layover the parts would be rejected.

Again, this could be overkill if this is the first time this has happened in ten years, but it is just a thought.

As far as the 8D is concerned, I would think your response could depend on how "strict" your customer is. I have had similar occasions before where I was required to complete an 8D for a fluke, one in a million, human error like this and our 8D basically explained how the situation happened and our corrective action was to complete a re-training record with the operator. Some customers will accept that, but others may not. When it comes down to it, we are all humans and we all work with humans. People tend to understand that errors like this may rarely slip through.

That being said, some sort of checking aid may help in ensuring that product does not get out the door again. :cfingers:
 
H

Hodgepodge

#20
Re: How could this Hole Diameter and True Position problem have been Detected & Preve

Frank T.,

It seems unlikely that both the programmer and the person that created the inspection report made the same mistake (though possible). Did the programmer use the inspection report to write his program?
 
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