Measuring Wall Thickness on Socket Head Cap Screws

D

DaddyDow

#1
Wall thickness is depicted on the ANSI/ASME B18.3 as item G and Key Engagement as item T Please look at this to see a picture depicting what I am discussing below.

Both Items are located off of the same line, what is the best way to measure G?

Our customer is measuring it very differently than us, we have tried to measure it their way (however the method is flawed in our opinion). Does anyone on here have to measure this item, and if so, how do you go about it?

We currently use a hex gage member to verify wall thickness. We zero out the caliper on the hex gage length, insert the gage into the part and measure the parts head height and our hex gage length as an assembly, the reading is wall thickness per this standard.

Our customer zero’s the caliper while measuring the head height, then using the Depth Probe of the caliper tries to insert it along the edge of the hex, bottoming out the main scale against the top of the head and the resulting reading is their wall thickness measurement (way too much variation and not reliably located where the standard details)

Any help in providing evidence to validate either technique (ideas, useful links, etc) would be appreciated,

Thanks,

David Dow
 
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Stijloor

Staff member
Super Moderator
#2
Wall thickness is depicted on the ANSI/ASME B18.3 as item G and Key Engagement as item T Please look at this to see a picture depicting what I am discussing below.

Both Items are located off of the same line, what is the best way to measure G?

Our customer is measuring it very differently than us, we have tried to measure it their way (however the method is flawed in our opinion). Does anyone on here have to measure this item, and if so, how do you go about it?

We currently use a hex gage member to verify wall thickness. We zero out the caliper on the hex gage length, insert the gage into the part and measure the parts head height and our hex gage length as an assembly, the reading is wall thickness per this standard.

Our customer zero’s the caliper while measuring the head height, then using the Depth Probe of the caliper tries to insert it along the edge of the hex, bottoming out the main scale against the top of the head and the resulting reading is their wall thickness measurement (way too much variation and not reliably located where the standard details)

Any help in providing evidence to validate either technique (ideas, useful links, etc) would be appreciated,

Thanks,

David Dow
Hello David,

Welcome to The Cove Forums! :bigwave::bigwave:

How much tolerance is specified for dimension "G" ?

Stijloor.
 
D

DaddyDow

#3
Hello David,

Welcome to The Cove Forums! :bigwave::bigwave:

How much tolerance is specified for dimension "G" ?

Stijloor.
None, both T and G are minimums, I would have included this information if I felt it was needed to help answer my question, I am not sure its relevance. But if it helps, cool.

thanks Stijloor.
 

Jim Wynne

Staff member
Admin
#4
None, both T and G are minimums, I would have included this information if I felt it was needed to help answer my question, I am not sure its relevance. But if it helps, cool.

thanks Stijloor.
Welcome to the Cove. You might not be aware that people ask questions here fairly frequently without providing information necessary to a sensible answer, so if we're not sure, we'll usually ask. Nonetheless, I'm not sure how you figure that tolerance might not be relevant to choosing measurement methods/devices.
 

Stijloor

Staff member
Super Moderator
#5
None, both T and G are minimums, I would have included this information if I felt it was needed to help answer my question, I am not sure its relevance. But if it helps, cool.

thanks Stijloor.
Letters in a drawing usually indicate tabulated dimensions on the drawing or another relevant document such as a Standard with associated tolerances. If T and G are minimums, what are their allowable maximums? This is very critical to answer your question because the tolerance will determine what proper measuring device must be used and a possible measurement system study. (Gage R & R). Sorry for being a little "technical", but as my friend Jim Wynne already pointed out, more info is required to generate a satisfactory answer.

Stijloor.
 
D

DaddyDow

#6
Welcome to the Cove. You might not be aware that people ask questions here fairly frequently without providing information necessary to a sensible answer, so if we're not sure, we'll usually ask. Nonetheless, I'm not sure how you figure that tolerance might not be relevant to choosing measurement methods/devices.
Thanks for the welcome, I think ;).

I am aware, I have been around here a while, just never needed to post my own question. As for peoples insights, I am all for giving them what they request in order to solve my dilemma, however tolerance, in this instance does not apply in my opinion. Which is why I replied as I did, not being rude or indifferent, simplying explaining why I did not bother to include that information and wanting a reply to explain why I may be wrong in this particular case.

If you have a reason where tolerance would be needed in this case, please do share. However I have given two measurement methods, asking which one is better for a given dimension (not wanting scale or size to muddy the waters). Tolerance just simply does not matter when both methods are using the same measuring device, we need only focus on the method, which should not vary as a result of specifications or tolerances.

You can never have too much information, not in my world, so please bring it on. I have been in fasteners for 20 years, it just seems odd that I have never had to cross this particular bridge before.

Thanks again.
 
D

DaddyDow

#7
Letters in a drawing usually indicate tabulated dimensions on the drawing or another relevant document such as a Standard with associated tolerances. If T and G are minimums, what are their allowable maximums? This is very critical to answer your question because the tolerance will determine what proper measuring device must be used and a possible measurement system study. (Gage R & R). Sorry for being a little "technical", but as my friend Jim Wynne already pointed out, more info is required to generate a satisfactory answer.

Stijloor.
Please do not focus on MSA or a particular device, we already have two methods using a prescribed device, widely used through out my industry detailed above.

We have a bolt head height specification of .368/.375 inches. Call the head height "H". "T" is the key engagement or drive depth, Specification for "T" is .182 inches minimum. "G" is the wall thickness and the specification for "G" is .143 minimum.

Now I could have just listed 3 different specifications with 3 different tolerances and that would or should not change the answer to my question. Which of the two methods listed is more closely capturing what the standard is looking for in terms of wall thickness?

thanks again.

David
 

Stijloor

Staff member
Super Moderator
#8
David,

I must now defer to other Participants in The Cove Forums who have much more experience with the fastener industry then I have.
Sorry that I was unable to help. I try to do better next time. :agree1:

Allow me to add that the problem you're having may have originated during contract review.
It's very important that there is concurrence of inspection methods between customer and supplier.

Stijloor.
 
D

DaddyDow

#9
David,

I must now defer to other Participants in The Cove Forums who have much more experience with the fastener industry then I have.
Sorry that I was unable to help. I try to do better next time. :agree1:

Allow me to add that the problem you're having may have originated during contract review.
It's very important that there is concurrence of inspection methods between customer and supplier.

Stijloor.
Once again thanks Stijloor, but this is a long time customer who just started inspecting the parts in this manner. Bring on the comments though, don't let my responses dull your postings.
 

Jim Wynne

Staff member
Admin
#10
Once again thanks Stijloor, but this is a long time customer who just started inspecting the parts in this manner. Bring on the comments though, don't let my responses dull your postings.
A few observations off the top of my head:

  1. If there's a dispute, it means that the feature must be at or near the minimum. Go deeper.
  2. Both methods seem questionable if #1 is true. Using a caliper depth rod for this sort of thing is always a little iffy, but using a hex member is too; how are you making sure you're uniformly bottoming out against the internal surface?
  3. If you need good evidence of the most reliable method, take 10 parts and measure them your way, then give the same ones to the customer and have them measure them, then section them and make direct measurements.
 
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