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How to accurately measure Internal Thread Pitch


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Related Topic Tags
internal threads, thread pitch, threads (of fasteners such as nuts and bolts), validation testing
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  Post Number #1  
Old 29th April 2011, 04:18 AM
Validation2011

 
 
Total Posts: 18
Please Help! How to accurately measure Internal Thread Pitch

Hi All,

Im in the process of validating a part that has an internal thread (8-32 UNC -2B). In order to calculate capability on this thread i need a method of accurately measuring the thread.

If we validate using the go/no go gauges and 100% verify the threads this will mean that we will need to continue 100% verification on this feature going forward.

We are trying to reduce the ammount of inspection required on our parts by proving capability and based on previous parts that we have validated our threads are one of the most capable features on all parts we machine.

It would be a shame to have to 100% check a feature that we know is capable.

We have looked at a number of options, thread clock (cannot get one small enough), thread putty (not accurate enough), sectioning and measuring on comparator (too expensive, 150 sample of parts required).

Can anyone offer some advise on a method of measuring this feature or alternatively a method of validating this feature that will not lead us to a 100% verification on all parts going forward?

Thanks

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  Post Number #2  
Old 29th April 2011, 04:38 AM
Gert Sorensen's Avatar
Gert Sorensen

 
 
Total Posts: 1,274
Re: Measuring Internal Thread Pitch

How about using a laser device for measuring the diameter of the thread? There are several available.
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  Post Number #3  
Old 29th April 2011, 05:36 AM
Validation2011

 
 
Total Posts: 18
Re: Measuring Internal Thread Pitch

Do you know if the laser would give me a measurement of thread pitch or just the thread dia?

Im assuming just thread dia?

I am more interested in the pitch.
  Post Number #4  
Old 29th April 2011, 06:04 AM
Gert Sorensen's Avatar
Gert Sorensen

 
 
Total Posts: 1,274
Re: Measuring Internal Thread Pitch

Ahaaa, just a little language barrier here

Can you clarify: What is the product? Why does it need to be validated?
  Post Number #5  
Old 29th April 2011, 06:25 AM
silentrunning's Avatar
silentrunning

 
 
Total Posts: 537
Re: Measuring Internal Thread Pitch

Would your customer allow you to do a representative number of parts with a Go/ NoGo gage? If you could do 25% with zero defect, would they accept this? This would cut the inspection cost considerably from the 100% inspection.
  Post Number #6  
Old 29th April 2011, 09:10 AM
bobdoering's Avatar
bobdoering

 
 
Total Posts: 4,011
Re: How to accurately measure Internal Thread Pitch

Quote:
In Reply to Parent Post by Validation2011 View Post

We are trying to reduce the amount of inspection required on our parts by proving capability and based on previous parts that we have validated our threads are one of the most capable features on all parts we machine.

It would be a shame to have to 100% check a feature that we know is capable.
I would sample your process over a run - from beginning to end - or if there is a tap change within the run, over the life of the tap. Carefully section the parts and measure the pitch with a device of adequate gage R&R (vision system, measuring microscope, etc.) Show the variation over that period of time and develop a plan based on that variation. Unfortunately, taps are like drills, and they are not precision machining (their variation is not primarily from tool wear alone), so you are going to have to look at that variation rather holistically.

Quote:
In Reply to Parent Post by Validation2011 View Post

.... that we know is capable.
Got to love the calibrated gut feel! Why can't the customers buy into that?
  Post Number #7  
Old 29th April 2011, 11:15 AM
topnotch

 
 
Total Posts: 4
Re: How to accurately measure Internal Thread Pitch

Check out Johnson Gage. They make thread pitch measuring gages that will tell you the accually pitch diameter. They are very nice. Starrett also makes something like this.
Thanks to topnotch for your informative Post and/or Attachment!
  Post Number #8  
Old 29th April 2011, 01:31 PM
bobdoering's Avatar
bobdoering

 
 
Total Posts: 4,011
Re: How to accurately measure Internal Thread Pitch

Quote:
In Reply to Parent Post by topnotch View Post

Check out Johnson Gage. They make thread pitch measuring gages that will tell you the accually pitch diameter. They are very nice. Starrett also makes something like this.
http://johnsongage.com/images/catalo...PDFs/GJ-GJ.pdf
Thanks to bobdoering for your informative Post and/or Attachment!
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