Thread gages 3

[yates]

I would like some feedback from fastener manufacturers on the following points concerning (external) thread gaging :

- Has anyone experienced different results (i.e. same thread being conform or not conform) when using a) standard ring gage, b) adjustable ring gage c) roller type snap gage (functional) d)segment type snap gage (functional) ?

- Any ideas on the reasons for the differences above (assuming all gages are satifactorily in calibration ?

- How do you deal with a customer who throws out your bolt because he didn't find it conform with a different (but legal) gaging method than the manufacturer ?

 

[BillPSU]

Different gaging methods can give different results. Thread ring gage shows the thread is correct however the first thread may be the only thread large enough to stop the no-go gage. when a thread snap gage is used it is used in the middle of the thread and the PD in the middle may differ from the end. Thread form variation may also be a problem.
All thread ring gages are adjustable and are set with a setting master.
Thread gages are a composite gage trying to cover several different features (PD and form) at the same time and even if the PD of the thread is correct the major diameter may still be in error.
Talk to your customer and find out what method of checking they are using and if their gages have been calibrated and check your parts with the same method if possible.

 

[MechEng13]

A Star for that BillPSU.

At my last employer, thread rings were often problematic for accepting/rejecting parts, between ourselves and customers,and ourselves and vendors. In many cases we had to end up supplying rings to the customers and receiving rings from the vendors, such that we were all checking the same way.



Alan M. Etzkorn
Product Engineer
Nixon Tool Co.

http://www.nixontool.com

 

[diamondjim]

You might want to consider buying the
same type gages that the particular
customer is using if the quatity of
parts can justify the cost.

 

[yates]

Thanks for your comments guys. No real correlation is possible with customers, however, since we sell same product to several customers. I would prefer gages (roller or segment types) which measure several threads 'cos, as pointed out by BillPSU, the first chewed-up thread may be the one stopping the bolt from going on a no-go gage. One remark though 'all thread ring gages are adjustable' ?? - we do not use these, only solid ring gages. The adjustable types tend to act like a thread die on soft (cad, silver...)
plating and chew it off.
In problem described above, all gages are new and certified as calibrated. The offset described between the two methods is always in the same direction which enables us to purposely roll threads for ring gage gaging or for functional type roller or segment gaging; The problem arises when several customers need this product. There does not appear to be a reference method.

 

[Billybaru]

You might want to get a copy of ASME B1.3M ("Screw Thread gaging Systems for Dimensional Acceptability - Inch and Metric Screw Threads&quot. Have run across this problem in the past. Section 6 (b) in the ASME B1.3M contains a statement "Within each gaging system, a choice of gages is specified for each characteristic. Acceptance by any one gage specified for a characteristic shall be the criterion for acceptance of that characteristic." Showing your customer this spec may help in these situations.

 

[yates]

Many thanks Billybaru, I KNEW I'd seen that somewhere.