Roll Form Thread Standard

Dr.mr555

Starting to get Involved
#1
We have a supplier that has used a roll form tapping process on parts we specify a thread requirement of UNF 10-32 2B. My research on producing internal threaded parts using a roll formed tapping process indicates that we cannot specify a thread standard if we wish to allow the roll form process to be used which produces an inconsistent minor diameter. The minor diameter limit of size is clearly defined for the for threads produced to the UNF standard. The inspection method used by our supplier is to use a go no-go UNF 10-32 2B gauge only, which is why we received parts which the minor diameter measured .180? plus. Obviously an oversized drill was used. I would think we cannot specify a standard if we allow roll forming. I understand that a higher quality thread is produced, but how can I allow this process in a ISO 9001 controlled environment? Please help!
 
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J

Jamie_

#2
I don't know how helpful this will be, but our supplier only uses a go/no go gauge as well and it's never been an issue. That said it's not a huge part of our fabrications so I may be completely deficient in this and it's never come up. I'll be following this thread with great interest to see what the consensus is on this.
 

Michael_M

Trusted Information Resource
#3
We have a supplier that has used a roll form tapping process on parts we specify a thread requirement of UNF 10-32 2B. My research on producing internal threaded parts using a roll formed tapping process indicates that we cannot specify a thread standard if we wish to allow the roll form process to be used which produces an inconsistent minor diameter. The minor diameter limit of size is clearly defined for the for threads produced to the UNF standard. The inspection method used by our supplier is to use a go no-go UNF 10-32 2B gauge only, which is why we received parts which the minor diameter measured .180? plus. Obviously an oversized drill was used. I would think we cannot specify a standard if we allow roll forming. I understand that a higher quality thread is produced, but how can I allow this process in a ISO 9001 controlled environment? Please help!
A roll form thread still requires the UNF 2b class of fit to apply. Class of fit requires both pitch diameter (thread gage) and ID (gage pins).

As I understand it, a roll form thread is a bit stronger than a cut thread but both still require the form of the thread to be correct:

ID
OD
Pitch diameter
Angle of cut
Threads per inch.
 

Wayne

Gage Crib Worldwide
#5
We have a supplier that has used a roll form tapping process on parts we specify a thread requirement of UNF 10-32 2B. My research on producing internal threaded parts using a roll formed tapping process indicates that we cannot specify a thread standard if we wish to allow the roll form process to be used which produces an inconsistent minor diameter. The minor diameter limit of size is clearly defined for the for threads produced to the UNF standard. The inspection method used by our supplier is to use a go no-go UNF 10-32 2B gauge only,.... I would think we cannot specify a standard if we allow roll forming.
A roll form thread still requires the UNF 2B class of fit to apply. Class of fit requires both pitch diameter (thread gage) and ID (gage pins).
I agree with Michael M, but wish to expand on his reply a little bit.

Know that screw thread plug gages do not test the screw thread minor diameter for over-size condition. This is true regardless of the method of manufacturing the screw thread. In all cases inspection of any internal screw thread requires the use of GO/NOGO Screw Thread Plug Gages, to check most of the screw parameters; used in concert with GO/NOGO Plain Pin Gages, to test the Minor Diameter.

From a manufacturing perspective; regardless of the method of manufacturing, if the tap drill hole is larger; less work is required of the machines and tooling (less broken/worn taps) to make the screw thread. This means cost savings for the manufacturer. If the manufacturer can convince you that a feature (the minor diameter) is not controllable, he can save on his cost of making the part and have greater profit. (Profit is not a bad word, but it should not be to the determent of the understood/specified conditions of the part.)

The minor diameter is controllable. The size is defined in ANSI/ASME B1.1 and the test methods in ANSI/ASME B1.2. Work with the supplier to correct his error; or find a new supplier.

I hope this helps.
 
I

ISOCOP

#6
A go/ no go thread gauge will not detect an oversize minor ID. If the minor is oversize it will have a negative impact on thread engagement and strength.
 

ncwalker

Trusted Information Resource
#7
I cut a LOT of threads at my factory, well, roll form them.

They absolutely meet the UNC/UNF thread classifications. The major difference is if you have a forming tap, you must use a different tap drill size than a cutting tap. The tap hole for a roll formed tap is larger, you need the negative space to "squish" the material in to. And yes, they are typically stronger.

Two users also very correctly stated (I apologize, I don't know how to scroll up and see who they were) that a thread gage does NOT check for an oversized minor diameter condition. This has burned us in the past, don't make this mistake. They must be checked with a go/no-go thread gage AND a no-go pin sized to the minor diameter.

If your supplier is having minor diameter issues it is typically:
1) They have the wrong tap drill size (too large, making too much negative space)
2) Their tap drill is wobbling. (They should write a CMM program have a special CNC program that skips all the taps leaving just the tap drill holes. You burn a part or two, but you get to check the form of the tap hole AND you get much better measurements for true position, not probing threaded holes).
3) If it is a casting you are tapping, there's porosity in there. (The porosity ALSO makes negative space and when the form tap squishes the material out of the way, some of it fills the voids, resulting in partial threads with the material missing from the minor diameter. Another reason for the intermittent program in 2) above, you can see the porosity. Sometimes forming covers them).
 

Wayne

Gage Crib Worldwide
#8
A go/nogo thread gauge will not detect an oversize minor ID.
Thread gages are made as PLUG and RING gages.;) This chain is speaking of plug gages. :rolleyes: Thread PLUG gages do not test the part thread minor diameter. :( For the record; thread RING gages do not test the part thread major diameter. :agree1:
 
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