Specifying that threads be cut not formed 3

[EDSantos]

I have a part with two 2-56 holes, in which screws tend to gall because they are catching the valley of the formed thread. I would like to ask the supplier to cut the threads. Other than adding a note. Does anyone know of guidelines for specifying that a thread be cut as opposed to formed?

 

[MadMango]

How are you calling out the threads now? I assume this is for internal threads. I would think if 2-56 UNC-2B is not acceptable, then perhaps 2-56 UNC-3B might make your vendor second guess his tooling.

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of these Forums?

 

[KENAT]

ASME Y14.5M-1994 1.4 (e) The drawing should defined a part without specifying manufacturing methods.... However, in those instances where manufacturing, processing, quality assurance or environmental information is essential to the definition of engineering requirements, it shall be specified on the drawing or in a document reference on the drawing."

So you can add a note saying "THREADS INDICATED SHALL BE CUT NOT FORMED" or similar.

However, I'd double check you really have the right cause & effect before you do this. Fundamentally if correctly formed, cut or otherwise formed threads should not encounter the problem you're seeing over normal engagement lengths.

Have you inspected the threads with 'go gauge' or similar? If they are failing inspection then the parts don't meet the existing print - what makes you think this vendor will make them meet the new print?

Sounds like it may be a quality problem, not a drawing problem.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[powerhound]

I couldn't agree more with KENAT. I seriously doubt that the problem is that the threads are formed instead of cut UNLESS the form tap is just completely dull. If they are running a dull forming tap then they are just as likely to run a dull cutting tap.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech