What's the benefit of the modified thread

[Ariesbolt]

When we read a drawing of a US mechanical Company, a modified thread was used in the equipment. Does anyone can tell us why and how the modified threads are usually used?

Thanks a lot.

 

[MikeHalloran]

Well, I'd start by asking the company that decided to use the modified thread.


Mike Halloran
Pembroke Pines, FL, USA

 

[desertfox]

Further to Mikes post when you have done that, it might help to tell us what thread you have and what the modification is.

desertfox

 

[Cockroach]

Modified threads are used for commercial consideration. I use modified threads extensively in order to keep the competition from cutting complementary pieces or simply reverse engineering the component.

A modified thread offers several advantages, namely recuts are performed only by qualified machining vendors, threads are kept under the control of my company as a professional corporation, there may be some strength or stress consideration associated with the change in geometric profile, reduce piracy in addition to others.

Primarily it is used out of commercial consideration.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[btrueblood]

We have parts that we want to be able to disassemble many years later, in the face of corrosion. We deliberately make the male threads several thousandths less (p.d.) than the spec. value to help ensure this.

 

[KENAT]

Is it a modified or a special? Your description is so if you want a better answer give a better (more detailed) question.

Posting guidelines faq731-376

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

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

 

[mfgenggear]

Any thing special or modified drives the cost up.
My opinion only do it when absolutely necessary.

special or modified threads require special gaging &
depending on the quantity special tooling.

MfgEngGear

 

[ewh]

Is it modified as in a "J" thread?

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[mfgenggear]

"j" Threads, root radius specified is not a modified thread.

a special is a thread that is not a standard size or threads per inch/MM , a modified thread is basicly a thread that is just that modified standard, major dia or pitch diameter changed. ect. ect.

some of the prints I have manufactured to, had special threads for assembly constraints. clearance, or to throw off the after market guys.

MfgEngGear

 

[KENAT]

faq404-1480 is appropriate if it's a special.

However, the OP does say modified, lets hope he realizes the difference.

If it's important to the OP I'm sure he'll come back and clarify. Though of course if he has a print in isolation as the OP implies he may know little about application.

In which case make it to print, don't worry about the why, and charge the customer appropriately.

Posting guidelines faq731-376

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

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

 

[mfgenggear]

Kenat

This is a well done explanation, also ANSI b1.1-1989 page 14 para 6.4. It would be nice if engineers followed this guide.
mostly the manufacturer has to decipher the major, minor & P.D.

MfgEngGear