What's new
What's new

Internal thread gauging (plug style)

Spelunker

Aluminum
Joined
Sep 20, 2007
Location
Central Valley CA.
Hi Forum,

Perhaps in all of you infinite wisdom, you all could help settle a minor disagreement in our QA department. Here it is:

I have been machining since 1987(thats not an indicator of my skill, I know, so dont bust my chops please), and the whole time, I mean the WHOLE TIME, whenever I have tapped a hole and then gauged it using a Plug style GO/NO gauge I have been using 1 1/2 turns on the NOGO to determine if the thread is good. My QA guy says that 3 turns is allowable on NOGO. Who is right???

any help, as always is much appreciated.
Thank in advance.

Kev
 
1.5 turns is what I use under normal conditions. When things are working as they should it's usually under 1/2 turn. 3 turns would tell me that something is very wrong with the setup.
 
Without getting into the ISO stuff and class of fit, my general rule of thumb is 1-2 turns meaning 3 turns is not acceptable. My quality guy is Pratt & Whitney old school/ISO and he will not accept anything more than 2 turns. Hope this helps.
 
From Inspection and Gaging, page 470

Thread Plug Gages

"The NO-GO end must not enter more than a turn and a half, else the tapped hole is too large."

Also, from the preceding paragraph on the same page...

"... a plug gage must be made for a specific thread size, class, and tolerance. A plug gage with Go and No-Go member tolerances for Class 1 threads, for example, is of no use for Class 3 fits."

- Leigh

Reference: Kennedy, Hoffman, and Bond Inspection and Gaging, Sixth Edition, 1987 Industrial Press, New York ISBN 0-8311-1149-6
 
I think I am going to roll with " The Real Leigh" on this one.
For no other reason other than it DOES jive with what I have been practicing over the years , as well as he referenced some pretty notable sources.

Thanks all for your input. as always, this forum ROCKS!!!!!
 
I copied this from Handbook H28, Screw-Thread Standards for Federal Services (1969), Section 6, 3.1.1

"Threads are acceptable when the HI thread plug gage is applied to the product internal thread if: (a) it does not enter, or if (b) all complete product threads can be entered, provided that a definite drag from contact with the product material results on or before the third turn of entry. The gage should not be forced after the drag is definite. Special requirements such as exceptionally thin or ductile material, or small number of threads, may necessitate modification of this practice"




Found this in a Glastonbury Southern Gage brochure
http://www.factorylink.com/Technical Data/Glastonbury/PDF/GSG_Technical.pdf


Inch: Acceptable when gage does not enter product more than three complete turns. Thin or soft material, or small number of threads may require altering three-turn limit. Per ANSI 81.2-1983, page 13, par. 4.2.1

Metric: Acceptable when a definite drag from contact with the product material results on or before the second turn of entry. Per ANSI B1.16M-1984, page 15, par. 4.2.1
 
Thanks mrainey,

Just what I need " more" notable sources.
I was happy to go with the 1 1/2 turns as mentioned in my earlier posting,but now............

I used to be indecisive..........now I'm not so sure!

So, If that is to say that 3 turns is acceptable, then 1 1/2 must be even closer to nominal sizes. Yes?

Again, thanks to all.

Cheers,

Kevin
 
"Threads are acceptable when the HI thread plug gage is applied to the product internal thread if: (a) it does not enter, or if (b) all complete product threads can be entered,...
There's something seriously wrong with a spec that says both "no entry" and "full entry" are equally acceptable. :crazy: :willy_nilly:

- Leigh
 
From another book, "Technology of Machine tools"

" The no-go end should start into the hole and become quite snug before the third thread enters "


"Quite snug" a bit like " thats quite snug, now how do we get it out? "
 








 
Back
Top