2A Thread Limits

[Ox]

It came up today that a customer of mine is running their [before plate] 2A spec threads, to "finish" 2A guages, and using 3A GO's as their "after plate" guages.

I don't generally use "pre-plate" guages as a rule, but we make sure to run on the low end, and even slightly under the "no-go" limit to allow build-up in plating.

I was getting dinged for being slightly under "low" before plate, and I told them that after plate that they would be fine, but these folks Shirley plate a whole lot more of these than I doo, so I was cornfused as to why they thought this way? Obviously it's working for them, but .... ???

So I was telling the QC guy (not his full time position) that "2A" is not a "pre-plate" spec, but it's _ it's own spec, and 3A is too. I have been given "2A Pre-plate" rings to work to before, and of course - they are slightly smaller in PD's than the "finish" rings are.

So - then the boss pulls out the Machinery Handbook (V23 - same as mine) and shows me a sentence or two about 2A being used as a "pre-plate", but there is mention of Class 3 in there as well, but we did agree that as long as the 2A "No-Go" didn't go on after plate, that all was well with the world.

So I git home and pull out my book to read the whole schpeal, and not just one sentence or two, and I find that they are more right than wrong, and near as I can tell, most of the rest of us are actually wrong.

The book tells that a plated 2A is allowed to guage up to the 3A "Go" size. Which in this case was 3/4-16, and the 3A high limit was .0015" bigger than the high limit of the 2A version of the same. The 3A low limit is just not used in this app.

I've never seen it done this way before, but that doesn't make it right.
"It" being - not using the 3A high limit."

What I am used to running to is what is known as a 2AG, which does NOT allow build-up beyond the 2A high limit guage after plate. Up to now - I had never known that term, and if I had seen it used somewhere before, I prolly would have ass_u_med that to mean that it was a ground thread, but apparently not.


So tell me, for those of you that deal with this in any regularity, how doo you handle this in your shop?


-------------------------

Think Snow Eh!
Ox

 

[Ox]

To help y'all out, for anyone not believing - as neither would have I:

Glossary "Unified Screw Threads"
Maybe 4 pages in with be the sub heading "Thread Classes" in small bold.



Or even up front under "Contents";
Sub Heading "Threads and Threading"
Section "Unified Screw Threads"


It starts on page 1486 in the 23rd edition.

Y'all doo have a Machinery Handbook eh?


Or maybe this is how the rest of you have always done it?


---------------------

Think Snow Eh!
Ox

 

[rogertoolmaker]

Meeting thread requirements after plating

It came up today that a customer of mine is running their [before plate] 2A spec threads, to "finish" 2A guages, and using 3A GO's as their "after plate" guages.

I don't generally use "pre-plate" guages as a rule, but we make sure to run on the low end, and even slightly under the "no-go" limit to allow build-up in plating.

I was getting dinged for being slightly under "low" before plate, and I told them that after plate that they would be fine, but these folks Shirley plate a whole lot more of these than I doo, so I was cornfused as to why they thought this way? Obviously it's working for them, but .... ???

So I was telling the QC guy (not his full time position) that "2A" is not a "pre-plate" spec, but it's _ it's own spec, and 3A is too. I have been given "2A Pre-plate" rings to work to before, and of course - they are slightly smaller in PD's than the "finish" rings are.

So - then the boss pulls out the Machinery Handbook (V23 - same as mine) and shows me a sentence or two about 2A being used as a "pre-plate", but there is mention of Class 3 in there as well, but we did agree that as long as the 2A "No-Go" didn't go on after plate, that all was well with the world.

So I git home and pull out my book to read the whole schpeal, and not just one sentence or two, and I find that they are more right than wrong, and near as I can tell, most of the rest of us are actually wrong.

The book tells that a plated 2A is allowed to guage up to the 3A "Go" size. Which in this case was 3/4-16, and the 3A high limit was .0015" bigger than the high limit of the 2A version of the same. The 3A low limit is just not used in this app.

I've never seen it done this way before, but that doesn't make it right.
"It" being - not using the 3A high limit."

What I am used to running to is what is known as a 2AG, which does NOT allow build-up beyond the 2A high limit guage after plate. Up to now - I had never known that term, and if I had seen it used somewhere before, I prolly would have ass_u_med that to mean that it was a ground thread, but apparently not.


So tell me, for those of you that deal with this in any regularity, how doo you handle this in your shop?


-------------------------

Think Snow Eh!
Ox

We are really only concerned with: "meeting the requirements in the finished part". The 2A gage for a 2B threaded hole is .001 over the basic dimension. And the 3A gage for a 3B threaded hole is .0015 over the basic dimension. Meeting a 3A requirement before plating to allow for the plating is common shop practice to meet a 2A thread requirement after plating. I suggest you contact your Manufacturing Engineer and have him clear up the confusion in the shop with written instructions.

Roger 06/18/2017

 

[Ox]

One of us has no idea what you are talking about.


----------------

Think Snow Eh!
Ox

 

[Gordon B. Clarke]

I've known this guy for years and he's usually "spot on".

Class-of-Fit: 2AG for UN-series screw threads

Over and out.