Data for NS Thread Type (For Bearing Locknuts)

[pdybeck]

Can Anyone point me in the direction for information concerning NS thread types? The particular thread is a 1.563-18 NS-3A. I have located the nominal pitch diameter and minor diameter, but I am unable to locate any tolerance information for these dimensions. Is there a good reference on this thread type - a website possibly? Thanks in advance.

Pete Yodis

 

[Timelord]

Machinery's Handbook lists 1-9/16-18 UNEF & UNREF thread forms and gives tolerances for classes 2 & 3, internal & external.

 

[mrainey]

Extensive info about NS and many other thread types in this program. Takes the place of several handbooks and a pocket calculator. Demo version.

http://dl.winsite.com/bin/downl?19500000038161

Manufacturing Freeware and Shareware
ME Consultant, ME Threads, ME Weights

http://mrainey.freeservers.com

 

[Tmoose]

http://www.ame.com/pdfs/locknut.pdf

tolerances for mating part (shaft) on page 2.
-------------------------------

 

[pdybeck]

I've managed to learn the history of the NS (American National Thread-Special)thread type and how the American National Standard was absorbed (in a way) into the Unified Series during WW2. Apparently there were/are "subtle", "benign", or "minor" differences between the NS and UNS thread. The mating parts are interchangeable, but what I want to know is can I use a 1.563-18 UNEF ring gage to inspect the 1.563-18 NS thread? Our 3rd party test and measurement calibration house claims they have trouble in locating a ring-gage for the NS thread type, so I was wondering if we could spec a UNEF gage.

 

[unclesyd]

Here are some people that you could contact for the information and if needed they maybe able to regrind your gage to the proper clearances.

http://www.accu-gageandthread.com/index.html

 

[pdybeck]

I'm still having trouble here. I am trying to find out what the differences are between the 1.563-18 Class 3 NS and the 1.563-18 Class 3 UNEF. Any information I have been able to find just mentions again "Minor" or "benign" differences. I get different answers from different people. I think there is a real fundamental lack of understanding on this subject (myself included) and we have people that claim to be experts, but yet don't seem to know some important information and offer conflicting information compared to other "experts". Our 3rd party testing and calibration house may have problems in checking gages for a 1.563-18 NS thread type compared to checking gages classified under the 1.563-18 UNEF thread type. I want to see if we could use a ring gage (go, no-go)made to check 1.563-18 UNEF class 3 and if that would cause problems. We don't want to send parts back to the vendor that made the 1.563-18 NS thread claiming they were not in spec when our method of checking is flawed. We don't want to measure each possible thread variable as that will get costly (way too much time). We would like to check thread function using a go, no-go ring gage set. Are there any "experts" out there? I have called around to different "experts" to no avail. Any additional help would be greatly appreciated. Maybe I needed to give some addded background information that I should have listed in my original post.

 

[mrainey]

I’m not truly an “expert”.

From Machinery’s Handbook, Twentieth Edition, page 1278, and referring to the Unified series as the “now” and the American National series as the “then” :

“Somewhat greater tolerances are now provided for nut threads”

“As contrasted with the old “classes of fit” 1, 2, and 3, for each of which the pitch diameter tolerance on the external and internal threads were equal, the classes 1B, 2B, and 3B (internal) threads in the new standard have, respectively, a 30 percent larger pitch diameter tolerance than the 1A, 2A, and 3A (external) threads. Relatively more tolerance is provided for fine threads than for coarse threads of the same pitch. In cases where previous tolerances were more liberal than is required in manufacture, they were reduced”

I think I’d assume that the gages for your two threads might well need to be different.


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[funnelguy]

pdybeck,
Your last post intrigued me, so I went back to my 23rd Machinery Handbook for a look. No details were available in tabular form on the NS tolerances in my handbook for your specific size. Specifics are available for the UNEF form, but not the NS series. There is a notation explaining that PD tolerances were evenly split between internal and external forms prior to the adoption of "current" standards. "Current" standards allow 30% more tolerance to be applied to internal thread PD's than external.

So, pdybeck, the short answer would seem to be "No". Sorry.

Perhaps someone else has an older set of standards that would provide you with better specifics.

I think a call to a reputable gage manufacturer would answer all your questions. You might want to consider ordering duplicate gage sets for your subcontractors to avoid these types of problems in the future. Especially if you must stay with the NS specification. Of course that adds complexity to your gage maintenance and calibration program.

 

[pdybeck]

funnelguy,

You seemed to have hit the nail on the head. It certainly adds complexity to our gage maintainence and calibration program (3rd party). The tolerance information for NS (NS really means special, and that could really mean anything) thread type is found in the bearing locknut section of Machinery's handbook of all places. The text at the bottom of the table states the values are from American National Thread Form Class 3. Based on this information and what the Unified Thread Series defines, it appears that only an NS gage should be used to check as a UNEF gage would except threads that an NS gage might accept.

 

[funnelguy]

Mrainey and I must have been typing at the same moment! Anyway, there seems to be a consensus about the details of some of the tolerance allowances, splitting of same and such. All of this info being discussed is from some old Machinery Handbooks. It has been well over 2 decades since I looked at published thread standards from the appropriate organizations. You might want to purchase an up to date set from the appropriate body.

Now, having said all that…
The drawing callout is 1.563-18 NS-3? I would change the drawing callout. I find only a .0005” difference in the nut PD. The difference looks to me to be acceptable and in the direction that it would be safe to mix the standards in this case.

N-08 Locknut
PD 1.5269 min / 1.5314 max
Minor Dia 1.5029 min / 1.5089 max

1.563-18UNEF-3B specs
PD 1.5264 min / 1.5312 max
Minor Dia 1.5020 min / 1.5105 max

1.563-18UNEF-3A (shaft?) specs
PD 1.5264 max / 1.5227 min

A locknut made to either the AFBMA standards or using the ANSI standards for 1.563-18 UNEF will certainly work on a shaft with the 1.563-18 UNEF-3A callout.

My Handbook provides no tolerance range for the shaft PD recommended by the AFBMA. Instead it references the external shaft threads to be “American National Class 3”. I’d change the shaft callout on the drawing to 1.563-18UNEF-3A and go from there. Alternatively, add all relevant thread form info to the drawing. Now there can be no confusion between yourself and your vendors. The vendor is not using a ring gage during the manufacture of the shaft. Most likely a thread mic or dial snap gage. The ring gage would only be used as a final inspection device, anyway. Purists may fell free to differ, but at some point I think we are just beating a dead horse. Let’s ship some parts!