Thread Call Out

[draftsman101]

I have a part that has an 1.95 ID and a 2.13 OD. It has internal threads that are 20tpi. the insert for the part is 1.95 OD and has external threads that are 20tpi. Both will be machine threads.
My question is how do I lable the call out on a print?

 

[namdac]

There are a couple of different ways to do this. There are the purists who recite ANSI from memory that are in this forum. Then there are the cut and dry people who do the machining themselves. If you are a GDT type you will follow ANSI Y14.XXXXXX. I myself would just call out the thread type and call it good. The Machinist will know the rest.
Regards,
Namdac

 

[MadMango]

Instead of 1.95 od on your insert, can you use 1.94 (1.9375)? If so, then 1-15/16-20 would be a standard thread call out.

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

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

 

[KENAT]

Assuming you're in the US and using unified thread then the correct standard is ASME B1.1

I'm not at work today so can't reference it but I suspect the size you want, if you can't adjust it to a standard size, will be a special thread. For a unified form this will be UNS designation.

Callout would be something like 1.95-20 UNS – 2A for the screw and 1.95-20 UNS – 2B for the nut.

If you don’t know the A or B designates male/female while the -2 is the tolerance class. There are other classes. For instance if it needs to allow for fine adjustment then class 3 may be appropriate.

My checker makes me add the major/minor and pitch diameter & tolerance underneath the callout for UNS threads. I’m not in 100% agreement with this but he has around 40 years more experience than me so I do it as he’s more likely to be right than I!

This website can calculate them for you, punch in the size you need in the UNS section and the results come up as a pop up window. The info you need will be at the very bottom of the pop up. Obviously note the disclaimer that anything you get off the net for free should be verified.

http://www.boltplanet.com/

You should also reference the relevant thread standard on the drawing. While this is not exactly common practice it is recommended in the standards, I know because this question came up before and I looked it up, can’t remember where in the standards it is off the top of my head though. A note up with the standard drawing notes saying something like “ Threads in accordance with ASME B1.1” should do it.

As namdac implies if you just put “1.95x20” you’ll probably get what you want from most machine shops, but is ‘probably’ adequate?

A Drawing is effectively a legal document in the event of a dispute between you and a supplier. In this case just saying 1.95x20 may not be considered fully defining the thread form & tolerance so you may be out of luck in a court case.

 

[CorBlimeyLimey]

What is the purpose of the thread?
The part with the internal thread has a 1.95" ID and the external threaded insert (mating part ?) for it has an OD of 1.95" ?????

Unless I am completely missing something, it doesn't matter what you label the call out, the threads won't engage.

 

[KENAT]

CBL, if 1.95 is the 'nominal' then its fine. Just like a nominal 1/2 inch bolt fits a nominal 1/2 inch nut (assuming same threadform/TPI etc).

 

[draftsman101]

I think that I found what I wanted in the Machinerys handbook pg. 1269. I would be a 1 15/16 - 20 UN. I am not finding an UNS or an UNC call-out.

B. Long
P 4 2.80 GHz
2.5 Gig Ram
Solidworks Office 2007 Sp. 2.2

 

[KENAT]

UNS is a special. Hence you wont find it listed in a reference like Machinery’s handbook.

For a UNS you actually have to calculate out the diameters based on formula in the thread standard, they are not listed in the tables as there are theoretically infinite combinations of diameter and thread pitch. UNS covers anything that isn't a 'standard' unified thread, i.e. not UN, UNC, UNF or UNEF.

If the 1 15/16 (1.9375)- 20 UN (per Mad Mango) will work for you this is a better idea than having a 'special'.

However you originally asked for 1.95x20, this would be a special as I detailed previously.

 

[draftsman101]

Thank you KENAT I will be able to use the 1 15/16 - 20 UN.

B. Long
P 4 2.80 GHz
2.5 Gig Ram
Solidworks Office 2007 Sp. 2.2