Unfamiliar screw thread 3

[metalonis]

Our customer is asking for a 0.668-20 UN 2B thread to be machined int a part. The thread is not to be coated. He insists it is not really an 11/16-20. There does not appear to be a metric equivalent, either. Any ideas where I can get info on this?

 

[MadMango]

Sounds like your customer is trying to define a M17 thread in ANSI format.

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

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

 

[MintJulep]

The geometry is defined nicely here:

http://en.wikipedia.org/wiki/Unified_Thread_Standard

Plug in 0.668 and chug away.

I'd suggest getting your customer's signature before you commit to any tooling.

 

[lumenharold]

A 17mm X 1 has a major dia of .6683 and a pitch of .039 instead of the .05 your client is suggesting. If it is not the metric thread then it is a UNS.

Harold
SW2010 SP3.0 OPW2010 SP1.0 Win XP Pro 2002 SP3
Dell 690, Xeon 5160 @3.00GHz, 3.25GB RAM
nVidia Quadro FX4600

http://www.lumenflow.com

 

[Cockroach]

This is a bastard thread, not a clipped 11/16 - 20 UN-2G thread form.

0.668 - 20 UN-2G - 1 Start
c/w 45 Degree End Chamfers

External Diameter Internal Diameter
Major Dia. 0.667/0.658 Minor Dia. 0.614/0.625
Pitch Dia. 0.634/0.630 Pitch Dia. 0.636/0.641
Minor Dia. 0.608/0.606 Major Dia. 0.668/0.671

Measure the Pin over 0.029 diameter wires for a pitch diameter of 0.673/0.678 (3 wire measure).

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

 

[ABritTurner]

You don't say if it is an internal thread or an external thread. An external thread has a large tolerence on the major diameter. But as the gentleman said earlier this is not a clipped 11/16 UN thread, it is a bastard thread. It is 1.6 thou less than a 17 mm thread but is not metric because of the pitch, this pitch (1/20) is 1.27 mm a non standard metric pitch.

When it comes to chosing major diameters to suit pitches there are tables of drecommended diameters for the pitches listed, however since this is not UN (your cutomers ahs said so) then these tables don't apply but could guide you.

I have faced this problm with my customers ona numebr of occasions, usually this problem occurs from them buying foreign equipment. The Japanese are notorious for defining thread of a non standard nature (which is frowned upon in the EU if not banned. When the aprt of the equipment fail they have to choose between manufacturing their own (cheaper) or buying in from Japan (expensive) then they find there is no standard for the part. The most dangerous thing the customer can then do is to parce out the thread without defining the standard, over time different copanies make the parts and the standard starts to drift. Over the years they get a whole bacth of parts that don't fit.

The first thing to do if you are makng the nut is to ask your custmoer if you can emasure a range of components. By doingbthis you will identify the major diameter of the male part. If you are amkign th emale thread thenyouhave to ask for the female part to measure. Once you have a table of results with the variations you can then design a thread table to make a tap.

In your case the tap wil be around 17 millimetre, not a huge obstacle and you cna then define your table to suit this tap with the normal tolerance and clearance for this effective diameter.

before designing this table you need to be up on thred forms and tables. A tap manufcaturer willa ssist you. It is quite easy once you have determined:
1. the thread form
2. the pitch
3. the effective diameter male and female, all other sizes come from these.

In your case it is realtively easy, you have:
1. the thread form (UN)
2. Pitch (1.20")
3. within 1.6 thou the major diameter (17mm)

You give the minimum of information and it seemes it has to be dragged out of you like pulling a tooth but if you were more open we could be more specific. I find the same story with most enquiries, there is limited information, and no mention of quantities or cost considerations. I have yet to recive a thanks for the dozen or so answers I have listed.

This thread could be a 17diameter x 1.75 pitch metric thread, but only if the cusotmer has mesured the pitch wrongly. There is almost 2 thou difference in the pitch. Go see your customer and measrue the pitch for your self. Keep your knowledge under your hat and solve the problem and earn your company years of work. Tell the customer and they may well put the work out to someone else.

 

[metalonis]

Thanks all for your input.

 

[mrainey]

"In your case it is realtively easy, you have:
1. the thread form (UN)
2. Pitch (1.20")
3. within 1.6 thou the major diameter (17mm)"


The pitch is what??



Software For Metalworking

http://closetolerancesoftware.com

 

[lumenharold]

As long as we are nit picking (which we typically do), the OP did state that it was an external thread that the client is asking for when they say "2B".

Harold
SW2010 SP3.0 OPW2010 SP1.0 Win XP Pro 2002 SP3
Dell 690, Xeon 5160 @3.00GHz, 3.25GB RAM
nVidia Quadro FX4600

http://www.lumenflow.com

 

[metalonis]

2B indicates an internal thread.

 

[CorBlimeyLimey]

mrainey,
2. Pitch (1.20") ... Obviously a typo ... should have been 1/20"


metalonis and lumenharold,
It's just the B which indicates the internal aspect. The 2 refers to the class of tolerance.

 

[lumenharold]

That's what I get for 1.) trying to be a smarty-pants and b.) trying to do so quicky! Doh!


Harold
SW2010 SP3.0 OPW2010 SP1.0 Win XP Pro 2002 SP3
Dell 690, Xeon 5160 @3.00GHz, 3.25GB RAM
nVidia Quadro FX4600

http://www.lumenflow.com

 

[KENAT]

faq404-1480

Posting guidelines faq731-376

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

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

 

[mrainey]

Details matter.


Software For Metalworking

http://closetolerancesoftware.com

 

[metalonis]

As it turns out, the thread is actually a special non-standard 0.668-20 UN 2B thread.

Thanks everyone for your input.

 

[KENAT]

That would be 0.668-20 UNS I believe. FAQ404-1480

Posting guidelines faq731-376

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

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