UNS thread

[Mike Farmer]

 

Hi gents.

UNS thread is a new one on me. I ordered a BSCy and received a UNS. They are listed together. Before I start chasing the supplier, are they the same, if not what's the difference? Stranger things happen.

Mike

[chaz]

Mike rather than baffle you here , have a look at google. UNS is a special Unified thread, not UNF Fine or UNC Coarse.

Unified form thread designations are represented by abbreviations such as UNC (unified coarse), UNF (unified fine), UNEF (unified extra fine), UNS (unified special) and UN (unified constant pitch), with the thread major diameter preceding the designation for example, 9/16” UNC, 9/16” UNF.

We usually use UNF, UNC or UNEF Extra Fine which would be similar to BSC, The UN series were generally American as opposed to our BS British Standard.

https://www.gewinde-normen.de/en/unified-special-thread.html

coincidentally, we have done Panzergewinde threads as well at work PZGW. nothing to do with tanks.

probably supplied as an alternative to BSC as the same thread angle 60', same as some suppliers send M5 for 2BA.

[JulianS]

The A10/A65 pressure relief valve thread is 7/8 inch x 16 tpi UNS. The only UNS tap I have was purchased to clean this thread on my A10.

[Mike Farmer]

 

Thanks for that.

I ordered BSCy 5/8 tap and die, crank shaft tread. the tap is correct so I need a different die?

OK Mike

[Mike Farmer]

 

I have had a conversation with the "tooling boys" and am informed that. 5/8 x 20 BSC, 5/8 x 20 UNS and 5/8 x 20 Whitform are all exactly the same.

I am waiting to hear back from engineers in Germany about PKZW. Its origins and usage reasons.

Who knows. I had never heard of half the things I found out today.

Mike 

[chaz]

Mike, err on the side of caution ..BSW and BSF threads were 55 degree, Cycle and UN are 60.
as part of our reclamation processes we used 26tpi Whit Form threads, giving more threads in casting walls when reclaiming scrap or damaged threads. these taps, (no longer used but I have a lot of them)  were made in our tool room using British Standards they were 55degree.

[Mike Farmer]

 

Situation is.

I re-tapped and cleaned the "new" nuts with the correct BSCy tap. Then ran the threads on the crankshaft with the UNS 5/8 x 20. Perfect.

So I am happy. New CS tap and die £30 inc and I have another crank to do. Insufficient projected use to buy an expensive set.

Take care.

Mike

[Calum]

probably supplied as an alternative to BSC as the same thread angle 60', same as some suppliers send M5 for 2BA.
[/quote]
I should.hope not! They're close, and often fasteners interchange but they aren't the same diameter or pitch (Or thread angle - 60 vs 47.5)

Using an UN form instead of BSCy isn't too bad, as chaz says they are indeed both 60 degrees with only minor detail differences on the peak and trough radii etc. BS at 55 degrees with the same major diameter and pitch won't necessarily go together with a 60 degree thread, the flank contact will be a little poor but the minor (root) diameter is smaller on a 55 degree thread. This means a 55 degree bolt will go into a 60 degree tapped hole, but a 60 bolt shouldn't go into a 55 degree tapped.hole.

A lot of this is looking onto it too deeply, as for a lot of mass produced fasteners the tolerances are quite large and as such some will go together when strictly speaking they shouldn't... this is helpful for low stress applications as it can get you out of a hole but not ideal!

[chaz]

probably supplied as an alternative to BSC as the same thread angle 60', same as some suppliers send M5 for 2BA.

I should.hope not! They're close, and often fasteners interchange but they aren't the same diameter or pitch (Or thread angle - 60 vs 47.5)

unfortunately, one of the biggest BSA parts suppliers sent me M5 screws instead of 2BA.
I ended up running a die down the thread to correct as best as possible.
ive also had M6 sent for 1/4BSW bolts.
on a tangent a major Ariel specialist sent a customer standard bearings instead of C3 ones for a pair of square4 crankshafts, when dropped in, they fell out when the castings cooled down.

as OEM parts are becoming fewer, rather than get new ones made they are getting what they can find commercially.

[Mike Farmer]

 

Hi. I have become quite intrigued by this and realize that my understanding of threads is limited. May I pick up on a couple of points and expose my lack of knowledge to the four winds.

Firstly I make the assumption that in cross section the greater majority of threads is triangular, or triangle based. Either Equilateral, Isosceles or scalene(inc R angle). and that all three are used in various thread requirements.

Further assumption is that scalene is the more common. This would then produce a "scarp slope" of some degree; I cant imagine a situation whence a 'backslope' would be used.

That in turn may explain why sometimes re-use of nuts on the same bolt etc will run better in one direction that the other, because the inner thread of the nut has been stretched/deformed by use.

There you have it gents, my lack of knowledge in a nut shell. I look forward to the answer but please not over technically.

Mike

[chaz]

Mike, the possible reasoning behind your one way and not t'other could be the force used or acting on the thread. Especially arising on crank or axle threads where higher torque figures are needed and you are forcing the thread to go in one direction. as an example, rebuilding Japanese bikes its not uncommon for axles and clutches and engine sprockets to be done up from 50 to 100 nm. Steel on steel, on the opposite side casing screws are steel on ally and anything in excess of 5 to 10nm could strip out the ally t hread so not a problem.

in the higher range applications, there is the thought that do them up tight one way then turn nut around next time and do up tight and so on , are you weakening the flanks with the possibility of breaking them off