162 replies to this topic

[midridge2]

http://www.gewinde-n...ine-thread.html

[GraemeC]

Well it looks like many have been wrong for many years and like Dan says does bring into question the technical standard of some of the A series specialists.

However I am still on the side that Whitworth Fine is not a documented and standards accepted thread however some may have adopted the name. Whitworth was, afterall, a more commonly used reference than BS, especialy when it came to the spanners/sockets etc.for the thread (bit like may people wrongly describing UNx bolts by their spanner size).
In fact I would argue that BMC were wrong in saying it is a Whitworth form as it is BS form, of which Whitworth is also one. I would expect the correct name would be BSS (British Standard Special).

But then, what came first - presumably the Whitworth thread which was then adopted and then standardised as BS, otherwise BSW woiuld simply by BSC(ourse) as with all the other standards based thread forms.

[DaveRob]

althogh I can see where Midridge is going with this WF link.... its actually data on BSF.... and for the 5/8th it shows 14 tpi....... not 16 as this thread is...... I can see the result is going to be a difference of opinion from both sides.... to me I consider it a Whitworth form thread due to the angles and peaks but with a 5/8th OD an 16TPI

Just my thoughts

Rob

[MRA]

I think it's obvious now that when I described the taps before, specifically which would interfere with the other thread I had managed to confuse the two in my mind. The reason the UNS tap that so many people own runs cleanly into the Whit thread is that it simply isn't contacting most of it (I think, I may have to draw this to help my confusion).

Well I drew it, very roughly and I was right the first time and as he said above Doug agrees. A UNS tap should remove material from an internal Whitworth thread. It must be purely down to tollerances. If I draw it to a higher precision including all the correct radii I suspect I will find why there is a clearance when there shouldn't be.

Med will obviously tell you it's fine and they have built many race engines that have not had a problem. It may be that their parts are made off site by a bolt specialist who is cutting them properly and they just aren't aware of it themselves. They haven't replied to tell me what thread they do actually cut yet.

Personally I would be very worried about using a high tensile bolt that had been cut......... Ok ok I am being a little pedantic here, however just for the record most bolts and any half decent bolts are rolled and not cut, this is also referred to as thread forming the action is of shifting metal to "form" the thread and not to cut it, this gives a far stronger thread form and higher fatigue tolerance.

[jn1702]

Ok how about this then? have a read

To change post-1992 head (including TPi variants) to pre-1992 fitment -

Drill 9/16"/14.5mm hole through counter-bored heater take-off hole (1/4UNF heater tap retaining stud holes are already in place) or remove blanking plate if fitted. For by-pass hose, either drill/tap 5/8" UNS (16TPi) port in required place and fit by-pass hose adaptor p/no. 12A2075, or drill/tap 5/8"UNF and fit adaptor p/no. 12H1405, or blank water pump port off with blanking cap p/no. CAM 4126 and either drill 6 1/8"/3mm holes around thermostat periphery or fit blanking sleeve (really not good for road use - recommend thermostat is fitted). For water temp gauge sender unit either drill/tap port out to 5/8"UNF thread or remove 5/8"UNF socket headed grub screw if fitted.



You'll see that 12A2075 needs a 5/8 16 tpi UNS hole tapping. If anyone has a 12A2075 how about trying it in the end of a crank to see how well it fits?

[midridge2]

http://www.britishfa...ges/catalog.pdf

[Nightrain]

The bypass hose is the same thread as the crank, 5/8 Whitworth Fine. Nobodies answered the question yet, your all telling me it's not Whitworth Fine but nobodies saying what they think the WF stands for. As proved above I can be quite gracious when I say told you so.

[[email protected]]

Whitworth Form, I think.......

But prepared to be proven wrong...

Edited by [email protected], 30 March 2009 - 06:55 PM.

[Nightrain]

The Tap was ordered as a 5/8 Whitworth Fine Tap.

[[email protected]]

Found using a websearch.....

BSF is a Whitworth thread form, meaning it has the same thread angle but it is a finer thread, i e it has more threads per inch than the BSW.

The Whitworth thread started out as being a coarse thread only and later they made fine threads which is why they are the same form.

Both were a whitworth size, but neither conform exactly to the correct 16 tpi size that is/should be in a mini crank

5/8 BSF would only have 14tpi, not 16
5/8 BSW would only have 11

Edited by [email protected], 30 March 2009 - 07:16 PM.

[DaveRob]

Nightrain...... I understand your frustration..... going back to Guessworks analogy.. some people thought the world was flat at one point in time. I think the consensus has moved to believe at this point your findings are correct re the thread form being a Whitworth dimensions. Its just that 16 TPI isnt normal in that 5/8 size.... BSF is the closest standard Whitworth form and even that in 5/8th is only 14 TPI and as I pointed out earlier was considered to be Whitworth FIne back in the day

Your photo of the tap is very interesting and I agree that that it indicates WF and logically it would refer to Whitworth Fine...if ever their was such a beast....... can you tell us the name of the tap manufacturer..... maybe we can refer to them for confirmation of a British Standard that details the spec of Whtworth fine.... as it can logically apply to more than just 5/8 16 TPI.

And thanks for the perseverence by the way.... bit edgy sometimes.... but point well made..... lol

Rob

[dklawson]

Regardless of what WF stands for I have something I'd like to show.

I constructed CAD models of 5/8-16 in Whitworth and UNS forms. The standards are not that hard to apply:
Whitworth
55° thread angle and a thread depth of 0.640327 p and a radius of 0.137329 p, where p is the pitch
therefore: 16 tpi, minor diam = .625-(2x.64*16) = 0.544959125, R = 0.0085830625

UNS (UNF/UNC)
60° thread angle and a flat top thread (p/8) Rounded root on male threads. (p/4) across minor root.
Therefore: Flat Crests: 0.0078125 wide, Flat Roots: 0.015625 wide

The JPG below shows what you see if you superimpose the two thread forms. Note that there is minimal interference between the two due to the way their geometries overlap. A 5/8-16 UNS tap would barely cut the major diameter of the female threaded hole... hence, almost no swarf would be removed if the UNS tap is run in a Whitworth form threaded female hole. Owing to manufacturing tolerances, I'd say that the UNS tap will only cut material when the MINOR diameter of the female threads have been damaged.

EDIT: Note in the JPG that the UNS thread is shown in blue in all instances and the Whitworth form in grey. The UNS thread form has the flat crests. The root radius/bottom of the UNS thread is not defined by any standards I've seen. While I show potential interference there, it's not likely to exist as it's probably removed by the tap drill for the Whitworth form tap.

EDIT2: I went back and took some information from KC's earlier emails. He mentions that the tap drill is called out on the drawings as 0.557"diameter. Superimposing the tap drill on the section view details in the picture below... there's virtually no contact between either tap's minor diameter and the tap drill hole. The only interference will be the minor amount occurring at the crest of the threads.

Attached Files

•  Whitworth_UNS_Profiles.jpg   189.13K   84 downloads

Edited by dklawson, 30 March 2009 - 08:34 PM.

[Dan]

Excellent that means I don't have to draw anything!

No there is no description of the root of Unified threads in the stanadard, that's because they were originally flat bottomed as well as flat topped. That made them very weak. They were invented in 18 something or other though at the dawn of standardisation and industry in America and at the time people didn't know that a radius would be stronger (although Whitworth already had radii in his thread at this time). As cutting tools wore out the threads produced developed a radius and people noticed the radiused thread was stronger. For details of a standard for the root radius look up UNJF or UNJC, these are aeropsoace threads. I don't know whether people apply this specification to regular UN fittings now or not but there is at least a standard there.

As for WF, I'm never going to accept that there is a Whitworth Fine. Whitworth was the first and original standard thread, the first one ever. Before Joseph Whitworth threads were custom made for every machine or fitting and nothing was interchangeable. When the thread was adopted as BSW it should have become BSC but didn't out of respect for the man and for history. There was never a fine thread devised by Whitworth, he created one singl thread and specified it from 0.1" 48 tpi to 6" 2.5 tpi. All the derivitives of his thread were made later by others and so have BS names. There are many besides BSW and BSF including BSCy, BSB, BSP, BSPT and others but none of them has 16 tpi at 5/8". This is a custom thread, plain and simple. It may appear in other parts of various Austin engines and they may have originally designed it but it is not on any standards tables. People in other countries may refer to BSF as Whitworth but they are not right. This tap may have had WF stamped on it by a Chinese machine shop but they aren't right either. Then again, WF could be the name of whoever made it.

[Guess-Works.com]

Whitworth Form, I think.......

But prepared to be proven wrong...

That is what I would infer, basically didn't say that earlier as I thought it was a bit ****ing obvious...

They could not stamp it Whitworth as that would be wrong, Nor BSF, as that would also be wrong... which is why when you do an 'odd' UN thread it's called UNS, cause it's not UNC or UNF... and there is only one Whitworth thread.

Ok, in theory maybe WS would have been better.... but that's by the by...

Think I'll get them to stamp it with 5/8" 16 BMC CRANK !

PS MG's etc have the same thread

[MRA]

Nightrain...... I understand your frustration..... going back to Guessworks analogy.. some people thought the world was flat at one point in time. I think the consensus has moved to believe at this point your findings are correct re the thread form being a Whitworth dimensions. Its just that 16 TPI isnt normal in that 5/8 size.... BSF is the closest standard Whitworth form and even that in 5/8th is only 14 TPI and as I pointed out earlier was considered to be Whitworth FIne back in the day

Your photo of the tap is very interesting and I agree that that it indicates WF and logically it would refer to Whitworth Fine...if ever their was such a beast....... can you tell us the name of the tap manufacturer..... maybe we can refer to them for confirmation of a British Standard that details the spec of Whtworth fine.... as it can logically apply to more than just 5/8 16 TPI.

And thanks for the perseverence by the way.... bit edgy sometimes.... but point well made..... lol

Rob

BS84 does not include Whitworth fine, however it does include Whitworth derivatives ie. specials. So if the Tap is a Whitworth form and its finer than standard then you can call it Whitworth Fine. It just does NOT exist in BS84 which is the specification for Whitworth Form threads.