Paraffin blow torch thread?

[Andrew TinsleyParticipant @andrewtinsley63637]

I am refurbishing a 1/2 pint paraffin blowlamp. One of the threaded connections is damaged. It is 3/4″ OD and 18tpi.

The dimensions are accurate. I note that taps are available, so it is probably a recognised thread. But what is it? It certainly isn’t the expected BSP or NTP series.

Andrew.

[Andrew CrowParticipant @andrewcrow91475]

If it’s British made it will probably be of Whitworth form, in the place I once worked we had a number of constant pitch series taps which were generally above 1/2 inch and up to about 1 1/2 diameter but with finer pitches, 16tpi, 20tpi and 26tpi being the most common, but there were others.

Andy

[howardbParticipant @howardb]

It fits the dia/tpi data for UNS thread.

The UNS thread, with the full form being Unified Special Thread, is a designation from one of the major screw thread systems nowadays – The Unified (Inch) Screw Thread System.

[Speedy Builder5Participant @speedybuilder5]

Name, make and country of manufacture of blow lamp would help.

[Andrew TinsleyParticipant @andrewtinsley63637]

Yes, name make and country of origin would be very helpful , but unfortunately their is no indication of any of those things on the blowlamp.

The UNS system sounds far to modern to be applied to a vintage blowlamp. I am pretty certain that the thread is 55 degree Whitworth form, but eyesight isn’t what it was.

Andrew.

[Bo’sunParticipant @bosun58570]

Hi Andrew,

I’m not sure if they still exist, but a company called “Base Camp” in Peterborough might be able to help.  They specialised in all kinds of Paraffin Stoves and Lamps.

[Andrew TinsleyParticipant @andrewtinsley63637]

Hello Bo’sun,

Yes Base Camp exists and I have had some dealings with them recently about circular wicks for a couple of my oil lamps. I doubt if they are into detail on blowlamps, but worth asking.

I need to clean up the threads and I will make male and female threads in silver steel and harden and temper them. I think that will work rather than making full taps. I will try that first and see how it goes.

I am just curious about the thread type, but I suspect it is a special dreamed up by the blow lamp manufacturer!

Andrew

 

 

 

 

[howardbParticipant @howardb]

There is this website about blowlamps.

https://blowlamp.co.uk/

 

[bernard towersParticipant @bernardtowers37738]

Why not experiment by screwcutting various female test pieces to see what fits

[Andrew TinsleyParticipant @andrewtinsley63637]

Hello Bernard,

That is what I intend  doing. There is NO doubt that the thread is 3/4″ x 18 TPI almost certain that the thread angle is 55 degrees. The female thread on a brass retaining nut is smeared, which is the best description I can think of.

The nut is on a length of 5/16″ copper tube with brazed fittings either side. So I need to cut the nut free before I can work on it. I can then set the nut in the lathe and screw cut the smeared area of thread. Repairing the damage is trivial, although I will need to make up new fittings and purchase a new piece of 5/16″ copper pipe.

My curiosity is about the thread itself. Howardb has said it is UNS, but I suspect that the blowtorch predates the UNS system. Looks as though I am unlikely to satisfy my curiosity!

Thanks everyone for your posts.

Andrew.

[old martParticipant @oldmart]

The thread may be proprietry to the manufacturer to make people buy genuine spare parts, which has been common practice. I have a tin of special size taps hidden away at the museum, accumulated over the years to prevent the unwary from messing up their work.

UNS means Unified National Special which covers just about every odd size imaginable. I could make something with a Unified thread form in, say 2 3/16″ X 28 and call it UNS.

[Andrew TinsleyParticipant @andrewtinsley63637]

Yes,

I assume the thread is propriety to the manufacturer, whoever that was!

Andrew.

[Andrew Tinsley]

On Andrew Tinsley Said:

Yes,

I assume the thread is propriety to the manufacturer, whoever that was!

Andrew.

Doubtful – If you search for a 3/4″ x 18 UNS thread tap on Amazon.com taps and dies are available – quite a few of them.

[old martParticipant @oldmart]

Did you notice that Andrew thinks that the thread is Whitworth form, what kind of UNS is that?

[Andrew TinsleyParticipant @andrewtinsley63637]

I am fully aware that there are plenty of taps size 3/4″ x 18TPI on Ebay. From what I know of the history of this particular blowlamp. it is at least 85 years old and belonged to my grandfather. So would this align with the introduction of the UNS system?.

I have now put the male thread on my Shadowgraph and there is no doubt that it is 55 degrees Whit form. I assume that the UNS system would be 60 degree.

It would look as though this thread was a propriety one?

Andrew.

[Andrew CrowParticipant @andrewcrow91475]

<p style=”text-align: left;”>Hi Andrew, yes the UNS system is 60 degrees and I believe the Unified system was introduced during the second World War to integrate the US and British thread systems. Although very much based on the ANF/ANC thread system ie angle and pitches, it also brought in better accuracy standards so that fit was measured on the pitch line rather than diameter. It was adopted here particularly by the aircraft and motor industries.</p>
Andy

[Andrew Tinsley]

On Andrew Tinsley Said:

I am fully aware that there are plenty of taps size 3/4″ x 18TPI on Ebay. From what I know of the history of this particular blowlamp. it is at least 85 years old and belonged to my grandfather. So would this align with the introduction of the UNS system?.

I have now put the male thread on my Shadowgraph and there is no doubt that it is 55 degrees Whit form. I assume that the UNS system would be 60 degree.

It would look as though this thread was a propriety one?

Andrew.

I don’t understand why this topic has focussed on UNS and proprietary threads!  What Andrew describes is consistent with WHITWORTH, as suggested in the very first answer from Andrew Crow.

Confusion is possible because Whitworth Threads are standardised for two reasons, and the thread form is used in both contexts.  Whitworth form is shown below, note the rounded tops and valleys:

The form is applied separately to standard sized fasteners, as in this table:

When applied to nuts and bolts, the form and fastener dimensions both apply.   But Whitworth form threads can also be applied to objects that aren’t fasteners.  Things like Blowlamp fittings!   Manufacturer aren’t obliged to follow the fastener dimensions: they can put a ¾” 18TPI Whitworth thread on a brass tap if that suits their purpose.   The standard fastener dimensions are irrelevant.

Not long after Whitworth introduced his thread, an American defined an easier to make thread form.  Sellar’s Thread became the US standard National Thread, which was Unified after WW2, giving us UNC, UNC and UNS.  It has a number of advantages over Whitworth, one being flattened tops and valleys.   The thread angle is 60°, and took the form pictured below, or something like it. Standards  changed over time, and a bit murky, but I think I’m correct in saying that Sellar’s originally allowed V valleys, then flat, and since WW2 UN allows rounded too.   Rounded threads are good for sealing pipe connectors, these are not fasteners!.

 

Metric form is similar to the US system, also with a 60% thread angle, but specified with metric dimensions and pitch.   BA is metric with a 47.5° thread angle and rounded tops and valleys.  BA and Metric also standardise fastener dimensions.

All thread forms have been used on stuff other than fasteners.  If that’s been done, the fastener size standard won’t identify it.  I think Andrew’s blowlamp is an example.  Although standard Whitworth nuts and bolts do not come in ¾” 18TPI Whitworth, his lamp is still threaded in Whitworth form.

Using a standard thread form on other than fasteners isn’t really proprietary because the form conforms.  Proprietary involves changing the form, angles and dimensions.  Sometimes done for good reasons like anti-vibration in aerospace or anti-tamper, and often for bad, such as deliberately forcing owners to buy costly proprietary spares.

Andrew is well-placed to confirm what he has.  Owning a shadowgraph makes it easy to see the shape of a thread form and to measure it. Any chance of a picture please?

As the blowlamp old and probably British, I’ll be amazed if it’s not Whitworth.  That ¾” 18TPI happens to exist in UNS is a coincidence.  Whilst UNS addresses specials, it’s a high-end US standard unlikely to be adopted by a British Blowlamp maker.  No need – Whitworth thread form is good on an oil filled blowlamp because the coarse form with washer makes a good seal.  For the similar reasons the thread is unlikely to be early French, German, Russian, or Japanese Metric, UNJ etc.   It might be one of the many old thread systems that existed before standardisation: gunsmiths, instrument makers, private firms.  At one point Admiralty threads were quite common.

Nowadays less need for Whitworth or a Pipe thread in this application because O-rings seal better than washers.

Dunno about others because I make experimental stuff rather than working to other people’s plans or doing repairs.  Often convenient to thread non-fastener connections with non-standard diameters in 1.0 metric pitch.  For what I do, doesn’t matter that I ignore standard metric fastener sizes.

Another observation, I suspect many Model Engineers who lathe cut Whitworth threads are also way off British Standard Whitworth. Though individual their threads aren’t proprietary.    Problem is, a V cutter can’t easily create the rounded form demanded by the Whitworth standard, and amateurs need not fuss with tolerances.  Unlikely to matter provided the results mate, but beware if strength and/or a close fit are important.   When people say “I cut a Whitworth Thread”, they probably mean “I cut an approximation that’s close enough to Whitworth for my purposes”.   Doesn’t matter if the form is off-spec because Model Engineering rarely requires the strict conformance needed to ensure parts exchangeability.

There are many deviations from the exact standards in manufacturing and workshops that could make identifying a thread tricky.

Dave

 

[Michael GilliganParticipant @michaelgilligan61133]

Just to add a little to Dave’s notes … Here is a properly specified description of a manufactured Whitworth-form thread

… from those who still know how to do a job !

MichaelG.

.

[Andrew TinsleyParticipant @andrewtinsley63637]

Yes Dave, as I and others said earlier in the thread, the 3/4″ x 18TPI is a manufacturers special.

Andrew.

[vintagengineerParticipant @vintagengineer]

It could be Admiralty fine or a brass thread.

[Andrew Tinsley]

On Andrew Tinsley Said:

Yes Dave, as I and others said earlier in the thread, the 3/4″ x 18TPI is a manufacturers special.

Andrew.

You actually said proprietary.  I added value by explaining that’s not so.  Perhaps the point is too subtle!

🙂

The form is standard Whitworth (probably), which is very helpful.  The lamp doesn’t conform to the fastener standard because there’s no reason why it should – it’s not a fastener!

Don’t assume the thread is proprietary because you can’t buy off-the-shelf 3/4″ 18tpi Whitworth taps and dies.  Taps and dies mostly come in fastener sizes because that’s their main application; lots of call for them.   Not so blowlamp threads. The market for 3/4″ 18tpi is tiny.

Only a small problem if you own a lathe because Whitworth form is standard, and so is 18tpi. Only the 3/4″ diameter is “non-standard”.  Whitworth form isn’t difficult – buy an off-the-shelf carbide insert and use it to put an 18tpi thread on the diameter.  Easy.  Also, not difficult to make your own taps and dies from of silver-steel; done it several times.

Proprietary threads are much more difficult because both form and pitch are non-standard.   A 50° angle at 17tpi with unusual rounding radii is much harder to make than 3/4″ 18tpi.  Count your blessings!

Dave

 

 

[Andrew TinsleyParticipant @andrewtinsley63637]

Dave,

Your dissertations are way over the top for such a simple subject. As far as I am concerned and as are others, the thread is a simple special. No need to reproduce reams of internet information. The topic simply does not warrant it.

Andrew.

[John HaineParticipant @johnhaine32865]

This posting sequence seems to have morphed into a paraffin blowlamp thread…

[Michael GilliganParticipant @michaelgilligan61133]

Do you mean ‘reverted to being …’ John ?

The opening line was:

I am refurbishing a 1/2 pint paraffin blowlamp.

MichaelG,

[SillyOldDuffer]

On SillyOldDuffer Said:

Don’t assume the thread is proprietary because you can’t buy off-the-shelf 3/4″ 18tpi Whitworth taps and dies. 

Suggest you read the first post again where it was mentioned they are available

The only 18tpi I can think of around that size is conduit but nearest would be 0.730″ and you should be able to see it’s much flatter angle.

[Author]

Posts