To Cap It All

[martyn nutlandParticipant @martynnutland79495]

Hello Everyone

I wonder if I might pose a couple of questions and try out an idea on the experts?

I want to make a bronze vintage radiator cap (I do know I could buy one but they seem disproportionately expensive and I like to make things!)

I thought… if I bought a nut of the same thread as that on the neck of the header tank, I could turn off the hex on the lathe, mill a bronze replica of the original cap and solder or braze it to the nut. Simples! Job done.

However, I can't for the life of me, and after consulting every table I can find, determine what the male thread is. The major diameter is 37mm 16 TPI. Any ideas?

Now I acknowledge the proper way to do this job is start with raw bronze and cut the female thread on the lathe, but I don't feel I have the competence or confidence to do this, not least because there are a few fundamentals I'm unsure of.

I use a Chester Super B lathe configured for metric. Assuming I know the lead screw pitch, can I gear a metric lathe to cut imperial threads, as would be required (I guess) for the radiator cap. And if I can, and someone knows the thread I'm talking about, what change wheels might I be looking at.

Hope all this is not too bizarre.

Best, as always, from la belle France.

Martyn

[martyn nutlandParticipant @martynnutland79495]

Making radiator caps

[martyn nutlandParticipant @martynnutland79495]

Addendum!

As regards the thread – I've seen the major diameter expressed as 1.475 inches, which is about 37.4mm isn't it?

Martyn

[Michael GilliganParticipant @michaelgilligan61133]

My trusty ‘Fractions Calculator’ gets 37 and 93/200 mm [37.465] … but, whichever way you express it, I don’t recognise that as a thread size for which you could expect to buy a standard nut.

MichaelG.

[noel shelleyParticipant @noelshelley55608]

A 1" brass commpression fitting might be worth a try – the nut ! Or the brass fittings used on plastc pipe may be big enough. I will see if I have one and can measure the thread ! Some had fine threads others much coarser. Talk to a plumber, or look in his scrap box. Good luck Noel

[john halfpennyParticipant @johnhalfpenny52803]

Vintage radiator threads are, in my experience, all over the place, but a Model A Ford is about 16tpi ( much larger od though). This Ford thread would certainly be 60 degree form. Vintage Vauxhall is much coarser at 8tpi.

[Clive FosterParticipant @clivefoster55965]

Martyn

According to Andy Pugh if its 37 mm diameter its a PG29 conduit thread to DIN 40430.

Andys list gives :-

Designation Pg29
Type COND
Major Diam imp 1.457
Major Diam mm 37.00
TPI 16.0
Pitch mm 1.588
Core Diam inch 1.3969
Core Diam mm 35.480
Thread Depth inch 0.0299
Thread Depth mm 0.760
Thread Angle mm 80°

Seems awfully shallow for a radiator cap thread but the numbers fit.

That said 16 TPI is a permitted constant pitch thread under the Whitworth system but you'd expect the diameter to be 1.5 inch if it were Whitworth. Constant pitch size nuts in Whitworth don't exist. Specials only.

Clive

PS Rattus Crappitus. Spent ages sorting that into a nice list with extra spaces and the stupid forum software just stripped them out.

Edited By Clive Foster on 28/08/2021 10:11:16

[JasonBModerator @jasonb]

It's quite possible it is 1.5" nominal with worn or over rounded crests and could be 55 or 60deg

Though the originally quoted 37mm x 16 would make it a PG conduit thread but usually only thin pressed steel nuts available for that

Beaten by clive, just

Edited By JasonB on 28/08/2021 10:10:20

[egaParticipant @ega]

I have a couple of larger radiator caps (c49mm OD) both with 16 TPI threads and deduce that this may have been the standard for this kind of thing.

I assume that your smaller cap is for an Austin Seven. My own 1931 machine came with a presumably non-standard one with built-in temperature gauge; after this was stolen I replaced it with one that resembled one of the couple:

Not an answer to your question I'm afraid but I thought this might be of some interest. In your position I would regard the machining of the body with its pleasing form to be the difficult bit; the screwcutting looks straightforward.

[Speedy Builder5Participant @speedybuilder5]

What vehicle radiator ?? British / American will use TPI and most others will be some form of metric generally.

37mm is about Austin 7 size. which I believe is 1 1/2" and the thread would be Whitworth form and any TPI the maker chose.

Bob (1932 Austin 7)

[roy entwistleParticipant @royentwistle24699]

What make of vehicle is it ?

[bernard towersParticipant @bernardtowers37738]

I’m with Jason it’s a worn 1 1/2” x 16, I have done one in the past.

[Clive FosterParticipant @clivefoster55965]

Probably made undersize rather than worn.

Radiator cap threads are usually made fairy slack to help dissipate pressure during unscrewing if the cooling system is still hot rather than blasting it off as it come to the end of the last thread.

The extra 25 thou clearance by making the majot diameter 1.475 inches rather than the "proper" 1.5 inches for a constant pitch Whitworth thread is entirely reasonable.

Clive

[WatfordParticipant @watford]

Posted by Speedy Builder5 on 28/08/2021 10:22:31:

What vehicle radiator ?? British / American will use TPI and most others will be some form of metric generally.

37mm is about Austin 7 size. which I believe is 1 1/2" and the thread would be Whitworth form and any TPI the maker chose.

Bob (1932 Austin 7)

and 1929 Chummy at 1 1/4" by 13tpi

Mike

[Martyn Nutland 1Participant @martynnutland1]

Many, many thanks everyone. An education in itself!

I'll pursue PG29; maybe ask our plumber, who, resident on the Somme, may not often deal with Austin Seven radiator caps,

Thanks again

Martyn

[JasonBModerator @jasonb]

You would do better asking an electrician than a plumber as it's a conduit thread. But as others have said 1.5" x 16 most likely on an A7

[HOWARDTParticipant @howardt]

Why not try ringing a radiator refurbished/maker, I have one near to me and there was one recently on a car rebuild program recently.

[Paul LousickParticipant @paullousick59116]

Martyn,

You have said that " if I bought a nut of the same thread as that on the neck of the header tank, I could turn off the hex on the lathe, mill a bronze replica of the original cap and solder or braze it to the nut"

Therefore you must have access to a lathe and mill so why not make a cap yourself. Not too difficult and will be a good learning curve for some new skills. Try plastic or aluminium for a trial first, then make one out of brass or bronze, A good feeling after you have mastered it.

Paul.

Edited By Paul Lousick on 28/08/2021 14:11:42

[Russell EberhardtParticipant @russelleberhardt48058]

I would be inclined just to buy one new. I've had good service from the Seven Workshop in the past. Probably cheaper than a chunk of bronze to make one.

Russell

[Martyn Nutland 1Participant @martynnutland1]

We have them as well – electricians!

I know…key in your credit card co-ordinates and you have one by return (or something) of post from the usual suspects. Or most other Austin Seven parts for that matter..

I just wanted to make one, which is what I thought we were about. And I wanted to learn.

Best

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Martyn Nutland 1 on 28/08/2021 16:20:06:

[…]

I just wanted to make one, which is what I thought we were about. And I wanted to learn.

.

That’’s the spirit

Unfortunately; if the original is like ega showed … I would think it's formed from tube, and then closed with a soldered-on cap.

I would love to see how they actually made that.

MichaelG.

[egaParticipant @ega]

MichaelG:

You are quite right – apart from the screw thread, the cap in my photos above is certainly formed as opposed to turned and milled. I can't see any trace of solder, however.

The other cap I referred to looks like a brass casting and is much larger in overall diameter.

[Speedy Builder5Participant @speedybuilder5]

Jason, the originals had a thin top hat machined in brass which formed the thread and cap. The outside is knurled and a Bakelite cap bonded to the brass. I think Martyns best chance is to find a bit of brass and if lucky enough a big brass nut with enough meat to turn the internal thread, machine off the hexagon, crewcut the thread,silver solder a thick plate onto it, and machine the cap. Expensive exercise but it would be the joy of achievement. Chance of finding a 16tpi thread here in metric land would be like finding hens teeth – BUT good luck.

French Suppliers

Brass stop ends 2" BSP may be a possibility (2" BSP 2.347" OD) but the finished wall thickness may be very thin or non existent.

brass stop end

Or possibly something like this ??

Solder stop end

Bob

[Speedy Builder5Participant @speedybuilder5]

Ps, if Martyn would like to PM me, I have both cast cored bronze and some scrap marine bronze that would make the 1 1/2" diameter threaded portion here in France.

Bob

[Michael GilliganParticipant @michaelgilligan61133]

Posted by ega on 28/08/2021 17:22:01:

MichaelG:

You are quite right – apart from the screw thread, the cap in my photos above is certainly formed as opposed to turned and milled. I can't see any trace of solder, however.

[…]

.

Thanks for the confirmation

I had assumed [always risky] that the highlighted ring would have a solder joint

.

MichaelG.

[Author]

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