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Member postings for Adrian Johnstone

Here is a list of all the postings Adrian Johnstone has made in our forums. Click on a thread name to jump to the thread.

Thread: Model engineering on BBC2
26/05/2020 11:07:36

Dear all,

some of you will have seen Royal Holloway's steam-driven Babbage Difference Engine designed and constructed by my good friend and colleague Dr Piers Plummer. The machine was awarded a prize by SMEE in 2019, and it also formed the centrepiece of our British Society for the History of Science Great Exhibitions prize in 2018. It is mostly constructed from 3D printed sintered nylon, with laser cut steel frames and a few stock bevel gears. It represents a 4x6 fragment of Babbage's Difference Engine 2, which is an 8x31 machine.

I popped up on BBC2 last night running the machine. It's powered by a Stuart No.9 running from a gas fired boiler - it can be coal fired but we didn't want to set the smoke detectors off...

Here's a link to the programme - our bit starts 40 minutes in.



There is a more explanatory video on Youtube:



Edited By Adrian Johnstone on 26/05/2020 11:08:43

Thread: More on starting with a resin printer
24/03/2020 19:20:50

Over in Gauge One land we have a public forum called the Gauge One 3D Circle and there are a couple of threads there on resin printing that might interest folk here - links below.

All of the messages in the forum can be read by anybody. If you want to post something, you have to join.

1. My own thread on starting with an Elegoo Mars:


2. Markus Neeser's thread on using special resin to directly print waxes for investment casting:



Thread: PayPal scam?
08/02/2020 20:44:21

Whilst I don't know what kind of scam you had to deal with, if it was identity fraud then a useful tip is to maintain a special bank account to back up the PP account with.

My bank was very happy to create a second account for this purpose. All of my salary and other payments goes into the 'real' account. The Paypal-backing account never has more then £50 in it as a float (for rail tickets etc). When I make a non-trivial purchase on PP, I use online banking to move the money over first - with my bank its instant. That way, if a fraudster gains full access to my PP account they can't steal much. It's a blunt instrument, I admit.


Thread: Making a combination lock
19/07/2019 07:51:55

This is a remarkable workshop exercise, beautifully filmed with no chit-chat:


Originally picked up from Hackaday at **LINK**


Thread: The Frrankenlathe
09/03/2019 07:42:27

Here's a home-built lathe to give you mightmares...



Thread: How do you fix a leak in steam loco copper fire box?
18/03/2018 07:07:43

It may (depending on the size of the gap) help in locating the source of the leak to do the following: obtain a length of polythene or silicone tubing of 5 or so mm diameter which you will use as a makeshift stethsocope. Using, say, an airbrush compressor apply low pressure to the boiler: 15-20 PSI over gauge will do. With one end of the tube at your ear, move the other end around the area of the suspected leak. Any small jets of air getting out of the boiler will show up very clearly.


Thread: Cutting 1.2mm Copper
30/01/2018 18:45:20

This is perhaps a little exotic, but for cutting circular boiler tube plates for gauge 1 engines (copper circles with holes of various sizes for flues) I use my Sherline CNC mill. It works beautifully and would certainly do 30mm circles. There's none of the distortion that a guillotine or flypress might introduce. I clamp or glue the copper to sacrificial bits of MDF as backing pieces. Of course it could also do your 80x30 rectangles too, and any other shapes you need.

The capacity of a Sherline is pretty small, so no good if you need big pieces done, and depending on the cutter the kerf can be pretty big so there is material wastage compared to a water jet.


Edited By Adrian Johnstone on 30/01/2018 18:48:48

Thread: Adrian Johnstone
08/10/2017 10:26:10

Thanks John I've sent you a message via the forum's email facility with my external addresses on it.

Best wishes,


Thread: LBSC's Designs
24/08/2017 12:55:12

I think the concept of design right does not apply to designs made before the introduction of the Copyright, Designs and Patents Act 1988 and I don't know if or what the equivalent rules were before then.


Thread: Spiritburners
07/08/2017 13:09:02

Hi Matthew. I run the G1MRA Surrey Group and nearly all of my engines are meths fired, including several LBSC designs.

A few points.

1. Meths can indeed be of very variable quality, especially if somebody has left the cap off since it is hygroscopic.

Most of my group use B&Q bioethanol which is sold for flame effect fires. As well as being very good quality, it is typically cheaper than most DIY available meths. Sometimes it is hard to find in store - just ask. I know the name is odd. It's not as though the ethanol in meths isn't bio in origin...

If you really want a fierce fire, then some folk like isopropanol. This makes my engines a bit too frisky so personally I stick to bioethnol.

2. Your observed loss of pressure when the blower is opened is more likely to be lack of water in the boiler than a problem with the drafting arrangements. When there is only a small amount of water inside you could still get a high registered pressure on the guage, but as soon as you take some of the steam off there isn't enough thermal mass of boiling water to replace it. On the other hand, completely filling the boiler is bad too because that leaves little steam space and will lead to priming (water in the cylinders).

For a new engine that you haven't yet got experience of running, I suggest you take the safety valve out and invert the boiler with the blower open so that it completely drains. Then use a syringe and water to fill it up completely so that you can see the top of the water in the safety valve, keeping a note of the volume of water you've put in. Now drain again, close the blower and half-fill the boiler.

3. The recomendation to use glass fibre wicks is optimistic, in my experience. Glass softens at the sort of temperatures you'll get in a meths fire box, and the ends will fuse into blobs at which point the wicking action is inhibited. The best wick material available at the moment is probably ceramic fibre. This stuff is used for very high temperature insulation but is hard to get hold of. Some folk like cabon fibre. If you contact me privately me I will send you some of my ceramic fibre. Cotton wicks are pretty much useless in high performance engines as they char away so quickly. Traditionally asbestos was used: if you have an old engine with odd looking wicks in it then I would dispoase of them carefully.

4. For most 'internally fired' meths engines, including Smithies boilers, you initially need a small suction fan to draw the combusting gases through the tubes (or through the outer shell for a Smithies). Once the boiler gets a bit of pressure up you can crack open the blower (don't open it too wide and lose all your pressure!) and the entrained air will do the job instead. If you don't use a blower, the meths flames often will just billow about under the engine, which is a hazard to paint and fingers and theormdynamically hopeless too. Some engines will, on a calm day, eventually get up to pressure without a fan - I have an LBSC Chingford express which can get going without a fan as I discovered one day when I was testing a burner and hadn't fully extinguished it...

5. I've never encountered problems with soot in G1 meths engines. Now, coal fired G1 engines are another story and need very careful cleaning after a run. However, the smokebox doors of my meths engines are rarely opened, and I've never cleaned the tubes of a meths engine.

6. If this is a new build engine, pay very careful attention to sealing the smokebox to the boiler barrel, and also to sealing the entry of the exhaust and blower jets into the smokebox. The 'entrainment' effect depends on there being essentially only one way for air to get out of a smokebox, and that's up the chimney. Most of us use bathroom sealant to give airtight seals.

Of course, you also need to make sure that the firebox door has a good seal too - I see you diagram requires a 'tight fit'

7. Check the positioning of your exhaust and blower jets. The normal way to do this is to fill the boiler with water, attach a compressor (or even just a bike bump) in place of the safety valve and open the blower or turn the wheels. You should get small jets of water shooting out of the centre of the chimney orifice. If the jets are off centre or colliding with the chimney tube then you need to bend the exhaust/blower connections at the bottom so as to get good alignment.


Edited By Adrian Johnstone on 07/08/2017 13:10:05

Edited By Adrian Johnstone on 07/08/2017 13:10:42

Edited By Adrian Johnstone on 07/08/2017 13:12:50

Thread: Small horizontal mill ID, celtic knot logo?
27/07/2017 10:27:55

See also the Wiki page on the North Staffs Railway which was called the Knotty, and has knots on its crest.



Thread: How did the external Firebox on Stephenson's Rocket work?
22/02/2017 08:30:22

Simon - the authoritative reference on Rocket is

'The Engineering and History of Rocket - a survey report' by Michael R Bailey and John P Glithero, an NRM book from 2000.

Rocket evolved over its lifetime, and this book is an extremely detailed look at the currently existing machine which was stripped down for the process, and an analysis of previous authors' attempts to reconstruct the original design along with Rastrick's contemporary notes. It's a fascinating read.

As built for Rainhill, Rocket did have a water jacket firebox, but the front and back plates were dry. Essentially there was an arch of water that went up and over the fire. Authorities differ on whether the external box was rectilinear or arched; but there is agreement that the inner firebox was arched, and that the two sides of the arch were copper. Rastrick says that the water gap was 3 inches; some believe that to be the external dimension which would have given an inner gap of 2 1/2 inches. The wrought iron backplate was lined with firebricks for insulation (and to protect the driver from heat, presumably).

This saddle has not survived. Probably around 1830, a wrought iron water jacket backplate was fitted with a 3 inch gap, stayed every five inches. This part survives.

The low down pipes you mention that went from the boiler to the firebox were water pipes, not steam pipes. It is a mistake to assume that the water in the firebox would be at a different pressure to that in the boiler. Even were the pipes to be so narrow as to cause a noticable pressure drop (they're 2 1/2 inches in diameter, by the way) the primary energy source is in the firebox, not the boiler, so the pressure would be higher in the firebox. So, you should assume that the water in the boiler and that in the firebox are directly connected and free to circulate. (There is some evidence to show that Rocket might have been part of later experiments to promote water circulation, and thus thermodynamic efficiency, by the way.)

There are also smaller steam connecting pipes from the top of the firebox arch to the top of the boiler; in side views these are often obscured by the cylinders, and since the arch and its pipework are missing on the current remains of Rocket they sometimes get left out of models.

The regulator was bolted directly to the back of the boiler tube plate. Unlike on a modern engine, the top of the firebox was below the top of the boiler, so there was space for the fitings. Originally steam was taken from the boiler directly, or perhaps via a small internal up-pipe. In its original form, Rocket had a serious priming problem (that is, water getting into the steam feed and from there into the cylinders) so, probably in Novenber 1830, a dome was fitted with an extended riser that went up into it.

Apologies for the length of this; I'm fascinated by early-stage technologies.


Edited By Adrian Johnstone on 22/02/2017 08:30:57

Edited By Adrian Johnstone on 22/02/2017 08:32:55

Thread: Olympic Class liners - building the engines
31/01/2017 07:59:58

The Kempton Park engines were of similar size to the Olympic and Titanic's (though designed and built by Worthington-Simpson quite a bit later in the '20's). As probably most folk here know, one of the engine is still run on ten weekends of the year - 2017 schedule: **LINK**

A visit is very well worth while. You will feel the earth move, and you can get a tour of the non-operational engine.


Edited By Adrian Johnstone on 31/01/2017 08:00:37

Thread: Why "Press Brake" and not "Brake Press"
26/01/2017 13:37:29

It's because a brake (as a noun) is a device for clamping and then bending metal.

You can have various kinds of brake for forming different kinds of folds, such as a box-and-pan brake (which uses inserts to form box shapes).

A press brake uses 'presses' which in this context are punch and die combinations allowing quite flexible folds to be formed.

To take your examples, in fly-press and hydraulic-press, the word press is the noun and the terms fly- and hydraulic- are modifiers telling you how they are actuated. In press-brake and box-and-pan-brake, the word brake is the noun and the press- or box-and-pan- terms are modifiers telling you what kind of folds they can make, and the names don't tell you how they are actuated at all. You can have manual press brakes, hydraulic press brakes or ones driven by a flywheel coupled to an electric motor.

Forgive the perhaps over detailed response, but you did ask...

Thread: Best Dremel type machine?
26/01/2017 02:06:35

If you havea look round on the net, you'll see a lot of discussion around these rotary tools. Dremel's reputation has taken a dive in recent years even amongst our friends across the pond who like to buy American. I have a Proxxon (the mains powered one) which is a very high quality tool that is quiet, has good bearings and will run up to 20,000rpm (which is good for engraving). It is expensive though, but only around three times what you paid at Lidl (if you shop around). I wouldn't go back to using one of the cheaper tools.



Edited By Adrian Johnstone on 26/01/2017 02:07:11

Thread: Greetings from Esher
03/12/2016 08:38:15


There is quitea lot of Gauge 1 activity near you: I run the Surrey G1MRA local group. See here **LINK** for general info and here **LINK** for newsletters if you'd like to know what we get up to.


Thread: MEX Photos for those that stayed home
17/09/2016 18:55:04

Well, I'm back from my (Saturday) trip to MEX and my experience was unirformly good. (I was one of the speakers today, by the way, but I have no affiliation with any of the organisers).

Brooklands is a treasure trove of British automotive and aviation engineering and to see our models and displays presented against the backdrop of, for instance, the extraordinary stratosphere chamber (**LINK**)was just great. Both the museum and the model engineering community benefit from this type of event. (I hesitate to use management speak like 'synergy' here: but that's what we have.)

There was a much better atmosphere at the museum than at a deserted race course, I thought. We had traction engines wandering around the buildings through the crowds rather than being coralled in a small display area. There were more families than at a typical model engineering event. The upstairs display of models was to a very high standard. The catering was excellent: much better than Sandown or Ally Pally. The staff and volunteers at Brooklands were uniformly helpful. Nobody who can read read an engineering drawing would have any difficulty at all reading the supplied maps, and every room I went into was jammed at lunch time.

If anybody is going tomorrow, I would particularly like to commend the live steam OO display by the OO live steam club (**LINK**) I was given a very detailed exposition of the internal workings of these tiny steam engines by one of their team.

The issue with traders falling away is real, but is caused by the shift to internet shopping not by the actions of show organisers. I believe that Chronos stopped going to all exhibitions after about 2010. If I ran a business with an enormous stock of heavy items, I might prefer to stay home and receive orders online rather than having to check out pallet loads of kit.

We are going to need new ways of doing engineering exhibitions if they are to survive in the future. I think this has been an excellent attempt to re-imagine the traditional approach, and I hope that the team will continue to develop the show, bringing in more of the maker community, more smaller-scale railway models along with, perhaps, RC aircraft and boats.


Edited By Adrian Johnstone on 17/09/2016 18:57:09

17/09/2016 11:46:02
I am at the show at the moment,and it is terrific. Great atmosphere. Come on down, there's lots to see and the catering is indeed excellent.

Thread: Tidal power getting going in the UK
29/08/2016 17:55:23

I think this is an interesting project:


Of course, the technology has been around for a while:



Thread: Risk Assessment
09/08/2016 08:36:51

Apart from the effect of the decline in heavy manufacturing on these figures which I am sure is real, we ought to perhaps congratulate the construction industry which seems to have transformed its record. Historically, it was to be expected that bridge building and tunnel digging would lead to deaths - by one count the Forth Bridge claimed 78 lives (see **LINK**). These days construction has a very strong H&S regime which seems to have really worked.

Personally, I am pretty keen to live a long time in good health, not fade away in my forties racked by an industrial disease as my grandfather did, so I don't begrudge a bit of paperwork and a few jobsworths if it genuinely reduces the sum total of human misery.

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