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Member postings for Andy Stopford

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

Thread: Any advice on how to cut/file a 45 degree chamfer on a 1mm steel sheet to EXACTLY 45 degrees?
23/03/2021 20:05:23

1 mm is very thin. Even if your 45 degree angle is absolutely perfect, you're going to have problems ensuring that the parts remain flat enough to obtain a <0.1mm gap all the way along the edge.

Given lack of space, equipment, etc., I'd make a simple jig out of MDF, flat-topped, with a piece of steel plate screwed to it, and an angled support at 315 degrees to it to clamp the part to. Use appropriate fences and dowels (through previously drilled holes in the part, as per your drawing) to register the part so that the edge to be chamfered is just above the steel plate.

Then file the chamfer level with the plate. You can let the file contact the plate to guide it. It will last long enough for the purpose.


Add fences, stiffening webs, etc. Draw filing is probably the way to go.

Thread: RH vs LH threads
15/03/2021 12:14:40

Zen and the Art of Motorcycle Maintenance?

Too much Zen, and not enough motorcycle maintenance, I thought when I read it as a teenager.

And he completely blew it for me when he's doing an oil-change and just lets the old oil run out onto the ground.

Quality, Robert, quality.

Thread: Design of boilers
05/03/2021 10:00:12

Go on, build one!

Thread: water level sensor
05/03/2021 09:34:05
Posted by duncan webster on 04/03/2021 21:58:33:

I quite like Noel's capacitance idea, but it's beyond my electronic expertise. Are we talking relaxation oscillator and phase locked loop chip? If so I've just bought some of those for another project, but I can't find them either!

Here's a fairly simple device for capacitive sensing, using a 555 timer and an ATMega 328 microcontroller (as in an Arduino). The schematic, MaquinaSafetyLevel.sch, is in the PCB folder, and is a KiCAD file.

It works in the opposite sense to what you want, switches on if the water is above a pre-determined level (to power a heater element).

The level probe is a commercially available one intended for espresso machines, though it seems to be just a stainless steel rod, with all but the last 10mm or so sheathed with acetal or something similar.

In main.ino, at line 10, I've commented it as voltage, however I think the values are arbitrary - it certainly doesn't carry 600 volts (I hope). These values were determined experimentally, and take a while to settle down; I'm not sure why, but I had to change them several times in the first few weeks of operation. They always drifted towards the 'safe' condition though, with shutdown occurring even when there was water in the boiler.

Thread: Design of boilers
04/03/2021 20:15:21
Posted by Nigel Graham 2 on 03/03/2021 23:09:22:

Thank-you. yes, I did discover the sorts of fields in which matrices are used, including graphics programming; but only much later. The course taught only their internal manipulations, no definitions, no purposes, no examples.


I think computers like matrices because they suit the physical nature of the circuits.

Indeed. When I was suffering O-level maths in the seventies, there was no hint of any practical application for matrices, or anything else; pointlessness was regarded as a virtue - hence the fetishizing of Latin, that most useless of subjects (academic linguists are free to differ).

The reason that matrices are used in CGI is that a common construct in computer programming is the array, and a matrix is, essentially, an array, and can be manipulated using simple rules.

Human-friendly controls in the program's user interface essentially manipulate vectors which conceptually aren't as easy to represent in the computer's world. It has to convert them into lower level arrays to actually work on them.

To comment on the thread, from which we've drifted, I think its interesting to consider whether boiler design can be improved, even if the practical answer is that there's no point/it's as good as it gets already, or whatever.

03/03/2021 21:12:47
Posted by Nigel Graham 2 on 03/03/2021 11:06:17:

Taking a GCSE Mathematics evening-class course over 20 years ago as a refresher for work reasons, I was baffled by the one topic new to school maths, hence to me: Matrices - taught as a pure abstraction linked to nothing else. I sought help from one of the scientists at work. Surprisingly, despite her PhD in Very Hard Sums, she could not explain the basic information I needed, so I was still baffled. She did though tell her work involved gigantic simultaneous-equation blocks soluble only by matrices; so I now knew their use - Finite Element Analysis (of vibrations, in her field). I realised the computer just made the arithmetic feasible. Though using a bought-in programme, she still needed to understand FE Analysis and extremely advanced mathematics.

As for the Matrix... It know the sort that is the clay in what used to be called "Boulder Clay"!

Matrices are much used in 3D computer graphics - a single 4x4 matrix can contain all the information necessary to Translate, Rotate and Scale an object, itself defined by it's transform matrix - how they do this is very non-intuitive, but computers seem to like it.

Thread: You think you have trouble starting your car on a cold morning?
17/02/2021 20:04:39

I used to own a Commer Q4 and replaced the (very thirsty) petrol engine with a Perkins P6. I didn't have a KiGass pump so I had to make one, guessing at the working dimensions. It worked fine, though I made the mistake of not bothering to figure out a mechanism to lock down the plunger when not in use and relied on a separate screw down valve to shut off the line from pump to manifold. On occasion I would forget to do this, and the engine would suck the reservoir dry, resulting in bad words being said the next time I tried to start the thing from cold.

Although very, very slow, noisy and vibratory with the P6, it used half the fuel and had an important safety advantage: in it's petrol-powered days, I'd been appalled driving it one hot summer night at the height of the Portuguese forest fire season to see showers of sparks being ejected from the exhaust on downward gear changes, straight into the tinder-dry roadside vegetation...

16/02/2021 19:40:51
Posted by Nick Clarke 3 on 16/02/2021 18:47:06:

One of the more senior members of our club was a fireman on the GWR and a driver on GWR and BR. He says that the multiple units would go flat overnight on shed so they were just left running instead!

Edited By Nick Clarke 3 on 16/02/2021 18:47:32

They used to do this at Tonbridge with the Hastings Line DMUs - when the inevitable letters of complaint were printed in the local rag, a BR representative would explain that the engines were worn out and would be unstartable if left to cool down overnight.*

Of course being left ticking over all night glazed the cylinder bores, making the engines even harder to start, and making them produce steam engine-like clouds of smoke. It wasn't limited to DMUs. BR was so cash-starved in its latter days that apparently they couldn't afford batteries for the big single unit diesels, and wrecked the engines by leaving them idling all night. Of course everyone involved with the motive power side of things knew this was a stupid thing to do, but ... politicians.

*I seem to recall it was said that the Sulzer engines in these had negative clearances when cold, so the donkey engine, which was plumbed into the same cooling system had to be started a couple of hours in advance to warm the engine up so it could be cranked over.

Thread: The new R Pi Pico
04/02/2021 19:56:36

I got one last week - my impressions so far are pretty favourable.

I've tried it with C, MicroPython and CircuitPython (the latter is a version of MicroPython put out by Adafruit, potentially useful if you're planning to use the kind of break-out boards they supply)

At the moment everything is all very new, and as SOD says, things will probably be easier when the Arduino toolchain is available. I managed to get a Neo-6M GPS module to work (fairly easy - I found a MicroPython library for it (, and an MCU6050 accelerometer/gyro (much harder figuring out how to use the i2c bus, but I've found these tricky to get working even with a pre-made arduino library).

i used Thonny for the MicroPython stuff - it's OK, but a little idiosyncratic.

If I can get it to work with a 480x320 TFT touchscreen it will be really handy for a project I'm working on, though this could be a real challenge - with a bit of luck someone cleverer than me will come up with the necessary magic.

edit: Looks like someone's on the case with the TFT -

Edited By Andy Stopford on 04/02/2021 20:04:00

Thread: It Is A Steam-Engine... Using the term loosely
14/01/2021 16:44:47

Nigel -

You're right in that there is some concern that widespread adoption of ground source heat pumps might freeze the ground under very highly concentrated housing and reduce the pumps' performance, but I don't think it is regarded as a problem for individual installations - if you've got a garden to put your heat exchangers under, you'll probably be OK.

David Mackay has information and calculations on the subject in Sustainable Energy Without The Hot Air:

13/01/2021 19:24:47

Just to add to SOD's explanation, thermal efficiency for a Carnot cycle engine depends on the difference between the peak temperature (say boiler temperature in a steam engine) and the temperature at the end of expansion (the exhaust temperature in most applications):

efficiency = peakT - endT / peakT

multiplied by 100 if you want it as a percentage.

This is just the theoretical efficiency, in practise there'll be all sorts of other losses, and I've presented it in a form which idiots like me can , hopefully, understand. It does show why diesel engines, say, with a very high combustion temperature are more efficient than steam engines, where the practical limit on maximum steam temperature is quite low.

Oh, and don't think you can get better than 100% efficiency by making it exhaust at below 0, the equation only works if you use Kelvin.

Thread: Nitrogen as an Energy Store ...
12/01/2021 14:59:40

It would seem that Sainsbury's trialled it in 2016:

No details as to how the trial went, unfortunately.

Most of the descriptions of how it works are mangled by journalistic Chinese whispers; it appears to be a piston engine which uses a warm water/glycol mixture to flash liquid nitrogen to gas, i.e. the water/glycol provides the 'hot' part of the thermodynamic cycle and I'm guessing that it's in the form of steam, since there are mentions of it being compressed prior to N2 injection, and that's suggested by this diagram;

12/01/2021 11:50:25

There was a more expansive discussion on this on Radio 4 yesterday:

The salient fact is that this is for a specialised purpose - refrigeration plants on lorries (as some have already noted), so simple Carnot efficiency may not be too relevant. Their is some discussion on the programme about the energy used to produce the nitrogen (disclaimer - I was busy at the time so only half listening).

According to the programme, 'a major supermarket chain' is converting their lorries to use this. If so, I very much doubt if they would be forking out in something which doesn't work.

Thread: Amadeal lathes - Any good??
02/01/2021 20:13:45

I bought a CJ18 from Amadeal about a year ago, and I've been pleasantly surprised at how good it is for the price.

It needed a little fettling, as others have remarked - namely the cross slide gib strip was poorly machined and completely the wrong cross-section. I though of trying to get a better one from Amadeal, but decided it would be better to make a new one, which greatly improved the cross slide location. I also scraped the sliding surfaces.

As Andy Gray mentions above, the calibrations on the cross and top slide dials are absolutely maddening with 0.025mm/division, and with major lines every 10 divisions marked 10, 20 etc.. 10 what?

As discussed in this thread:

I made new dials with diametral calibrations - a very worthwhile modification, and fitted roller thrust bearings to them which make for a smoother action.

At some stage I'll fit angular contact bearings to the headstock, but it works well the way it is.

Of course second hand industrial machines offer better value, but I don't have the room - I doubt the lady in the flat below me would appreciate having a Holbrook B-type arriving in her bedroom.

Thread: From a leaky nose to a bent nose
30/12/2020 19:18:56

I can't imagine what you could do to an L5 to bend the spindle (at least without gross damage being visible on spindle nose, headstock casting, etc.).

Has it been taken apart and the taper roller bearings incorrectly re-installed?

Thread: Christmas Disasters!
25/12/2020 20:36:39
Posted by Michael Gilligan on 25/12/2020 20:18:09:
Posted by Andy Stopford on 25/12/2020 19:52:06:

I received an Xmas greeting from the NHS this morning in the form of a positive Covid test result.

Having Covid for Christmas is definitely the most Grumpy Old Man thing I've done in ages; best time of the year for it in my opinion, so, Bah!, Humbug! to all (I just wish beer didn't taste peculiar at the moment).


My commiserations, Andy !

The only thing I can suggest is that you try Theakston’s with its subtly different spelling:



Ha! should have thought of that!

@Nick - I have no excuse, I made it myself...

Talking of which, I think I'll shut the computer down now and see if the beer-tasting situation has improved; if not, I believe I still have a bottle of vintage port (strangely, sweet things seem unaffected)

Cheers, chaps!

25/12/2020 19:52:06

I received an Xmas greeting from the NHS this morning in the form of a positive Covid test result.

Having Covid for Christmas is definitely the most Grumpy Old Man thing I've done in ages; best time of the year for it in my opinion, so, Bah!, Humbug! to all (I just wish beer didn't taste peculiar at the moment).

Thread: Which Laptop
22/12/2020 21:04:41

You can't really compare processor speeds for different generations of computer - a modern processor with the same on-paper specs will perform far better than an old one.

None of the programs you list should tax even the humblest of modern computers (having multiple browser tabs excepted - they can really hog memory).

Don't be seduced by the multiple processor cores thing - most programs can only use one thread at a time. From your list, I should think the only one that might use multithreading is the CAD one if it does ray-traced rendering, and LibreOffice Calc apparently does if you enable it.

Also: I recently did a clean install, as opposed to an upgrade, of the operating system on my 9 year old Fujitsu laptop, and it now boots faster and generally works far better than it has for a long time. This is using OpenSUSE 15.2 with KDE desktop which must make comparable demands on the hardware to Mint.

So you might as well give a new install a try - you might be pleasantly surprised, and save yourself forking out for a new machine.

Thread: Aircraft General Discussion
22/12/2020 20:30:01
Posted by JA on 21/12/2020 21:50:14:

Thanks Andy, agreed.


edit: It is worth seeing what Britain offered the USA under Lend-Lease.

Edited By JA on 21/12/2020 21:54:02

Interesting. I didn't know about Reverse Lend-Lease, I suppose I always had some vague assumption the Americans just paid for the British stuff they used.

re. the glider into IMC video - wow, sobering stuff. For those interested as to how they got themselves into this situation, there's an analysis here:

21/12/2020 21:02:39

The Nazis had a curious infatuation with wacky super-advanced gadgets, see all the projects for advanced aircraft, jet aircraft (often multiple designs to do the same job), ultra complicated engines, radio control, even flying saucers for goodness' sake.

Most of these weren't even wanted by the services who were going to use them, and never got beyond the prototype stage, but they represented an ongoing drain on resources.

It's said (haven't got a ref to hand, but its an oft-repeated view) that the expenditure on the V-Weapons was comparable with the Manhattan Project, but it was too late to do anything to significantly affect the outcome, and strangely there was little enthusiasm for building the device to put on the top of the V2 which would turn it into a real game-changer. Dodgy Jewish science and all that.

Although the Allies had their share of wacky ideas, they were kept under control, so that the vast majority of design and production resources were devoted to churning out effective, good-enough designs. As Stalin said, "Quantity has a quality all of its own"

As for the reason for this blindspot, it might be down to romantic delusions of 1000-year Reichs bristling with Wagnerian weapons, but another factor might have been that they didn't have a formal system of reserved occupations, so that if you were a geeky, techy youngster you had a very real prospect of being sent to the Russian Front, no matter how good your abilities at science/engineering, etc, and no matter how lamentably un-military your character.

So the reason for some of this stuff may well have been down to kindly departmental heads putting in a good word to the authorities about young Hans' flying saucer ideas and saving him from a pointless fate at Stalingrad.

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