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Member postings for SillyOldDuffer

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

Thread: What Did You Do Today (2016)
19/04/2016 20:25:42

Ban campus motto, "Bottoms up MacNab"

Thread: Black 5 first steam up
19/04/2016 20:08:38

Well done Ron!

Like many others I've been following your trials and tribulations with considerable interest. When things got difficult you hung on in there and made a success of it. I've been inspired by your persistence.



Thread: Jan Ridders Coffee Cup Stirling
18/04/2016 18:18:31

Thanks again for the advice everyone.

I now have the engine running with a new graphite piston. This one is a little too tight and it makes a scraping noise. As I can't see any sign of any damage to piston or bore I hope it will sort itself out in due course.

I failed again to tap the piston. It doesn't matter much because the screw protrudes through the piston and I can bolt it together. But I like a challenge.

I drilled a 2.6mm hole for the M3 tap and took a lot more care. It went well until the very last moment when all the threads stripped. I wonder if the tap is blunt at the end of the taper and tears the graphite when it should be completing the cut. Next time I'll use a new one.

Now I've had so much practice it only me about 10 minutes to make the piston, with another 20 or so polishing it carefully to a tight fit in the cylinder. Then I spent 2 hours cleaning black muck off the lathe - nearly as messy as the time I used an angle grinder to cut a chunk off a cast-iron block. I wonder where I can get an apprentice to bully into doing the dirty work?

The Wright brothers were a clever and determined pair. It wasn't just that they designed and made the plane, they also designed and built a lightweight engine with the necessary power-to-weight ratio.



Thread: Are dogs clever or stupid?
18/04/2016 16:12:44

The best kind of dog is the hot dog. It feeds the hand that bites it.

18/04/2016 16:10:53
Posted by David Colwill on 18/04/2016 12:54:26:
Posted by SillyOldDuffer on 18/04/2016 12:34:43:

The cleverest animal is of course the horse. Mr Ed had his own show on TV.

This is wrong! White mice are the most intelligent species followed of course by dolphins then humans. smile p



Only 42 people believe that, and they all work for Megadodo Publications!

18/04/2016 12:34:43

After a short paws whilst decoding the meaning of Clive's " I am sure more tails will follow." : I read somewhere recently (New Scientist?) that whilst dogs had to be domesticated by people, cats chose to move in with us.

That would conclusively prove that cats are smarter than dogs except that dogs have somehow trained their "owners" to run after them cleaning up dog poo. It's true, I know some quite intelligent people who are avid collectors of dog excrement.

The cleverest animal is of course the horse. Mr Ed had his own show on TV.

Thread: Jan Ridders Coffee Cup Stirling
17/04/2016 22:31:40

I've always thought that if people were meant to fly we would have been born with feathers! I only know 4 flyers and they've all been in crashes, two of them bad ones. An uncle was in two "minor" incidents, no one hurt but the aircraft were written off both times. All of them due to pilot error, we humans can be very unreliable. Now I have to worry about the ground crew using the wrong oil as well!

Back to hot air engines, I tried flushing the first set of ball bearings used on the Coffee Cup engine with acetone and it initially helped. But only for a while. The bearings eventually failed, mainly due to sideways forces, but there was also a gummy residue in the race. I think this might have been the remains of the rubber seals.

Looking online later for replacements I found that these bearings come in a range of different types. Now I believe flushing may or may not work depending on the bearing you happen to have. There isn't a universal answer, you have to experiment.

I had a frustrating afternoon machining graphite for a new piston. It's the first time I have worked with graphite. Apart from being very messy it wasn't difficult to machine. Unfortunately the diameter of my first attempt was exactly 1mm too small. That's what I get for trusting my mental arithmetic.

My second attempt went very well until I broke it getting ready to part off. I bumped the cross-slide into the work when I meant to retract it and graphite's not very strong.

The third attempt is a near failure too. I took just a little too much off leaving the piston a tad loose in the cylinder. Although the engine works with an undersized piston I shall have to make another one. More mess.

The graphite piston seems to have solved my corrosion problem. Despite a strong smell of vinegar there is no sign of scratching or corrosion after a 40 minute run.

The engine spent the last couple of days sat on a radiator in the hope that the sealant would finally cure. It seems that completing the cure needs a higher temperature than my central heating system.

On the hot-plate at 40C there's still no trace of vinegar. But at 102C the engine reeks of it. I may try baking it in an oven.

I have, of course, got a new problem. How do you tap Graphite? Jan Ridder's design calls for an M3 tapped hole through the piston. I drilled a 2.5mm hole in the piston and tried to form the thread with an M3 tap in the usual way. At first the tap was reluctant to cut, then it started in squishy way, but most of the thread stripped just as the tap was about to finish. The flutes were clogged with powdered graphite.

Is there a preferred way to tap a soft material like graphite?



15/04/2016 21:07:56

I couldn't find much on the web to suggest that there's any kind of problem with Molybdenum: instead it seems to be a jolly good thing.

The lubricant is Molybdenum Disulphide rather than the element and it's a solid with properties akin to Graphite or PTFE. The only negative comment I found was "Thermal stability in non oxidizing environments is acceptable to 1100C (2012 °F), but in air it may be reduced to a range of 350 to 400 °C (662 to 752 °F)." That doesn't sound too bad.

Either I'm misremembering or maybe there was some sort of FUD campaign back in the day.

Does anyone know if small ultrasonic cleaners are any good for 'our' purposes? They seem to be aimed more at jewelry than the filth I have in mind.

No workshop progress today apart from keeping the engine toasty warm in the hope of getting rid of the vinegar.



Thread: Flying Scotsman
14/04/2016 22:12:25

Sorry for the diversion Eric and Martin, though it was fun.

I will of course be watching the programme thanks to Eric's helpful post.



Thread: Jan Ridders Coffee Cup Stirling
14/04/2016 21:59:12

I've been interrupted by domestics again! After re-polishing and carefully cleaning both cylinder and piston I reassembled the engine and it went an absolute treat with no oil. Unfortunately after 35 minutes it began to scrape again before literally grinding to a halt in about 10 minutes.

Inspecting the piston revealed a new coat of rust on the head and the first 1mm of the piston body. A careful sniff of the hot engine revealed a trace of vinegar.

I now think I had two problems: grit causing severe scratching coupled with rust that gradually gums up the piston whilst attacking the fine polish of the cylinder.

Careful cleaning seems to have stopped the scratching but not the corrosion. A Q-tip wiped around the cylinder after a run comes out an unhealthy greeny/brown/yellow colour. The source of the vinegar can only be the RTV Instant Gasket I used to seal the engine. It is still curing. I suppose it cures much faster in a full-size engine where there is much more heat. Also, any acetic acid vapour that gets inside the works of a much larger machine will be swept away before it can do any damage.

I'm going to leave the engine with the piston out warming on a radiator over the weekend. I hope that will finish the cure. Though the graphite has been delivered I probably won't have time to make and fit a graphite piston until next week.

Danny's suggestion of an ultrasonic cleaner is a good idea: I think Maplins sell them next time I'm out that way.

John's point about Silicone and heat is worth checking too. I vaguely recall being warned off Molybdenum Engine Oil years ago on the grounds that when it wears out it degrades into two components: one's an abrasive and the other's an acid. Don't panic - I might be remembering that completely wrong and it was 40 years ago!

Smart Bohm engine Ian and thanks also for the information that it needs regular cleaning. As a beginner I find it enormously useful to know what to expect. Otherwise I fix things that ain't bust and accept shortcomings as being normal when they are actually faults to be overcome.

Cheers and thanks again,


Edited By SillyOldDuffer on 14/04/2016 22:00:59

Thread: Flying Scotsman
13/04/2016 21:00:47
Posted by mark costello 1 on 13/04/2016 14:14:11:

Did anyone ever notice that the old days quality had more elegance along with their names?

Not quite everything Mark!


Though I admit almost all steam engines are drop-dead sexy!



Thread: New - Rod from Gloucestershire
12/04/2016 21:04:37

Greetings and welcome Rod,

Nice oscillator and congratulations with your successful publication of a picture.

Have lots of fun with your new lathe, I'm in love with mine!



Thread: Jan Ridders Coffee Cup Stirling
12/04/2016 20:58:23

Thanks again chaps, I think Neil and Ian S C are correct. Good news as I might not have twigged to it and might have been a dirty boy again. I distinctly remember washing the piston carefully, but don't recall doing the same to the cylinder - it may only have got a wipe through with some tissue. Attention to detail is not one of my strong points.

This afternoon I re-polished both cylinder and piston and this time carefully washed both of them. Interestingly the first wash of the cylinder (in paraffin) didn't get all the grit out. A second wash did and then I rinsed and polished both with unperfumed Nail Varnish Remover, which is slightly diluted Acetone. I shall try the engine again tomorrow.

Never heard of Jojoba Oil before, might be worth a try. Using Sperm Whale Oil would ruin my green credentials even if I could catch one! Sewing Machine Oil is good stuff though.

Noggins End metals have sent me an email confirming dispatch of the graphite rod needed to make a graphite piston. With luck one of the solutions in hand should give me a reliable engine so I can start measuring again.



Thread: 'Modifications' banned
12/04/2016 15:51:55
Posted by Sam Longley 1 on 11/04/2016 20:20:07:
Posted by SillyOldDuffer on 11/04/2016 14:52:56:
Posted by David Colwill on 11/04/2016 12:37:50:

No doubt the rest of Europe will ignore it, Britain however, will employ 2000 civil servants to enforce it!


No bribery -- sorry mate but having spent my life in the building industry I can assure you that you are deluded- Say no more - nudge nudge , wink wink!!


Scary stuff, I believe you. But why didn't you report it at the time? Why don't you report it now? Do you really have direct knowledge that your employer or employees were or are bribing officials? If so please do something about it, these are serious offences.

You may be aware that the 2010 Bribery Act beefed up the law in this area. In addition to simplifying and clarifying previous law relating to offering and receiving bribes, it introduced "A new offence applicable to a commercial organisation that fails to prevent a bribe being paid by a person associated with it with the intention of obtaining or retaining business or an advantage in the conduct of business for the organisation. "? And "Even if the bribe is paid by another company to which you are contractually linked, your company may still face prosecution." The act sets a maximum 10 year prison sentence for individuals but company fines are unlimited. As I said, serious stuff.

Is there more bad-practice in the trade than just bribery? The building industry has above average H&S issues, and as discussed elsewhere in this thread, a range of other problems. Is it usual in your line of business to look the other way and do nothing whenever something illegal happens? If so, it might explain a lot.

Golly gosh Model Engineering covers a wide range of interests and issues! And I only came online to look something up.



Thread: Jan Ridders Coffee Cup Stirling
11/04/2016 18:14:26

Memory's a funny thing. John's description of his fun and games with hydrogen reminded me of a school lesson where we punched a small hole in the base of a largish tin can and discarded the lid. The can was inverted and a thumb placed over the hole. Then the can was filled with hydrogen and placed bottom down on a laboratory tripod. With a lighted match at the ready thumbs were removed and the gas lit at the small hole. It was difficult to see the flame I remember. Anyway after 30 seconds or so enough air mixed with the hydrogen to cause a very satisfying bang. Most of the cans hit the ceiling which was about 15 feet up. Teenage boys, hydrogen, naked flames, no safety gear of any kind - what could possibly go wrong?

Anyway, the real purpose of this post is to ask advice about pistons!

I've decided to replace the EN1B piston in the pictures with one made from graphite but would like to know if anybody recognises what's going wrong here and how to fix it.

First problem is the orange pitting on the piston head in the picture. (The flaky ring is the innocent remains of some silicone. The blurry yellow thing in the centre is the out-of focus brass thread of the connecting rod clevis fork that lives inside the piston. )

My guess is that it's due to moist air causing alternating condensation and evaporation as the engine operates. But it seems very severe for an engine that works on hot air, usually only about 90C. It might be something coming off the RTV sealant but if so it's odourless. Any suggestions please?


Second problem is that the steel piston (13mm dia by 10mm long) is being scratched by the brass (or possibly bronze) cylinder. The two were carefully polished to a tight fit and then lapped together.

In operation the brass cylinder seems to retain its polish whilst the piston gets scratched: it takes 30-40 minutes to get into the state shown in the picture. The worst scratch is shown. The very fine scratch lines running around the circumference of the piston were made with 2500 grit emery paper used to touch up the piston after an earlier run. These lines weren't evident on the piston when it was new - it had a better polish. I followed the advice to run the engine without lubrication.


I'd be very grateful for suggestions as to what is causing this. I think the piston and cylinder are being made the usual way but am I doing something silly?



Thread: 'Modifications' banned
11/04/2016 14:52:56
Posted by David Colwill on 11/04/2016 12:37:50:

No doubt the rest of Europe will ignore it, Britain however, will employ 2000 civil servants to enforce it!


Fine body of men, when was the last time you had to bribe a British public servant!

Excessive employment of civil servants is a popular misconception. About 400,000 civil service jobs have gone since 1975. These people weren't doing nothing, their work was transferred to the private sector and it is still being paid for by the taxpayer.

Privatisation often worked well, but there are plenty of examples were services were disrupted, standards dropped, and costs increased.

If a real civil servant is giving you a hard time remember they don't make the rules: they are obliged to implement government policy, even if it's stupid.



11/04/2016 13:38:57
Posted by Sam Longley 1 on 11/04/2016 12:21:13:

Why do so many people run down the Daily Mail. Discounting the Sun - which is after all just a comic- the Daily Mail has the country's highest circulation. So something it does must suit the population. Or do those that berate the DM think that the entire population has less sense than them?

I like it by the way!!

My poor old mum believes everything she reads in the Daily Mail and every week my sister and I spend about half an hour each trying to calm her down. The Mail is a jolly good read if you like a good sprinkling of overheated reports about health issues, crime, lefties, bad neighbours, or the misdoings of young people, minority groups, Europe, China, and foreigners. The spoof headline "Rumanian Supermarket Trolleys Cause Cancer" is a parody of the Mail style, but I feel it sums them up quite neatly.

Sam's defence fails if you substitute "Pravda" or Der Sturmer" for the Daily Mail. Thus "Pravda has the country's highest circulation. So something it does must suit the population. Or do those that berate Pravda think that the entire population has less sense than them?" Yes, especially during Stalin's time.

I don't think anyone should be embarrassed by enjoying the Daily Mail provided they read it critically. Many other papers and periodicals have agendas too. If you really want to know what's going on you have to wade through all of them.



Thread: Jan Ridders Coffee Cup Stirling
10/04/2016 17:03:40

Thinking about it in reverse indicates that high pressures would be beneficial - an open to atmosphere Stirling Engine couldn't operate in a vacuum.

I can't think why a leak would be beneficial, but then as confessed earlier I don't quite understand how the engine works. The only advantage I can think of is that leaks would tend to keep the cold end cooler. But it would also mean that the engine was losing pressure. It makes my head hurt!

Putting the whole engine in a container and pressurising it to a few bar wouldn't be difficult. I'm thinking domestic pressure cooker drilled to accept a nozzle and inflating it with a car tyre pump. It would be safe because they're professionally designed pressure vessels with a safety valve.

It should also be possible to try different gases. Of course it's all been done before . I found this table on the web showing that Hydrogen, Helium and Air have the highest specific heats of the gases. So at the same temperature they store more heat than other gases.


Specific heat capacity at
constnat volume (J kg-1K-1)

Specific heat capacity at
constnat pressure (J kg-1K-1)







Carbon dioxide



Carbon monoxide















Water vapour



If I could guarantee that no oxygen could ever mix with the hydrogen a trial wouldn't be dangerous at all. It's a big "if" though! Nonetheless I shall order Igor to will take the risk next time we have a thunderstorm. The Hindenburg was full of hydrogen and that went well didn't it.

Back in the real world a bigger objection is that I'd have to hire a hydrogen cylinder, regulator and hoses. That's pretty expensive for a one-off experiment inspired by idle curiosity.

I found a British Made HSS M2 tap that I don't remember buying and it had no problem whatever tapping into a 1.7mm hole in mild steel. Job done.



Edited By SillyOldDuffer on 10/04/2016 17:05:22

10/04/2016 13:29:09

Don't tell the foreman but I discovered this morning that the bloke who drilled the pillars for an M2 tap used a 1.5 mm drill thinking it was 1.6 and he didn't bother to check. No wonder the taps were a bit stiff, doh! When the replacement taps arrive I'll try 1.7 clearance as John suggests: no doubt plenty strong enough for this application.

Ian: do you know what the advantage of pressurising a Stirling engine is? Is it just that you can get more heat into a working fluid when it's more dense? Also, do you have a suggestion for what the IHP of a Coffee Cup engine might be. Anything I calculate is highly accident prone and it helps me very much to know roughly what the right answer is in advance! I wasn't too unhappy with 0.5W IHP from a 10 to 15W input, and of course the power that actually reaches the flywheel will be very much lower again.

The results you get from an 18W mug warmer and boiling water are very interesting. In comparison my engine starts at about 80C and it works noticeably better when the room temperature is low, say 12C. Central heating and warm days are very unhelpful.

My engine doesn't speed up as expected with increased temperature. I've had the lower plate up to 105C only to unexpectedly see the engine speed up as it cooled off after the test. It works best at about 88C with the top-plate 50-60C lower.

I'm pretty sure these odd results are because my engine still has faults, not least that the piston rubs when the engine gets hot. At one point it was chuffing like a baby steam engine and that's definitely not right. I ordered some graphite rod today in the hope of fixing that problem.

Back to the workshop! At least I'm getting my money's worth out of all that tooling, until I break it that is...




Edited By SillyOldDuffer on 10/04/2016 13:30:29

09/04/2016 21:50:38

Very many thanks for the encouragement, Michael and John. I need some TLC at the moment because the engine has stopped working again!

I suspect that the power piston and cylinder bind when the engine is hot: certainly the polished piston ends up marred by fine scratches after 30 minutes or so. It also gets rusty on the inside face.

Originally I put the corrosion down to acetic acid from the sealant, but I'm still getting rust even though the sealant is long since cured and there's no smell. Possibly moisture in the air is repeatedly condensing and evaporating on the piston as the pressure alternates.

In the circumstances a graphite piston sounds like a very good idea. Thank goodness I can keep the cost of this endeavour secret!

John's suggestion that the engine might work better if pressurised is interesting: I shall have to do some more research. I don't really understand how the engine works either. On one level I think I get it, but it's not difficult to upset my mental apple-cart. For example I can't explain why the piston and displacer operate 90 degrees out of phase rather than any other angle.

Michael's suggestion of using plastic strip in the Mk2 dynamometer feels right too. I have some strip that might do if only I can find it. I have to get the engine working reliably before making a start on that though.

I made some changes to the program I wrote to analyse the data. Unfortunately the code that produces indicator diagrams has gone gaga and everything I've done to fix it has made the problem worse. Any computer experts reading this won't need to ask if I took a copy of the last working version: the professionals know that only wimps take backups.

On the other hand I think my earlier question asking how to calculating the area of an indicator diagram was based on a misunderstanding, so that's a bit of accidental progress. The pioneers needed to do it that way because their indicator diagrams were produced mechanically. I have the advantage of modern technology that captures many actual pressure readings throughout the cycle. It's easy to calculate the average pressure when you have actual numbers: I don't need to draw an indicator diagram to obtain the information needed to calculate Indicated Horse Power. IHP is derived from average pressure, piston face area, and the stroke length. My unchecked calculation using this approach suggests that the IHP of the Coffee Cup Stirling is a little under half a watt, which might even be about right!

Indicator diagrams are still worth producing because the shape and consistency of the curves say much about the health, or otherwise, of the engine.

In the workshop I snapped two M2 taps in improved pillars for the engine due to clumsy over-enthusiaism.  One of them jammed in the pillar so I will be following advice from the thread that recommended Alum as a way of dissolving the tap,






Edited By SillyOldDuffer on 09/04/2016 21:53:18

Edited By SillyOldDuffer on 09/04/2016 21:55:40

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