Here is a list of all the postings Andy Ash has made in our forums. Click on a thread name to jump to the thread.
|Thread: Thin walled frames.|
Why would you not make this from three layers of 1/16" MS?
Presumably one could invisibly rivet the three together to avoid any hassle, but the middle piece would have a different profile to the outer ones.
|Thread: Take a look?|
The thing that interests me about this thread is the interpretation of the Category 1 vs "Sound Engineering Practice" group of boilers.
By the letter of the directive, the Juliet boiler should not fall into the Category 1 class. I did not accurately calculate the volume of the boiler, but I did look at the drawing. Doing the sums the boiler has a volume around 1 litre which is well less than the 2 litre limit for sound engineering practice.
Though I've not done the sums, I'm expecting that a 5"G 4-6-0 would be more than the 2 litre limit, and if not that a large 5"G pacific would certainly be so. Obviously these fall into Category 1.
All of the above would be within the scope of an average model engineer. The question is "Should the Juliet boiler be CE marked". Strictly, it should not.
The thing with this is that across the hobby there is uncertainty about the meaning of the CE mark. If the hobby were bigger or more valuable the regulatory authorities would be worried about that. The idea that a broad category of "products" should have ambiguity is not a good thing for the CE marking its self. Certainly, pressure vessels used in specific applications are regulated within those applications for exactly those reasons. The trouble is that it is not worth having a classification solely for model steam locomotive boilers. We as hobbyists get a general framework and it does not fit very well. No-one really cares about the boilermakers. As far as the authorities are concerned, the CE mark is for the hobbyists, not the boilermakers.
My opinion is twofold.
Firstly, setting aside the practical implications, there is no harm in attempting to certify a boiler in a more stringent category. Broadly common sense dictates that as the pressure volume product (bar-litres) increase, the consequence of a boiler failure increases.
In practice, the directive cites different approaches for SEP and Cat 1 boilers, and to me there are elements of both which would be best practice in either other. There are actually no limits, bar the application of the CE mark, to a boilermaker using best practice from one in the other. Equally, there is no mandate for it, so it should not be expected.
In my opinion, this is the wrongness of claiming the "CE mark high ground". What should matter is that it is a good boiler, not that it is CE marked. Perhaps some of the lesson that the directive presents, is that it might be better to buy a boiler without a CE mark if you actually know better.
The second element of my opinion relates to the reasons behind the 0.5 bar and 2 litre limits for safety and SEP. I think that the 0.5 bar limit is fairly obvious. The way I see it is that if the vessel only has 7 (ish) psi inside, it cant do much harm, even if it is made of cheese. Indeed all mice know of the dangers of squashed Emmental. (It's not the exploding bubbles in the cheese that get you!)
I don't know for sure, but I think that the volume limit of 2 litres, has been arrived at to allow for monotube (flash) steam raisers. These are reasonably common in consumer grade products, and are normally seen as safe from explosion. The thing with flash boilers, is that they have no significant volume of liquid water above the boiling point. If a breach were to occur, there is no significant volume of water that would flash to steam.
Obviously the authorities would have the difficulty of onerous regulation over products like flash boilers that do not warrant concern. These authorities must have to draw the line somewhere. In the end I guess they say that 2 litres of water at any temperature cannot cause harm. This is clearly not the case, because in my mind even the Juliet boiler is going to be a little nasty if it actually does go pop.
If you wanted to bend the rules to be as dangerous as possible whilst still being compliant then this would be one loophole to exploit. You can build a 1.99 litre vessel and run it at 100,000 psi, but you don't need a CE marking, even if it is made of Emmental.
Realistically, the Juliet boiler is only a mild form of these boundary cases since it probably only works at 90psi which is around 6 of the potential 25 bars available to boilers of the same size, in Cat 1.
To me, not CE marking a Juliet boiler is classifying it as a flash boiler, which it is not.
Is it wrong to CE mark a Juliet boiler? I don't think so.
Is it wrong to claim the CE mark high ground? Probably.
It's just my opinion.
I did read the post above, but for me the ambiguity remains.
It's on a "Buy it now" and critical information is not present.
For me it's that simple.
Good luck to anyone trying to start a business, but I think quality is a holistic thing.
I don't think any steam generating boiler is an area where quality is a compromise, and for me that includes the whole proposition.
If the seller is reading my post, I would hope that he takes it and understands it for the better of his business.
If he choses not to, then it is his business.
Edited to add;
The pressure equipment directive speaks of supplying vessels with guidance notes and instructions. To me this implies that it is the responsibility of the builder to guide the buyer in correct use. "Buy it now - ask critical questions if you want" doesn't seem to me to carry that same "best practice" ethos.
Edited By Andy Ash on 27/12/2016 20:09:37
Readding the regulations, it seems to me that the boiler should not be CE marked.
Given that many model locomotive boilers might fall inside the 50 bar litres constraint for category 1 it would not seem inappropriate to CE mark if the regulations for category one had been met. The seller claims that he has.
What worries me more is that the seller is ambiguous about the builder. It is not clear if the seller is the builder, or if someone built the boiler and the seller is selling it on his behalf.
The regulations, and indeed all good practice guidleines recommend that new boilers should identify the builder. This applies both for amateur and professional boilers. I am sure that many old boilers do not follow this guideline, and it does not make them bad boilers. Equally if someone makes boilers that consistently fail and cause harm, then good boiler makers should not fear presenting their details for scrutiny.
For mere mortals tracability provides a means to systematically root out dangerous pressure vessels should they come to exist.
For me, there is no way I'd buy a boiler, unless I could personally speak to the traceable maker and get confirmation of his build. I'd probably want to ask somone knowledgable if they knew the person who I spoke to.
To suggest that these critical markings are not shown because the photographed boiler might not be the one sold, is woefully inadequate. If I'm going to spend, then I want to see the boiler I'm buying. Just by looking at one of them, I can see they're not exactly coming off the line faster than they can be photographed.
The idea that it might be attributable to Blackgates, is pretty low. Maybe it was an accident, but I wouldn't buy that either.
Edited By Andy Ash on 27/12/2016 19:19:05
|Thread: Can anyone identify this type of scissor jack|
You can find the file at the link below.
Sadly I have been unable to make it so that the file will download, rather than open directly in the browser.
In any case, if you are careful the file is actually just plain text. You can copy the whole text from the browser, paste it into notepad and save it to a file of your choosing. The extension should probably be specific however. If you decide to call it "Scissors", then the filename should be "Scissors.linkage2". (Obviously without the quotes).
Notepad will try to call it "Scissors.linkage2.txt", if it does this just rename the file, with a normal file explorer window.
The actual linkage has not been defined accurately. I just wiggled the links until it looked O.K. I'm sure you can be more scientific. The positions of all the links can be controlled by co-ordinate, and the whole thing scaled metric or imperial.
You can't import a drawing from a CAD system easily, but you can export your link pivot positions directly to DXF or DWG so you can get accurate positions directly into 2D cad if that's what you need.
Edited By Andy Ash on 20/12/2016 00:42:38
|Thread: 140 Amp Polarity Reversing switch|
I completely get that.
If you were thinking about making something yourself, I would say that it is completely within the bounds of a normal ME workshop capability.
The one we used to use had a copper braid onto a rocking top. The solenoid was at one end and the contacts at the other. The pivot was across the middle looking down on top. The switch was double pole, single throw so it had one contact either side.
P.S. Because of the rocking action the contacts would wipe each time the switch was made.
IIRC the contacts were unplated copper, so one of the yearly service items was to dress the contacts with a diamond file.
You could make the body of the switch out of Paxolin on the mill.
P.P.S. Normally in a modern welder you can find a low voltage supply to pick off for control purposes. On my TIG welder I added a gas purge facility and the relay is powered from the welders own low voltage supply.
Edited By Andy Ash on 18/12/2016 15:07:14
A place I worked at a while back had a consumer product with an unrated contactor which was fine for a real 80 amps RMS continuous.
We never had to use it to switch the load because we used a transformer to generate the 80 amps from a 240 volt supply. The supply was not high power and it was controlled by standard 240V switchgear. If the unrated contactor had been used to switch the power directly I'm sure it would have died quite quickly.
I'm sure the high current contactor was as bulky as any knife switch I've seen. The use of such is no bad call. The thing you are going to be interested in is keeping the contacts clean. You ideally want a wiping action, perhaps silver or gold plate.
For a modern product, I would have to say that a Solid State Relay is the best way forward, but I don't think you'll get what you want off the shelf. I am equally certain that technology is up to the task, it's just that no-one much wants it, so it's hard to come by. If you were developing a product it would be worth developing a supplier for such a thing, because it would be more reliable than any mechanical solution.
I think the unrated contactor was a non-standard Crydom product. It was Bakelite/Phenolic with an open frame about the size of a playing card, perhaps an inch and a half thick.
Edited By Andy Ash on 18/12/2016 14:26:53
|Thread: Can anyone identify this type of scissor jack|
Above is a short clip of an experiment I did to figure out a new free tool I got.
It's been a while since the last post on this thread, but at the time, I had no time.
This mechanism stays parallel at the top and the bottom because of its symmetry. The thing is that the screw-link does not necessarily stay level unless you position the links carefully. This may not matter if you don't mind the hand-wheel going wonky.
Anyhow I finally had time to sit down with this new software tool I got and give it a go. You will see that I had to anchor the screw and have the top and bottom fly freely. This is actually a limitation of the simulator, but it does not prevent a clear understanding of accurate and optimal link sizes.
The tool is straightforwardly called "Linkage". Its good for locomotive valve gears too. Although its still not perfect from a user interface perspective, it still seems like quite a leap forward from some of the valve gear simulators I have seen.
It's free and you can find it;
Edited By Andy Ash on 18/12/2016 01:48:39
|Thread: MEM Electrics|
I will vouch for this type of DOL starter, which has been on my lathe and in regular use for more than two years.
The only thing don't like is the plastic box, but in every other respect these are good, despite being Far Eastern.
Even more expensive Schnider / Klockner switchgear comes in plastic boxes now, so what can you do?
You can easily wire in an e-stop chain if you wish. Only the contactor takes the motor load. The contactor won't wear out, but if it does you can replace it with any standard one without having to replace the whole starter.
It has an adjustable thermal trip also.
Edited By Andy Ash on 08/12/2016 23:19:58
|Thread: Boiler design|
I can't remember where I got it from, but you should be able to find it here;
|Thread: Carbon Steel vs HSS Taps & Dies|
You'll be fine with carbon steel.
HSS maintains temper at elevated temperature..... Just don't be power tapping into 316 stainless.
Really decent HSS taps and dies (skf,dormer,presto,clarkson,osborn,europa etc) are much better, but mainly because more attention has been put into the grind.
Properly ground tools are better no matter carbon or HSS.
Watch out for badly ground taps and dies. Often you will find that cheap carbon taps and dies have barely been ground. Sometimes you can even improve them yourself with a Dremel. I'd say that's a last resort though.
Really cheap taps and dies from China can be unusable, so watch out for those. Usually they come in sets but the button dies aren't split. There's nothing wrong with dienuts as such, but if you see a set where you would expect split dies and they aren't. Give it a wide berth.
Generally you get what you pay for.
P.S. Older is sometimes better. Older taps and dies were often just made better than their modern carbon steel brothers. If they're not actually worn, you might find old, second or third hand, is better than brand new. - Especially in imperial sizes.
Edited By Andy Ash on 27/11/2016 23:31:47
|Thread: Electric steel|
I think you're probably looking for soft iron, alternatively "pure iron" as in chemical element Fe.
You can get minor improvements by tweaking the alloy. The magnetic difference between pure iron and these special alloys is minimal compared with the difference between iron and steel. The latter are worlds apart for transformer applications.
If you want an attracting magnet, steel can be used to advantage, but you have to know how to use it electrically.
If you want a transformer, for electrical power transfer, then soft/pure iron is the way to go.
You might have more joy getting small quantities of pure iron from a chemical supplier.
Edited By Andy Ash on 03/11/2016 19:12:53
|Thread: Inverter with motor needed|
This all seems a little murky!
I'm pretty sure that you can't buy an ELCB any more. Someone is bound to prove me wrong, but broadly I would declare the ELCB technology obsolete. They work differently from RCDs although they do a similar job. An ELCB actually measures earth current. In situations like "TT" supplies where an actual ground spike is the only method of grounding, the ground impedance can vary wildly. If the ground potential does vary, it can render the ELCB useless, and no one will know.
RCD technology compares supply and return current. It calculates the difference and infers the earth current, even if that current is not passing through the earth conductor. It requires no earth connection and helps to make "TT" supplies much safer.
All modern switch mode supplies (of which inverters are a kind) usually require some kind of EMC filter to allow then to pass conducted emissions tests and gain CE and other approvals.
EMC filters work by providing a high frequency path from the live and neutral conductor down to ground. Generally the impedance of an EMC filter from LN to E is fairly high. Indeed there is normally some leakage even in a simple electrical appliance with a line transformer. Typically the coupling is capacitive from the primary into the frame of the of the transformer.
It from the perspective of the RCD these leakages can accrue. If you have a single RCD on a whole premises, then it is possible that all of the leakages can accrue to the point where nuisance tripping occurs.
In general, nuisance tripping of RCD's is much less pronounced than it is for the old, less safe, ELCB technology.
Most appliances leak much less than their allowable class limit, but it is a particular problem with motor inverters, because we all want nice (sonically) quiet motor drives. In order that the switching noise cannot be heard in the windings of the motors we all wind up the switching frequency so that it is outside of the audible range.
The downside to this is that it pushes electrical energy out into the network at frequencies which are quite tightly controlled. The regulatory authorities consequently demand EMC filters to prevent this from happening.
The EMC filters for motor inverters are usually quite big, because AC induction motors are a heavy load. The electrical noise is powerful and at high frequency. These signals can interfere more easily with radio systems. Appropriate EMC filters can leak quite a lot.
Most loads are not big motors.
In your workshop, you probably only need one inverter running at a time. If they have a proper isolator, then they probably don't all need to be connected at the same time. If they are not all connected at the same time, then their EMC filters cannot accrue leakage.
Decent inverters usually have selectable EMC filters. I bought a Schneider, and it says that if you disable the EMC filter then you should run it at a low switching frequency, to remain compliant. Sure you can hear the motor hum but so what. Mine actually has a dynamic mode. If the load increases, the switching frequency reduces. This maintains compliance, and is quiet most of the time. I actually quite like it. I get feedback about how I am loading the motor, by the sound it makes.
I commissioned a medical robot a while back which had several powerful (>1HP) axes, all of which had their own inverter. Obviously the axes all had to be on at the same time to achieve co-ordinated motion. Being a medical robot it had to be compliant. The answer was to provide external EMC filters. A single combined filter does not have to have the same leakage as the sum of each filter together.
Conducted emissions are only high when the motor is loaded. It is not likely that all axes will be maximally loaded at the same time. Even if they are, it is only a temporary situation.
Increasingly electrical switchgear manufacturers are promoting RCBO's. These provide discrete RCDs combined with traditional thermal-magnetic breakers. Instead of having a single RCD each "fuse" has its own. By using these RCBO devices, accrual of leakage can be managed, and nuisance tripping reduced.
In high load situations perhaps greater than 50A it might be the case that it is hard to find an RCD capable of the job. It should always be remembered that inverter systems can often be isolating.
The isolating nature prevents the controlled AC voltage generated from being directly hazardous. Clearly, if a circuit with no RCD protection is used and used in a fixed wiring scenario (supply side trunking/conduit) then safety hazards are inherently constrained.
Obviously no RCD with a non-armoured trailing cable has its hazards.
Edited By Andy Ash on 21/10/2016 23:09:31
|Thread: Dewhurst Type A Specifications|
I have a Dewhurst drum switch on a single phase 3/4hp Myford.
It does O.K., but it is important to realise that the handle can get out of sync with the contacts. The handle detent looks right from the outside of the switch but the actual contacts are not properly aligned. If this happens the contacts can deteriorate fairly quickly. I spotted mine fairly swiftly by the smell.
If I was wiring mine up again, I'd use low power mains rated push button switches, and have a box with a forward and reverse contactor.
The thing with the contactor is that you can always get a bigger one, and you can put them in parallel if you want.
The best is that if it burns out you can just buy a new one and swap it out. Cheap and easy.
Edited By Andy Ash on 21/10/2016 21:47:00
|Thread: Cutting clock wheels using a myford dividing head|
There was a thread I posted on a while back where I did exactly such a spreadsheet.
The spreadsheet shows the exact ones in green. The "nearly" ones are in yellow. The nearly ones are prefixed with a minus sign (which can be ignored) purely so that they can be highlighted yellow. You can change the acceptable error (along with other things) to make more or less approximate yellow matches show up.
I notice that the OP is making a new plate. That is really the right way to go, but there are other options.
I guess you will have to do some sums to find out if you can tolerate the differential error, but.....
If you use the Number 1 Myford plate, I think you can get to 144 by using 32 holes on the 77 circle.
If you do this, then every 12 divisions you will need to use 33 holes on the 77 circle.
I suspect no-one will notice the difference, and you will save having to make a 12 hole plate.
I suggest the usual caveats about checking my sums, which can sometimes be amiss.
I can compute the maximum angular error at every 12th division, but it is more meaningful if it is understood as a linear dimension at the periphery of a gear wheel. To calculate the maximum accrued error in thousandths of an inch at the periphery I need to know the diameter of the wheel.
Irrespective it would be approximately 1/32 of a tooth. It accrues as 1/384 of a tooth at each tooth and would be corrected every 12 teeth by 1/32 of a tooth. At the end of a complete revolution there are exactly 144 teeth.
So for a 4" wheel that seems like 2 and 3/4 thousandths worst case every 12 teeth.
Edited By Andy Ash on 07/10/2016 21:10:29
|Thread: when not to use mild steel ?|
As someone with "the shed of a mere mortal" I think this is as much about what tooling you have to attack with, as it is about the design of the thing one is making.
I doubt I would ever go anywhere near complex alloy steels, except maybe for springs.
I'd use silver steel for holding an edge. If I'm going to weld it then I will buy EN3 for the job, but otherwise it's EN1. If I already have EN1 then I'll weld it, but I shouldn't. If I know it's leaded then I'll avoid welding it, unless I have no choice, and then that its only a small job.
If you have mainly small machines and HSS tooling, using tougher grades of steel gets pretty tiresome.
There's really nothing wrong with other materials like plastics and ally, grey iron. I love a nice bit of leaded bronze.
For a woodworking machine I would have thought a mild steel nose is going to last a good while.
With steel, I think the need for high grade steel comes from light weight, low density, applications. All the time you don't mind how massive the thing is, mild steel is all you need.
Mild steel is incredibly strong. Just get an old bit of 2" 1/8" thick box and see how difficult it is to bend. How strong does it need to be?
|Thread: Greenly's Halton Tank|
O.K. So I finally managed to get my OCR software working......
The image above comes from a booklet produced by the SMLS in 1976 charting the first 25 years of the miniature railway at Beech Hurst. To be honest, if you read through it, it's a bit like a who's who of the model engineering hobby. Indeed the inside rear cover is a poem recited by Edgar. T. Westbury at the 1966 Christmas dinner.
From this booklet I have extracted the following excerpt;
"In Chapter 2 the gift of the late Mr. W. M. Hebblethwait's locomotive was mentioned, it is now time to finish the story of this episode.
The locomotive had been under construction for about 10 years and was very nearly complete. As is well known, it is an example of the Henry Greenly design of 1930 which was evolved as a training exercise for the R.A.F. apprentices at the training school at Halton.
What is not so well known is that the builder did not want to incorporate the Greenly valve gear of the original and therefore replaced this with a Walschaerts' gear designed for him by Mr. E. A. Steel, thus this locomotive is a prototype of the improved design. Items requiring completion were the draincocks, injectors, the fitting of nameplates and painting. K. N. Harris designed the name and maker's plates after consultation with Mr. Lionel Woodhead of Brighton, while Harold Lovell took on the task of completing the mechanical items.
It was decided that the locomotive should be entered in the 1958 "M.E." exhibition by Mrs. Hebblethwaite although it would not be painted; a silver medal was awarded, possibly the first time that this had happened posthumously. After a lot of delay in finding someone to paint the engine, with various changes of plan all was at last ready for a steam trial in May 1959.
Work on the locomotive was finally completed during the following winter, the painting finally being done by a member of the Bassett-Lowke staff in his spare time. The formal presentation ceremony was arranged for July 3rd, 1960, Mrs. Hebblethwaite making a special trip down from Yorkshire for the occasion.
Mr. Whittington presided in the unavoidable absence of the President, handing the silver medal to Mrs. Hebblethwaite who in turn formally presented the engine, which was received by Mr. Ayliffe on behalf of the Society. It was then driven round the track by Harold Lovell in procession with Mr. Brown's 4-6-0, "Hank", Arthur Yendell's "Princess Marina" and others.
The doner was also made an Honorary Life Member.
The fine photograph of the engine which hangs in the Restaurant at Beech Hurst was taken by Jim Ewins, a copy also being given to Harold Lovell in recognition for services rendered."
I can't actually find the reference in Chapter 2, otherwise I'd include it. I don't think Mr Gettings could have said much because it's hard to find.
Obviously it's not explicit, but one could read it that Wharfedale is the engine you are looking for. The quoted text is exactly as it is in the book. You must draw your own conclusions. I think it depends if Mr Hebblethwait had anything to do with the RAF.
The photograph referred in the final para, actually adorned the front of the club newsletter, at least for the years Mike Killick was editor. The quality of the picture on the newsletter was poor, but I think the club might have it in archive. I know they had a pretty large throw-out just a few years back and I understand a lot got thrown away.
Sadly the copy at the restaurant has probably gone too. The original house on the Beech Hurst site which eventually got converted into the restaurant, was demolished when Harvester took over. I doubt they kept the picture taken by Jim Ewins.
I am sure you can still see the actual engine if you write to the club. It is my concious choice not to be a member of the society presently. If I were I would do all I could to help you see it for yourself.
Hope it helps.
Edited By Andy Ash on 01/10/2016 01:54:58
Edited By Andy Ash on 01/10/2016 02:06:57
I have a picture of the presentation ceremony that Bob mentions.
It was the first steam engine I ever got to drive back on boxing day in 1984. I seem to remember being bewildered as someone said "The regulator is that big one in the middle!". I won't forget that moment. Happy days.
Edited By Andy Ash on 01/10/2016 00:06:43
|Thread: Audi recall|
You know, I'm probably wrong.
The only reason I posted was because I have noticed myself, that it always seems to be an Audi, these days.
Indeed I also have a motor car of Germanic origin (not an Audi or a BMW). I know how it can divide opinion. Some will go out of their way to lavish praise, others have actually spat on it!
All I know is that it always seems to be a nearly new Audi in the rear view mirror. I'm sure there must be others, but when I am caused to look and make an assessment, it's always an Audi.
Edited By Andy Ash on 24/09/2016 17:42:04
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