Here is a list of all the postings JA has made in our forums. Click on a thread name to jump to the thread.
|Thread: John Wilding Regulator|
Thanks John. I have made a note of your modifications for when I revisit my regulator later this year.
|Thread: machinery covers|
Garden centres sell fabric/plastic covers for outdoor chairs, barbeques etc which will fit over a lathe or milling machine. I have used one to cover my milling machine for over seven years - no rust but the plastic eventually starts to rub off.
|Thread: Top Slide Lock|
I have done this mod twice now (on different lathes) and it is really well worth it.
A couple of comments. GHT was before Loctite. I glued the dowel instead of using an interference fit. There is a good chance that the little handle ends up pointing in the wrong direction. Initially make the screw out of hex bar and tighten it to the gib strip with a spanner, mark the flat most convenient for the handle, drill the hole, machine off the hex flats and fit the handle.
Once you have done this mod there is no excuse for drilling holes in the lathe as GHT did.
|Thread: Has the world gone mad|
I love this one.
Mercury is used in low energy lights, dentistry etc but is banned from "normal" use such as barometers, manometers and such like. Why? Because it is poisonous.
May I suggest another reason. Mercury, like Helium and Gold, is a material that has a very finite quantity on this planet. Very little more will be found so in normal circumstances its cost will go up with demand. So you ban it for normal use, which frees up an awful lot of the stuff for use in all these lights.
OK, it is poisonous.
|Thread: Combustion chamber temperature|
Further thoughts: Any adhesive (which will always be a poor conductor compered with bronze, iron or aluminium) will reduce the conduction of heat away from the seat so leading to a hotter seat. When the maximum temperature of the adhesive is exceeded it will start to degrade (probably burn slowly) and eventually a gap will form between the seat and the head. If the seat does not come loose overheating will increase because the gap effectively insulates the seat from the head.
If the seat is deeper than the valve lift it probably will not drop out but just rotate. I know this from experience having had it happen on a single cylinder motorcycle. The seat rotated and since its outside diameter was slightly eccentric to the valve compression was lost. The engine ran well at high revs but............. I must admit on a multi-cylinder engine the damage could have been greater.
On the subject of temperature a model engine is likely to run cooler than a large engine simply because the ratio of surface area of the chamber (through which heat flows) is greater that the volume of the chamber (the source of the heat). However I would not trust any adhesive to hold seats in place. For a model (I am building a Whippet side valve engine) I rather like the convenience of an integral valve seat and guide although it appals me as a retired fluid/thermodynamics engine.
|Thread: Bare essentials|
I promised a sketch showing my thoughts on this engine.
The structure is a single cast iron block with integral cylinder and main bearing. The cylinder is a deep blind hole with inlet and exhaust porting in the wall. The piston, a bit longer than the stroke, is cast iron with a tight running fit in the cylinder (similar to small two stroke I.C. engines). This should obviate the need for a piston ring. The steam enters and leaves the cylinder through passages in the piston that match cylinder wall porting at TDC and BDC. However it is unlikely that the engine will work if residual steam/water is trapped in the cylinder after the exhaust port closes (I suspect that a condenser would cure this problem but that would be way outside the design brief for this engine). Therefore the exhaust port is elongated and timed so that it remains open for most of the dead stroke. This is accomplished by a scroll milled into the surface of the piston mating with a guide pin held in the structure. This rotates the piston to allow the timing of the ports (I believe a similar scroll system was used in the Maxim Gun). If the cylinder was horizontal it would be wise to place the exhaust port at the bottom and leave it open to make the cylinder self draining.
A Scotch yoke is used solely to keep the number of parts to a minimum. It is located by the cylinder and side piece provided by the structure. To allow the piston to rotate the yoke has a cylindrical stud that engages with a tee slot cut in the piston. The yoke is machined from a block of bronze.
The yoke mates with the crankpin which is integral with the main shaft and flywheel. To allow the part to be slid through the structure as one piece the shaft diameter will have to be greater than the stroke plus the crankpin diameter. The part, made of steel, is held in place by a locating pin running in a groove cut in the shaft.
I believe the engine is viable with the following comments:
It will leak steam
I think the Scotch Yoke is quite simply a horrible mechanism
A good size flywheel is needed to take the piston through the dead stroke
The engine is not reversing and will have a fixed cut-off
It may need quite a bit of running in depending on the fit of the piston in the cylinder
The surface speed of the main shaft in the structure will be high and could be the limiting factor on engine speed
I have tried to keep the rubbing surfaces to cast iron on cast iron, cast iron on mild steel and bronze and bronze on mild steel. However I suspect the Scotch yoke will need lubricating frequently
Although there is a lot of machining the only difficult items will be the cylinder bore and the scroll in the piston.
After all that I suspect the next comment is “build it and see if it works”.
|Thread: What have you recycled today?|
I remember the ex-government surplus shops in Lisle Street in the 1960s. Oh how I wish they still existed. Lisle Street then was a real red light district and had the London hospital for sexually transmitted diseases half way down it. Years ago it lost its old "charm" and became part of Soho's China Town.
|Thread: Bare essentials|
Back to Mike’s question.
I believe a truely viable engine can be made using a total of 6 parts. It would be a single acting uniflow engine with a Scotch yoke type crank and overhung crankshaft. The parts list would be:
I will endeavour to produce a sketch in the next few days.
|Thread: Workshop Break in|
Following on from Michael William's comment (sorry for not quoting) I had a friend, a forensic scientist, who gave the following advise for marking property (it this case motorcycles). Find an area of metal, ideally steel, remove the paint and stamp into the bear metal identification letters (post code will do). Then gently file the surface back so that the letters disappear and repaint. When it comes to reading the identification scrape the paint off, polish and etch the metal. The letters will be easy to read in a good light. This will work on unpainted aluminium.
The main reasons for doing this is that the courts will not accept identification by any old marks that could be the result of normal wear and tear and that the identification mark cannot be detected by the thief unless he already knows it is there.
Jason and Mark
Many thanks for the information. I have bookmarked the links and will be following them up when the cold drives me out of the workshop. Also I have to decide whether to go to the Karlsruhe or Dortmund show.
I have often wondered what other countries have to offer. The casual searching of magazine stands etc at continental railway stations and such like never yields anything model engineering wise. I have thought about going to the Karlsruhe show this January to find out what is available. I might still do so but it will be on the spur of the moment.
|Thread: supercharged V12 2 stroke|
I am sure you have looked into this in great detail but I don't believe all blown four stroke engines have large valve overlaps. Pressure is far more effective at scavenging than a working exhaust system so the need for, let's say, 60 degrees of overlap disappears. In fact with an external fuel system, carburettor or injection, all you would be doing is blowing fuel down the exhaust system. Not what you want with a petrol engine and if you are interested in fuel consumption. However if you are burning methanol, with its low calorific value and, particularly, high latent heat of evaporation, large overlaps can be a major advantage due to the evaporative cooling from the fuel. This comes at the expense of fuel consumption. Alfa Romeo used this system in their early 1950s GP engines, they had a fuel consumption of something like 3/4 m.p.g.
The RR Crecy was complex even by the standards of aeroengine engine design towards the end of War. In its full form it was a V12 two stroke with a typical RR engine driven supercharger. It used sleeve valves with only inlet ports, the gases exhausted over the top of the sleeve. The fuel was injected directly into the engine. Thankfully the jet engine arrived.
Rolls-Royce Heritage Trust publish an excellent book of sectioned drawings of piston aeroengines which includes the Crecy and Junker Jumo, a typical opposed piston diesel engine similar to the Roots engine except that it had two crankshafts.
|Thread: Holding piston|
Super Glue. An American, W R Smith, wrote a very interesting chapter in his book "Clockmaking & Modelmaking - Tools and Techniques" on using Super Glue instead of Shellac on wax chucks. I have used Super Glue to hold small difficult to hold parts when machining. I have not had the glue fail during any operation but I have kept machining loads low. After machining the part can be separated from the mounting, or chuck, by a light tap with a mallet. If that does not do the trick boil the assembly in water for about five minutes and repeat.
Super Glue is amazing stuff but not really a very good general glue!
|Thread: Could Concorde ever fly again? No, says British Airways|
After the crash at Charles De Gaulle a lot of regular passengers started to use private jets. They found that their journey times, from door to door, were quicker since local airports were used. Towards the end Concorde passenger numbers were low. It came down to who, BA or Air France, would blink first and withdraw it from service. The only thing keeping it in service was prestige. In the end Air France had to withdraw it and BA followed immediately.
As for it flying again: the Vulcan is flying but fuel costs makes its operation very marginal. Concorde at low altitude would probably burn more fuel. As for supersonic flight............
|Thread: #209 - new look|
I am glad you have received your MEW.
As a digital subscriber I am still stuck with issue #208. I guess the newsagents in the high street has the latest issue.
|Thread: Can soluble cutting oil damage equipment?|
I don't think I have seen an article in MEW on coolants/cutting fluids. Surely a short article is required?
|Thread: New Look|
Change for change's sake - OK with me. It seems to work OK with SeaMonkey (a Mozilla product) and I don't get upset about colours for links, adverts and lay-out in general.
However the list of "Latest Forum Posts" is too short. Ideally it should be two days long. Think about it - How often do you look at the list and do you want to be up to date with the postings?
|Thread: How accurate is your 3 jaw chuck?|
Both these seems very good.
I would not expect anything from a three jaw chuck even when new. They weren't even mentioned during my machine shop training as a mechanical engineering apprentice.
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