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Member postings for Tim Stevens

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

Thread: Plan/Design for spanner roll?
19/07/2019 20:25:43

Whatever tool roll you make (or buy) will be wonderful until you go to the next boot sale and there is the 1/4 Whitworth obstruction spanner you have lusted after all your life, and no slot to put it in.

cheers, Tim

Thread: Cruise meeting crash
19/07/2019 20:17:33

I have a few comments:

Plasma is not well informed about insurance (at least in the UK). If you have ordinary road insurance, the insurers are not allowed to decine their responsibility because the driver was going too fast, was drunk, was racing, was on the phone, etc etc. That applies only to the bit of road traffic insurance that is compulsory.

Jason B is not up to date on the requirements and costs for entering any speed event in a motorcar. All such events require special boots, gloves, helmet, fireproof suit, etc. And most of this stuff has to fit properly and goes out of date fairly quickly. Say £500 just to turn up, never mind getting the car to comply etc. The MSA has the sport firmly in its control, and the insurers know that any non-MSA bunch is not going to play by the recognised rules, so they will not offer insurance for the organisers, land-owners, etc.

The 'event' took place on a car park, which is different from the highway. Not for insurance, it isn't, though - a car park is regarded as a public place so road insurance is needed (along with lots of other boring stuff).

And every employed person has a contract of employment, but some jobs don't have them in writing.

I'm not against anyone having a rant at such activities, just trying to make sure they are not making claims that might lead to others saying 'We can ignore them as they obviously don't know what they are talking about).

So please don't rant at me ...

Cheers, Tim

Thread: Milling Problems
17/07/2019 20:52:15

The skin of cast iron can be nothing like the 'real' stuff underneath. The skin can be chilled - forming iron carbide, which is very similar to tungsten carbide, and just as difficult to machine. It has a silvery appearance, whereas the body of the casting is going to be dark grey, with included carbon which rubs off on a finger. This darker material can be machined using old fashioned tools of carbon steel, which is one reason why it was used so much in the 18th and 19th centuries for engineering.

It might be worth trying to remove some of the carbide by heating the casting to redness, and allowing it to cool in the ashes of a fire (such as a barbeque). This slow cooling should help to ensure that some at least of the dead-hard problem material changes back to iron, and carbon. The ashes serve as a blanket and prevent any sudden colling from drafts, etc.

Hope this helps


Thread: Angle grinders - Dangerous or not
17/07/2019 20:39:56

A feeble tool like a jewellers piercing saw can be dangerous, too. If the blade breaks at the wrong moment (and they do) you can have a blade through your index finger. Every jeweller I know has permanent blue marks on his left fingers where this has happened. So, all tools can be dangerous, even when every caution is used.

But just sitting on the sofa can be dangerous too.

Cheers, Tim

Thread: V-Twin 100cc Design & Build
10/07/2019 12:31:56

My concern about valve guides is only partly to do with strength - and others have commented on that aspect. The other part of the problem relates to heat transfer. The exposed exhaust valve stem takes in heat from the exhaust gas, and the part in contact with the guide loses heat into the cylinder head. In your design there is too much exposed and not enough in contact.

Another heat concern is the cooling of that area of head, which is exposed to a large area of exhaust port, and has no fins. You might think that modern engines don't seem to need fins here, but they are drenched in oil, which carries the heat away. Your system relies on no fins and next to no oil ...

It may also be a problem with the whole exhaust port as a separate insert of bronze. This adds an extra joint where heat must be conducted, and this relies on real firm contact at all times. The port will heat up faster than the surrounding metal (although its coeff of expansion is going to be similar), so even if everything is tight on manufacture, the joint will soon cease to fit firmly everywhere. If you are reconsidering this area, I would suggest that the sides of the port are directly in the head aluminium, with a lid comprising the guide and a flange, in bronze. If the flange extended as a fin, that would be an advantage.

But then, what do I know?

Tim Stevens
[Silver medal, motorcycle engineering C&G]

Edited By Tim Stevens on 10/07/2019 12:32:49

Thread: Forging brass; how easy would it be?
09/07/2019 23:12:25

If you soften (anneal) the brass it should be easy to squeeze out a 50mm disc to over 53mm, using a hydraulic jack, for example.


Edited By Tim Stevens on 09/07/2019 23:12:42

Thread: V-Twin 100cc Design & Build
09/07/2019 23:09:27

Might the valve guides be on the short side? - resulting in valves not seating firmly, perhaps.
And is the plate through which the valves work a separate part as drawn (but not illustrated in colour) - (increasing the problem, perhaps)?

Regards, Tim

Thread: Corrosion or Stale Oil (in joint face)?
05/07/2019 17:45:52

old mart claims: Sulfuric acid, H2SO4, will not attack glass, the sediment must have some other explanation.

I beg to differ, but I hope that someone more up to date with industrial chemistry can advise. Glass includes Calcium Silicate and Sodium Silicate, and the conc acid will be dead keen to change them to calcium sulfate and sodium sulfate - as the Silica is a much less 'strong' acid. But what do I know?

Cheers, Tim

Thread: Phillips vs Pozidrive and portable drills
05/07/2019 17:38:51

Roberton heads were used on Vauxhall motor cars for the bodywork, in the days when they were made in Vauxhall, London UK (up to about 1928). Or, to be more accurate, until they were taken over by General Motors, at least.

Just in case anyone thought they were 'just Canada'.

Cheers, Tim

Edited By Tim Stevens on 05/07/2019 17:40:31

Thread: Square Headed Screw Supplier
05/07/2019 17:28:56

It is relatively easy to make your own from square key steel. This has the advantage that you can have heads the size you want - ie to fit an existing small spanner.

Dare I also suggest ? that you could set the job up in a four-jaw chuck but not 100% tight, and knock the stock through a bit at a time - saving the tiresome setting up each time.

Cheers Tim

Thread: Curious
05/07/2019 17:20:35

If you need carbon for case hardening, charcoal seems (to me) the most readily available or makeable solution. To case harden, you need a furnace and a closed heat-resistant container. So, you have already got what you need. Fill the container with wood - hardwood seems to be preferred - and close the lid but not airtight. Heat in the furnace for an hour or so (remembering that the fumes will be inflammable) and allow to cool.

Much better than guessing what your pellets are (and possibly getting it seriously wrong).

Cheers, Tim

Thread: Corrosion or Stale Oil (in joint face)?
05/07/2019 16:14:09

I was advised by an industrial chemist that nothing is really proof against bacteria, moulds etc. He put it this way:
Throw whatever you like out in the open air, and sooner or later something will come and live on it'.

The brown top layer (Nigel Graham 2) was, I suspect, a layer of un-mixed oil which had risen to the top and any remaining water had evaporated from it.

And remember that in order to work well, cutting oil needs to form a layer on the work or tool (ideally both) which sticks there and resists being wiped off by the shaving. The layer only needs to be a few molecules thick, but over time, it can build up and stain. The same trick is used in hypoid axles (etc) which are worm drives with an extra wiping action. The hypoid additive reduces friction and wear by forming this thin layer of resistant compound. We are warned on the tin (sometimes) not to use it where there are bronze or brass components as the friction-proofing attacks copper compounds badly.

And finally I wonder if the white stuff at the bottom of a conc sulphuric acid jar was actually silica dissolved from the glass by the acid?

Cheers, Tim

Thread: The website needs an update
30/06/2019 15:50:48

If you click on the Model Engineer Magazine icon above, you will read:

'The latest issue of Model Engineer in the shops is issue 4610 (12 - 25 April).'

As it is now the end of July ...

Regards, Tim

Thread: A Chinese puzzle!
29/06/2019 16:55:11

I think you are both victims of a process which seems to be relied on by some (many?) e-bay suppliers. My guess is that decent makers of quality stuff have a rejects section, which accumulates parts which fall outside the standard spec. The firms are (another guess) run by accountants, like many UK firms, and so they see the scrap as a source of income. Along comes an e-bay supplier, and buys up a heap of the scrap, going on to sell it as though it is good to use. And we buy it.

Effective quality control is an expensive process, but not having one is more expensive still.

Regards, Tim

Thread: A puzzling design in Nurnberg museum
29/06/2019 14:46:22

Sorry Hopper, but your physics is letting you down. To get twice as much power, the two pistons must each move the full stroke. Here we have double the piston area working over half the distance, so no advantage.

I wonder whether the idea was to get the benefit of a reduced crank throw and so higher rpm, which of course matches smaller wheels - and that is a further benefit for tight curves. And at the same time putting the bores head to head reduces any heat loss through the cylinder head (as in effect, there are no such things). Were these engines better at producing power and coping with tight corners, and known to be capable of sustaining high rpm?

Regards, Tim

Edited By Tim Stevens on 29/06/2019 14:47:47

Edited By Tim Stevens on 29/06/2019 14:48:19

28/06/2019 22:59:12

The photo from MichaelR resembles what I saw (but it seems also very close to the Bavarian carriage in the first response to my query. But remember, I could only see the bogie under a sheet in a fairly dark corner of the yard.

And it does seem that my second guess (two separate pistons moving in opposite directions) is the answer which solves the question. Thanks Howard, and duncan, for your helpful comments.

Has anyone every made a model of this type of engine, does it work, and most important, what was the benefit intended compared with a single piston moving twice as far?

Cheers, Tim

28/06/2019 20:06:36

Journeyman - the loco you offer is not the same in the relevant bits - your cylinders are at the end (front or back) whereas my problem device has cylinders in the middle, driving axles front and back. Sorry.

I did come across one of these Linz engines at work in the 1970s, somewhere in (probably) Austria. My interest was arroused because I had never read about such things in the tecnical steam history stuff.

Cheers, Tim

Edited By Tim Stevens on 28/06/2019 20:07:17

28/06/2019 18:08:19

Brian: what I saw was certainly very like the front (left) end of your Bavarian carriage, but only as far as the front bogie. In other words, it might have been a shunting device or similar adaptation of the front end of the carriage, but no longer that the 5th window from the left. The tarpaulin was tied down and prevented any examination of the bodywork as distinct from the undercarriage, and I admit I spent the few moments I had gazing at the power unit.

And if I used the term loco wrongly, sorry, I just meant a self-propelled engine - and is the term I would apply to other four-wheeled devices like the Rocket and Catch-me-who-can. It was more than a bogie - the tarpaulin covered a shed-shape extending up well over 2 metres from the track. Unless, of course, my 'bogie' is not the same as your 'bogie'.

If the horizontal bar between the wheels on your picture is not an outside connecting rod, what is it?

Still puzzled, Tim

Thread: Removing Broken Tap
28/06/2019 15:45:22

Long ago I had a related problem, with a crankcase through-bolt seized firmly in the casing. It was removed using Nitric Acid, a process which dissolves the steel but does not attack the aluminium. It also produces lots of brown fumes and annoys next door's cat, so needs to be done at the bottom of the garden and not too near to other means of transport. I expect it is ruled out nowadays. The remains of the steel through bolt came out with nicely pointed ends, where the acid had attacked for longest.

Cheers, Tim

Thread: A puzzling design in Nurnberg museum
28/06/2019 15:36:48

I recently spent an hour or so in Nurnberg Railway Museum. [It is an ideal place for a family visit as right next door is a wonderful shop full of dirndles]

Just as I was leaving I noticed a loco of some sort under a tarpaulin. It was short, with two axles, and may have relied on steam supplied from elsewhere (as used in some explosion-prone mines). The cylinders were outside the frame, and in the centre, between the axles, and each end had a conventional but short connecting rod to the wheel nearby, one forward, one to the rear. Outside all this, the two axles were also connected by long rods in the standard loco manner.

This seems to me to be a geometry which cannot work. As the axles rotate, the outer rod maintains the axle-separation distance between the crank pins on the wheels, so that the wheels rotate together. But the shorter rods to the pistons must pull the crank pins together at the top and bottom positions, relative to their positions when both the short rods are central and in line.

I did wonder if the cylinders each contained two independent pistons, as this would avoid this problem - but surely it would add other problems including what happens between the two pistons, and the cylinder did not look (to my amateur eyes) long enough for this.

Do I need to go back and have a proper look, with photographs,or can anyone explain, please?

Regards, Tim

PS the museum also included a wide range of railway models, many of which were of superb quality.

Edited By Tim Stevens on 28/06/2019 15:39:24

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