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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.

17/12/2021 18:38:47

There are several ways to absorb the output of a wheel (or two) - favourites in industry include driving a friction brake, stir water or oil, whirl a fan, or generate electricity. The last is probably the easiest to measure, as the current and voltage are easy to measure, just multiply them for Watts. With modern belts, arranging a variable pulley system would also be simple, for the fairly low power outputs involved.

And it is much easier to compare outputs, than to be sure what the output is, as none of the stuff involved is 100% efficient.

Hope this helps - Tim

Edited By Tim Stevens on 17/12/2021 18:40:10

Thread: Box Joint Pliers
01/12/2021 17:26:42

The object of the box joint (just in case you were wondering) is to have a joint which can withstand twisting in both directions. Very useful for manipulating body parts and bending wires etc. With a conventional joint you can only twist one way without risking the joint pulling apart (and so, the blades not meeting properly).

Very popular with making jewellers, as well as the Surgeons who like the whole tool to be a) polished) and b) stainless.

Cheers, Tim

Thread: Is there a demand for Whitworth tools?
01/12/2021 15:42:50

Of course there is such a demand. Anyone owning a pre-war car is likely to need them regularly, as will anyone with pre-war machinery including railway engines and traction engines.

the idea of grinding something no longer available to do a one off job comes fairly high in the scale of vandalism, in the eyes of the cognoscenti (like what I hope to be one day).

So - if you are keen to get rid, let me know.

Cheers, Tim

Thread: pantomime sword
01/12/2021 10:53:56

Fancy - the very idea of changing a Saracen for a Viking for the convenience of the props dept!

Whatever next? Jesus as a white man?


Thread: Call for Classified Ads for MEW
30/11/2021 18:19:37

Its a funny world when someone trying to get things right is called a pedant.

Just remember - if you don't care about words, you might promote vacillation when you meant vaccination. But perhaps someone in high places has beaten you to it.

cheers, Tim

Thread: Is Model Engineering "green"?
30/11/2021 17:48:20

Let's try for a moment to think within the box, but also to realise how big the box really is. Which box? The box marked 'Model Engineering'.

There is no rule which says it has to be anything to do with railways or steam, or coal, or petrol, or electricity. It is just as legitimate to make a model of any engineered product, or even anything which might be engineered in the future, by carving it out of wood or bone, if that is what the job requires. Good models of the Eiffel Tower (and no-one can deny that is engineered) can be made from paper and straws.

And the topic is not limited to hobby activity, either. An inventor near me wanted a miniature of a life-size idea, based around the workings of a car differential, but not using it for power transmission. The job was done and he went away happy, having paid a fair price for the work. Was it model engineering? Of course.

There will be changes in the future, but there will still be blokes in sheds making stuff.

Cheers, Tim

Thread: Boiler fittings
30/11/2021 10:23:09

I foresee no problem with stainless in place of bronze, for threaded fittings. The expansion with heat is a bit less, and the friction characteristics are not so good, but let's hope you only need to tighten them once or twice.

There will be a violent reaction from the odd purist, of course, especially if your design originally started life before about 1930. In my experience, these tend to generate a lot of heat, but no illumination.

Cheers, Tim

Thread: An unusual thread size- Stanley 78 rebate plane
30/11/2021 10:17:33

Ady refers to a thread as 'Imperial' but the implication of his comment is that this was a US standard thread.

In my view, the term 'imperial' means relating to an empire, and so covers Whitworth, BSF, etc, and not the American standards. This is because the US never had an empire but the UK did.

If I am wrong, please explain.

Cheers, Tim

Thread: Filing Technique
30/11/2021 10:00:28

I wonder if Mr Dobson (see Mark rand's post above) ever thought hard about his advice. To affect the temper of steel you need to get it hot enough to change its temper colour or 'blueing' - starting (as every metalsmith knows) with the palest yellow and ending with purple. His advice - if based on good science - would mean that filing quickly produces blued swarf. Not in my (60 years) of experience it doesn't.

Regards, Tim

Thread: Single point tool profile for milling.
28/11/2021 14:48:25

The Moiré pattern you describe can be caused by vibration of the machine, and the pattern is likely to change at different speeds as the resonance causes more or less vibration in the various parts. Another cause is a very careful set up (so the trailing edge cutter follows the path of the leading edge exactly) used with a small cutter radius or a large feed. the cutter leaves grooves, and on the return sweep cuts into the peaks between the grooves.

You can also get rainbow effects if the cut surface is shiny (rather than rough or black). This is especially the case with a fine feed, and is a bit complex to explain, although it is vaguely related to soap bubble colours. The effect is greater if the light source is small such as one bright LED. It will disappear altogether if illuminated by a laser beam, though.

Hope this is helpful

Cheers, Tim

Thread: Belt tension
28/11/2021 14:27:30

To try an answer to the original Q: How tight?

It depends on what can happen if there is slackness - how much can you turn one pulley to and fro without moving the other. If the belt drives a cutter, then the slack should be eliminated, and it should in other cases never be slack enough to risk skipping a tooth or sliding over the pulley flange. This latter is more likely (so tension is more critical) if the alignment is iffy, or if it goes iffy under load. This depends on the design details.

Otherwise it is a good idea to try the belt and pulley temperature now and then, and be aware of rubbery smells, which would point to overtight conditions (or overload, mislignment, etc).

Toothed belts are generally more forgiving than roller chain drive, or direct gear drive, but no so capable of really heavy loads.

But as you have discovered, the belt must fit the pulleys.

Regards - Tim

Thread: Filing Technique
28/11/2021 11:43:12

Hi Peter

Double-cut files tend to have the teeth all pointing away from the handle end, arranged in two rows 'tilted' to left, and right. So, both sets of teeth cut on the forward stroke. Draw filing gives better results (in my experience) using single-cut or 'mill' files, as there is less tendency to 'pin' (where a lump of the filed metal sticks to the file) - but good results can be obtained with double-cut files too.

If you use draw filing a lot, you might look at the 'lathe files' sold by ARC. They have the single sets of cutting edges at a steeper angle to the blade, and they might be more effective for draw-filing too.

Yes, files do tend to be less than perfectly straight. I think this is an effect of the hardening process. It can be very useful to use such curves to smooth a surface hollow, for example. It is also possible to create a bend (temporary) by holding the file in a distorted grip, for the same outcome. There are files deliberately made with bends - they tend to be shorter, and often double-ended, and are called rifflers.

I expect all these names are UK only - our cousins over the pond were very careless in inventing their own words for things with perfectly good English names.

Keep at it - Tim

28/11/2021 10:34:32

Modern files may be cheaper than in the old days, but they are not remotely as 'good'. Not the steel, exactly, but the care and expertise with which they are made. Flat files are not flat, for instance, the edges are not square to the faces, etc. Files for serious professionals seem to be OK still - chain-saw files are still excellent for slotting the holes that you went to enormous trouble to position accurately. Some of the worst examples are sold as needle files, - they really are hopeless.

Cheers, Tim

Thread: Does charging your car battery on fast charge damage it?
25/11/2021 17:55:00

Sorry, Noel. but NO! The output of a three-brush dynamo depends directly on the battery voltage - more volts = more charge. So if you forgot for more than a mile or two, the battery was starting to destroy itself. And acid was splattering around, and the plates overheating.

The odd thing was, that proper voltage regulators were known and used, on coaches in particular. But perhaps the motorist was - er - frightened of technology ... ?

Cheers, Tim

Edited By Tim Stevens on 25/11/2021 17:55:14

25/11/2021 12:16:09

Andrew J reminds us all 'The quickest way to kill a lead acid battery is to over-voltage it.' Very true - so imagine the failures caused when vintage cars had three-brush dynamos, with no voltage control at all, and the driver was expected to turn off the dynamo when the battery was fully charged. How did he know? Well, if he was lucky there was an ammeter which would slowly creep towards the plus as the charge overshot the 'full' state. No other clue.

Once turned off, in daylight, the dynamo could stay off with most UK and Euro cars, as they had magnetos and no other drain of current*. US cars were almost all coil ignition (well, it was invented there) so the battery trade must have been a worthwhile investment.

* no brake light, no indicators, no electric wipers, etc.

Makes you think, though. Aren't we all glad that no products are so badly designed nowadays?

Cheers, Tim

Thread: Big threads on small lathe???
24/11/2021 17:13:25

It might be worth thinking about an alternative material - such as Delrin. This is a stiff plastic which is a good engineering material but a lot easier to turn and to cut threads.

Delrin is a trade name - so if it means nothing try Acetal, polyoxymethylene, Hostaform C, Ultraform.

Cheers, Tim

Thread: Does charging your car battery on fast charge damage it?
24/11/2021 16:49:29

Batteries do not respond well to high current on charge. But of course, we don't know how high the high setting is in practice, and we don't know the size of the battery (in Amp-Hours). My answer would be: Get yourself a modest ammeter reading up to 10 Amps, and measure the current going into the battery on High, and on Low, charge settings.

A normal car battery of about 50 Ah can be charged at 8 to 10 Amps - as long as you turn it off when the process changes to 'gassing' - with lots of bubbles and gurgling - which means that all the chargeable stuff is now fully charged. Much more than that - either more amps or more time - will tend to overheat the battery - it should never get hot enough to feel more than warm. This causes damage to the chemicals and reduces the available charge.

Hope this helps

Cheers, Tim

Thread: china/India - Cop 26
18/11/2021 20:45:31

Dear J Hancock

Heat pumps are the sort of 'wheeze' that your mum and dad kept in the kitchen so your baby food didn't go off. Don't just be grateful, try to understand. Sillyness should have been given up with the baby food.

Cheers, Tim

Thread: How do you stop brass tarnishing
18/11/2021 20:21:29

Avoid heat, and fumes of any sort. Particularly fumes of animal origin, and any veg containing sulfur*, such as onions, leeks, chives, garlic.

* the spelling Sulphur has now been abandoned to avoid confusion. I await with interest the attack on our honour, along with colour, jewellery, axe, etc etc.

cheers, Tim

Thread: Can red oxide primer be painted on to Rust?
17/11/2021 20:10:17

The answer is Yes. But if you do it won't last long. There are a few fancy paints that will 'combine' with rust to form a strong layer, but red oxide primer is not one of them. The red oxide is in the paint, not on the surface.

But I'm not sure if there is anything special about Met spike posts that might offer a more hopeful or helpful answer.

Cheers, Tim

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