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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: Broken Handle
27/10/2019 15:02:31

I'm not surprised that you are suffering breakages. Die-cast zinc alloys - especially from older machinery - are known to be unreliable. And even when new and sound, they are not strong. I would not consider for one moment using such a handle that had been soldered - when as you can see, easy alternatives are at hand, and need only a drill and a square file by way of tooling.

Regards, Tim

Thread: The wonderful world of gauge blocks
27/10/2019 14:53:09

Silly-Old-Duffer says:

In metalwork 1/64" is about the best that can be done by eye, and this was the highest standard of professional accuracy up until about 1850.

I think that S-O-D is forgetting (or failing to remember) those trades which worked by eye, and were capable of much better than 1/64" - think about the fit of a diamond in an engagement ring, or the making of pivots for a clock movement in a watchmakers lathe using a hand held graver. And then wonder why the makers of printing type use points rather than fractions. Whichever system you use, the point is rather less than a sixty-fourth of an inch.

My understanding of fractional dimensions on engineering drawings is that these dimensions are non-critical, with a tolerance of plus or minus a sixteenth. Where better control was needed, dimensions and tolerances would be given in decimal inches. Except in the rest of Europe, of course ...

Regards, Tim

Edited By Tim Stevens on 27/10/2019 14:55:17

Thread: Bronze bushing
26/10/2019 17:39:29

Yes, in theory, Jason. But this is an old car, and will have been messed with by several past owners, many of whom had no knowledge, no tools and no money. So everything (yes everything) may be way off 'standard'.

Tim

Thread: The wonderful world of gauge blocks
26/10/2019 16:10:50

Ian J - A gauge block which is one tenth of a thou thick? Are you sure?

My set has a series of blocks which are 0.1001, 0.1002, 0.1003 etc. Much less frail.

Cheers, Tim

Thread: Silicon piston ring
26/10/2019 15:55:11

Please - how do you measure your bore so accurately? 25.90000mm indeed?

And it might help to know that internal conbustion engine rings are expanded by the pressure which builds up behind them - with the ring pressed firmly against the bottom of the groove. But these rings are proper Ramsbottom's Metallic Packing, invented by a steam engineer for steam engines.

Cheers, Tim

Thread: angle plate
20/10/2019 20:37:40

Oh, them. Then you don't indeed need an accurate square to start with, but you do need a pair of accurately 'right' cylinders. That's right as in right triangle.

All cleared up now - thanks.

Tim

20/10/2019 18:02:57

Sorry, but my (mother tongue) English cannot cope with circular squares.

Tim

Thread: Limiting pressure to a gauge
20/10/2019 17:26:22

I've had a further thought about my claim above [every four-stroke ...]. One or two engines did not have a PRV - they were engines without plain bearings - rollers or balls everywhere. Examples include Manx Norton and Ducati singles and twins. In these engines, the major volume of oil is directed at overhead camshafts, from whence it flows over the head and takes lots of heat away to the sump - or separate oil tank.

But that sort of engine is not what we are considering here.

Tim

20/10/2019 15:43:26

I suggest hat the only problem you might have (apart from bending the innards of the oil gauge) might be an overload of the pump drive gears. This depends on how well engineered and how substantial they are.

But I keep asking myself - this engine has been rebuilt to something like the original, but surely the original would not have over-burdened the oil gauge as it now does? Perhaps if the oil pump has been rebuilt, the new parts are a better fit, etc? And perhaps an unnecessarily better fit?

Tim

19/10/2019 18:08:36

Every four-stroke I have ever had in bits has an oil pressure relief valve somewhere to solve exactly this problem. Engines are designed to run with hot oil - ie thin. Many designs use the 'blown-off' oil rather than just letting it flow to the sump, eg by feeding it between skew gears which always benefit from the lube.

It may be that the oil-way from the original blow-off valve is blocked, squashed etc, and this stops the blow-off from working with cold oil.

And at that age the big-ends are likey to be lubricated by dippers, tubes on the bog ends which dip[ in an oiled trough as the crank rotates. This system survived until fairly recent times on Honda 50s and lawn-mower engines.

Tim

Thread: Bending stainless rod
19/10/2019 17:52:27

If the first attempt ends in disaster, somehow, I suggest that your second should delay machining the flats until the bending is done. That way you line the flats up with the bend (easy) rather than bending a red hot bar in line with flats you can't see.

303 should bend OK with my method, but don't cool with water or anything else. Just allow to cool. And the blackened surface will respond to fine abrasive just like mild steel.

Tim

Edited By Tim Stevens on 19/10/2019 17:54:35

19/10/2019 17:11:47

Let me guess - the part to be bent is shown held in a collet-holder, and the bend needs to start as close as possible to the radius where the long smaller-diameter section starts to increase in diameter? And the part is solid and made of mild steel?

If so, I suggest that you abandon the collet idea (it is likely to get too hot), and find two steel tubes, one large, one small, to fit over each end of the part. The fit needs to be loose enough to fit easily over the small end even when it has expanded with heat (say 1-2mm clearance); the tube for the larger end can be a light push fit, or if looser than that, make a slot along it so the vice will close it onto the part to hold it firmly in the vice. The larger diameter tube will be held in the vice horizontally (so the full length of the tube is held firmly with the part inside it). Then heat the length to be bent with a fairly large flame (a big propane job or oxy-acetylene), and when the relevant length is nicely red-hot, slip the short tube over the end of the part which is sticking out, and pull it towards you keeping the newly-bent section horizontal (or it might slip round in the vice).

Depending on how accurate your 45 degrees needs to be, it would help, before you start heating, to mark a template (eg cardboard) with the required angle as a guide to the pulling operation. To get the angle exact, if your first go is not good enough, it would be best to wait until the whole set-up has cooled (eg overnight) before you heat the bent section again, otherwise the whole thing is going to get much too hot - vice as well. It might be possible to tweak the angle a degree or two when cold, using the same tooling, if you handle-tube is long enough, the vice is firmly bolted to the bench, and the bench to the wall. The more you can concentrate the heat on a short length, the tighter the radius will be, and the harder you will need to pull.

The heat will of course cause the heated surfaces to blacken in the really hot bits, with various colours working outwards. These surface effects can be removed back to bright steel with time and emery cloth, or using a soft abrasive wheel in a polishing rig.

If the steel is not a mild steel, it is likely to be harder to bend, and the heat treatment is likely to modify its properties - especially hardness. How much this matters depends on the use of the finished article. In this case do not risk cooling any part of the job more quickly by spraying with water (etc) as this is likely to cause odd heat-treatment effects. With a mild-steel part, cooling in water should not have any effect - that's why it is called 'mild'.

I hope this helps ...

PS just read the title again - the olny place it says 'stainless' but which spec of stainless, I wonder?

Tim

Edited By Tim Stevens on 19/10/2019 17:18:00

Edited By Tim Stevens on 19/10/2019 17:19:21

Thread: Creating Heat for Hardening
10/10/2019 14:45:25

The link from John F includes an excellent colour chart of the various colours involved in the hardening and tempering processes. But, what is does not explain is that the lower half of the chart (up to 800F) is what you see by reflected light, and the steel surface needs to be cleaned and bright to show the colours properly. In reality, the coulrs are due to the thin layer of oxide on the steel surface (thicker as the temperature rises) - rather like the reflected colurs of a soap bubble. Above that temperature (top half of the chart) shows the colours of the radiant light (glowing) from the steel. These colours do not rely on a shniy surface, and can be seen in pitch darkness because the heat itself is producing the light. If this is not explained it is difficult to see how or why the colours change from red-ish at 500F, through blue, and back to red-ish again at 1200F.

The top half of the temperature chart is for hardening colours, and the lower half for tempering colours.

Cheers, Tim

Thread: Exactly...
10/10/2019 13:43:28

Oh dear! Tarmac roads were not invented or introduced by Macadam. The improvements to our road network which started about 1750 relied on Telford, Macadam, and several others, but they all used stone in various forms, but NO TAR. The resulting surfaces were 'water-bound' - ie stuck together by dampness. In other words dusty in the summer, and muddy in the winter. The surface was maintained by constant attention from 'lengthsmen' filling holes with new stone, and levelling the ridges, and promoted by the use of steel horse-shoes and carriage and wagon tyres which ground the stones to ever finer dust.

Only from about 1900 when motoring involved speeds over 15 mph, and rubber tyres, did the problems become unbearable, and the use of tar as a binder (adhesive) was found to be a big help. Tar was a waste by-product of turning coal into gas (for lighting etc) and coke (for heating). The term 'Tarmac' was applied to a further development, in which crushed slag from steel works was used instead of stone for metalling, and this when coated with tar proved to be a very useful, long-lasting, and cheap surfacing material. It was patented, of course, and the term 'Tarmac' was applied to the patented compound.

So - a new product which relied entirely on the waste from other processes - clever indeed. Just like Marmite - but can you tell us of any others?

Regards, Tim

Edited By Tim Stevens on 10/10/2019 13:45:16

Thread: Resistance Soldering question
10/10/2019 12:22:05

The term 'soldering' with no other words is often interpreted as soft or lead soldering, with a melting point around 200C - because in ordinary (non-specialist) workshops soft soldering is a much more 'normal' practice. It is also the case here that the OP (original poster) may not rely on English as his 'mother tongue'. Clearly the amount of heat involved here is greater than soft soldering requires, and looking at the job illustrated, would not be strong enough.

My comment was not intended in any way as a criticism of the original message, but I hope to clarify the use of the term 'soldering'.

Hope this, er, clarifies?

Tim

08/10/2019 18:16:19

I wonder whether there is a source of confusion here ?

Could the term 'soldering' as used by the OP mean 'hard soldering' - or what we might call 'silver soldering' ?

Tim

Thread: Metrication of models
04/10/2019 17:45:52

There is a lot of tosh written about the 'benefits' of the pre-metric measurement systems. Most of them seem to forget that the metric system grew rapidly in popularity around the world of commerce because it enabled everyone to overcome most of the objections to the older systems. Not only the confusion of how may whats make a wossname, and a different number each time - think ounces, inches, stones, shillings, barleycorns, pennyweight, drams (apothecary, avoirdupois, troy), grains (ditto), scruples, bolts, cables, chains (4 sorts) fathoms, furlongs, hands, miles (5 sorts), nails, points (3 sorts), rods poles and perches which were the same or not, depending, and townships. A further difference for us was being able to order material from anywhere (except the USA, where the postage rules it out anyway) and know what you were going to get.

I suppose the next solution to the problems of metrication is going to include logarithm tables, slide rules, and quite likely, the casting of lots - good luck.

Cheers, Tim

Thread: Final drive toothed belts?
04/10/2019 17:26:58

My guess is this:

Properly used - in line with the design criteria - there is less likelihood of patterning than with a gear drive, or a chain drive. Or even, perhaps, from an electric drive driven by AC.

But if the very thought gives you the shivers, why not a poly-V belt drive? No thicker than a toothed belt, and lots of torque capability.

Cheers, Tim

Thread: 3 jaw runout problems
02/10/2019 17:28:28

Mary?

Tim

Thread: Leadscrew material ?
02/10/2019 17:26:44

I'm not sure a square thread is easy to arrange with a split-nut attach & release system. Of course, yours might be different. But remember that square threads were abandoned long ago as sodding difficult to machine ...

Cheers, Tim

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