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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: Remote starter system - identifying parts
01/02/2022 20:37:48

Any cyclic speed error, if I understand your pictures properly, will be minimal, and surely nothing to worry about. Any starter has its own cyclic variation because of the compression in each cylinder.

As to the sprag clutch, I am at a loss to help. If the one you have has failed, there may be room to fit an alternative somewhere in the length - but this would require a firm attachment as the reaction on the clutch if there is a kick-back has to be accommodated. What jolly fun ...

Cheers, Tim

Thread: Cyclemaster engine rubber bushings
30/01/2022 18:32:02

An alternative to rubber is polyurethane. The tuning shops tend to stock a range of sizes for suspension eyes - as do Land-Rover specialists.

Cheers, Tim

Thread: Advice and assistance sought - kickstart gear quadrant
29/01/2022 20:57:57

Remember - the loads on a gear like this are serious, if ever the engine is tried without proper attention to the advance-&-retard lever. Legs have been broken, as well as gear teeth.


Thread: What are the yellow fittings please
29/01/2022 20:54:29

Surely, they are there to bolt the electric rail to, if ever there is enough current to support it.


Thread: Steel tyres on alloy rims
28/01/2022 18:23:57

The problem you are likely to face is 'electrolytic corrosion'. This involves two different metals in contact, and damp or wet conditions. This creates a feeble, but continuous, electric cell - and the more reactive* metal is corroded most. With iron and aluminium, the iron will rust a bit but the Aluminium will corrode to a white jelly of aluminium oxide. Separating the two metals will only help if there is NO contact - iron rivets in aluminium and you've no chance. Unless you live is Death Valley etc. Or you could completely cover the rivetted area with a permanent layer of insulator bonded on all over. Not easy.

If you use rivets of aluminium (ideally the same recipe as the rim) then you have a better chance, but the, steel spokes will then become the problem. Aluminium spokes will then help, and lift the area away from the main source of damp.

* yes, normally we think of aluminium pans etc as not reactive. This is because of a surface layer of impervious oxide which prevents the metal showing. Electricity will cut through this layer, and the corrosion starts in earnest.

And copper rivets, or brass, will be worse than steel ones - sorry!

Cheers, Tim

Thread: Electro etching
21/01/2022 18:49:37

I wonder if I am the only one thinking 'What material is going to be etched? - What electrolyte is in mind?'

But then, we all enjoy a good guessing game now and then.

Regards, Tim

Thread: Piston ring grooves
17/01/2022 18:25:25

In use - when pressure is applied - the gas fills the space behind the ring and pushes the ring out against the bore. With a petrol or diesel engine or a single acting steam engine, the important face of the piston ring is the one away from the pressure - normally the underneath with a conventional layout. This means that the opposite (top) face is not critical in terms of flatness. If the rings are stamped or etched with numbers, etc, this is where they are put for this reason.

With a double-acting steam engine, both faces of the ring need to be properly flat, and the gap in the piston needs careful control as the ring is forced, every stroke, to flop across to the other side of the groove.

My thanks to Mr Ricardo (saviour of the side-valve engine) who discovered this while sitting in a WW1 tank trying to find out why it smoked so much.

Cheers, Tim

Thread: Ba 2 castellated locking nut
17/01/2022 18:06:16

According to my (limited) resources, a hexagon nut with slots across one end is more often called 'slotted', while if the slotted end is also reduced in diameter and round, it is 'castellated'. The two terms are often used less carefully, though. Both styles tend to have more depth than a modern plain nut. Because they are a bit on the small side for split pins, adjacent nuts are often wired together instead.

Cheers, Tim

Thread: Digital Caliper - again, sorry
02/01/2022 20:57:53

What I really need is a caliper which remembers not just where I left it but also has a way to remind me where I left it.

But I don't think I'm alone in this ...

Cheers, Tim

Thread: Smoothing a bore.
02/01/2022 20:43:53

Whether an OHC, or DOHC design is 'appropriate' or 'over the top' depends on whether valve bounce is a limit to the output without this added cleverness. But it also depends on what the engine is for. If 'merely' to produce power, that is one question, but how about if it is intended to demonstrate the abilities of the designer, or maker, or both?

Cheers, Tim

Thread: Running 'nukes' in the red
02/01/2022 18:14:20

Its funny, really - power stations don't like being turned off and on too often, but computers (wonders of the age) often don't respond at all unless you turn them off and on again.

it must be because of the electricity, which seems to work best when used with points which are flat, brushes with no bristles, and current which relies on electrons moving backwards.

Cheers, Tim

Thread: VFD - which is best please ?
01/01/2022 18:11:43

The question asked for 'any advice as to most reliable make'.

This can only be answered by someone who has put a all available makes of VFD through a test process and recorded the results. Also, any test of reliability is certain to take a long time. Together, these factors make it unlikely that anyone reading this could answer the question.

Is reliability the only criterion? It is certainly a factor, but how about ease of setting up? Or availability of spares? Or someone to help sort you out when you get stuck? Or efficiency - power in compared with power out? The most reliable kit in the world is no use if you cannot read the instructions.

Help us with these questions, and we might be able to help further.

Hoping this helps - cheers, Tim

Thread: What tool do I need? I need to measure the radius of a tiny fillet on a 90 edge.
30/12/2021 18:31:24

the link sent by Peter H was caught by an oddity in the software used by ME* - it came out like this:


Some typesetting and word processing programs use an extra 'hidden' symbol or two to tell the computer what it intended. Here the extra symbols include %, followed by a number, calling up a letter or symbol not in the 'standard alphabet' used in the days of 8-bit and 16-bit computers. I'm not sure what you or I can do about it, except wait for ME to update - or, * perhaps the fault lies within the computer used by Peter H. I wonder ...

Cheers, Tim

Edited By Tim Stevens on 30/12/2021 18:33:09

Thread: Suitable Metal for Electro-magnet Levers
28/12/2021 10:55:17

I would start by experimenting with mild steel - as it seems you are not sure of proportions etc yet. And - it seems that your application is not critical about size or weight, so although MS is not the most magnetic material, it has a major advantage as it is easy to machine, and some of the 'clever' magnetic materials can be difficult.

When you know more about the factors applying to your application, such as the degree of magnetism left in the material when switched off, which may be critical, you will find it useful to look at a reference such as Machinery's Handbook, which list material with special magnetic properties. Then, of course, you will need to take advice on where to get such material without having to buy 30 tonnes at a time ...

Regards, Tim

Thread: ML 7 Acme threads,
27/12/2021 18:18:28

Don't forget that there are other sources of backlash than the fit of the nut on the thread. How much slack is there between the end of plain bore and the face of the screw (one side) and the calibrated knob (the other side)? Taking this slack up as much as possible is free, and takes a few moments, but I have found machines where this has been completely ignored or overlooked.

There are pictures in the manuals which should make this adjustment clear.

Cheers - Tim

Edited By Tim Stevens on 27/12/2021 18:19:09

Thread: 43 TPI
27/12/2021 18:11:30

Chris - It was actually the BA threads which were based on Thury dimensions, not t'other way round.

Cheers, Tim

Thread: To harden or not to harden that is the Question
27/12/2021 17:16:59

A dodge for the next time: To help holding them when milling the sides, drill and tap the holes first. Then each long T-nut can be bolted to a straight-sided off-cut, and you can mill as much off as you need.

In passing - I note that there are off-cuts listed on auction sites. What I don't understand is 'How do they know what sizes you are going to want?'

Seasonable wossnames to y'all - Tim

Thread: Darwin's long-lost microscope
18/12/2021 17:06:24

The earliest microscopes, as used by Hooke and others, towards the late 1600s, were made in the way Bob describes, except that instead of a blob of glass, the scientists used a spherical diamond. This had the advantage of a higher 'refractive index' - it bent the light more effectively - so you got more magnification than with glass.

Quite how they managed to grind their diamonds into spheres was not explained ... They can't have melted them into blobs.

Cheers, Tim

Thread: French tools-of-the-trade stamps
17/12/2021 20:14:37

I think carbide was invented by accident, when hardening steel - quite likely by a combination of accident and inherited mystery, in the iron age. It was then discovered - much later - as the scientists got to grips with what was going on in the hardening processes. Late 1700s is my guess.

Cheers, Tim

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

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