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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: Switch gear for 2 speed motor
20/09/2020 15:22:48

Should you have any problems with the Brooks 2-speed motor I have one which was working a week ago (on a Colchester Student).

Tim Stevens - Knighton (near Ludlow)

Thread: How to clean a fusee cable
20/09/2020 15:03:46

On brake and throttle cables I have found it helpful to make a punch with an end boring to fit over the cable - just, and with a countersink. Mild steel will serve. Grip the cable in a soft-jaw vice, with the nipple above the jaws, leaving about 3-5mm between the nipple and the punch (depending on cable and nipple size), hold the punch dead in line and tap gently. With luck and/or skill the cable will open out into a tiny rosette. Keep tapping until the rosette expands to fill the nipple countersink, remove the punch and cut (or grind) the end of the cable and knock the ends down into the nest. Apply killed spirit, dip into molten solder, allow solder to set, and then into hot water where it can stay for a few minutes (to remove the flux).

And acetone or petrol is best to remove mineral oil - best done outside on a dry day.

Cheers, Tim

Thread: What rivet to use to join aluminium?
13/09/2020 18:16:15

Aluminium does not rust,

It crumbles to a greyish dust,

And most of that which you can see

Consists of Al 2 O 3

A popular ditty at the Alcan factory when I were a lad.

Cheers, Tim

Thread: BSF and Whitworth "Across the flats " sizes.
13/09/2020 18:10:51

I have some difficulty with the notion that before WW2 all BSF bolts had the original BSW size heads. My view (based on evidence which is now in the loft) is that all BSF sizes have been the same since the beginning of BSF in about 1905, and were the 'next size down ' of the original Whitworth sizes. That is certainly the case on all the pre-war motorcycles and cars that have been through my (mainly grubby) hands. Except of course for foreign ones.

There is one Metric size which is within about 0.002" of a Whit/BSF size - 18mm = 3/8W, 7/16BSF. And as 18mm is not a 'popular' metric size, they do crop up in unworn condition at shows etc. And many cheapo 7/16 AF and 11mm will fit 3/16W, 1/4BSF.

And 19mm = 3/4 AF, within the tolerances of even well-made spanners.

Cheers, Tim

Thread: Model Turbines
06/09/2020 13:53:36

My recall of the science involved in air-resistance dynamometers is that the power required to drive a (subsonic) fan etc increases with the cube of the speed (rpm). This relates well to the effort required to shove a vehicle along on a flat road.

As the cube of next to nothing is next to nothing, this explains why the power required at very low speed is itself next to nothing. Any bicyclist will confirm this.

Cheers, Tim

Thread: How to move a Colchester Student ?
04/09/2020 17:36:37

The trailer I am offered is a four-wheel job with low bed and ramps. The access from the old site to the road involves a 180 degree turn, and until we try the trailer empty I'm not sure it will manage.

The difficulties I anticipate are:

1. The capability of the engine crane - and this is why I ask about dismantling so the bits weight less.

2. the headroom above the current lathe position which will not allow access for anything much chunkier than an engine crane.

At the other end the problem is that the garage where it is to go has a sloping drive - with a Subaru on the trailer and a competent driver we should be OK, swerve across onto the level forecourt, and do the unloading there.

Thanks for the comments so far - I have a collection of wood chunks, and rope, straps etc. Short lengths of scaffolding should arrive next week.

Cheers, Tim

04/09/2020 15:51:19

I need to move a Student lathe (just over half a ton) about 15 miles by road, so I would like to hear from anyone who has done this. I have offers of a 4-wheel low car trailer, an hydraulic engine lift, etc, and several mates. I think the best option, as access at both ends of the journey is not wonderful, will be to dismantle the major parts so that lifting is easier. This would mean the chuck, tailstock, saddle, etc off, and the motor and drive pulleys off, and then what? Take the headstock off? Remove the bed assembly from the stand?

The lathe will need a decent overhaul in its new position, and the electrics are known to need sorting, in any event, so disturbing all the bits should not create too much extra work (I hope). And yes, I do intend to take photos of everything before a screw is turned.

So - have I got it about right?

The move is mid-way between Hereford and Shrewsbury, in case that is relevant.

Looking forward to comments

Regards, Tim

Thread: COMPRESSION RATIOS
02/09/2020 17:25:39

Please don't forget that in the USA there was a rule that 750 side-valves could compete against 500cc ohv or ohc machines. Only in the USA, mind, I wonder why that was ...?

And any comparison of maximum speeds needs to take into account the fuel used. Was the super-quick 750 Harley on petrol, or methanol, or a nitro mix? In this context you might recall that Opel set maximum speed records in the 1930s without a cylinder or a piston. Comparisons which ignore relevant detail are vacuous.

Cheers, Tim

31/08/2020 15:34:28

Sorry, Howard, but fuel with Tetra-ethyl lead was available from the early thirties. The Shell petroleum handbook 1933 says it is used in aeroplanes and US gasoline, and the 1938 edition refers to it as a regular constituent of motor spirit. Such fuel was often called 'Ethyl' as distinct from Benzole (with benzene etc from coal) and Discol (with alcohol from the Distillers Company Ltd.

Cheers, Tim

PS The idea of a racing Harley Davidson always reminds me of an expression relating to sows ears.

Edited By Tim Stevens on 31/08/2020 15:35:03

Thread: Boiler
30/08/2020 16:23:17

An interesting idea - using a bioler instead of the more usual type. But as usual, we might guess that you need a boiler to raise steam for a model - is that correct? Then there will be questions like 'how big' and 'what pressure', as well as 'have you done anything like this before - ie made something that could blow up in your face and take the shed roof with it?'

Regards, Tim

Thread: COMPRESSION RATIOS
30/08/2020 16:18:50

Remember that fuel before the war (WWii) was nowhere near as good (regarding its resistance to pinking etc) as modern stuff. Not only that, low compression engines were favoured for 'ordinary, non-racer' machines as they would slog without needing gear changes. So a ratio of between 6:1 and 7:1 would be a maximum. Unless the head was aluminium, which I bet it wasn't, not on a side valve.

And not-done-it-yet's method is only accurate if the piston is flat-topped, rises exactly to the height of the barrel, and the head is flat across.

Regards, Tim
Ex Norton, ex BSA, ex Hesketh

29/08/2020 18:31:33

Twostroke engines can be much more complex than fourstroke - and working out the compression pressure in advance is almost hopeless. Do you count the stroke as BDC to TDC or from the top of the exhaust port to TDC? And what do you do about the slug of gas that went down the exhaust pipe, was bounced back into the cylinder by sound waves, and did not have time to get out again (or did, depending on the engine revs) as the piston rose?

Cheers, Tim

Thread: Harrison M300 Gear Casing
29/08/2020 15:32:52

During the 39-45 war, even ships were made of concrete. By my grandad, incidentally.

Cheers, Tim

Why twice, I wonder ... ?

Edited By Tim Stevens on 29/08/2020 15:33:31

29/08/2020 15:32:51

During the 39-45 war, even ships were made of concrete. By my grandad, incidentally.

Cheers, Tim

Thread: COMPRESSION RATIOS
29/08/2020 15:30:32

As Howard says, the compression pressure in use (not calculated) depends on the heating of the mixture by the compression process (less the cooling of the fins, water jacket, etc). But there are two other factors that complicate the issue. First the valve timing, which is not designed to be 'right' at cranking speed (when you measure the pressure with a gauge). It relies on the effects of inertia and resonance in the inlet and exhaust systems, to fill the cylinder properly at running speeds, so the actual running pressure is generally higher than what you see on your gauge. It also depends on how wide the throttle opening is. And these resonances are greatly affected by the combustion itself, so the running pressure depends to some extent on the size of the most recent bang, and this too depends on the throttle opening. Finally, measuring with a gauge in a running engine is not easy, as both the spark and the gauge rely on the same plug-hole.

Books have been written on this topic. Look for Ricardo as a reliable author.

Regards, Tim

Thread: Advice on buying a milling machine
27/08/2020 18:37:18

Paul: Your idea of milling stainless parts (as your picture) from solid will take hours, and is likely to wear out your cutters and your patience. Cutting away most of a solid block, when angled stock of the right thickness is available (as your picture) offers no advantages, and is likely to end with distortion of the workpiece as you have removed any internal stresses. If good finish is what you seek, I suggest a polishing spindle and a selection of mops.

Howard: I invite you to consider your advice - Climb milling is when the cutter rotates in such a direction as to push the workpiece. This is surely wrong?

Regards, Tim

Thread: Stainless steel
27/08/2020 18:25:17

The pump-type hand wash bottles seem (when rinsed properly) to be ideal for oil in the workshop. And within the pump is a stainless spring - very handy.

Cheers, Tim

Thread: Change to the Code of Conduct
27/08/2020 15:31:34

I am not suggesting that the plan is bad - but a plan with no competent enforcement is really worse than no plan at all. It penalises those who always do what they should while giving free rein and its advantages to those it is meant to control. We surely have enough experience, recently, of government instructions which turned out to be fundamentally cock-eyed, because they weren't thought through properly. Algorithm, anyone?

What would help, perhaps is some idea of what exactly is meant by 'sellers who may be supplying goods not properly covered by UK safety or consumer legislation.' A few examples of relevant legislation would help.

As an example, there are many suppliers of useful stuff who also sell other products of no interest to us. Amazon, for example. Does the code only apply to those products of use to model engineers, or to the whole range?

Regards, Tim

27/08/2020 15:03:25

The recent debate following my query about LED failures (Coping with Voltage Spikes) shows that some UK readers are not at all clear about what the regulations require (ie what is legal or not) in the UK. I wonder what qualifications the overseers of this forum have to carry out the new policy without getting it wrong themselves?

Who shall police the policemen?

Regards, Tim

Thread: Advice needed on filling a gap
25/08/2020 17:23:51

There is a polyurethane filler made for car body repairs, which is much stiffer than silicone, sticks like stuff and blanket, and unlike silicone is designed to be painted. As you only need a few inches rather than a whole dent-full, you might get a couple of squirts for a pint of ale at your local body shop.

Cheers, Tim

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