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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: Porsche 951
11/05/2021 18:07:34

I wonder if you are confused by the term 'capacity' ? Engine capacity is really a confusing term, as engine size is measured as the volume of mixture which would be taken in under ideal conditions, in one full rotation. Swept Volume (swept by the moving piston) is a much clearer term. It doesn't matter how thick your gasket, or how much you plane off the head or block, the swept volume does not change. Honest. I'm not a betting man, but I'd put money on that statement.

Cheers, Tim

11/05/2021 17:31:50

Head gasket thickness has no effect on the swept volume (or capacity if you like). What it does affect is the compression ratio.

And if the combustion space is decreased, the compression ratio goes up.

Cheers, Tim

Thread: Can one buy pliers with parallel jaws that lock like mol
11/05/2021 17:12:25

Why not improvise or use what is at hand and get on with life?

Why not indeed? The same question was asked of Hero, Gallileo, Leornado, Cugnot , Newcomen, Watt, and many others. I think they knew why not.

Cheers, Tim

Thread: Cutting holes in copper
10/05/2021 17:45:05

I would use a piercing saw followed by a fine (fairly new) half-round file. Depending, of course on how critical the roundness is, as well as the measured diameter.

Cheers, Tim

Thread: Porsche 951
10/05/2021 16:36:19

Roy - following your concern about 'model engineering'

Just imagine you are standing at Edge Hill just before the civil war battle. Charles's army of cavaliers is poncing about, and into the field marches Cromwell's new Model Army. 'Goodness me' says the King, 'They don't look like models to me. We are in for a full-size fight indeed'. 'Quite right, Sir,' says his ADC - 'I was expecting a load of skinny tarts ...'

There are many words that have two or more meanings. Model is one of them.


Edited By Tim Stevens on 10/05/2021 16:37:02

Thread: silver soldering
10/05/2021 16:28:38

I guess that you were concerned about getting the job too hot and destroying it. For reassurance, do the same things but with a piece of scrap copper (or perhaps an old penny etc?) and you will be better able to judge how hot is hot enough. And see what melted flux looks like, etc.

hope this helps

Regards, Tim

Thread: Can one buy pliers with parallel jaws that lock like mol
07/05/2021 16:16:04

Facom made a truly parallel tool in the 1970s. Like a Mole Grip with a lever to release, but the moving jaw slid along the tail end holding the fixed jaw. Nice design, I'm still using mine.

If anyone is interested I will try to send a photo, with model number details.

Cheers, Tim

Thread: Portable vice - buying advice sought
29/04/2021 21:49:54

John Smith 47 asks, following a message of mine:

Either you are intending to hammer stuff on it, or you want no marks on the table.

I don't get you. Are you talking about damaging the part or the vice itself?

A simple matter of action and reaction. If you hammer down on a lump of metal, it will tend to move downwards. What stops it can be whatever it is resting on - and in this case, an area of table already partly loaded by tightening a clamp. And I'm talking about damaging the table. (The clue is the reference to wanting no marks on the table)

Cheers, Tim

Thread: Problems trying to sell-on a 'Swiss' Army knife
28/04/2021 20:31:18

I stopped at a roadside cafe in Bulgaria in the 1970s, and took out my Swiss-Army knife to open a beer. The landlady leaped at me, saying 'Goodness, Sir, Please sell me your knife - with a knife like that I can open a business'.

Cheers, Tim

Thread: Portable vice - buying advice sought
28/04/2021 20:25:47

It seems to me that there is a contradiction between:
a) the need not to mark the surface its clamped to, and:
b) the need for an attached anvil.
Either you are intending to hammer stuff on it, or you want no marks on the table.

In my experience any clamped-on vice is going to be a problem sooner or later - never mind attacking it with a hammer. If it is done up enough to be firm, for filing, sawing, tapping a thread, etc, it will mark. And if it is not done up tight it will mark worse as it screws round ...

Sorry - Tim

Thread: Greetings from sunny south wales !
26/04/2021 11:00:24

I expect that you might find problems with the electrics - depending of course on what has been changed over the years. Several owners of Colchester lathes have changed the whole electrics to a modern Variable Frequency system, which can run from a 13 Amp plug and yet gives completely variable drive speeds with further 'clever' options like Jog and Reverse by clicking a switch. If you have a 3 phase supply already, this might not help so much, so do let us know what your machine has (motor, controls etc) and what still works and we can help with advice (and sometimes, with parts).

Cheers, Tim (Mid Wales)

Thread: Gear, Gauge, or Cutter ?
26/04/2021 10:51:36

Right, Michael - what else do you need to start work on a Skeleton Clock ... ?

Cheers, Tim

Thread: Turning a part ball between shoulders
25/04/2021 17:43:32

An alternative: Create a cutter which is a hollow cylinder of the diameter between your design shoulders. Cut teeth around the sharp edge, of a shape that will cut as the cutter rotates. Harden and temper the cutting edges. Set up a machine (mill or lathe) so that the workpiece can be rotated slowly, and the cutter so it can turn more quickly - with the cutter at right angles to the axis of the rotating workpiece. Traverse the cutter slowly along its own axis, into the workpiece, as both revolve. It will cut an exact part-sphere with sharp grooves each side. It will not cut anything but a sphere, though, vase-shapes etc cannot be generated by this method. In reality it is likely that only one or two teeth of the cutter will do the work, so take your time - and do make sure that there can be no movement of cutter or work along the axis of the workpiece.

Hope this helps - it does depend, though, on whether the ball-shape you need is a sphere or not.

Cheers, Tim

Edited By Tim Stevens on 25/04/2021 17:44:54

Thread: JD Metals
25/04/2021 17:17:59

I have had two deliveries from them, fairly recently. In neither case did I get what I ordered. In the first case I had great difficulty getting a response from them (via ebay) of any sort. In the second, the response was 'Oh dear, I'll have a word with the chap that does the work'.

A further problem is that the site I name has no system for dealing with a delivery order which is not what was described. The only sense I got was to complain under the heading 'goods not received' - and take a photo of what is delivered to show that it really does not match the advert. In my case - offcuts which were ordered as strip and what arrived was hex bar.

Cheers, Tim

Edited By Tim Stevens on 25/04/2021 17:18:48

Thread: crankcase construction
25/04/2021 16:46:34

There is one factor in your question which is particularly important - the difference in the pressure generated by direct combustion, and by the expansion of steam. Direct = much fiercer bangs.

As long as there are direct (straight) lines of strong material (usually steel) holding the the cylinder head and the main bearings in a firm permanent relationship, you are on the way to success.

Cheers, Tim

Thread: Advice on Choosing A Mini Lathe
15/04/2021 13:46:41

It is a fact of life that we - all of us - put things into categories. The most pressing reason we do this is WORDS. Without categories, words wouldn't work. So it is just something we have to cope with.

Cheers, Tim

Thread: Was this embrittlement, or what?
15/04/2021 10:29:59

A useful and informed discussion, gentlemen. Many thanks. I now suspect that the galvanised plate I started with was rather more fancy than 'just a bit of steel'. Next time I am offered a few offcuts I will take more care to ask 'Offcuts of what, exactly?'

All part of learning by experience - the only way that seems to work.

Thanks again


Thread: An odd ball
15/04/2021 10:25:57

Also used to block the outer ends of oil drillings in crankshafts etc.

Cheers, Tim

Thread: Was this embrittlement, or what?
15/04/2021 09:54:18

for Keith Hale:

The only reason for using a zinc-coated plate was that I had some of the required thickness. The next one I now need to make will be plain steel.

Brazing rod was plain and looked like brass, but may have been a low-silver alloy. The supplier is not going to be around, as they are old stock (but flow nicely).

Heating was by propane torch.

Bolts placed, not tacked, in place.

Hope that fills in some detail for you.


14/04/2021 21:34:45

My (limited) understanding of the process of embrittlement relies on the atoms of hydrogen worming their way along the stressed crystal boundaries until they separate. Like a drop of water will cause the collapse of a sugar cube.

Problems (for me):
- Zinc has much bigger atoms than hydrogen, so clearly the process is not of the same order at all.
- I have no knowledge of any related process happening with brazing of steel parts, in which red-hot zinc is a major ingredient.
- In my experience the time between plating and failure has been short - hours only. And it has always involved 'strong' steel, and tensile loads (as in fully tightened socket screws). This steel was ordinary (mild) and weeks, perhaps months after it was plated.

Can anyone offer answers?

If I have another go, with plain un-plated steel, should I also use un-plated bolts to fix to the plate? And are there brazing or flux compounds I should avoid?
NB the brazing is needed because there is no access behind the plate in service, and the bolts must be firm and water-tight.


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