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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: motorised z axis on mill
18/05/2014 17:32:01

I have recently built a power feed for my Champion 20V mill - yes, horizontal but the same principle. It involved attaching a toothed-pulley instead of the handle, and fixing a small 80 rpm 12volt motor to drive it with a 12:60 ratio. Total cost of the parts was about £30 - e-bay mainly - and the most challenging bit was wiring up switches with movable stops to limit the travel. I see no great difficulty in making a Z version except that there might be fewer holes etc to clamp things to.

If members are interested I can make up a sketch or two - just ask.

Cheers, Tim

Thread: Running small stationary steam engines
18/05/2014 16:46:42

We are an odd bunch, don't you think?

Someone goes to a lot of trouble making steam (or water*) drive a motor driving a generator, and this makes electricity. So what do we do? - we use the electricity to drive a motor to produce compressed air to drive a motor. And then some of us use the motor to drive a generator ...

* added so that our Swiss and Norwegian colleagues don't feel left out.

cheers, Tim

Thread: Silver Solderin
18/05/2014 16:35:58

If the boiler is being re-built from one which has been soft soldered, you may have a serious problem. When heated above its (low) melting point the lead or tin (etc) from the slightest trace of soft solder left in place is liable to soak into the surrounding brass (or copper) giving a very odd alloy which will not take the hard solder.

Secondly, battery acid (dilute sulphuric) is perfectly good to remove hard-solder flux residues. Half an hour should be enough. Use the acid as it comes (new and not out of a battery) or let it down 50/50. And as it is dilute acid, do not panic about adding water to acid or vice versa. But do resist the temptation to plunge the still-hot job into the acid - the splashes will make holes in your jeans, your vest, and anything else around. Was away any splashes with a solution of washing soda (Sodium Carbonate) or baking soda (Sodium bicarbonate).

And do practice hard soldering first, on some off-cuts of the material you are using. Get both sides to the same 'just red in the dark' temperature, and remember that the solder will flow into the hottest part of the joint.

Hope this helps.

Cheers, Tim

Thread: Tuftriding ?
15/05/2014 17:08:35

The camshaft on the Norton Commando (750 twin m/cycle, 1970s) was tuftrided to reduce wear, and it worked very well. I also understand that as the process introduces a compresive layer in the surface, it improves fatigue resistance (for the same reason that shot-peening does but without roughening the surface). This is a further benefit for crankshafts.

Cheers, Tim

Thread: Should I fix my lathe stand to a concrete floor?
12/05/2014 22:02:52

It seems to me that you may have a double problem:

1. The stand is distorting when bolted to the lathe. This causes a twist in the lathe.

2. The weight of the assembly is distorting again when on its stand feet.

So, you need to examine the stand to see what is out of square, and whether the stand is strong enough. It wil be strong enough to support the lathe, ie it won't collapse, but is it strong enough to avoid distortion from the weight?

Does the stand look like a proper job, I wonder? As strong in torsion as the lathe itself?

Cheers, Tim

Thread: cleaning brass/bronze fittings
12/05/2014 21:28:05

I would suggest a complete dismantle, check the condition of the tapers (if they are indeed taps of a sort) and other sealing surfaces, and if OK, grease with silicone grease, put in a polythene bag, and hide them under the bench for the next 20 years.

The green is called 'patination' if you want it, but corrosion if you don't.

Cheers, Tim

Thread: Precision diameters
12/05/2014 21:22:32

So, if there is any justice in the world, half a degree (approx = 0.57) gives you 100:1

But if next door comes home and slams his car door, you may be surprised how much difference that will make ...

BSA had trouble with 175 Bantam big-ends, ground steel for roller bearings - there was a ripple which promoted failure. The cause - a press at the other end of the works. So, they did press work and bearings on alternate days - it worked.

Cheers, Tim

Edited By Tim Stevens on 12/05/2014 21:23:34

Thread: Dynamos
07/05/2014 21:18:52

Can I suggest that unless you can reposition the third brush so that it is 'the other side' you may just have found a quick way to burn out your windings. The field in a 3 brush system is fed from the output but not earthed. Instead it is connected to a section of the commutator which produces a low back-voltage that increases a lot with speed - thus compensating for the increase in output volts as the speed rises. So, the field coils see a reducing voltage and the output is steadier. Moving the third brush a small amount (2-3 degrees) will vary the output a lot - so having it in quite the wrong place may be a disaster.

You can run a 3 brush dynamo in the 2-brush manner, but unless you play with the output control the field coils (which are designed to work on lower than output voltage) will be likely to overheat and so overheat the armature as well (ie melt the commutator soldering).

The bearing type is only a problem if you drive by belt etc - with a side load at that end. If you can drive without a side load - by a quill shaft, for instance - your bronze bearing should be OK.

Most 3 brush car dynamos should not be set to produce more than about 8 amps, or you will have overheating problems. This is for a 12 volt system and a 4-5 inch diameter dynamo. Some big cars (and trucks) had bigger than this - but still nowhere near as much as the same sized alternator, and about half as much as a plastic insulated, ventilated, post-war (2 brush) version.

Changing the polarity is easy, and needs no rewiring - let me know if you need to know about this.

Cheers, Tim

Edited By Tim Stevens on 07/05/2014 21:21:25

Thread: What is this fourth (threaded) hole in the die stock holder ?
04/05/2014 18:20:15

And while we are on the topic, why do the makers never leave enough metal thickness for the grub-screws to engage properly? The average tap has a small chamfer in the slot, and this means that most of the point of the screw is up the hole, leaving too few threads enaged.

And is there an advantage in using grub screws rather than hex heads (or socket heads) ?

Cheers, Tim

Thread: Cleaning alloy castings
04/05/2014 18:07:19

In case it helps someone ... the black or grey residue on Al castings when cleaned with alkali (or some acids) is mainly silicon, along with any other alloying elements. And silicon is fairly inert stuff, which is why cleaning is not so easy. The same problem causes some light alloys to look dull or dirty after anodising.

Strong nitric acid is seriously noxious, but can be very useful as it attacks iron and steel but not aluminium. Ideal for removing broken taps or engine bolts that have corroded in place.

Cheers, Tim

Thread: Can low pressure steam boilers be soft soldered ?
28/04/2014 17:57:29

Ordinary No-lead 'soft' solder has a rather higher melting point than old-fashioned soft solder (183C is the lowest for tin/lead, 227C for the cheapest tin+ 0.7% copper solder, more complex alloys can be lower (or higher)), with strength not much different. Some soft solders do contain a small % (less that 4%) of silver, but it is confusing to call them 'silver solders'. Soft solders rely on resin-based fluxes, or 'killed spirit' which is zinc chloride solution with some free hydrochloric acid. Some early bicycles were soft-soldered together (eg Dursley Pederson).

Silver solder (also called 'hard solder' is quite a different set of alloys, requiring a different range of fluxes, usually borax based, and applied as a paste in water or alcohol, or dry powder. As well as a much higher melting point range, they are stronger, and tougher, so more suited to the higher pressures as well as temperatures. Many silver solders - which contain 50% silver or more - are silver-white in colour, some a bit nickel-pale-yellow.

Brazing involves a further range of brass, bronze, and similar alloys, with an even higher melting temperature. But the distinction between soft and hard solder is much clearer that between silver solder and braze. The answer to your question is 'yes, but don't expect worthwhile performance'.

Cheers, Tim

Edited By Tim Stevens on 28/04/2014 18:00:43

Thread: brake material
26/04/2014 11:28:27

One problem you might find is that the contact surfaces will not always be dry - they will be contaminated by water or oil. Either way, the friction will all but disappear, and your brakes will fail.

What is wrong with conventional brake lining material, which can be rivetted or bonded to the shoe (or plate, etc)?

Cheers, Tim

Thread: Fly Cutter Milling Speed?
25/04/2014 16:21:23

If the shavings come off even slightly blue you're going too quick, I reckon.

cheers, Tim

Thread: aluminium
25/04/2014 16:10:32

For the record, the original Vincent idler gear was a bronze casting, and it tended to clatter and clang. The factory 'solution' was to use a forged light-alloy wheel which would expand along with the crankcase. But they still sounded like a dustbin being dragged across cobbles. I had one.

The rest of the train (crank input & camshafts) was steel gears.

cheers, Tim

Thread: Which indexable thread cutting tools and chuck to buy?
17/04/2014 17:09:59

One factor to remember regarding the size of tooling -

In general, the bigger tools are stiffer, so less springy, which can help with vibration and chatter. But the main concern must be the tool holder(s) you have. The tool tip needs to be central to the work, and if the tool shank is too big you will not be able to get it low enough. This is worse with carbide tips as you cannot grind a bit off as you might with HSS. So, put a centre in the headstock, and measure vertically between the end of the centre and the base of the tool-holder platform. This will give you a maximum for conventional straight tools. If the tool shank is too small, you can raise it with packing - mild steel strip or shim.

Of course, some fancy toolposts have an up and down adjustment, but I am assuming you have the standard arrangement.

Cheers, Tim

Edited By Tim Stevens on 17/04/2014 17:11:24

Thread: How to remove oil from a boiler system?
14/04/2014 16:45:44

In answer to the query 'what does it matter?' the problem is that the oil is likely to be an insulating layer, with a double effect. It reduces the heat flow from the engine, as well as the heat flow out of the radiator.

Tomorrow I will try the effect of running the engine with plain water until it gets to near boiling (no fan) and leave it like that for an hour or two to reduce the oil viscosity and hope that some of it will float to the top. Then I will overfill the rad so the oil overflows (rather than draining back over the internal surfaces). Then I will have a go with soap, and overfill again. Two or three of these treatments might be enough.

Of course, I have just rebuilt the engine and I hope to have found and cured the leak, but perhaps not ...

Cheers, Tim

14/04/2014 16:29:28

Thanks chaps. So, I need half a pint of 'liquid soap' - so will washing-up liquid do?

Interesting for me as a newcomer to the forum - most of the responses were about related experiences but not really an answer to the problem. Such is life ...

cheers, Tim

13/04/2014 16:50:01

I need help from an experienced boiler user - I have a car engine & radiator in which oil has been getting into the coolant. I think I have solved the leak, but I still have an engine etc which is coated internally with oil in all the wrong places.

The engine is all cast iron (yes, that old) and the water pump is quite separate, and tha radiator is brass, so the only 'vulnerable' parts are the water hoses which are silicone rubber. Should I fill with plain water, run the engine up, and add some Gunk to emulsify the oil, then drain and refill with distilled & antifreeze? Would this work? Or is there a better way?

Many thanks - Tim

PS its a 1932 Wolseley Hornet Special, just in case that helps ...

Thread: high tensile stainless steel
12/04/2014 18:03:48

Stainless fastenings have been used on motorcycles (and aeroplanes) with light alloy engines for over 60 years - both factory fit and rebuilds. First on the Vincent HRD, from memory. And I know of no serious corrosion difficulties. Many motorcycles - especially older ones that only rev to 4000 - tend to have oily surfaces, which helps, of course.

I would not recommend a home made big-end nut, never mind a bolt. They are the most highly stressed, and fatigue susceptible, parts of an engine. Modern big end bolts are usually rolled threads and sometimes ground, neither of which is easy on an old Myford.

Cheers, Tim

Thread: Making a DIY tap
12/04/2014 17:54:01

Remember that the flutes iof the tap have to be large enough to take all the material removed as it turns. With only a short lead-in taper, this can be a serious problem - as all the swarf is heaped up in the first couple of threads.

Cheers, Tim

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