Member postings for Andy Ash

I'm not sure your advice about not using the armour as a protective earth is quite right there.

If you use SWA, it would certainly be bad practice not to use the armour as an earth conductor. It is very much more than sheathing. Indeed it is the very definition of an electrical protective earth. It is virtually impossible to damage a phase conductor without first cutting the protective sheath. The very act of encircling the phase conductors with the earth offers a method of electrical protection and essentially guarantees fast circuit breaker action if the cable is accidentally cut.

There is much uncertainty out there on this matter, so lack of awareness can be excused. One thing is certain, poor implementation will not be excused by mother nature under fault conditions.

People have generally noticed that corrosion can set in at glands and where the outer plastic sleeve becomes damaged. This can compromise the earth bond, and provide less than adequate protection.

Some recommend using an additional copper earth conductor inside the armour, others an additional copper earth conductor outside the armour.

Both schemes have problems;

1) If the armour is electrically damaged then neither scheme can guarantee to expose the earth conductor to the phase if the cable is cut. If the digger bucket scrapes along the length of the conductor then phase can be exposed without shorting to the protective earth. One is dependent on soil resistance to operate the circuit breaker in this situation, and it is not good.

2) If the parallel wired copper earth conductor leads an electrical test operative to believe that the armour is intact during test, then no-one may know that the armour has actually become damaged.

In conclusion; if the armour is not good enough to do the job because of corrosion, then it has not been monitored and maintained properly.

In most cases there is no reason why a steel wire armour cannot perform the function of a protective earth. If the calculations show that the armour can trip the fault circuit in the prescribed time, then my opinion is that it is safer only to use the steel wire armour.

Like all engineered installations it is important to periodically check and maintain equipment to ensure safety.

Edited By Andy Ash on 20/03/2017 20:13:54

Silfos "appears" to be phosphorus bearing.

I believe the conventional wisdom is that such solders can be a poor choice for steam boilers. I think the idea is that sulphurous gasses embrittle the joints. Obviously this is less than ideal in a boiler, especially if it is coal fired.

I'm not left handed, but I am pretty cack-handed. And this for me is the most important thing.

It's beyond all that by-rote run-of-the-mill H&S standard speak.

1) If you've not thought about it, don't do it.

2) If you've thought about it and you're not happy about it (that includes situations where use of mandatory safety kit is it's-self the problem), don't do it.

3) If you're confident that it's O.K. to do the thing you thought about; don't worry about it, because the worry will distract you and cause you to have an accident.

4) If you're experienced with welding, upside-down on the end of a rope, nude, inside of a half filled petrol tank, and you're still alive, you must be pretty smart; because there is nothing else keeping you alive.

I think most of them use diamond discs for ceramics.

The threat is slightly different with diamond cutting discs I'd say.

That they're using diamond probably shows they're smarter than most!

Radio transmission was one of the things that Tesla was messing around with.

I'd bet he tried all sorts of stuff.

Generally though I think the early VLF transmission were probably morse code.

If you have high power CW transmitter you can modulate it with a broomstick and some drawing pins!!!

I think they get away with it in the drawing because they only define the pressure angle for a pinion against a rack.

The rack has an infinite pitch circle so its involute tends to a straight line.

Perhaps the consequence, is that the pinion does not have to define a specific pressure angle.

I'm guessing that you could use any number of involutes for different pressure angles on the pinion, and control the actual pressure angle simply by the tooth profile on the rack.

This might be the same as meshing a 15deg and a 20deg gear pair. The actual pressure angle is a different number again, but whatever it is, that is the pressure angle.

I suspect that that if you did this with two gears, then you would get a pressure angle that varies as the teeth pass each other. With the rack (infinite pitch circle), the pressure angle is constant as the pinion rotates. I suspect it's like this because one of the involutes is a straight line.

Even if I'm wrong, I would suggest that it's not a very helpful drawing, especially if you know anything basic about practical implementation of straight cut gears.

Very similar to your synchronous motor would be the Alexanderson alternators they used to generate high power VLF (long wave) transmissions in the early days of radio.

They didn't have thermionic valves big enough to use as oscillators, so they did it mechanically instead!

If it is 1mm would recommend PCB drills. (For drilling circuit boards).

They're solid carbide, they're sharp and they're very cheap. They don't wear so they don't get blunt and break, but if you do break one at about 40p ea you don't really mind.

They normally have a large shank typically 1/8".

Just run them as fast as you can and it will be fine.

I reckon you're on the right track with that, but I've never made silver solder work with TIG. It's a bit expensive to be making a mess with silver solder anyway. I think the contamination issues and the low temperature of silver solder reflow would be the reasons. The trouble I find, is that I can't get silver solder close enough to the arc. If I lower the arc energy, then the steel isn't hot enough to accept the solder.

Silicon bronze (SIF do a good Silicon Bronze), is the route here I think.

Silicon bronze TIG brazing wouldn't be so susceptible to contamination as Silver solder would be.

I've never tried this particular combination but I might give it a go and report back.

I would offer to help but it's a bit distant and I imagine my skills would probably let me down anyway.

I imagine they would have used a special fluxed brazing spelter and an oxy torch back in the day.

Edited By Andy Ash on 01/03/2017 23:58:16

Citric acid can be pretty potent if you heat it up.

Below is a link to a paper showing how citric relates to other acids.

**LINK**

The tests describe weight loss in standardised steel test subjects at different concentrations and temperatures.

At room temperature citric is so benign and in any case cheap, I don't really understand why one would use anything else for small parts fabrication. With large objects like whole boilers it is different, I accept that up front.

If you get citric nice and hot, you can dunk a small steel silver soldered assembly into the acid and see the oxide layer just "pop off" in just a few minutes. It is literally left floating in the acid like a lizard shedding it's skin.

I use a stainless pan I bought in Sainsburys. I have a temperature controlled hotplate and a thermocouple inside an Inconel shell suspended in the acid by a spider. The thermocouple allows the hotplate to directly control the temperature of the acid.

I made the acid up using de-ionised water (for lead acid batteries) and I bought industrial cooking citric acid granules, from e-bay. The first batch I actually made on the kitchen cooker, and I just kept stirring the granules in until no more would dissolve.

I regularly filter the acid into a plastic container for storage, with Rombouts coffee percolator filters. You lose water by evaporation, so I just top it up each time I use it with the DI water. I originally made my current pickle about two years ago, and it still works nicely now.

I typically use it at around 65-70deg C.

The thing I like about citric is that it does the job. When it is cold even if you spill the whole thing, the only problem you have is a sticky mess that you have to clear up.

Watch out when it's hot though!

Edited By Andy Ash on 26/02/2017 00:15:09

I should think that the required accuracy of quartering will depend on the throw of the crank and the slop in the axle-boxes and coupling rods.

If you make them all the same maybe you'd be all-right but it's possibly going to mess with your valve timing if it is an outside cylinder engine. Possibly it's going to make the beats sound uneven.

I would have though the point of using a quartering jig is that they all come out the same. If the first one is wrong because of the jig, then if all the others are the same, then not too bad.

If you didn't have a jig (or a proper scheme) and that's why it went wrong, don't make a jig to ensure the rest are wrong the same, because they'll be wrong and different. Make the jig to make them right and correct the first one properly.

If you don't have a jig and don't plan on one, then they'll all be wrong anyway, so just carry on!

If/when you want to fix them, just warm them up and the glue will let go. The data sheet says maximum working temperature for the glue is 150C so it ought to be releasable with a gas oven, or if not, a blow torch.

In the end the glue is just plastic. Unlike metal it melts at quite low temperatures.

Edited By Andy Ash on 18/02/2017 21:17:52

I don't know if it's right but I looked up 14 shillings in 1934, and the conversion tells me it's the equivalent of £45.

It might be a reverential position but I think I might give it a miss at that rate.

**LINK**

When I'm thinking about metric and imperial, and I have no calculator, I usually stumble across the memory that 1/128 is very close to being 0.2mm.

What I find interesting, is that 0.2mm x 128 is 25.6 (a naughty metric inch) but then that 25.6 x 5 is exactly 128 again.

Obviously that's a millimetre out.

Had it not been for the physicists they might have got metric right.

Edited By Andy Ash on 31/01/2017 23:03:09

I don't think there's anything inherently wrong with simplex/duplex pumps, you see them fairly commonly.

I've never built a duplex pump, but I imagine it to be simpler than having to build up a crank and machine a flywheel.

Glands will always be a problem, and for a new build I would suggest o-rings, but you do need to be able calculate squeeze and machine to good tolerances.

I have used duplex pumps on other peoples engines, and you cannot fault them for ability to whack water into a boiler quickly. For obvious reasons this is a huge benefit if you suffer from injectors that refuse to pick up. On the other hand they use a lot of steam, and they tend to make quite a rattly racket.

Generally they're best when they can be coaxed to run gently and slowly, but with no rotating elements it is difficult to implement a governor. Without the governor and its feedback loop, no matter how good the throttle valve, they always seem to be "flat out" or "nothing".

I think you could make the pump rotative, by putting a scotch crank in the middle, and then you would have something to run a governor from. With a governor, you would get a very controllable pump.

Edited By Andy Ash on 20/01/2017 22:13:58

I don't know if you plan to implement a guide for the crosshead.

My thought was that if you load the pump, then everything will be fine, but if you load the crank then possibly not.

It looks to me from your model that if you load the crank then the piston rod will tend to rotate when the piston is pushing towards the crank.

I think you will need guide bars to prevent that behaviour.

Edited By Andy Ash on 20/01/2017 07:43:04

They've been going for four of five years now, which is the best I've ever done, so I'm not planning to stop keeping them in the house.

I don't doubt what you're saying though. My batteries are NiCad, but I'd always assumed that NiMH would be similar if not slightly better.

I've not been able to find much about self discharge with temperature, but I do know there are fairly strict limits on charging at lower temperatures. Maybe you know something about that too?

Edited By Andy Ash on 19/01/2017 16:18:24

I think there must be something wrong with one of your assertions there.

In electric welding CO2 is an *active* gas.

The energy in the plasma liberates one of the oxygen atoms from each CO2 molecule and the oxygen atom can then either bond with an iron or a carbon atom in the weld pool.

As I understand it the oxygen would prefer to bond with carbon. It is more mobile than the carbon in the weld pool which is at a lower energy. The oxygen forms carbon monoxide in the solidifying metal matrix, and becomes entrapped.

Porous welds are generally unwelcome so manufacturers add other more attractive elements into the feed-wire alloy, and avoid porosity.

In any case you know CO2 is active, when you weld with it; by the shower of sparks.

Edited to add;

I wonder if you were describing acetylene welding?

Complete combustion there (neither oxidising nor carburising) produces CO2 as a by-product of combustion, and since there is little ionisation, the CO2 can act to shield the weld pool.

Edited By Andy Ash on 17/01/2017 14:26:07

This advice seems a little irrelevant now since a new drill is likely to have Li-ion batteries. These don't seem to suffer in quite the same way.....

If you want to keep your NiCad or NiMH batteries alive, try keeping them warm.

I realised if I leave them in the car or in a cold shed, they die pretty quick.

I keep them in the house during the winter now, and I get much longer life.

It might be bunkum but it seems to work for me.

You could try the following;

**LINK**

Contrary to my own suggestion it does not have an Arc Force control, but it is intelligent in MMA mode.

It comes with a ground lead, MMA torch, TIG torch, gas hose - but no regulator.

It is DC only but is 200A amps and has HF start.

Inside £300 budget.

I don't have this model, but one similar which also does AC and plasma cutting.

I wondered if the OP needed to work outside because of the mess that stick welding makes.

My shed is so small I would never bother with stick welding indoors. TIG welding in the shed is no problem however. If you weld recently machined parts, prep is often fairly minimal anyway. With little grinding you only need to clear any oil contamination, and welding is fine. The actual welding process makes little mess, and on a grotty day you may not even need to open the door.

If you get a multiprocess TIG welder, then there is nothing stopping you from trailing the leads outside and using standard welding rods instead.

On a calm day, outdoor TIG welding is O.K., but slight draughts will set you back. Obviously stick welding is not immune to the wind, but it is more resilient to wind effect.