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Member postings for Andy Ash

Here is a list of all the postings Andy Ash has made in our forums. Click on a thread name to jump to the thread.

Thread: P-Power hacksaw
16/04/2017 17:47:21

All motors are different, which might sound obvious, but a windscreen wiper motor has been designed to wipe windscreens on cars.

So, they have to deliver high torque, and have to be compact, so as not to impact on the "look" of the car. On the up side, it's pretty easy to have them sited in a high flow air-stream.

A compact high power motor is always going to get hotter than a large heavy one. For the same number of wire turns, the wire can be thicker and the magnets stronger. Weaker magnets means more current required, and thinner wire means more heat for that current.

One way to fix it, is to attach your new saw to the front of your car, and drive around whilst sawing. smiley That way you would get the required airflow.

A more practical solution would be a bigger motor, or different/better gearing.

I suspect you won't achieve cooling equivalent to the automotive environment with a practical fan setup.

Edited By Andy Ash on 16/04/2017 17:49:16

Thread: LBSC Owl - Any Info On This O-gauge loco?
16/04/2017 10:59:42
Posted by Steven Greenhough on 16/04/2017 09:27:52:
Really? Wow how would 2 cylinders be squeezed between the frames?

I would still like to see a few images of an Owl if anyone has any and it wouldn't be too much trouble...

I don't know about Owl, but I have the drawings for Bat.

If you want to find out about Owl, then TEE Publishing do the combined book, "Introduction to Bat & Owl".

I expect you would find most of the information you want there. As Julian has said, the back issues of ME will carry most of the details too. If you're new to Curly's engines, expect to have to make leaps and jumps. His engines are quite deceptive, they look simple, but often there are critical details missing.

In truth, I think that might be half the fun.

16/04/2017 01:01:39

Under my bench I have a half complete Bat.

The garden railway fraternity have moved on a bit these days. I must say that although the modern engines look superior, I'm not certain that they really are. As I understand it, many of these locomotives are purchased as kits. I have nothing whatsoever against kits, but it is much nicer to me to see a scratch built engine.

I think many of the kits are gas fired and often only have a single inside cylinder with cosmetic cylinders and motion outside the frames.

Say what you like about the appearance of these smaller gauge offerings from Curly, but they can usually be coal fired and the cylinders are in the right place. It depends on what you want to do, of course, but I'm pretty sure I know what Curly would have thought about the modern models.

Good luck with it. Nothing wrong with the old un's as far as I can see.

Thread: Metal combinations for plain bearings
14/04/2017 23:29:51

I don't know if I'm right, but I feel like saying, polished stainless pin, with a PTFE bushing in the brass wheel.

Thread: Citric acid as pickle
14/04/2017 22:56:35
Posted by Speedy Builder5 on 13/04/2017 11:36:49:

Ian, it wasn't a problem of finding Citric acid, it was the problem it caused with lead solder. Unfortunately Neil's suggestion of meths for cleaning up the solder joint after the citric damage didn't work either. In the end I had to resort to mechanical cleaning before using an active flux. The solder I used was a flux cored (Multicore) solder 60% Tin 40% lead (I happened to have a lot of that to hand). For the second fix, I used some 50/50 unfluxed solder and finally in one awkward corner used form lead free to 'Caulk' up as it has a better gap filling property.
BobH

I'm an advocate of Citric, particularly hot Citric, which is every bit as effective as other more powerful acids.

Some of those more powerful acids don't benefit (as much) from heat, not that you would want to use them that way anyhow.

I've only ever used acid pickle on hard soldered joints. Mainly because the borax flux is so tough to remove.

For soft soldered joints, especially with acid flux, you can just use warm water to clean up. For that I usually use Fry's Powerflow flux and it just works very well indeed.

If you use Rosin cored solder, then you do get a residue. Meths is a disaster for that. It won't shift anything and you get a white deposit which looks really gross. The best stuff I've ever come across for rosin cored solder flux removal is from Electrolube. It's in an aerosol, called LFFR (Lead Free Flux Remover). It even smells fairly nice. Don't breathe it though, it's Cyclohexane. I've no idea what that is, but rest assured that one day someone will recognise it as being bad to small furry nylon bears.

Farnell Pt. No. 1098276

It will lift the sticky deposits. All you have to do is make sure that the solvent has been wiped away before it evaporates. Wherever the solvent evaporates, the Rosin residue will be left. The aerosol has a brush nozzle. You give it a squirt, mush it in with the built in brush, and then dry the solvent with a paper towel. Job done.

Edited By Andy Ash on 14/04/2017 23:00:04

Thread: Armoured cable - what size would you reccomend
20/03/2017 20:06:39
Posted by Brian Wood on 20/03/2017 18:04:51:

Hello Dave,

​I wired out the supply to my workshop with 6mm armoured cable. The total cable distance from the consumer unit and destination is comparable to yours and voltage drop calculated at under 5 volts. Remember to buy 3 core cable so that you have a copper cored earth, the armour is steel sheathing and not really good enough for a reliable earth. and will get failed if you put it up for test certification.

​You will also need the appropriate size of glands at each junction point.

​Regards
Brian

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

Thread: Silver soldering
15/03/2017 19:25:40

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.

Thread: >Ouch< well, almost...
10/03/2017 16:16:12
Posted by James Alford on 10/03/2017 15:41:41:

I am very wary of angle grinders these days. A couple of years back, I was using one with a sanding disc attached. The person for whom I was doing the job told that I was holding it all wrongly and showed me how to do it "properly". The thing promptly snagged and kicked back into my face: "properly" is not the same, it seems, if you are left-handed like me..........

James.

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.

09/03/2017 14:11:56
Posted by vintagengineer on 09/03/2017 14:07:57:

They are builders, not the brightest of tradesmen.

Posted by Tony Pratt 1 on 09/03/2017 12:23:13:

I'm always amazed by the builders/block pavers who use angle grinders without any form of protection, stupid is not really a strong enough word.

Tony

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!

Thread: Why don't we make models of things like this?
05/03/2017 23:29:31

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!!!

Thread: Involute Gear : Pressure Angle
05/03/2017 23:19:40

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.

Thread: Why don't we make models of things like this?
05/03/2017 22:52:51

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!

Thread: Drilling tiny holes.
05/03/2017 19:32:43

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.

Thread: Silver Soldering Long Sections
01/03/2017 23:54:53
Posted by Neil Wyatt on 01/03/2017 18:47:52:

I was thinking that tig as a heat source for a compatible filler, which could be silver solder. the advantage with TIG being you could stitch it at intervals along the length, then fill in between (if required) to minimise distortion. I suppose you could do the same with an oxy actylene or oxy propane torch.

Neil

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

Thread: Cleaner for Silver Soldering
26/02/2017 00:10:02

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

Thread: Inaccurate wheel quartering - recovery action
18/02/2017 21:17:20

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

Thread: Pattern Making
01/02/2017 22:00:22

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**

Thread: An interesting co-incidence of units
31/01/2017 23:01:31

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.

smiley

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

Thread: A simple pump - is this design feasible?
20/01/2017 22:05:27

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

20/01/2017 07:41:03

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

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