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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: >Ouch< well, almost...
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

Thread: Electric Drill-drivers with dead batteries
19/01/2017 16:17:55
Posted by Muzzer on 18/01/2017 15:24:31:
Posted by Andy Ash on 16/01/2017 17:35:42:

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.

Yes, I'm afraid it is bumkum. Self discharge is particularly bad for NiMH chemistry. It's a result of an unwanted chemical reaction and like most chemical reactions, it increases with temperature. Basically, leakage current will double for every 10C increase in temperature. It's one major disadvantage of NiMH chemistry but at least it doesn't contain heavy metals like cadmium.

Murray

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

Thread: Welding Gas
17/01/2017 14:04:06
Posted by Neil Wyatt on 16/01/2017 22:31:52:
Posted by Muzzer on 16/01/2017 21:57:18:

John - you wouldn't want to use anything other than argon (or possibly argon-helium mix) with aloominum. CO2 isn't inert, which is why MIG used with CO2 (steel) is technically "MAG" ie metal active gas.

CO is used to refine iron ore into iron i.e. carbon is more reactive than iron, so in steel welding the CO2 is inactive.

CO is less reactive than aluminium (which is why you need to use electrolysis or other fancy techniques to purify aluminium) and why it is not suitable as a shielding gas for it.

Neil

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

Thread: Electric Drill-drivers with dead batteries
16/01/2017 17:35:42

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.

Thread: Need to get a Welder!
15/01/2017 14:26:04

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.

15/01/2017 13:46:12

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.

14/01/2017 23:54:22

I don't know if it helps, but I'd offer the following;

If you can, get an inverter welder, whatever sort you get. Modern inverters are so far ahead of any of the old fashioned transformer machines its just not worth thinking about buying a new transformer welder now. It will make your newbie welding experience better in two different ways.

Firstly it will make your welder easier on your power supply. Transformer welders have all sorts of extreme electrical demands, which inverters eliminate. With a marginal supply an inverter will do a better job of giving you a stable arc.

Secondly, if you give an inverter a less good supply than a transformer welder, then the inverter will still give you a more stable arc.

Internally, inverters make use of closed loop control and this affords better consistency of electrical output. In electrical terms, a closed loop regulated supply has better load *and* line regulation than an open loop scheme like a raw transformer.

When you then add to this that inverters can be dynamically controlled, you begin to see incredible capabilities like "arc force" control emerge. I know you are not explicitly looking for "ghastly stick welder" but if you get any kind of inverter welder, you probably want to be looking at a "multiprocess" welder, just to get value for money. Normally this would be MMA (stick) and some other capability. So if you get a multiprocess welder make sure it has an arc force control. If it has "arc force" then it is no longer a "ghastly stick welder". The two are mutually exclusive.

There are very few situations where your old transformer welder will outperform a new inverter. If you get a DC only inverter then, when doing MMA you can experience "arc blow" when say approaching the inside corners of angle iron. An AC transformer welder will help in this scenario, but it's the only one I know of. If you are worried about that, then get an AC/DC inverter.

Generally you are going to find two kinds of inverter welder, MIG/MMA, TIG/MMA. You can get MIG/TIG/MMA machines, but normally they're in the "Tom Lipton" realm.

Naturally, MIG welders will focus on the benefits of having a wire feeder, and if they are multiprocess will switch between constant voltage (MIG) and constant current (MMA). In a general sense, any welder that can do MMA can also be converted for TIG welding, and given that a MIG welder will have a gas valve, it will probably do TIG welding better than most. Why would you then bother to get a TIG/MMA welder?

TIG/MMA welders do not usually bother to provide a constant voltage capability. Obviously you can get separate wire feeders, but these are the "Tom Lipton" territory. If your machine cannot support constant voltage then a wire feeder is not going to be useful to you. On the other hand, proper TIG welders will usually offer an AC capability.

An AC arc will help in certain MMA situations as already described. Critically AC is pretty much a requirement for Aluminium welding. If you get an AC capable TIG welder make sure it has variable AC balance. This allows you to control the cleaning action. I won't bother with that here but if you end up welding any aluminium you're going to be very interested in that.

Most TIG welders come with a variety of pulse options, slopes and ramps, which can work with your foot pedal. These features are easy for manufacturers to offer, but I must admit to not using them much. For TIG the foot pedal its self is not mandatory, but do get one because you will want to use it.

If you go for TIG, reckon on getting more than one torch. A high current torch will be clumsy on delicate work. A delicate torch will quickly overheat doing high current work. I won't talk about water cooled torches, I understand that these are the panacea, but they are a bit "Tom Lipton" for me.

If you get a Chinese welder it might be quite good. Mine is German badged, but made in China. It's all right, and I would recommend one. Be mindful that Chinese welders generally have metric gas fittings. Most US/English welding equipment is..... English. If you have a lathe and a bit of imagination this isn't going to bother you too much.

I really would recommend TIG, for the workshop. TIG is definitely indoor welding. For jigs and fixtures it is perfect. You can do the smallest of welds with ease. For high temperature fixtures it is a godsend. For any "visible welding" TIG is "the way".

If you do a lot of sheet metalwork, perhaps MIG is the way. For sheet metalwork TIG cannot do everything that MIG will do, but if you're not happy with a lumpy seam on the inside of your outer wings on the car, TIG is still what you're going to need.

TIG is technical, but if you're happy with that, you'll do fine. Quality MMA welds are *MUCH* harder.

For TIG you need a bit of brain. For MMA it's less brainy, but you really have to have actual skills if you want anything approaching a proper weld.

MIG can give you a proper weld on heavy plate work jobs, but on light work it will never be "nice".

Thread: Cheap 3 in 1 tig welder - any one used one?
11/01/2017 00:10:12

You can use helium for TIG but it is mighty expensive. Over in the states it is common to call the TIG/GTAW process Heliarc because they often use helium by default.

To save money you can mix helium and argon. Typically you would need a regulator for each and some kind of mixing valve.

You would only need to mix if you wanted to get some of the helium advantage without fully paying the price.

The advantage of helium is a higher power arc. Helium gas has a higher ionisation potential than argon, and that means the voltage generated across the arc gap is higher. If the voltage is higher for any given current then the arc is more powerful.

You might want to use this for say copper welding. I don't think there is a reason why you couldn't weld copper with argon, but most hobby welders run out of welly before they can be usable on a material like copper. With helium, perhaps you can get a bit more energy into the material.

I don't know exactly how big the practical advantage is, but I'd hazard a guess that it's about 1.5 times on the current setting. If you have a 200A welder on argon that might be the difference between a silver soldered and welded copper boiler.

Edited By Andy Ash on 11/01/2017 00:18:14

10/01/2017 18:40:44

I've been using http://www.sgsgases.co.uk/.

Last time I looked they were cheaper than BOC.

 

I get their argon from the local motor factor. The only trouble is that they are geared up for the motor trade.

I phone up and as for pure Argon, and when I get there, they only have Mig Mix.

They're usually coy but I think it's because they they think they know better.

 

If you go in and ask they will give you a price. A proper bottle should be £90 inc vat, nominal. Will last a year with maybe four small projects and one bigger one.

The Mig Mix is cheaper but it's no good for TIG.

CO2 is active, and it makes a mess of the welds.

Sadly Pure argon isn't very good for MIG either.

 

Have fun, and feel free to ignore.

Edited By Andy Ash on 10/01/2017 18:41:07

I should say, you do get about £20 on the bottle when you return it.

Edited By Andy Ash on 10/01/2017 18:55:34

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