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Member postings for SillyOldDuffer

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

Thread: Milling around with bits
17/04/2021 10:57:17
Posted by Stuart Munro 1 on 16/04/2021 22:02:02:

...

As to milling speeds, for a novice without someone looking over my shoulder its quite unnerving pushing the feed rate up yet I theoretically understand that the balance between Surface feet per min (Have I got the term right), the cut depth and feed rate sometimes needs me to increase feed rate. As an alternative I reduce the RPM.

...

But I've not been lubricating on my mill; I have an oil/water mix a friend gave me for a bit of iron I turned on m lathe - also a Sherline. But might try the WD40 - seems to be akin the the wild west elixir cure all but for engineers!

... although I still don't understand quite why - important to my satisfaction not to the machining as long as I follow the 'rules'. Is it that somehow uncoated cutters are sharper because the coating itself thickens the cutting edge?...

... any other ex office dwellers moving into a useful pastime in retirement ...

Stuart

In reverse order:

  • ex-Office dwellers are the salt of the earth!
  • Don't get hung up on 'rules' : look on them as guidelines. The number of combinations of rpm, doc and feed-rate that will cut satisfactorily is often broad and the sweet spot is often determined by the limitations of your machine and cutter relative to the material rather than the book. Use a rule a thumb to get into the zone and experiment for best results. Varies by machine: heavy, rigid, powerful machines are more tolerant than light, bendy, weedy ones. Hobby machines are all on the light side. By all means look up Surface Feet per Minute, but working from rpm = 10000/dia in mm is more scientific than it looks. Be aware time is far more important to professionals than hobbyists: time is money. Handbook cutting speeds are for economic production, which is rarely practised in hobby workshops. Book values are useful for 'difficult' materials, because these cut within a much narrower range, if at all! For a hobbyist, the two most important things are to go in hard enough to cut because rubbing ruins tools in short order, but not so hard as to challenge the machine's rigidity, gears, or motor! Gorillas and weeds are equally bad machinists. Both are common beginner mistakes - I was a weed until Andrew Johnston put me right.
  • Cutter coatings are extremely thin and unlikely to reduce sharpness. Coatings don't mix well with Aluminium, and cutters made specifically for non-ferrous metals are sharper than others because optimum sharpness depends on material. Using the right cutter just makes it easier to get a good finish and they last longer too; it's not that coated cutters fail miserably on Aluminium or uncoated cutters fail on steel.
  • Don't use suds (oil and water emulsion) on aluminium or paraffin on steel! Why not is another essay question! I'll leave it to someone else!
  • I like to set the RPM and adjust DOC and feed-rate to load the machine by ear. I only reduce RPM to stop chattering when reducing the other two risks rubbing. This depends on the motor: speed controlled electric motors tend to lose power and torque when their rpm is reduced. I find it pays to keep RPM high if possible.

Reading about how all these variables interact is intimidating. Don't worry because starting by rule of thumb and experimenting reveals what's needed and it soon becomes second nature. Theory is essential to making money in cut-throat production but absolutely not vital to producing results at home. The hobby is a mix of art and science and skill is more important than theory.

Practice!

Dave

Edited By SillyOldDuffer on 17/04/2021 11:02:32

16/04/2021 19:27:06

Posted by Stuart Munro 1 on 16/04/2021 17:56:59:....

Argh, number of flutes, helix angle, coated or uncoated, type of shank.....now to lubricate or not. That's before discussing SPM, feed rate etc. ... can read a lot on the 'net' but would really like to know what really works and why.

...

 

Well I like to keep it simple! I use the same coated HSS cutters on steel, brass and Aluminium, simply adjusting feed rate, depth of cut and RPM for best results.

Two flue cutters, aka slot drills. can plunge and cut slots. The big gap between flutes helps eject swarf. Four flute cutters are for flattening and edge cutting - they remove metal faster and produce a better finish provided the swarf can get out of the way. They can't plunge (usually). Keep meaning to try some 3 flute cutters, which are a compromise between 2 and 4 flutes, but never got round to it.

Coated cutters have a thin covering of something extra hard like Titanium Nitride to extend tool life, but Aluminium tends to weld to it, spoiling cut and finish. Not a big problem if spotted because the Aluminium can usually be scraped off, or dissolved in Caustic Soda solution, though having to stop does delay work.

I don't lubricate brass or cast-iron. Aluminium benefits from a light oil such as paraffin or WD40. On steel I use neat cutting oil, mainly because I have an irrational fear of suds causing rust. Or I go gently and don't lubricate at at all.

RPM, DOC and feed-rate are all a rule of thumb. Recommended industrial parameters are chosen to balance tool-life, metal removal rate, and economic use of power. They are more aggressive than most hobby machines are comfortable with, so back off! Don't expect a Sherline mini-mill to perform lanything ike a hefty Horizontal milling machine

I determine RPM by dividing 10000 by the cutter diameter in mm. This is about right for mild-steel, increase for Brass and Aluminium. Slow down by half for cast-iron. Depth of cut, up to 10% of the diameter of the cutter, feed rate fairly fast. It's important to cut rather than rub. I adjust DOC and feed-rate by ear; I like the mill to sound as if it's working, but not labouring. Reduce rpm if chatter occurs, and increase DOC and feed-rate so it sounds right. The exception is finishing cuts, which can be much lighter or climb milled, but avoid climb milling whilst taking deep cuts because 'our' machines are too weedy!

All this assumes the material is a machinable alloy rather than unknown scrap. Many alloys don't machine well, and some are downright evil! Learn on the right stuff so you know what to expect before experimenting with scrap just in case your junk box is full of rubbish. Mine was!

Dave

ps I don't think the people I buy cutters from offer different helix angles!  As I understand it, they are optimised for roughing or finish, or in between.  I think mine are all 'in between'.  I doubt helix angle matters unless something special is in hand.

 

Edited By SillyOldDuffer on 16/04/2021 19:45:07

Thread: Bassett-Lowke
16/04/2021 13:59:12

Like everything else toys are a thing of their time, and time flies. Meccano made models that looked like the truss bridges, cranes and other riveted structures common before 1950. It's not so good at representing streamlined objects like aircraft, spaceships, and sleek concrete bridges! Meccano and similar are out of step with the young mind, as are transistor radios and yoyos, and no doubt games consoles will eventually bite the dust too.

I'm a little concerned that so many forum haven't noticed that the world moves on. As Mr Robert Zimmerman made clear in 1964:

Come mothers and fathers
Throughout the land
And don’t criticize
What you can’t understand
Your sons and your daughters
Are beyond your command
Your old road is rapidly agin’
Please get out of the new one if you can’t lend your hand
For the times they are a-changin

Mr Zimmerman, better known by his brand-name 'Bob Dylan', was famously called 'Judas' by his fans when - shock, horror - he switched from acoustic to electric guitar. A few of my friends have never forgiven him, yawn.

Silly Old Duffers always think the young lack imagination and energy. Not so, they've just moved on. They're more interested in drones, extreme-sports, computing, internet trends and 3D-printing than the obsolete artisan skills that tick my box. Don't worry, the march of time will bring today's youngsters back to the mother lode. Retired gentlemen enjoy manual skills and retro-technology. I do! Steam engines and mechanical clocks are irresistible!

Dave

 

 

Edited By SillyOldDuffer on 16/04/2021 14:01:46

Thread: Simple test to distinguish mild steel rod from silver steel rod.
16/04/2021 11:52:02

Spark test, plenty of advice on the web, like this example:

Takes a bit of practice. Grind and watch known examples of various steels to see the difference before tackling an unknown metal. Silver steel sparkles more than mild-steel, but the difference is easier to see by comparison.

Dave

Thread: Advice on Choosing A Mini Lathe
16/04/2021 11:38:38
Posted by Stuart Munro 1 on 16/04/2021 06:52:13:

...

I can see and agree with the aim of a single category discussion such as this, yet also agree with those (I was one of them) who sought to define the edges of the 'Chinese family mini-lathe' by exploring the options around that are in many ways similar, yet still different. Indeed this must be of great help to those considering the purchase of a mini-lathe.

...

Stuart

I sympathise because I started without a clear idea of what I wanted a lathe for!

As an ex-software engineer I'm trained to insist on Formal Requirements rather than go with whatever solutions the customer offers. Most users tune into stuff they like they look of rather than do a hard-work analysis of actual need! The ignorance is bliss approach works well with consumer items like teapots, shoes, and motor cars, but failing to define requirements fails as soon as the answer has to address any kind of speciality. Machine tools are a case in point.

Best to define what the lathe is for before choosing one if you can. Much easier to advise when a newcomer asks:

  • I want to make clocks; what sort of lathe should I buy? Or,
  • I want to repair traction engines, what sort of lathe do I need?

Knowing the requirement is only the start. It sets a baseline against which compromises will be made. Nasty constraints like money, space, availability, and domestic authority!

Not knowing a newcomers limitations or purpose makes it hard to answer Sherline vs Mini-lathe type questions in isolation. If the questioner works on model railways under the stairs, a Sherline is a good bet, but it isn't a motor-bike mending bruiser! And maybe Sherline isn't good enough either, a Cowells is needed.

Best general lathe advice is to get the biggest you can afford: it's because big machines can tackle large work whilst still being able to do small stuff. But small work on a big lathe isn't comfortable, which is why some own more than one.

A mini-lathe is the biggest machine I consider sensible in a domestic setting: they'll sit on a dining table or spare bedroom and are fairly quiet unless the job chatters. But a big mini-lathe makes far more mess than a Sherline, and a weakling like me wouldn't want to lift one on my own. (No problem for two weaklings!) Ideally a mini-lathe goes in a dedicated workshop, and anything bigger definitely should. And the workshop should be dry and comfortable with adequate power and good lighting, plus a workbench, vice and all the rest. The budget has to tackle that too, maybe over several years.

Practically, the Mini-lathe, next size up Far-Eastern, Myfords and similar are all about the right size and capability for a small dedicated workshop doing mid-range work.

There are always exceptions. If a newcomer doesn't quite know what the lathe is for, I suggest the answer is to buy general purpose and experiment. With hindsight I dithered too long before buying a mini-lathe and getting stuck in. Using one taught me far more than reading about them; I found many books and opinions only made sense after using one in anger. The mini-lathe is a good "don't know what I want" learner machine: not too small and has screw-cutting and the other basics. Availability and relatively low cost new are big advantages for a beginner. Doesn't mean mini-lathes are perfect. Far from it. Although they do the job, they are quite rough, likely to annoy chaps brought up on smooth professional gear.

To me buying the best you can afford and making it last a life-time is an out-moded idea. Dates to a time when there was a sharp divide between good and bad tools. Not so today: we are surrounded by medium grade tools, fairly decent, but not intended to last. Made to be used and replaced, not cherished. So, I bought a mini-lathe fully expecting to replace it. 3 years later I changed up because it was too small, not because it was junk. At the time, it was convenient to buy the biggest Chinese lathe that could be squeezed into my workshop with a milling machine. Buying new eliminated all the bother and risk associated with second-hand, which back then I didn't have time for. I got a WM280 fully expecting to replace it later with an ex-industrial machine, but in practice it does all I need, and I haven't bothered.

Not many of these considerations involve make or country of origin! To my mind it's a mistake to eliminate technical options based on secondary considerations like brand too soon. Though reasonable for hobbyists to spend their money as they want, at least try to recognise the difference between logic and emotion. Although supposed to be cold evidence based thinkers, several studies have shown purchasing decisions made by grizzled engineers are positively influenced by scantily clad young ladies draped over the equipment. This is true even after the fools have loudly denounced the girlies as an obvious attempt to influence them! We are all human. The important thing is to enjoy the hobby.

smiley

Dave

 

Edited By SillyOldDuffer on 16/04/2021 11:45:22

Thread: Laptop with a SD card slot
15/04/2021 16:49:07
Posted by Michael Gilligan on 14/04/2021 23:59:27:

...

I have recently acquired 128GB and 256GB cards which are not compatible with my Mac slot, or with my USB 2 reader.

...

How old is the Mac, or rather which version of OSX is it running? Could be hardware or software incompatibility Cards bigger than 32Gb are formatted with exFAT which requires Snow Leopard or later.

Otherwise, might get a clue by trying this: start a terminal session (console) and then plug in the SD-Card. In the terminal immediately run the command 'dmesg' which should list the kernel log, showing what happened when the card was plugged in. The relevant messages will be near the end.

Dave

Thread: Was this embrittlement, or what?
15/04/2021 09:46:23

Having been pointed by Michael and Jouke to Liquid Metal Embrittlement, I see the Wikipedia article says loud and clear: The practical significance of liquid metal embrittlement is revealed by the observation that several steels experience ductility losses and cracking during hot-dip galvanizing or during subsequent fabrication.

As Tim was indulging in 'subsequent fabrication' of a galvanised plate, and brazing would melt the Zinc, he's ticked both of the necessary boxes. LME seems far more likely to me than Hydrogen Embrittlement, or any other cause.

I find it very difficult to imagine the effect one element will have on the physical properties of another when the two are in solution. The effects can be dramatic, for example distilled water is an electrical insulator, but the addition of a tiny amount Salt (Sodium Chloride) converts it into a conductor. The salt also alters the freezing and boiling points.

Likewise in metals, it seems small electronic changes can have beneficial or detrimental effects on the crystalline structure of solids. Carbon dissolved in Iron makes wonderful steels and useful Cast-Iron, and both can be improved by adding certain other elements like Manganese. However, other elements, such as Phosphorous and Sulphur, have highly negative effects on Iron.

In steel, I conceive sheets of Iron atoms where a tiny amount of Carbon fills gaps to reduce slipping, while too much Carbon lubricates them. Much too simplistic, because there is no physical contract: the forces involved are electronic interactions between atoms, altering the crystal structure of the metal. And the crystals are related to orbitals, taking us straight into quantum mechanical weirdness.

Soldering and Brazing exploit the good effect of creating a solution between two metals but as we know there are many ways joints can be ruined by contamination, oxides, poor choice of metals etc. Mistakes result in a flawed solution at the boundary.

LME seems to be due to another phenomenon: a crack propagated as a result of a liguid metal causing, or following, a local weakness. Due to leverage, the forces at the front of a crack can be enormous, even if the energy is only built in stress.

Dave

Thread: What Did You Do Today 2021
14/04/2021 11:31:54
Posted by Nick Clarke 3 on 13/04/2021 14:01:56:
Posted by SillyOldDuffer on 12/04/2021 20:33:56:

Clue is in 'Page Description Format', the files are printable rather than editable.

Dave

pdf actually stands for 'Portable Document Format' and while readers are free the format was originally a proprietary one, developed by Adobe, and based on their 'Postscript' page description language to enable documents to be produced using paid for software but read using free readers on a range of different devices.

Doh! Of course it does. I really must stop trusting my memory and check before hitting the 'Add Posting' button. Reckon I conflated Page Description Language with PDF; my poor old brain must be full of bad-sectors!

Blush,

Dave

Thread: Any Ideas please?
14/04/2021 10:32:30

The 'Mill Engine' design has been around a long time: it's very similar to the 1901 Thompstone Engine Jason is reinvigorating in ME at the moment. (Part 1 is in 4662.) Pretty much the same layout as Stewart Hart's PottyMill, and one of my old text-books describes a full-size engine of the same type. A sort of small simplified mill engine, no reverse, or condenser, slide valve driven by an eccentric, only a couple of HP, plain build, and presumably intended for a small enterprise mixing dough, making butter, driving a laundry or whatever. I believe the type was very common before electric motors took over, and they make good model - not too difficult in basic form for beginners, castings or fabricated, and can be made more elaborate if required. For example the PottyMill's plain Aluminium cylinder is mounted on a block, whereas Jason's Thompstone has turned brass feet inset into a Bronze cylinder with tasty decorative bands.

The polish and fine finish suggest the engine was made by someone who had plenty of spare time. The absence of spokes suggest he or she had access to a lathe, but not a milling machine, and perhaps decided to tackle them later. I agree the flywheel should be in the slot, which suggests the engine has been assembled incorrectly. Possibly someone made it, got it into running condition, and then passed the engine on to a new owner who beautified it, but didn't have the facilities to cut spokes, quite understand the flywheel, or realise the slotted-screws were temporary.

My first PottyMill is rough because I built it to exercise my weak machining skills: it wasn't intended for show, and the result is purely functional with many unfixed blemishes. Maybe when I'm dead it will be refurbished and sold in a glass case as an attractive antique, claimed to have been handmade by James Watt in 1760...

Dave

Thread: Anodising and Passivating
14/04/2021 09:10:16

I think the difference is simply down to how the protective layer is created. Anodising is an electrical process producing a protective oxide layer; Passivating is a chemical process, including oxidisation by heat, but also paint, and plating.

Anodising is most useful on Aluminium because the Oxide is tough, firmly attached, corrosion resistant and can be dyed. Applying the same process to steel produces rust, which is weak, flakes off, holds water, and plug ugly. Anodising is a rotten way of protecting steel, fortunately steel can be passivated in other ways. And many passivation methods good for steel, like bluing, don't work on Aluminium.

Dave

Thread: Advice on Choosing A Mini Lathe
14/04/2021 08:23:27
Posted by Stuart Munro 1 on 13/04/2021 07:09:59:

I also have Sherline but thought here we were defining mini-lathe as the Chinese manufactured family.

i think most readers will be considering a mini- lathe for one of 3 factors; small footprint and light to set up, affordability and 'big enough for what I need.

Reading these blogs eliminates the 'big enough' argument - it invariably applies that the biggest machine you can get will likely be needed at some stage so it really comes down to the first 2.

So the question that I would like to see explored is; are the Chinese mini-lathes the way to go, or the non Chinese variants like Sherline.

I have no experience of the Chinese lathes so cant make the comparison but chose the Sherline lathe and Mill for their size, I have an 8ft by 4 ft shed for all my hobby work.

Thoughts - or am I drifting too far from this blogs remit?

Stuart

Confusion abounds! I understand a mini-lathe to be one of the many variants of the same basic design like this example from Warco. It's not a general term for 'any small lathe'.

Mini-lathes are modern design (about 1960), weigh about 35kg, speed in two ranges variable between 100 and 2500rpm, motor between 400W and 800W depending on model, they take a 90mm ( 3½" ) flange bolt-on chuck, and the bed has about 80x250mm usable space. Spindle bore 20mm (3MT), tailstock 2MT, tool-post takes up to 10mm tools. The Imperial version cuts metric threads and vice-versa.

Sherlines are not mini-lathes. Different design. The 8" version weighs about 10kg and has a 90W motor. The spindle bore is 10mm, and they don't screw-cut.

Though mini-lathes and Sherlines can do similar work, they're aimed at rather different markets. Sherline are good for small precision work, mini-lathes are more general-purpose, where the extra power and weight pay off. By analogy, if a Sherline was a scalpel, then a mini-lathe would be a bread-knife. Both are useful in their place.

Mini-lathes are a convenient way for beginners to get into metal turning. They're inexpensive, have all the basic features, and are big enough to tackle small jobs, whilst not being so massive as to require a crane! (I'd describe them as semi-portable, an easy two person lift.) I learnt a lot from mine, chiefly concluding it wasn't big enough for about 20% of what I wanted to do. Someone into O-Gauge railway models or smaller might well decide mini-lathes are too clumsy for delicate work. In my opinion what the tool is for is more important than who made it. Whether or not a mini-lathe takes WW collets is irrelevant in my workshop because I don't need them. Cowells take them, though they're a lot more expensive than a Sherline...

Zeb's says of mini-lathes: 'I know for certain the runout is much higher and the plastic gears on a lot of them wear out prematurely and are noisier.' Not my experience. Run-out measured at the spindle taper was undetectable with a 0.01mm DTI, the plastic gears didn't wear out, and they're much quieter than steel ones! Wouldn't describe the mini-lathe as a paragon though! Crudely finished and obviously made down to a price. Based on negative web comment I expected mine would need a lot of work before doing anything useful. Wrong! It worked out the box and only needed minor fettling.

Stuart asked: are the Chinese mini-lathes the way to go, or the non Chinese variants like Sherline. My answer: Horses for courses. It depends on what the lathe is for.

Dave

Edit: I hate smileys!!!

Edited By SillyOldDuffer on 14/04/2021 08:25:22

Thread: Hobbymat MD65
14/04/2021 06:48:56
Posted by Bazyle on 13/04/2021 22:02:12:

People shorten the taper because they get annoyed by the item ejcting before the tailstock barrel retracts back to zero graduation. But it can backfire as you found...

All too easy to chop a little too much off the end. You can guess how I know!

sad

Thread: Distorted ship's hull steel panels
13/04/2021 17:03:43
Posted by Mick B1 on 13/04/2021 15:40:01:

Posted by SillyOldDuffer on 13/04/2021 13:42:41:

...And as an anti-ship guided missile has considerably more punch than the largest 18" shells ever fired in anger, it's not unreasonable to hope a powerful missile might pass clean through the ship without exploding, which favours light-weight construction.

...

Dave

At 1710 lb arriving at 1047 ft./sec., an Exocet doesn't quite compare to a WW1 - WW2 British 15" battleship round (1938 lb. at 1430 ft./sec @ 19,500 yds range), less still an 18" with 80%-odd more mass. The competitive Harpoon missile is lighter, slower, but with a bigger warhead. Both have larger warheads than the bursting charge of 15" HE shells, and much larger than AP, which formed the majority of capital ship ammunition outfits. These latter certainly did pass through lighter ships without exploding - eg. Warspite's fire at German destroyers at Narvik.

The missiles' kinetic energy is thus a good deal lower, but with current fuzing capabilities the prospect of passing through without exploding doesn't look realistic. The Exocet that hit HMS Sheffield may or may not have exploded - I can't imagine how the detonation of such a substantial warhead could be unclear - but the wrecking fire was caused by residual propellant. The missile body didn't pass through.

Yes, but most of the energy in a guided missile is explosive, not kinetic. The explosive in an Exocet warhead weighs 165kg compared with 24kg in a Japanese 18" Armour Piercing Shell plus it has more zip because it doesn't have to withstand the shock of being fired from a gun. And as the rest of the missile is mostly propellant, any unburned when the target is struck adds to the devastation.

The maximum range of the Japanese 18" shell was about 42km and at that distance a 9 shell salvo would be dispersed over 600m. In comparison, the Exocet is good for up to 120km and unless disrupted it will hit the target.

The other problem with big guns is their weight. Breech and barrel of an 18" gun, 180 tons. Three guns in a turret, with all the gear needed to fire them, 2700 tons, about the same as the total weight of a Tribal Class frigate. Pretty clumsy compared with a pair of missiles fired from an aircraft.

Dave

Thread: Bearing tolerances
13/04/2021 16:12:37

Or the second table on this page, where ABEC 1 ( 'Normal' ) allows -13um i.e 25.987

Further down the page a bunch of other bearing tolerance standards are listed. Possibly one of them allows slacker fits?

Dave

Edit: pesky smilies, '

Edited By SillyOldDuffer on 13/04/2021 16:13:18

Thread: Oddball inverter
13/04/2021 14:34:37
Posted by Ian Parkin on 13/04/2021 07:23:52:

That’s strange I’ve never seen a VFD where the input terminals are marked R,S,T usually they are L1,L2,L3 if 3 phase or L1,N if single

Not that unusual, there are several conventions kicking about including U,V,W; R,Y,B; T1,T2,T3; A,B,C; 1,2,3 and probably others. I've a vague memory RST is a German acronym. R,Y,B refers to Red, Yellow, Blue, which is an obsolete wiring colour code but I believe the others, including L1, L2, L3 are just sequences. We need an expert on the international history of 3-phase labelling systems!

Dave

Thread: Laptop with a SD card slot
13/04/2021 14:15:01

Nothing wrong with Dell Inspiron 17 3000 kit except check the specification carefully. It's not a particular computer, rather one of a series ranging from basic to rather good. For example, the first one I found has only 8Gb RAM and a 128Gb SSD with a relatively slow CPU, the second has a faster CPU, 32Gb RAM, 128Gb SSD and a 1Tb Hard Drive. Check the detailed spec before buying - they might not all come with an SD Card.

Dell aren't the only firm selling rather different computers with the similar names; maybe they are all doing it now. Price is a good clue; the budget version might cost a quarter of the top of the range machine. Don't buy the expensive games machine when the budget version would do, and don't accidentally buy the budget version expecting top of the range features and performance!

I own an expensive Dell laptop, very pleased with it because it's super-quick and the graphics are excellent. No good at all for this requirement: it only has two USB-C ports, no DVD, SD-Card or anything else useful. Although USB-C is faster and more general than older USB, I have to use an adaptor to connect anything to it because all my USB peripherals are old-school. Ho hum...

Dave

Thread: Distorted ship's hull steel panels
13/04/2021 13:42:41
Posted by norm norton on 13/04/2021 10:09:48:

Thank you all for joining the chat. But I still cannot see why, when they build a big Naval ship, the plates (panels?) all appear indented at launch.

...

are we thinking that the Naval ships are made with much thinner plates, to make a lighter and faster ship, and try as they might they cannot make them neatly curved all over, and have to resort to seven tonnes of epoxy filler?

So why can't thin steel panels be rolled to a correct curve, and welded to the curved bulkheads and ribs, so that it all looks neat? There is something we are not understanding, and that was the whole point of my first question.

...

Since big guns were rendered obsolete by aerial bombs, torpedoes and guided missiles, warships have all but abandoned armour in favour of high-speed, manoeuvrability, and automatic defences based on electronic counter-measures, anti-missile-missiles and chain guns etc. And as an anti-ship guided missile has considerably more punch than the largest 18" shells ever fired in anger, it's not unreasonable to hope a powerful missile might pass clean through the ship without exploding, which favours light-weight construction.

Warship hulls and superstructure are as light as possible consistent with remaining seaworthy and shaped to reduce radar reflections without regard to neatness. The hull is only faired as necessary to improve performance, and looking neat is well down the list of requirements.

If the indentations mattered, they could be fixed . A Type 26 Frigate costs about £10Bn so spending a few hundred million more on the hull isn't a problem. I suspect the indents either have no effect on performance, or there's a mildly positive benefit such as a reduced radar or acoustic signature, or maybe even a go-faster improvement as provided by the dimples on a golf-ball.

The cause is simple; distortion due to welding a thin plate to a frame. Merchant ships also have indented hull plating, but it's less obvious because cargo carriers are strongly built of thicker plate. Again, indents could be fixed if they caused a problem such as poor fuel economy, but I suspect they simply don't matter. It just looks untidy, and is only worth hiding on passenger ships.

Passenger ships have a long history of cosmetic engineering designed to attract customers. Classic liners built with four funnels rarely needed more than two or three. Four funnels created the impression of speed and power by imitating fast warships, even though the commercial vessel sailed at profitable speeds and, unlike a warship, was as comfortable inside as a good hotel.

Dave

Thread: High Temperature Air Source Heat Pumps for Domestic Heating
13/04/2021 11:51:31
Posted by J Hancock on 13/04/2021 11:25:56:

Imagine today is in the year 2030+.

Wind is producing 0.52% of electricity demand.

That ole heat pump isn't keeping you warm.

True the wind isn't blowing hard today, but Solar is contributing more than Nuclear, and far more than coal, hurrah.

Nonetheless I agree interesting times ahead when gas runs out or if the Russians turn the tap off! Whatever the answer to the UK's energy problem is, it's not fossil fuels. Urgent attention required to both energy efficiency and storage methods or we will be caught with our pants down!

Dave

Thread: Help from the collective wisdom re ME 32 &40 TPI on a Myford 254S
13/04/2021 11:33:47
Posted by Darrell McCulloch on 13/04/2021 10:44:37:

Farkkikng hell I am dim

Page 12 of the 254 manual does mention the train that should be the one to do it.

I best go back to preschool.

Suitably embarrassed, so I will crawl away and not bother any one any more and drift off into my insignificance

Ciao

Naw, don't do that. Happens to me all the time. Few months ago I bought an expensive selection of tiny SMD oscillator chips and carefully put them in an envelope for safe storage. Can't find them despite three serious CSI-style searches.

Pretty sure the envelope hasn't been stolen by elves. I've forgotten where I put it, and it might just as well have fallen through an inter-dimensional wormhole. The project has ground to a halt!

One day I'll come across the envelope while looking for something else. It will be in plain view...

sad

Dave

Thread: Citric acid pickle
13/04/2021 11:21:01
Posted by Peter Simpson 1 on 13/04/2021 09:37:44:

I have a nice gallon container with a sealable lid what is the best ratio of citric acid to water.

Unless working on something delicate as strong as possible.

Citric Acid is a weak organic acid. Advantages are it's safe (food product), easy to buy, and the salts produced by using it are water soluble, i.e easy to wash off. Disadvantages are it's slow acting, eventually goes off, and relatively expensive. Citric Acid is good for delicate pickling, such as jewellery, and OK rather than excellent for bigger objects like model sized copper boilers. Delicate pickling 1 part Citric Acid to 6 parts water by weight, otherwise stronger.

In comparison, dilute Sulphuric Acid is fast acting, cheap and it doesn't go off. Industry's first choice for pickling, though it does require careful handling - nasty chemical burns etc. Unfortunately Sulphuric Acid is difficult to buy. Violent crime and terrorism resulted in Sulphuric Acid becoming a controlled substance and a license is needed to buy or store it in the UK. Even with a license many sellers won't supply private individuals.

Drain Cleaner is a possibility. One type is mostly strong Sulphuric Acid and it's available because widely used by small tradesmen who have a valid need for it. Strictly speaking it's criminal to buy Drain Cleaner for any other purpose and the punishments are potentially severe. Whether or not or silly old duffer would be prosecuted depends on local police policy: anything between a caution up to jail time as an example to others! I doubt the law would be concerned about an elderly half-empty bottle in a workshop, but the roof might fall on a chap ordering Drain Cleaner while acid throwing attacks are in the news, or the terrorist threat level is high.

Sodium Bisulphate is a reasonable substitute. 'Half-neutralised sulphuric acid' isn't useful to criminals or terrorists, no license required, and it's a faster cheaper pickle than Citric Acid. Not as safe though - more care required!

Dave

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