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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: Myford super 7 with gearbox - leadscrew stopped turning
24/08/2021 09:30:24

Chris mentions the shear pin, and that would be my first suspect. On my Chinese lathe I crashed the saddle and all seemed well, except it wasn't! The pin had sheared but there was still enough grip to turn the lead-screw apparently normally. A few months later the remains gave way and the lead-screw stopped turning. The clue is everything works apart from the lead-screw.

Work back from the stopped lead-screw to find the point where the rest of the lathe is still turning.

Dave

Thread: Midlands Exhibition
23/08/2021 12:40:49

Times are far from normal. Though Chris feels safe to travel to an exhibition, plenty of others are still nervous, thus anyone running a public event is gambling they will get enough customers to make a profit. High risk for organisers who lose big money if the event doesn't pull enough people in.

Of my extended family during the lockdown only my daughter caught Covid. Since lockdown ended last month, six of them have picked it up. Vaccination much reduces the chance of hospitalisation, but Covid is still highly active in the community and although mostly mild one of my six describes Covid as the worst illness he's ever had. With that in mind quite a few people are minimising contact until the figures improve. Makes it hard to plan anything at the moment.

Dave

Thread: Unusual Go-No Go Tool?
23/08/2021 11:57:13

Pondering if it's a spark voltmeter (electrostatic, not power) I looked up the formula in hope it would match Michael's graph of the instrument's scale.

The formula is:

kV = 3 * air_pressure * spark_length + ¹·³√spark_length

Although it contains an exponent, ¹·³√, I don't believe the formula curve matches the instrument.

And if it's a spark device, I agree with Michael's comment - 'seems like an accident waiting to happen.'

Possibly 'Micrograph' is a reminder, 'this tool belongs with the micrograph', and isn't the name of the tool itself or a tradename. Another meaning of micrograph is an instrument for making small engravings, though I don't see how electrostatics would play a part in that. Some sort of scale reducing Xerox machine maybe?

Dave

Thread: Brainteaser
23/08/2021 10:50:46

Solving cryptic crosswords is a bit like engineering. An interesting challenge, where the individual answers aren't always obvious, but come together as a satisfying whole. Cryptic crosswords and engineering both require a fair amount of free time, and just like engineering, not everyone enjoys doing them! Crosswords can be deeply frustrating, just like engineering!

Crosswords have rules that must be learned and practised too; cryptic answers have to go 'ding, ding, ding':

  • Machine part = cog
  • Only women = 'no men'
  • Name = 'cognomen', (and women conventionally take the male family name on marriage)

The big difference is engineers can blame their tools; no excuses if you can't do a crossword...

devil

Dave

Thread: Clinging to the Past
22/08/2021 11:00:46

Imperial measure popping up in new kit shows technologies are rarely replaced outright, because there are always edge cases where old ways remain competitive. A few examples of Losers and their nemesis:

  • Canals versus Railways (except Suez and Panama are both doing well)
  • Railways versus Roads (except heavy goods moved long distance overland and mass commuter traffic)
  • Steam versus Internal combustion (except for Nuclear Power Plant)
  • Long distance Railways versus Aircraft (except for heavy goods)
  • Sail versus steam, (except for recreational use)
  • Wrought Iron versus Steel (apart from decorative blacksmithing)
  • Steam versus Diesel Locomotives (except for heritage railways)
  • Diesel Locomotives versus Electric (except where traffic is too low to pay for the infrastructure.)
  • Pencil and paper versus CAD (except for small or amateur work)
  • Cast-iron versus plastic (except where mass is an advantage)
  • Electronic Valves versus transistors (except for repairing old radios and pleasing HiFi aficionados )
  • Computers versus mechanical mechanisms (except where physical strength is essential)
  • Imperial and English measure versus metric (except for back compatibility and the USA)

Many other examples! I don't suggest these are 'good' or 'bad', it's just how it is. Technology is driven by user needs, which vary by time and place. If your country happens to sit on a large coal-field, makes sense to get rich by exploiting it. When coal runs short, the old reliable of making money breaks. Time to forget coal and move on to something else.

I'm all for celebrating our technical heritage, but not if doing so cripples what needs to happen next. Engineering is about solving problems, not defending time expired methods because they worked well when I was young. The manual machining I do for fun in my workshop has very little relationship to modern manufacturing, which is driven brutally by economics, not by craftsmanship, nationalism or a glorious past. I hate change, but pretending it wasn't happening didn't save me!

Dave

Thread: Sherline lathe
21/08/2021 11:09:57

Probably not what Geoff wants but Denford Ltd are the other UK supplier. The difference seems to be the Denford machines are safety protected for educational CNC; fully shielded and computerised etc.

The cheapest way of buying American goods used to be buying on holiday and bringing them back as hand-luggage. May not be possible now airport security is so careful about terrorism.

Also possible to buy Sherline from various European suppliers. I doubt there's any advantage - doing so would lose UK consumer protection and be liable to customs duty and VAT. Not keen to get into paperwork aggro myself, easier to let an importer like Millhill sort it out behind the scenes.

I'm theorising: anyone actually imported anything expensive themselves this year?

Dave

Thread: Full size steam train goes off cliff for entertainment
21/08/2021 10:50:05

Of course they did railway spectaculars far better in the good old days.

(Picture from Wikipedia: By Jervis C. Deane (b. 1860) - Southern Mysteries Episode 65 The Crash at Crush, Public Domain, https://commons.wikimedia.org/w/index.php?curid=106267731)

The Crash at Crush event of 1896 didn't go well! 'the air was filled with flying missiles of iron and steel varying in size from a postage stamp to half of a driving wheel...'

Engineers got the blame: they said the boilers wouldn't explode! Interestingly, the accident proved there's no such thing as bad publicity.

Dave

Thread: Chinese "K40" laser
21/08/2021 10:22:31

For what it's worth, this Australian gent concludes his 40W CO² laser won't touch Graphite. (Youtube Video)

Graphite is the go to material for rocket motors because it has extremely high melting point and heat capacity. You can boil steel in a Graphite crucible.

A wild guess, it's not just about power. CO² lasers work in the infra-red, which may not be the ideal wavelength for Graphite? Another web source describes engraving graphite with a 20 watt q-switched ytterbium fiber laser and 160 mm focal length lens. ytterbium lasers produce higher frequency light.

Dave

Thread: Unusual Go-No Go Tool?
20/08/2021 14:45:53

How about a Disappearing Filament Pyrometer?

The peephole and square holder takes a plug-in battery, filament, on/off switch and lens module. Does turning the base knob vary a resistance inside the handle? If so, the temperature of the filament could be altered to determine if furnace is close to correct operating temperature.

I agree 'Micrographs' defies logic!

Dave

Thread: cutting spur gears on a mill
20/08/2021 14:21:31
Posted by brian jones 11 on 20/08/2021 13:27:22:

Remember the original proposition

" Primitive but very quick and only suitable for light load low speed apps and probably noisy "

Some mentioned mechano gears - well Im not pompous - it worked for a million kids

I asked if anyone else had actually tried this method rather than generate a whole sheaf of plausible conjecture

I don't think the thread suffers too much from 'plausible conjecture'! Using a tap to cut gears isn't new. I've experimented with it, but got much better results with a Sunderland Rack cutter and Rotary Table:

dsc03599.jpg

Neil Wyatt made a lot of gears this way for his Jovilabe Orrery a few years ago.

Unlike a tap, Rack Cutters get the number of teeth right and, with a little care, they cut an accurate involute. Rack cutting and Hobs do take longer!

Boils down to how much the operator needs an accurate gear as opposed a quick approximation. If gashing gears with a tap is 'good enough' for the job in hand, go for it! No-one objects. But I suspect better specified gears are needed almost all the time. If there was an easy quick way of cutting good gears, everyone would be doing it. They don't because the method has significant shortcomings. Tried and found wanting, so the Flat Earth Society wins this one on points!

devil

Dave

20/08/2021 10:23:05

Any Meccano experts available? Can't find my copy but I think Brian's method is described in the Meccano Constructors' Guide (BJ Love), where a ½" BSW tap is used in a Meccano Project to cut Meccano gears.

It's not an accurate system. One fault is a tendency to cut an extra tooth, which is bad news whenever an exact ratio is needed! Just as bad for most other gear applications is the poor tooth form. Ideally gear teeth are shaped 'just so' for efficiency, low wear and low noise. Two particular mathematical curves have this property, of which Involutes are best for power-transfer and Hypocycloid are favoured by clock-makers, who need large low-friction step up ratios. A BSW tap produces neither tooth form, it's a bodge.

Although the tap method "works", it's unpredictable and doesn't make efficient gears. OK if you don't mind the occasional extra-tooth, high-rate of wear, noise, and terrible backlash. (Meccano comes to mind!) I suggest the tap technique is rarely used in practice because alternative methods make much better gears.

Dave

Thread: Keeping fit and the economy
19/08/2021 14:09:00

I got the joke Derek!

There is no lighter side to keeping fit, which is why I'm off for a nap rather than a brisk walk...

smiley

Dave

Thread: Converting fractions to decimals
19/08/2021 10:02:20
Posted by Michael Gilligan on 19/08/2021 06:21:30:
Posted by Howard Lewis on 18/08/2021 23:11:09:

This looks be getting a little bitter and twisted, when we are taking of UNITS.

[…]

.

Thank you for trying to inject the Wisdom of Solomon, Howard … but the thread is [or at least was] really about converting between factions fractions and decimals.

MichaelG.

.

Edit: __ corrected my Freudian slip of a typo blush

Ah, but the subject has hidden depths. The discussion leads to the need for change, which is mankind's greatest enemy. Hard to teach old dogs new tricks because old dogs see no reason to change. This is why I'm handling my mother's hospitalisation by landline telephone while the rest of the family are in a WhatsApp group. I ring family to tell them the latest news and everyone in the group is already better informed than me. I resent it slightly, because they've been using new technology for years while I still hanker after dials, telephone directories and pressing Button B to get my 4d back in a red box smelling of wee.

Very upsetting - I have trusty old friends like Landline telephony, Imperial Measure and Fractions, and some young whipper-snapper barely out of nappies points out they're all actually a bit sh1t, giving reasons I don't understand or give two hoots about.

Our hobby sits on a fault line; is Model Engineering about retro-technology like steam engines, Whitworth and HSS on a 1947 lathe, or is it about Quadcopters, microcontrollers, CAD, laser-cutters and 3D-printing? I think it should be about both. I admire craftsmanship and enjoy my manual lathe and milling machine, but I'm also interested in state of the art methods and what's in the pipeline.

The history of engineering shows new techniques always win and it's a bad mistake to cling to the past. Discuss!

devil

Dave

Thread: Design Award
18/08/2021 11:58:58
Posted by Dave Smith 14 on 18/08/2021 09:58:37:

...

I think it is a nice elegant piece of design, that has a practical use and if that is the value of the prize good on him, because it will pay off a huge amount of his university debt. Remember we are talking here about product design (he will probably go onto to design white goods) not mechanical design which is a whole different ballpark.

Me too! The ladder has a huge advantage - unlike any of my Aluminium monstrosities it doesn't look out of place propped up against the wall in an average room. It will sell like hot-cakes...

Dave

Thread: Knurling tool
18/08/2021 11:31:54

Posted by Graham Meek on 18/08/2021 10:50:09:

...

Generally,

There seems to be some confusion between "Cut or Milled" straight knurling and the "Deformation, or Forming" process carried out by a conventional straight knurling tool.

...

My feeling too! Deformation knurling isn't the same as Cut Knurling. The DIN Standard recommends ratios for cut knurling and I don't think the same mathematical approach applies to deformation knurls, of the sort by the clamp tools under discussion!

Deformation knurling is like the page following Good King Wenceslas rather than an HSS knife cutting a thread:

“Mark my footsteps, good my page;
Tread thou in them boldly;
Thou shalt find the winter’s rage
Freeze thy blood less coldly.”

 
In his master’s steps he trod,
Where the snow lay dinted;
Heat was in the very sod
Which the Saint had printed.

Must be right - there's a sod in the carol too!

Anyway, I suggest deformation knurling isn't a precision process and I don't think it requires a 'quality' tool!

Dave

Edited By SillyOldDuffer on 18/08/2021 11:33:15

Thread: Converting fractions to decimals
18/08/2021 10:07:50
Posted by SillyOldDuffer on 17/08/2021 17:26:40:
Posted by Michael Gilligan on 17/08/2021 13:49:11:

Posted by SillyOldDuffer on 17/08/2021 12:03:49:

[…]

All fraction calculators suffer to some degree from this inaccuracy, though the more sophisticated versions do far better than simple minded digital calipers. Michael's example is close: his calculator (and Nick's) both give 1¹¹⁄₁₆ x 25.4 = ³⁴²⁹⁄₈₀. So does mine. However, the real answer is ⁹⁶⁵¹⁷⁷⁶⁹⁵¹⁴⁰⁸³⁹³⁷⁄₂₂₅₁₇₉₉₈₁₃₆₈₅₂₄₈. Don't panic, ³⁴²⁹⁄₈₀ is an excellent result, the error being only -²⁷⁄₁₁₂₅₈₉₉₉₀₆₈₄₂₆₂₄₀.

Highlights a serious problem with fractions because the level of inaccuracy of each calculation depends on the individual ratio and on the number of display digits available. […]

.

dont know

You must try harder, Dave

The fractional answer is correct

...

Sadly it's true, I've cocked up AGAIN!

Sorry,

Dave

PS Nurse says bed with no supper tonight...

embarrassed

Feeling a little happier with my foolish self this morning because my mistake was trusting a calculator; ironic because my post was about distrusting calculators doing fractions.

I used Python because it supports Fractions and Decimals as well as floating point. Floating point arithmetic is super fast because the numbers are in binary, but this causes conversion errors. 25.4 is actually stored as 0.25399999999999998579x100, which can cause trouble in long complicated calculations.

Decimal numbers are exact - 2.4 really is 2.4 but they are slow.

In Python, I typed:

fd = 1 + Fraction(11,16)
fd = fd * Fraction(Decimal(25.4))
print( fd, fd.limit_denominator() )

which gives the slightly wrong answer 96517769514083937/2251799813685248, which was approximated by limit_denominator() to 3429/80

Doing the same sum in fractions throughout gives the right answer:

ff = 1 + Fraction(11,16)
ff = ff * ( 25 + Fraction(4,10))
print( ff, ff.limit_denominator() )

3429/80 3429/80

So my blunder was caused by whatever method Python uses to convert Decimal(25.4) into a fraction.

Although I dislike fractions intensely in engineering drawings, they are perfect for gear ratios: change gears and threads. In that context, Python's limit_denominator() function is good for finding approximations, for example:

Fraction(math.pi).limit_denominator(10) = 22/7
Fraction(math.pi).limit_denominator(100) = 311/99
Fraction(math.pi).limit_denominator(1000) = 355/113

The various methods discussed in this thread are just tools. Tug's calculator may be good choice for him but other tools are available, and could be exactly the right tool for others. Calculators aren't the ultimate calculating aid!

Spreadsheets are calculators on steroids, but harder to learn. Programming languages even tougher but can do almost any calculation. As I've demonstrated though, just like physical tools, the operator has to choose and use them correctly. Banging screws in with a hammer is rarely a good idea,

Dave

17/08/2021 17:26:40
Posted by Michael Gilligan on 17/08/2021 13:49:11:

Posted by SillyOldDuffer on 17/08/2021 12:03:49:

[…]

All fraction calculators suffer to some degree from this inaccuracy, though the more sophisticated versions do far better than simple minded digital calipers. Michael's example is close: his calculator (and Nick's) both give 1¹¹⁄₁₆ x 25.4 = ³⁴²⁹⁄₈₀. So does mine. However, the real answer is ⁹⁶⁵¹⁷⁷⁶⁹⁵¹⁴⁰⁸³⁹³⁷⁄₂₂₅₁₇₉₉₈₁₃₆₈₅₂₄₈. Don't panic, ³⁴²⁹⁄₈₀ is an excellent result, the error being only -²⁷⁄₁₁₂₅₈₉₉₉₀₆₈₄₂₆₂₄₀.

Highlights a serious problem with fractions because the level of inaccuracy of each calculation depends on the individual ratio and on the number of display digits available. […]

.

dont know

You must try harder, Dave

...

The fractional answer is correct

MichaelG.

Oh no, one of us must be wrong! Surely not me?

Sadly it's true, I've cocked up AGAIN!

Sorry,

Dave

PS Nurse says bed with no supper tonight...

embarrassed

Thread: What features do you like to see in Youtube videos.
17/08/2021 17:16:31

Easier to list what I don't like:

  • Errors of fact
  • Bias, prejudice and opinion pieces
  • Bad Practice
  • Persons making videos before they've mastered the subject they're demonstrating.
  • Um, er, ah, like, erm, hmm, you know, unscripted incoherent blather
  • Failing to edit out trivia, delays, mistakes and inconsequential material, whilst failing to provide key information.
  • Pushing ill-advised 'improvements' to machines or methods.
  • Health and Safety infringements
  • Leaving dud material online and turning out more rubbish despite negative reviews
  • Ill-judged Product placement
  • Anything with me in it

Dave

Thread: Converting fractions to decimals
17/08/2021 12:03:49
Posted by ega on 17/08/2021 10:01:10:

Has anyone mentioned the "Digital Caliper with Fractions"? I find my Wixey brand version quite useful for converting between fractions/decimals/millimetres.

The fraction/decimal equivalents are not precise, however; eg "0.061 to 0.065" is shown as 1/16".

The 'not precise' shortcoming is an important point well worth emphasising! My Digital Caliper with Fractions is pretty untrustworthy in fraction mode, just as ega's Wixey demonstrates with ¹⁄₁₆" actually being ±0.002". In fraction mode, my caliper's reported ¹⁄₁₆" could be 4 thou out, which is a lot! In comparison, the same instruments decimal error is about 1 thou.

All fraction calculators suffer to some degree from this inaccuracy, though the more sophisticated versions do far better than simple minded digital calipers. Michael's example is close: his calculator (and Nick's) both give 1¹¹⁄₁₆ x 25.4 = ³⁴²⁹⁄₈₀. So does mine. However, the real answer is ⁹⁶⁵¹⁷⁷⁶⁹⁵¹⁴⁰⁸³⁹³⁷⁄₂₂₅₁₇₉₉₈₁₃₆₈₅₂₄₈. Don't panic, ³⁴²⁹⁄₈₀ is an excellent result, the error being only -²⁷⁄₁₁₂₅₈₉₉₉₀₆₈₄₂₆₂₄₀.

Highlights a serious problem with fractions because the level of inaccuracy of each calculation depends on the individual ratio and on the number of display digits available. Thus it's hard to tell when fraction calculators are:

  • exactly right as in 12 x ¾ = 9
  • nearly right, as in 1¹¹⁄₁₆ x 25.4 = ³⁴²⁹⁄₈₀
  • seriously misleading as in ¹⁄₁₆" being anywhere in the range 0.061 to 0.065"

Decimals are undoubtedly safer in engineering because the number of digits is a strong clue to the underlying accuracy. Safer rather than perfect, beware the dingbat claiming pi=3.1428571428571427937!

Dave

Thread: Mc Donald Model tractor
17/08/2021 09:37:10

Super work Fred, please keep it coming. Out of my league - I'm following progress in stunned silence!

smiley

Dave

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