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|
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.
|Thread: Midlands Exhibition|
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.
|Thread: Unusual Go-No Go Tool?|
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?
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':
The big difference is engineers can blame their tools; no excuses if you can't do a crossword...
|Thread: Clinging to the Past|
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:
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!
|Thread: Sherline lathe|
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?
|Thread: Full size steam train goes off cliff for entertainment|
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.
|Thread: Chinese "K40" laser|
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.
|Thread: Unusual Go-No Go Tool?|
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!
|Thread: cutting spur gears on a mill|
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:
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!
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.
|Thread: Keeping fit and the economy|
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...
|Thread: Converting fractions to decimals|
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!
|Thread: Design Award|
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...
|Thread: 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;
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!
Edited By SillyOldDuffer on 18/08/2021 11:33:15
|Thread: Converting fractions to decimals|
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)
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)
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
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,
Oh no, one of us must be wrong! Surely not me?
Sadly it's true, I've cocked up AGAIN!
PS Nurse says bed with no supper tonight...
|Thread: What features do you like to see in Youtube videos.|
Easier to list what I don't like:
|Thread: Converting fractions to decimals|
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:
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!
|Thread: Mc Donald Model tractor|
Super work Fred, please keep it coming. Out of my league - I'm following progress in stunned silence!
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