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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: Class 22 Diesel (next project)
16/10/2021 17:44:50
Posted by Ron Laden on 17/08/2021 16:06:37:

Hi guys,

... what I dont understand is how the 16v capacitor, 1K ohm and 100 ohm resistors and the way they are connected to the amplifier stereo jack are working. ... it would just be good to know.



Late answer, but here goes.

The 100Ω and 1kΩ resistors form a potential divider. It's purpose is to match the output of the sound board to the level required to drive the amplifier. Most amplifiers are quite sensitive and if the input signal is excessive, the amplifier will clip and otherwise distort the audio sent to the loud speaker. The divider's ratio is 10:1, which would be right, for example, if the amplifier input expected 1mV and the sound board output a 1V signal. It's a fixed volume control.

A useful property of capacitors is they block DC current whilst allowing AC to flow. The 16µF capacitor is a isolating precaution: it stops any DC that might happen to be on the sound board output from confusing the amplifier.

The divider and capacitor ensure the right level and type of voltage are fed from the sound board to the amplifier. The combination will also act as a tone control, but like as not the effect has been ignored by the designer. If the output sounds a bit shrill, or lacks bass, try increasing the size of the capacitor. Anything up to 220µF should do.

Although the amplifier is stereo the Sound Card is mono. The Potential divider drives both Right and Left Channels, a mild bodge. Reason for this is likely cost. Small stereo amplifiers being common as muck are often cheaper and easier to source than their mono equivalents. It's nothing to worry about.


Thread: Accuracy of Hand Drilled holes
15/10/2021 16:49:28
Posted by pgk pgk on 15/10/2021 13:31:07:

Lots of ways to accurately measure out the divisions without math. Stick your 6" disc down on some wet plaster and use string to scrobe a 10' circle round it.. you can then walk round the circle with a short stick to see how many times it fits and nibble the stick until you get it right.

... they obviously had a way of creating right angles for building projects...


I think the Antikythera mechanism is remarkable considering how limited the technology of the day was. It's more challenging than I first thought. Quite easy to get a feel for the problem by trying to transfer the entire millimetre scale of a 30cm steel rule to paper. Try it and see!

The ancients didn't have graduated steel rules and had to make their own with a straight-edge and pair of dividers. Making an accurate straight-edge from scratch is a tricky challenge in itself.

The stick method in basic form is out because it accumulates error. And it's not very practical when the requirement is to drill 354 holes on a 150mm diameter - allowing for the diameter of the hole, the stick is 1.131166mm wide.

Re right angles, the ancients knew how to create them: the method is in Euclid's Elements.


15/10/2021 12:28:33

Posted by Neil Wyatt on 10/10/2021 13:06:27:


They needed a circle of 'x' holes to step the mechanism around in 'x' steps per rotation.. Micron accuracy is not required, so there is no reason for them to go chasing it.

To me the obvious solution is scribe a ring, use a marked strip wrapped around a circumference as an index. Scribe or punch each hole, then drill by hand.


I agree, and I wonder if the practicalities of hole placing determined the size of the whole mechanism, said to be about the size of a shoebox. Could be all the mechanism's dimensions are driven by these holes deciding the size of the ring.

Shoebox width suggests a ring diameter of about 150mm. Using mathematics unknown to the Antikythera makers, we can easily calculate the angle and distance between holes. Assuming the lowest possibility (354), the angle is 0.983333333° and the spacing about 1.3314mm.

The Greeks didn't have our advantages. Their maths were restricted to whatever could be done with a plain divider and a straight-edge, which is a lot. But the workman's tools where behind greek mathematical technique - he had no graduated rules, screw-adjustable dividers or loupes.

Spacing graduations at 1.33mm by hand is quite challenging, and it may represent the smallest distance the Greek maker could see well enough to do the job.

To make the ring, I think he worked out a representative space between 8 or 10 holes (say 13.3mm), and used that to determine the approximate circumference of the ring by laying out a tape. The actual ring was turned with a somewhat larger diameter to accommodate a more carefully graduated tape.

A tape could be accurately graduated by rolling it around the newly made ring to mark the ends and then laying it out flat and dividing it into parts as described by Euclid, Proposition 9, Book VI I wouldn't attempt to mark all the holes by Euclid, perhaps marking every fourth hole would be done accurately and the others pricked in by eye.

Might also have been done by laying out a polygon, but this cramps the work because the diameter of the ring is divided into parts rather than the circumference, reducing the working length by over a third. I think Neil's way is easier and more accurate.


Thread: Accuracy of BDMS
15/10/2021 09:25:44
Posted by Andrew Johnston on 14/10/2021 21:01:04:
Posted by SillyOldDuffer on 14/10/2021 20:38:46:
.....Bright Mild Steel is made by rolling......

The clue is in the name - Bright Drawn Mild Steel.


What on earth was I thinking? Oh dear...



14/10/2021 20:38:46

Posted by Oily Rag on 14/10/2021 19:47:05:...

What is the generally accepted allowance for straightness in BDMS? ...

I don't think there is one. Bright Mild Steel is made by rolling, which is a rough process, not particularly accurate. Although Bright comes with a better finish than Black Mild Steel, both are cheap steels intended for structural work, maybe unsuitable for what you're doing. Buy a Ground Steel if accuracy is needed.

My experience of Bright Mild Steel for hobby purposes is it's 'good enough' rather than wonderful, but then it's not meant to be anything special.


Thread: Workshop lighting / energy costs
14/10/2021 10:40:57
Posted by J Hancock on 14/10/2021 09:09:02:


News is Freightliner can't afford the bill anymore, so are going forward to use diesel motive power instead.

Fuel of the future.

Diesel is only 'fuel of the future' until the price goes up. And at the moment, the price of oil is rising at much the same rate as natural gas. Choppy waters ahead.

Thing is, all the rules change whenever demand exceeds supply. In the near future, whatever the answer is, it's not burning fossil fuels.



Thread: LBSC Vera
14/10/2021 09:38:18

Hi Marc, can you post some photos of the engine? Someone might recognise it. How to Here.


Thread: Hornby on TV
13/10/2021 13:28:00

I wonder how well a TV Programme on Model Engineering would go down with the general public if it were made by Model Engineers to please other Model Engineers? I suspect we would find it fascinating while everyone else was bored rigid! You have to be something of an obsessive aficionado to get the best out of Model Engineering. And that's a good thing!


Thread: Rear Axle Breather Connector
13/10/2021 12:41:30
Posted by peak4 on 12/10/2021 23:26:24:
Posted by SillyOldDuffer on 12/10/2021 15:49:49:

Did you make it from an M8 bolt though? ...

Too late now, I was going to suggest adding a couple of shallow flats so an adjustable spanner could be used to nip it up.


Not a bolt no; I had some 7/16" stainless hex in stock.
Turned one end down to 8mm and threaded with a Herbert die head
7mm plain shank as requested on the other end.
Drilled from both ends as it went past the flutes of the first 3mm drill, and then through in one pass with the 4mm.

axle breather-sa120050_dxo.jpg



Gosh Bill, that's better than the original. It'll last longer than the rest of Clive's Trusty Trooper!


Thread: photos
13/10/2021 12:26:26

Not sure it's possible to merge threads so I've deleted the other two on the grounds this one says what's needed. Apologies if anything important got zapped.

Impressive machine. I've dallied with the idea of making an Enigma machine but it's much more work than I have time or enthusiasm for.



Thread: Vfd and motor efficiency
13/10/2021 10:54:21

Sticking to the theory and practice of electric motors, I wouldn't worry in this case about efficiency. Unless the motor spends a lot of time running, in practice the loss of efficiency won't add up to much. In my workshop the lights use far more electricity than the motors because the lights are always on, while the motors only run in short bursts. Efficiency becomes important when motors run continuously or for significant amounts of time. In a home workshop, a motor running at 60% rather than 80% efficiency might not show on the electricity bill at all.

My WM280 lathe is fitted with an 1100W out motor, 1½HP in old money. Not a massive machine - it's somewhat bigger than a Myford 7. 1100W is a measure of how much power the motor can deliver without overheating. The motor will deliver considerably more than 1100W if overloaded, but it won't be long before magic smoke and ruined insulation. In practice, putting a wattmeter on the lathe's input shows the motor isn't stressed at all. With the change-gears engaged, the lathe consumes just over 200W when idling. Normal cutting consumes markedly less than 1000W in. I've not managed to load the motor heavily enough to draw the full 1500W input. To load the motor to pull more than 1000W in, requires heavy cutting with carbide. Swarf comes off as a spray of smoking hot blue-steel chips; production rate cutting, not at all what I enjoy as an amateur.

Power is the rate at which the motor might do work if required. No harm done replacing a ¾HP motor 1HP provided the operator doesn't abuse the extra power and overstress the machine, perhaps by accident. Always possible to drop a big souped-up engine into an ordinary car, but the brakes, transmission, cooling system, and road-wheels also need attention. Might pay to fit a roll-bar as well! But 1HP instead of ¾HP isn't over the top. The uprated motor will do the same job as the small one 25% faster - if pushed.

I wouldn't uprate the motor from ¾HP to 1HP in hope of improving efficiency. Power ratings are just a hint because so much depends on the design and build of particular motors, and they vary a lot. Perfectly possible for a small motor to be more efficient than a big one. Safer to say a recent electric motor is probably more efficient than older ones because insulation is better and the design more optimised, but even that's a lottery.

In other words, I'd be happy with any motor than worked, and wouldn't fuss about efficiency unless the machine was doing production work. Instead, replace fluorescent tubes with LED lighting - that's well worth doing.


Thread: Rear Axle Breather Connector
12/10/2021 15:49:49
Posted by peak4 on 12/10/2021 15:06:33:
Posted by peak4 on 11/10/2021 20:18:46:

Just got home, and replied to Clive.
I'll sort one in the morning and get it in the post tomorrow.

In the post, should be with you tomorrow.

Well done Bill!

Did you make it from an M8 bolt though? Jason pointed out the difficulty of finding an 8mm bolt with a 7mm shank, and Nicholas suggested roughly taking the diameter down to 7mm. But I think Nicholas' mod wouldn't work because 1.25 pitch cuts deeper into the metal than 7mm, making it necessary to get rid of too much metal for the remains to be a good fit to the rubber pipe.

Too late now, I was going to suggest adding a couple of shallow flats so an adjustable spanner could be used to nip it up.


Thread: Solid Edge - Community Edition
12/10/2021 15:08:13
Posted by Dave Smith 14 on 12/10/2021 14:10:45:


I did say in a limited way...

I was not advocating people use multiple packages, just answering a question if systems can talk to each other which they can. I would always advise if possible to chose a CAD that does what you want of it and stick with it.


We are having a violent agreement! My fault, because I addressed a point that's come up in other posts, not what you said. I'm warning against the desire for a Universal CAD solution that can read and write historic files produced by any other CAD package, which is asking a bit much!

I'm probably out of date too: in the last 20 years, software has become much more compatible. In my day, almost everything was locked into proprietary formats. Today it's far more likely file formats will conform to a more or less open standard, hurrah!


12/10/2021 13:02:22
Posted by Dave Smith 14 on 12/10/2021 09:14:42:

All the 'good' CAD systems can talk to each other in a least a limited way.

They can, but jumping between CAD packages is asking for trouble. 'Lost in translation' is a common problem. There's quite a lot to go wrong converting from one drawing format to another and unsupported features like missing fonts have to corrected manually. Other problems are seriously challenging. Hoping to automatically convert from one format to another is fraught with compatibility issues, not least because vendors can and do change specifications.

What does work is moving between packages of a different type: workflows where the output is simpler than the input. For example, using a fully parameterised 3D-CAD package to generate STL (geometric slices), which are converted by something else into less clever G-code, which is interpreted by the CNC machine into simple tool movements.

My advice is to minimise the number of different drawing packages used and keep them apart. Though it's possible to transfer a FreeCAD model into Fusion, change it, and then move it to SolidEdge, the process is likely to be painful. Better, I think, to find a package that does what's needed for new work and stick with it. Don't get hung-up on legacy - if an old drawing must be converted, accept it might have to be recreated from scratch.

For what it's worth I use QCAD for all 2D-drawings, FreeCAD for 3D single parts, and Fusion360 for assemblies. Although deficient when it comes to assemblies and joints FreeCAD is free open source and doesn't use the Cloud. It's my safety-net in the event Fusion360 withdraws or severely restricts their free to hobby version. Not surprising when commercial vendors change the deal because they create software to make a profit, not to give Model Engineers a free ride. For 3D-printing I use Cura, which works with FreeCAD, Fusion, and pretty much anything else that can output STL.


Thread: Flexispeed Lathe
12/10/2021 10:08:19

Posted by Bob Stevenson on 12/10/2021 07:57:06:


Also, if you have a good 4 jaw then you hardly need to bother with a 3 jaw....It does take an hour or so to get the hang of centreing work using a dial guage but there after it's very easy and gives the best accuracy of any workholding method.


Bob makes an excellent point: if I could only have one chuck, it would be a 4-jaw. There are turners who, by choice, always use 4-jaw chucks.

The advantage of a 3-jaw chuck is speed. They are the quickest easiest way of gripping round work and hexagons, but after that are nothing but bad news. They're not very accurate in terms of run-out, which often doesn't matter, and it's difficult to reset work in them, which does matter. So 3-jaws are great for turning shortish round jobs, where it's not necessary to move the work half-way through to a mill, saw, shaper or bench vice, and then go back to the lathe. Perhaps 90% of what I do can be done in a 3-jaw.

Collets have low run-out, are good for close work, and support fast accurate resetting but can only hold round objects of particular diameters. Extremely useful for certain types of work, such as clockmaking, but otherwise limiting.

4-jaws chucks are versatile. They can be adjusted to minimise run-out, accurately reset, hold shapes other than round, and offset jobs for boring super-accurate holes. Offsetting is also useful for turning ovals. The downside is having to learn how to use them. Centring 4-jaws is best done with two chuck keys and a DTI :

  1. Using one chuck key, position the job centrally by eye, but don't tighten the jaws.
  2. Position the DTI to measure how far the job moves horizontally when the chuck is turned.
  3. Turn the chuck by hand so one pair of jaws are horizontal. Note the DTI reading. Turn the chuck through half a turn. If the job is centred, first DTI reading minus second DTI reading = zero. If not zero, use both chuck keys on the opposing horizontal adjusters to ease the job such that the DTI difference is halved. Repeat step 3, halving the difference each time until the DTI says the job is centred. Then go to step 4
  4. Turn the chuck through 90° and repeat step 3 on the other pair of jaws.
  5. When the job is centred between both pairs of jaws, carefully tighten them without moving the work. Confirm with the DTI.

At first adjusting a 4-jaw is tedious and fiddly, especially if attempted with only one chuck key. Don't give up! The good news is the technique gets faster and easier with practice. An experienced operator can often get close enough by eye with a few tweaks, for example by looking for wobble relative to the sharp end of a centre held in the tailstock. Lesser mortals, and those needing high accuracy should confirm all is well with the DTI. The accuracy of the method is limited by the sensitivity of the DTI as a comparator and even a cheapo one should centre within 0.01mm.


Thread: Could you get away with this today
11/10/2021 17:44:52

Is Benny Hill funny? I think so, but not all of it. Like most comedians he operated close to the edge, and the edge moves. Go too far, and jokes become offensive. Don't go far enough and they aren't funny - who laughs at Charlie Chaplin today?

Bad-language in jokes has been fashionable for a few decades, but it's fading now. In twenty years TalkingPictures will be prefacing early 21st century comedy with bad taste warnings. The next generation of old men will moan about it, whilst their youngsters try to explain why grandad of 2040 is crass, prejudiced, tactless and out of touch. Old folk never understand the young, and the young don't understand they will soon be old too.

Anyone serious about comedy should read Henri Bergson's Le Rire. Essai sur la signification du comique. Brief overview in English here on Wikipedia. Bergson determines the process of the comic instead of analysing its effects. So you're not allowed to enjoy Benny Hill unless you can explain why he's funny now racism, homophobia and misogyny are in disrepute. As laughter is a social mechanism, laughing at the wrong time is a gaffe!

It's no wonder I have a complex.






Edited By SillyOldDuffer on 11/10/2021 17:45:12

Thread: cutting spur gears on a mill
11/10/2021 15:47:35

Duncan Webster helped me out last month by writing a program in Python3 to draw involute gears. (I was and still am struggling with the maths!) Duncan's code, which requires the easygraphics module, is here on Dropbox.

Duncan's teeth aren't drawn with curves, instead the involute is approximated by drawing a series of straight lines, i.e. facets. By default, the teeth are drawn with 12 facets, so a 20 tooth Mod 1 gear looks like this:


I bodged Duncan's code to draw only one tooth with 1,2,3,4 and 8 facets, all scaled up so the eye can see the facets.

Single facet teeth are obviously notchy:


Two facets are a considerable improvement:


Four facets are quite good:


And at this scale, eight facets are almost indistinguishable from a true curve.


All of these 'involutes' are approximations because of the way they are generated by drawing straight lines, but there are more issues to come.

Duncan's program could be modified to produce G-code to make subtractive gears with a CNC mill or additive gears with a 3D printer. In both cases his mathematical involute could be an excellent approximation, say 24 facets or more, but the resulting gear will be degraded by the production process. Although both gears can be improved by cleaning up if necessary, the plastic and metal versions differ in strength while the metal version could also be greatly improved by polishing and hardening. The properties of a Duncan gear depend on the maths, the material, the basic production process, and the finishing. It's possible for Duncan gears to be either cheaply or better made as required. Most engineering objects are like this. They can be made up to an advanced specification or down to a price. Both useful, but don't waste money on uneccessarily expensive gear or on on cheap junk. It's the engineer's job to make cost effective choices.

My general point was lathe change-gears ain't anything special, and that it doesn't matter as long as they do the job.


Thread: SKY abandoning their satellite customers
11/10/2021 10:23:06
Posted by Anthony Kendall on 11/10/2021 08:42:21:
Posted by David George 1 on 11/10/2021 07:12:58:

The BBC will in the near future get rid of transmitters to aerials and expect all viewers to use the broad band network instead saving billions of pounds in maintenance and renewal costs. Progress? David

Who says?

Customers, loud and clear. Most customers don't want broadcast TV because programmes have to be watched at set times - the customer has to follow the schedules.

Recording is popular because it alleviates the scheduling problem. However, not all sweetness and light. The customer buys an extra box, studies the schedules, and has to set-up what's wanted for later consumption. Recorders have limitations: most can only capture two channels simultaneously and the owner has to make space by deleting old recordings. And the customer buys DVDs and another special box to watch them.

What most customers want is Video on Demand: programmes that can be watched at any time and in any order without having to wait for a broadcaster to schedule them. And most people today want to be able to watch TV on anything from a big fixed screen to a mobile phone. Some are also keen to watch high-definition services that cannot be transmitted by existing broadcast infrastructure without major upgrades, but can be accommodated by fibre-optic networks.

Terrestrial and satellite broadcasters are all losing customers and their outlook is bleak. In my family only one of the under 40s watches broadcast TV - eight others all stream programmes off the internet. If they want to binge watch an entire series in one sitting, they can. The move away from broadcast will continue, and at some point in the future, there won't be enough customers to justify providing it.

In similar vein, BT have announced the end of conventional analogue telephony, in 2025 (ISDN and PSTN). It's because replacing and maintaining the UK's ageing bandwidth-limited copper network exceeds the cost of replacing it with fibre-optics. And putting high-speed internet into every home opens the door to selling more services. It's also important for the ecomomy - failure to modernise UK telecoms has already damaged our business propects. There will be problems galore, but most customers will be delighted. As with moving from broadcast to video on demand, it's the majority who win, not the minority who are happy with what they have and just want to be left alone. That's me!


Thread: cutting spur gears on a mill
10/10/2021 15:16:19
Posted by JasonB on 10/10/2021 13:17:47:
Posted by SillyOldDuffer on 10/10/2021 10:55:19:
Posted by Nigel Graham 2 on 10/10/2021 00:01:52:


I must admit I have never thought the headstock gears and the change-wheels on my ML7 either "crude" or "square"; whatever those were meant to mean. If my screw-cutting comes out ragged, I blame the operator not the machine!


Myford and most other lathe gears are 'good enough' rather than well made. ...


Must say when I had my geared head Emco there were no crude " lathe gears" or short cuts taken with the gearing ...

Backlash on the screwcutting banjo is really all down to how the user positions the gears as the ctrs and therefor PCD are not fixed.

Edited By JasonB on 10/10/2021 13:21:12

Perhaps we should have a lathe gear beauty contest, with close-up photos of tooth form and carefully measured dimensions! I'm not suggesting lathe gears are rubbish, simply that they're not wonderful because they don't have to be!

  • Cast gears will always be dubious, some much better than others depending on exactly how they were made.
  • Hob made gears are an approximation, again some better than others
  • Generated gears, such as Sunderland, are usually good, but they too can be approximated.

What does good look like? I suggest true centre running with accurate diameters throughout plus close to involute curves, with teeth polished, chamfered and hardened. No need to adjust mesh with a sheet of paper as normally necessary with change gears.

The gears in my theodolite are more like it, but then they really do need to be good.


Thread: Polynomial Texture Mapping : .PTM files
10/10/2021 14:16:44

Try RTIviewer from CHI Michael. (Can't test it myself because daughter has left home with her Mac.)

My problem is getting a Viewer to run on Linux! Just hit a 32-bit iceberg.


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