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Member postings for Billy Mills

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

Thread: What did you do today? (2014)
06/06/2014 18:24:45

Car problem - all windows down and doors unlocked on a previously locked car. Happens when you press the boot release and unlock button at the same time on some models. ( can happen when you fall asleep with the fob in your pocket then roll over on it!)

The "fob don't work" problem is commonly experienced near Tetra transmitters (used by the emergency services) on fobs working at 433MHz. There are many places where people stop e.g. for a take-away.. then can't get in their cars, quite likely to happen near some Police stations. Basic cause is very poor quality receiver in the car and very strong local transmission. Holding fob near centre of windscreen or middle of driver's window may help. Could also be a dead/ corroded fob battery!


Thread: 3 phase and single phase wiring
13/05/2014 20:37:01

The issue of supply voltage is not a simple matter, there are a lot more complex issues than touched upon in the above extract from a book written more than a decade ago, a lot of other things have happened too.

Incandescent bulbs have been legislated out, the lifetime reduction figures mentioned only applies to incandescent bulbs, not other types such as mains or HF flourescents or LED's all of which are far more efficient and longer lived than incandescents ( apart from the cheapo flash in a pan ccft's) and now far more significant numerically.

Many new domestic devices using switching convertors have a negative slope i.e. the current decreases as voltage increases, so act as constant power loads. So much of the impact assesment in the old article is out of date.

So if your line voltage is 240V don't worry, it is within tolerance, your simple heaters will deliver a bit more heat but most of your newer stuff will draw constant power or just slightly more and not be greatly impacted.

And Three Phase Motors will still work much better than single phase types when driven by a nice VFD. Nice maker and age too!


Thread: Machining Bevel Gears
04/05/2014 14:31:07

P)erhaps this might put it in words...

The first pinion locks the tooth relationship between the gears or racks. Any extra pinions have to have the same amount of rotation as the first pinion. If a pinion is at a different rotation -say 1/4 tooth clockwise then the gear or rack needs to be 1/4 tooth around to fit one side of the pinion but the other side is then also 1/4 tooth clockwise whereas the pinion has been rotated so is 1/4 tooth anticlockwise i.e. the pinion cannot mesh both sides when at a diffferent relative position to the first pinion.


Thread: Proxxon 150/E
27/04/2014 13:48:05


Be careful with the mini router, you can adjust the height setting so that the spindle and motor go way too low, a drive pulley then rubs onto the case and burns out the motor. I do use a number of Proxxon tools some of which are not inexpensive, but they are most certainly "hobby" tools at a highish price and need gentle treatment. Think that your C1 is a better choice for the long term and you can get the extras ( which can be more than the cost of the lathe) for good prices.

Many small machines with DC drives use current sensing to produce a negative resistance in the PWM output. When the motor is loaded it draws more current which then slightly increases the speed input to the PWM controller to compensate the speed reduction due to the increased load. There is often a pre-set pot to adjust the amount of compensation.


Thread: Motor speed control
31/03/2014 13:21:48

Must also point out that the magnetic field does NOT keep the rotor turning, That is simply rotational kinetic energy. The magnetic field in a PM motor induces eddy currents in the rotor iron which hinders rotation, that is why the wound armature is not solid iron but laminated to minimise these losses. You can get ironless armatures- moving coil or "printed circuit" motors- especially for high acceleration servo applications. These motors have absolutly no iron in the armature apart from the drive shaft.


31/03/2014 13:06:34

Good job that this is only a heater application. After some time you can expect the mosfet leads to fracture. Putting an unsupported bit of copper on the mosfet makes matters considerably worse by increasing the mass and putting the resonant frequency closer to the peak range experienced in a vehicle. It does not take much to do the job properly, bolt or solder the mosfet to the board. Even a blob of epoxy around the leads will help a bit but firm fixing is better.

The use of I.C. sockets is inadvisable in a vehicle especially if the assembly is bulkhead mounted. Sockets are a real liability, the only reason to use sockets is where the designer is unsure that the design is sound, it makes changing damaged devices easier. I would also point out that there is no parasitic prevention which is a real issue with unspecified loads, and some mosfets, it would cost a penny to place a 22 ohm resistor in the gate.


Thread: Seeking help (cutting 3mm aluminium plate)
28/03/2014 01:53:02

Do you really NEED 3mm plate? In 60 years of electronics I have never ever seen any chassis that thick, 1mm would be plenty to support bits for a TRF. Once you put a couple of bends in thin sheet it is more than rigid for the use. It is not as if you need any great stability for a TRF with realistic Q values. Go THIN and save elbow grease.


But I do like sheet saws and nibblers.......

Thread: MEW 214
19/03/2014 21:20:05


Know what you mean about finding stuff in catalogs, Having used RS, Farnell and latterly CPC ( as a key a/c customer no less!) over a working lifetime I could find stuff quickly -associative memory as it is knowen. All three firms have very big websites that have been up for a long time but the indexing is absolutly terrible as is the level of engineering know how behind the cataloging- that makes their websites very hard work. RS file quartz crystals under "semiconductors" while Farnell don't know the difference between many semiconductor functions. But that is due to non-engineers compiling the data - not an intrinsic weakness of the medium.

However the paper catalogs have become very costly to produce, maintain and distribute once a year. The same data is the contents of the web shop window which people buy from directly, the paper stage has gone from the selling process. In the future we cannot expect paper catalogs to return, but we can at least suggest better ways of classifying items so that the ordering process is easier. When people run webshops their sales are proportional to the ease of using their site so there is a strong reason for improving the user experience, it will sink through eventually. It is also true that the more you use a particular site the better you find your way around as you remember waypoints and images- just like paper images.

Although a paper loving ancient, I do use the new media as much as I can as well. It also means that people with very specialised interests can reach like minded worldwide audiences as never before without the complexities and costs of paper publishing and distribution. Just as the web has changed the face of retail shopping ( and the High Street) so it is also to the domain of personal interests and communications, things are evolving - like it or not.

One other aspect of this is the emergence of "Maker Culture", the fusion of mechatronics and software, CNC and conventional/unconventional machining to make new stuff or play variations on existing ideas. There are now hoards of young people taking stuff apart to learn about making new stuff. Just like we did 4, 5 or 6 decades ago when we learnt our real engineering. Only now they can learn, share, program, publish and enjoy on a world wide basis at zero cost. I wished that we could all have done that when we were young.


Well I know what you mean about browsing paper, I love that. But you can do just the same- only over a very much larger library- through the screen. For example there was a bit about synthetic aperture radar in your backyard ( SAR can produce highly detailed images -almost photographic- by microwave methods) using surplus bits on Hack a Day. That lead me to a book about Radio Astronomy that I had never seen before which is now sitting on a hard drive -when I've time - then on to several other links that were very interesting to me that are now bookmarked. Electronic paper browsing but covering a wider range and thanks to the links -immediatly available on my screen- and dumpable onto paper if needed. One of my other interests is the technology and history of WW2. Through browsing a Finnish site I found a link to a Dutch site which linked to a museum of WW2 German electronics. Well I never expected to see the circuitry of German Radar's, it takes about a week to get updated on the whole story which includes the V's and the Magnetophon. So yes you can browse very nicely on the web and find stuff that was not on paper but is now.


Paid up subscriber to Paper.

19/03/2014 13:15:08

I cannot agree with the last post. We live in a changing world, paper publishing is a very old media which is expensive, cumbersome and restricted. The future is more towards on-line publishing and individual initiative. If you are not on the web you are already missing out badly ( and not reading this forum ).

If you don't want to look at a screen then that is a self exclusion plan of your own - for whatever justification you want to make- but it has no influence on what happens in the years to come.

Paper publishing will disappear eventually. It is too restricted and expensive compaired with electronic media. The combination of text diagrams and pictures that is current publishing benifits from motion video and sound, For example you can show a beginner how metal is turned, they see chips come off and hear the sounds made by the process. If one picture is worth a thousand words then a video sequence with sound is worth ten thousand words- you see and hear the dynamics of the process.

I subscribe to some U.S. e-mags. I get them at a fraction of the cost of the paper version weeks before the printed issue. I can very quickly print any or all of the e-mag ( it uses a much better reader than ME or MEW use) and can instantly follow links to other external sites. I also watch Hack a Day which over say 28 days covers a massive range of ideas- some are trite or trivial but others are very good- you get to choose from the menu rather than the Editors preset minimal menu. Other dedicated forums also give the two way communication advantage of the e-media.

As an older person on a pension ( although still working) I do love the printed page, I have thousands of books and many magazine collections that I treasure however economics dominates and determines all human actions. As we read our last pages those that follow are a new kindle/ texting version of ourselves, to them e-mags will be the future.


Thread: Looking for 250W 4 pole motor.
13/03/2014 18:07:50


if you read 1/3 HP, 250W makes sense. That would be plenty for a fretsaw blade ( it is only one arm power after all).



Edited By Billy Mills on 13/03/2014 18:08:57

Thread: 3D printing seems to have gone quiet. Where are we all at?
12/03/2014 19:52:36

To answer Les's question, many thermmoplastics are reusable but colour sorting, addatives and contamination make it a little complicated. Bad batches of extrusions or mouldings go into a Chipper to be turned back into granules that can then be remelted.

Rather than cast blocks for machining you can extrude or inject the recovered material. The solid rod that 3D printers use is produced from regular plastic pellets melted then extruded from a nozzle. It's one of the accessories for a 3D printer sometimes made by printer owners to reduce their running costs as home squirted fillament is a fraction of bought in material.


Thread: Laser Centre Finder
09/03/2014 10:04:13

Clive- you have stated that you cannot focus a laser as it is coherent light- that is simply not true. Light from a laser can be reflected and refracted in exactly the same way as any non-coherent source excepting that laser sources are normally substantially monochromatic (i.e. single frequency/one colour) so chromatic aberation is not the issue it is with wide spectrum sources so focus can be much better. The coherence will make diffraction issues much more obvious however that is a useful property in many ways.

As was indicated in the previous thread, the beam intensity often makes lines appear much wider. By increasing background light levels the apparent line width will decrease. Bright illumination is also good from an eye safety viewpoint.


Thread: MEW 214
09/03/2014 01:52:33

Perhaps any Editor who could get JS1 and BS2 to contribute to their pages would be very fortunate. I too would like to see the end of 4, 6 and 12+ serials (Apart from Stepperhead). There is the slight issue of how many good ideas there are in the metalverse although the boundary may have been pierced by the injection moulding article and the mention of 3DP into the thermoplasticverse.

There are also a fair number of other clever people who don't appear in MEW but do contribute good stuff to the forum, perhaps NW1 will make them published writers in a while.

I would like to say thanks to DC1, I don't know how on earth you put out 3 titles per month for so long without cracking up. You certainly taught this subscriber a few things. Thank you David.


Thread: electronics
28/02/2014 23:40:10

No Neil, not unless there is considerable source resistance or a constant current source, which is the reverse of normal conditions ( Perhaps you are thinking of Pendulum clocks mounted on a common wall, they will sync). A brushed PM motor has it's own tacho built in as the rotor back EMF. Each motor's V/rpm slope will be very slightly different but is trimmable externally so two motors can be closely matched. A very good way of doing this is to put the motor into a bridge circuit. The effect of the bridge is to drive the motor from a negative resistance which exactly matches the average internal resistance of the motor so that the motor speed is independant of motor load. This also allows very smooth very low speed running.( Many mini lathes and mills use this method to get smooth low speed running when delivering torque).

Perhaps the simplest solution would be two PWM controllers with a trimmer to match motor speeds.

If you can cope with very high motor speeds then outrunner ( or inrunner) style motors offer very high power in a very small cost and space. They are high speed three phase motors derrived from the motors long used in floppy and hard drives. Connecting two motors to one suitable controller will give virtually locked rotation and avoid other issues.


27/02/2014 21:35:35

One aspect of electronics overlooked by many is the number of specialized fields within the subject. Depending on specialty people react in different ways to different perceptions. So a small DC brushed motor controller might be an analogue Pulse Width Modulated project to some, a digitally proportioned PWM to a software inclined person and a bridge feedback circuit( using back EMF as a tacho) to analogue types. They will all work but each approach has different strengths and weaknesses.

AofE is a landmark good all round book but the second edition now needs some revision. Where it does work particuarly well is in conveying a "flavour" of good engineering to a very wide subject and in almost completly avoiding heavy maths, they also do what good engineers have always done- they revel in and love their profession.

I would agree with Andrew about the 555 except that I would not be seen dead with a 555 in my bin. By the way the 555 has two comparitors for 1/3 and 2/3 rail thresholds, the three resistors were all 5K ohms in the original which some say is where "555" came from.


Thread: Ruby Loftus Screwing a Breech-ring
22/02/2014 00:25:17

Perhaps we have the U3A mag to thank for this thread!


Thread: Anecdotes_05 ' In the dark '
22/02/2014 00:22:27

Would sugest that wells and mines could give a better view because only a small part of the sky glow ( from street lighting) would be visible so after a while in real darkness ( with the mine lights off) the human eye would reach high sensitivity. Urban Canyons might not work as well because most buildings loose a lot of heat so there is a lot of thermal turbulance as well as a bright sky and local lighting to contend with.

Some astronomy is done through optical filters which reduce the brightness of the sodium d lines ( the bright yellow ones), that helps quite a bit. The eye is quite sensitive to yellow however if you take a picture under sodium streetlighting it is mostly red.

Perhaps one of the most strange aspects of the human eye and vision is that the retina is not a continuous light sensitive surface, it is covered with many blood vessels yet when we are awake we normally experience no trace that our eyes are not so perfect. Sometimes when you wake in the morning or when you are at the opticians you might glimpse the blood vessels tree trunk appearance but it then dissapears in a flash as it is " computed" out of our perceived vision.


20/02/2014 09:43:46

Locally street lighting goes off between midnight and 6 am as an energy saving measure so the sky change is very apparent. In some areas the street lighting electricity is not separately metered, they are charged on the number of lights, estimated consumption and hours on, it's too expensive to wire up metering.

Some towns have a "dark skys" policy, street lighting is directed downwards and of limited power so the stars appear against a velvety black background. When you are getting near some towns at night you can see a foggy dome of light enveloping the town, light spill upwards illuminating dust and mist in the air.

With most people city dwellers they don't get to see a starry dark sky, just a dim fog with a few stars. There are only a few places in the UK where the skys are really dark as you need to be perhaps 20-30 miles from urban areas.

One real weird UK lighting madness is that local councils light side roads with no cars per hour and people inside buildings but very busy Motorways -such as the M25 and A1M - have no lighting in many places.


18/02/2014 18:45:06

Before fast digitization and storage came along fast events were recorded on oscilloscopes with fast photographic film. One off events gave too little light to record on film so "pre-fogging" was used, a very low level light exposed the film so that less light was needed to record the scope trace. Tektronix then built a multichannel electron multiplier into their crt's so that the apparent intensity on the screen could be increased by 1,000 to 10,000 times. This enabled recording one off experiments that were impossible to repeat such as atomic weapons testing. There is a very good museum devoted to atomic testing in Los Vegas, they have very knowledgable staff who really know their atomic physics and instrumentation, just downwind from the Nevada test site.

The multichannel multiplier is now used in some image intensifiers.

X-ray film was very expensive, it had a thick silver containing emulsion, nowdays silicon sensors replace the film, more sensitive, no storage issues and no development needed, the image is produced immediatly and the radiation dose is much smaller.


16/02/2014 21:17:30

There was a program on Discovery about a year ago using marine very low light imaging. They had some state of the art cameras working in a very dark night at sea. The wake from the boat glowed brightly, a kind of phosphorescence from bacteria in the sea when hit by the pressure wave. Almost everything glowed underwater, many creatures were light producing -when they wanted to be.

At very great sea depths it is always thought of as being very dark, most creatures at these levels ( and cave dwellers) are not pigmented or marked. Many are blind. There is the most extraordinary creature of the deep , the Giant Squid which has by far the largest eye knowen at around 12" diameter. That eye would not have evolved if the Squid did not gain an advantage from it's low light performance.

Our eyes are relativly insensitive and slow to adapt, it can take up to 30 mins - dependant on life style and health- for the human eye to reach maximum sensitivity, older eyes tend to have smaller fully open apertures too. We also tend to avoid extreem dark wherever possible, we have developed to avoid situations where we are at a great disadvantage to other preditors which is a pretty good idea! So we may well lack detailed knowledge of common low light events , let alone the unusual ones.

As a wiser man than me said " It's only the hole in the ear that lets in the fear, that and the absence of light"


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