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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.

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Thread: Machining very thin materials
03/10/2011 02:03:05
Luc
You will find good descriptions of basic design principles in most good works on acoustics however I had the advantage of working for an offshoot of a German manufacturer after graduating so I am very aware of the way that capacitor and dynamic microphones are designed, tested, manufactured and serviced. I was involved in evaluating different designs and in designing test instrumentation so have a little background in the subject.
 
You are the first person that I have ever met that thinks that a ribbon is simpler than a capacitor microphone. The tolerances in the capacitor microphone are no great shakes, you are talking about a simple single step of a few thou, there is no difficulty at all in cutting this step, if it was +/- 10% it would have around 1dB impact on sensitivity. Some of the best units have a cast ceramic body with a cast in rim, this is rubbed down on 1000 grit wet and dry in manufacturing to get the spacing standardised. The hole pattern is no black art, a regular pattern of about 50-100 holes with around 20- 40% of the backplate area works well. If the holes go all the way through you have bidirectionality, closed off you have omni, with some all through and some stealth, wideband cardiod.
 
If you make a metal backplate then a quick acid dip will etch out micro burrs because they have a very big surface area /volume ratio. It is also very good to use a real ultrasonic cleaner before assembly. Give it a go.
 
Billy.
02/10/2011 17:19:15
You can cut thin plastics with a very sharp punch against a hard rubber pad, with a lathe the punch is a simple cylinder with the sharpest corner you can get. You can elaborate by turning a knife edge or use a sharpened thin wall tube to make small holes. Even a Knife used with a washer template will give a good edge.
 
I would not agree that capacitor microphones are difficult to build or design, they are the simplest microphones possible, the theory and practice could not be much simpler, it is just that manufacturers keep their exact processes under their hats and very few homebrew designs have ever been published. With care and some time Luc will get there.
 
Billy.
 
 
02/10/2011 12:48:23
The article must be around 40-50 years old, it reflects ancient methods. The clamp rings that clamp the mylar to the capsule body can be etched from brass or copper using ferric chloride as the etchant however there is NO requirement for them to be a thou thick, they could be readily made from thicker material that is stack drilled with sacrificial material above and below as already described. There is NO need for insulating spacers, that is done by the perspex outer rim.
 
The article glosses over the film tension issue, high film tension is a very important part as are the holes in the back plate. Many commercial microphones have the film glued to a ring. After curing a second ring is forced inside the first ring to tension the film then the film is glued to the backplate assembly. When cured the excess film is trimmed off and the edges trapped under another ring forced over the backplate assembly, no screws through the film are needed or desirable. The ring becomes the front electrode connection. Currently back electrodes with holes and the spacing rim are normally cast or moulded then the inner part of the back electrode is coated with evaporated aluminium or gold.
 
Most modern capacitor microphones use electrets in the back electrode to avoid the need for the polarising voltage. However the quietest microphones around use a very different method which was glossed over, the capsule is used to tune a discriminator which is driven by a crystal oscillator.
 
The high polarising voltage -100V- is applied over a gap of 0.0015" . This requires extreme care and ultra clean degreased parts to avoid insulation failure. Commercial microphones of this type are made in "clean rooms". Not an easy home project.
 
Best of good machining luck,
Billy.
 
PS don't bother with valves, use fets or suitable opamps.
Thread: Honey pump
27/09/2011 18:40:28
How about a Peristaltic Pump? good for blood or slurries, no valves, very simple to make, self priming and very easy to keep sterile. A length of Silicone tubing and a couple of rollers does the job. Have a look on Wikipedia for their little animation.
Must fly!
Billy Buzzzzing off.
 
PS Peristaltic pumps are widely used for metering so you could easily arrange to fill a jar with a known number of turns of the rotor.
 
BM 

Edited By Billy Mills on 27/09/2011 18:43:18

Thread: cutting round bar
20/08/2011 18:11:32
Very nice work -as always- Mr Engine Builder. One of the nice things about sawing machines is that they can be quite precise- more so that someone wishing that they had never started. So with a bit of care, a good blade and good bearings you can save a lot of time cleaning up by letting the machine cut a nice surface.
 
In another video Mr E.B. uses a Rage circular saw. Got a sliding version from a B & Q offer some while back - what a nice tool. Does a great job on metal and wood. If you are into welding then it is a very handy chop saw for cutting sections to the same ( or in my case all different) lenths.
 
Billy.
Thread: digital tv switchover
20/08/2011 17:53:09
There may be one simple way of transfering the azimuth angle from an already lined up local dish to another. Just watch the shadow of the LNB from about 10.25 am GMT find the time when the shadow is on the centreline of the dish. When you have the shadow on centre set up the other dish. As the Earth rotates at 15 degrees/hour or 1 degree every 4 mins this is quite a sensitive test.The only big issue is cloud in the UK! If only we would get a bit more Sun.
 
Pat's method is certainly one way of making a dish. Often larger dishes appear as surplus but lots of people make them out of "chickenwire" on ribs, glassfibre dishes cast on foam or wet sand or by riviting sheet segments together. The latest ultra low noise blocks allow much smaller dishes to return the same performance as the old big ones.
 
Billy.
Thread: Turning
18/08/2011 13:10:52
Visit a model shop and get some telescoping brass tube/rod/wire to fabricate the part. Soft solder or epoxy it together. O.5 mm is VERY tiddly.
Billy.
Thread: Bridgeport Milling machine help
18/08/2011 13:00:45
If the controller pcb is the same as the diagram you can use a two wire connection to the pot by wiring 10 and 9 together and then wiring the centre pin of the pot to 9 & 10 and an outside pot tag to 11. Would repeat the advice to check that the slow speed preset is not open.
Billy.
18/08/2011 01:48:53
Would think that the pot is 500 ohms NOT 50K. Fitting a 50K pot would not allow the 500 and 250 ohm presets to have any effect. The pot is only one of many parts that could cause the problem-it don't have to be the pot! The dissipation rating is not just about internal heating with wirewound pots, the resolution is also a factor. The log taper is extreemly unlikely with a ww pot, that would make it a very rare and expensive part
 
A 50K linear part will work, adding a 510 ohm resistor accross the outer tags will make the part look like a 500 ohm pot so that the limit presets will then work as intended. If the low speed preset has been damaged- i.e. gone open circuit then the speed would be uncontrolable and high, worth checking first.
 
Billy.

Edited By David Clark 1 on 18/08/2011 11:16:01

Thread: Curved flywheel spokes
12/08/2011 21:14:25
When iron was first cast the composition of the metal and it's tempriture was very variable. Many straight spokes cracked on cooling or in service but curved spokes absorbed the stresses by bending slightly. So early handwheels and flywheels have curved spokes. As the art of casting progressed less curved spokes can be found, eventually becoming straight.
 
Billy.
Thread: MEW180 CAD Article
11/08/2011 00:55:20
I would agree that the "virtual project" is a good idea that could come in useful sometime. Often ideas may have no relevance today but be invaluable a few weeks or years later.
 
Perhaps a few more people might come forward with unusual ideas which have not yet been turned into hardware but could solve real workshop problems.
 
Billy M.

Thread: Milling Machine
04/08/2011 16:16:57
Would not advise anyone to use an air blast for cleaning- especially if the line pressure is very high. Any oil or coolant will end up as a very fine mist which then gets straight into your lungs.
It is very hard to remove it.
 
Same for dusts, fine particles can hang around in a workshop for much longer than you might think because the surface area /mass ratio is very large, it is the 1-20 micron size particles that can hang around for 15 mins or more that are killers, wood, metal and abrasives from sawing sanding and grinding being some of the worst. Woodworkers don't use dust extraction for fun, it is there to let them work longer and enjoy their retirement.
 
Blowing stuff around is just bad practice, how do you stop it getting inside ventilation slots or anyone who walks into the area? How long does it take to get a brass or glass sliver from an eye? Do you really want to replace a motor or a control board?
 
Much better to wipe or slowly brush debris up so that it does not get into the air.
 
Billy- just back from the Hospital for a Lung Function test.
Happy cleaning.

Thread: The perfect ME Lathe
21/07/2011 11:51:14
There are a lot of good examples of how traditional stuff was updated with modern production methods and electronics, often there is an outcry of "it'll never be as reliable as the old hand fitted stuff" well tell that to people who drive modern cars, use digital cameras, washing machines, PC's, printers/scanners. The general effect is to make products very much cheaper, easier to use and to vastly extend the range of things that can be done.

In 1946 expert opinion was that only one advanced computer in the UK could do all of the calculations needed. No one thought that we would have more than one machine per person. In 1960 a mobile phone was installed in the boot of your car if you were very rich. Now every kid has one in a pocket. The list is very long! The lesson is that traditional products can be made more popular by re-considering their function and construction and adding enabling features. It is a decision made by the buying public, they choose to have more tech gear at a fair price.


Manufacturers that don't listen to the card machines close down eventually despite the sad grief of their loyal customers. But if you fail to adapt you get rubbed out by the people who do.
I am sure that there are good markets for CNC machine of all sorts, the Hobby market is perhaps the smallest, but there are a lot of small businesses that would love to have affordable basic CNC at an introductory level price so that they could prototype and do small scale production without massive costs. The KX1 & 3 and the Tormach are three examples, a man in a garage can make a living making stuff that bigger outfits can't do. So If I was Rod's imaginary new machine business person I would be thinking of making millions by following the exemplars of consumer manufacturing, design machines with new capabilities with the home and small business user in mind. But the plain vanilla version is too well done by the far east, it is now a commercial death trap.
 
Happy plotting
Billy.
 
PS Sir John's "it is going nowhere" is absolutely true, it is just a pass time for us Meldrew's but it is interesting to read the variety of different viewpoints and sometimes you learn something too!
 
20/07/2011 01:34:51
Well we are speculating about our personal lathe ideas and so our different views emerge.
 
Perhaps 99% of home CNC conversions use steppers rather than servo motors so we collectively tend to think of steppers as the way to drive an axis. However the "encoder" on the back of a PM motor can be a plastic injection moulded disk and a pair of slot sensors costing a couple of quid total and that can be much better than the 5% step angle accuracy of a Stepper motor - it does not need to be an absolute but a relative encoder- that would give you the potential to PID autotune the loop.
 
I don't see it a problem to make complex shapes easily, that classifies as a very big selling point and a useful feature. What is needed is a simple range of options for people to unleash the power of the processes without having to spend a lot of time training how to do it. So if -for example- you could turn an item by hand control then replay the motion you could fuse manual skills with the repeat accuracy of the machine to knock out as many parts as needed.
 
So my version is a lathe that looks like a lathe with a DRO box with knobs on. You drive it the same way as of old, you still use your skills of control, still see and hear the cut but you can also do loads of what was very specialised stuff as almost a free extra. You do it by getting rid of the change gears and gearboxes, fitting two PM motors to drive the two leadscrews with great big long plastic nuts - in the style of Henry Maudsley. ( If you want ballscrews Squire that'l cost you a little more). By the way, most of the other Accessories on the Mills WonderFord Special do add up a bit more than you might think but you are buying a very versatile machine......and it is an absolute bargain!!!!.
 
Happy saving up!
Billy the Industrialist.
 

Edited By Billy Mills on 20/07/2011 01:37:15

19/07/2011 22:27:58
Well everyone's going to have a different spec! But there is a halfway point between a full CNC lathe and manual control, by simplifying the mechanics you can swap out gearwheels for a few lines of code, you can have a hand operated machine -like power steering on a car- but the work is done by motors.
 
Steppers are an obvious but not the only power source, a lot of volume manufactured machines use PM motors and encoder wheels- much better than a stepper, more torque, much greater acceleration, more holding torque and no missed steps worries as the system becomes closed loop not the normal open loop with most steppers. It's also cheaper which is why most modern printers don't use steppers.
 
Would agree that G code is a bit like hand coding machine code, but a powered lathe does not have to take G code, you can have a simple controller- perhaps like a DRO display which could be used to display tool position, to set up thread pitches and to spec taper angle and length or the diameter of a ball. If this appears a bit much then think about the modern automated sewing machine which now makes buttonholes and all other kinds of fancy stitching- Why should SWMBO's have toys that we don't?
 
Happy planning
Billy.
Thread: A Little Light Relief - Mine's Bigger Than Yours...............
18/07/2011 23:32:13
I had a longer one than you but it went rusty and dropped off. How did you manage to do in the first pair of socks Andrew? is your lathe fitted with foot wheels? the Mystery deepens.....
 
Happy Risk Assessments
 
Billy.
 

Thread: The perfect ME Lathe
18/07/2011 20:36:04
Thanks Jason!
Was just thinking about cost reduction and getting rid of iron and time by using a mechatronic approach. It's an interesting question because lathes have had a very long development history yet the average manual machine is just about the same as a machine from 1900.
This is just a little different from the evolution of -say- aircraft in the same period.
 
Anyway we all have our own ideas about machine tools-long may it be so.
 
Happy costing
Billy.
18/07/2011 20:04:40
Here's another go!

1 DC brushless drive with 2 belts to two wheels dog clutch for Hi/Lo and instant stop, encoder wheel on spindle and brake to clamp spindle allows indexing of chuck.
.
2 Leadscrews with steppers and anti backlash nuts, encoder counting for DRO so electronic leadscrew and full anythreadyoucanthinkof screwcutting.
 
3 Expanding single post toolholding a la Mike Cox exchangable for tool changer add on.
 
4 NO top slide- don't need it, with stepper drive to saddle and cross slide you dial in the taper.
 
5 Headstock and ways might be skimmed plate on rectangular tube filled with epoxy granite
 
6 Camlock Chuck, ER accessory and big hole down spindle to take plug for C5's so Sir John don't moan ( can't G/tee this).
 
7 So you get rid of the expensive mechanical bits,replace with cheap as chips bits, take whole thing upmarket as it is a CNC lathe with manual drive.
 
8 Market it WORLDWIDE at a fair price. three sizes, Micro 2" swing, 6" swing 14" swing
 gapless bed. ( much stiffer for material cost and weight)
Only thing to stop it is that we are too stupid in the UK to get up and go.But we might be able to buy it from China in a year or two although they would cast it conventionally. ( Most of the heavy metal in a lathe does very little to add stiffness because it is too far from the spindle/ways/saddle/toolholding loop.)
 
 
Happy dreaming
Billy
 
 
 

Edited By Billy Mills on 18/07/2011 20:11:40

Thread: Proxxon machine tools
18/07/2011 19:31:33
Well if you are a hobby user you are not going to be running the same job all of the time so such factors as the hardness of the ways is not so important. Equally if the machine packs up it is an inconvenience rather than a disaster. I would not want to run any of my Proxxon tools continuously -they are NOT industrial tools but they are well designed for hobby use, many of their machines use plastic and ali ways.
 
I do use Proxxon tools, my use is in small scale prototyping in soft materials. It is all down to what your applications and expectations are and finding your own best value. My opinion is that Proxxon tools are very well styled and attractive but they are mainly hobby level tools.
 
If you can get to a stockist - such as Axminster - get to have a good look, feel the weight and get a test drive if you can.
 
Lathes and all other machine tools are a bit like religion- everyone has their own set of ideals and values. I would suggest that if you are going to use your new machines much then visit some local ME clubs and find out what other people use and have a try if possible. My own workshop is based around ex-industrial and industrial machines with Proxxon tools here and there for low volume small stuff.

Happy Milling
Billy
18/07/2011 16:38:57
The table saw is very useful and quite unique. Would think carefully about the lathe and mill.
The lathes are very expensive against other kit of comparable quality.
 
The MF70 mill has an Ali and plastic table and is VERY small but is one of the few small mills that will run up to 20,000 rpm for 1-3mm tooling. Well suited for very small work on soft materials in limited quantities.
 
Worth considering Sieg small mills and drills against the Proxxon's.
 
Would not rave about build quality at all, we are talking plastic and Ali extrusions for most models. These are miniature hobby tools well suited for miniature work in soft metals, plastic and wood with mostly very small brushed motors.
 
A few other posts have appeared, search PROXXON as the keyword.
 
Happy milling
Billy.
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