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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: Anecdotes_05 ' In the dark '
16/02/2014 17:49:39

Interesting that MW remembers very low level colours. Cones come in three colour sensitivities, Red Green and Blue and are clustered together, they don't work at all at low light. There are roughly 20 times as many rods which do go down to single photons when very well adapted. So for normal humans as light level drops we see less colour, red tends to dim first, the peak sensitivity at green- blue gives way to grey at around 100 times min detection level. At very low light levels we cannot see colour at all, you need a telescope or binoculars to see the colour of stars.

Broadcast Colour TV has taken advantage of these properties for years, We have only ever watched black and white pictures with the coarse detail coloured at lower bandwidth, matches out eyes!

There is a third type of photo receptor - not many people know about so handy for the pub quiz- photosensitive ganglion cells which respond to high general illumination.


Thread: 3-D Printing
14/02/2014 18:37:45

Depends what you are casting, in what and how big, I do centrifical tin casting using a Centricast machine in rubber moulds, very safe and easy process. The machine is a very easy project to make in a SHED. But you need to make a few identical bits to be worthwhile. Moulds are 10" or 7" diameter.

Alloy casting is now a low cost deal, there are several good furnace designs made from cement and cat litter on the web. Some people do lost plastic using plastic foam bits stuck together to produce oversize castings that can be machined down e.g. Often the plastic foam is shaped with a hot wire cutter, all very suitable for real model engineers at home in their SHEDS. Mike Cox has some very well written projects on his excellent web site **LINK**. There is also the very good video series by "Myfordboy" on the tube that covers home casting.


11/02/2014 18:55:41

Congrats Neil and very many thanks to David. Nearly all home made 3D printers are extruders. As a user I would suggest that the stiffness of many machines is not a great issue, the material is deposited at very low pressure in a molten state. Rather there are many other reasons for poor finish, stringing and striations. The last Sandown showed a few different ideas in extruding machine design, although there are some good commercial models some of the home made ones are every bit as good. A machine of this kind is a whole lot of challenges for home workshops, it's bits we all have with some cheap other parts. It's turning and simple milling but more it's using your brain and hands to make a better one.

Extrusion and plastic are not the only options, for example you can shape a hard wax block to produce a lost wax casting with very high precision. You don't need to use a cast iron machine weighing 100Kg to do the shaping, a home made wax shaper could well be an interesting project. Hot wires or heated blades for cutting linear features, conventional milling / drilling or heated tubes for recesses/ holes. The wax is re-useable too! Aluminium and other non-ferrous casting is well inside the ME domain and practiced by many.

There are many other 3D printing methods, plaster powder and water drops, UV cured liquids and metal spraying are just a few different forms. There are a great variety of different ways of making 3D objects but what is very striking is that a lot of the actively interested young people have the ideas but not the engineering experience or facilities to produce great machines while those older people have a vast skillset and machining abilities that the young need . Pity the two groups don't get together more.

In the UK we have the additional irony that -having removed machine tools from schools- kids don't get hands on ( and therefore brains on ) with milling and turning while the machines that are ex-school are in the hands of the people who now don't have industrial jobs but have a super abundance of fabrication skills and technical knowledge.

So my take on 3D in MEW is to suggest that MEW have a competition to make a machine that can produce a variety of complex shapes by addition or subtraction directly or can then be cast via resin, wax or metal by any method up to the sides of a 150mm cube ( say 6", machine weight to be under 30Kg. So a CNC mill would be too heavy, A 3D extruder could do it but another type might win out on sheer finish or build speed. Perhaps the competition could specify a test object that should be printed to qualify, then anyone who could would be challenged to print a new mystery object at the next Show. Or is that too hard?


Thread: Rotary Laser centre finder
31/01/2014 13:07:29

The simplest target is a cylinder. A small cylinder with a vertical axis gives higher sensitivity than a larger cylinder. It is also simpler than a cone and can be the rod that you have or are going to turn. The patented device with the laser on the outside of a chuck i.e. say 30mm from the axis of rotation produces very low sensitivity on targets of 1-20mm. My suggestion in the two year ago thread implied that the laser is much closer to the axis of rotation. Indeed this is what Chris made and exhibited at AP. He spun the device in a Myford 3 jaw witha beam just off axis to demonstrate. The beam hit the tailstock centre and gave a nice slanted line across the cone. Not quite the same animal as the patent, but the patent allows drills & mills to be held while being aligned.

The geometry of the device is the key, Think of the axis of rotation then a beam crossing the axis at 45 degrees and hitting a round rod also having the same axis as the beam rotation. We would see the circle drawn around the rod. If we move the rod 5mm at a right angle to the axis of rotation then the circle is tilted into resembling an elipse, with the high point 5mm up and the low 5mm down on the other side of the rod.

Now if we move the pointer so that it makes an angle of 5.7 degrees ( roughly 6 will do fine) we only have to move the rod 0.5 mm to get the same apparent movement of the beam . If we can set about 1.1 degrees then the 5mm displacement happens with 0.1mm ( 100 microns) of movement so this a sensitive arrangement but demanding on beam quality.

The vertical displacement for a given displacement is only related to the beam angle from the axis of rotation so a smaller target makes the sloping elipse proportionally steeper so easier to see.

Fuzzy spots do limit shallow magnification, as suggested earlier increasing the background illumination will help. There are some well known optician tricks such as stopping the source down or placing an occluder in the beam path to produce sharper spots, worth a try.

The beam colour will not make any great difference for a given beam quality, absolute sensitivity is not an issue.

Engineer's Buttons don't need mods, you can use a shallow angle on the sides - which should have a lovely smooth surface. But a sensitive arrangement might have a very round plug in the hole as a target , a turned step around the hole or use the hole( the top feature allows several buttons to be located without moving the buttons which could be bolted down.) .

Another suggestion that was made originally was to be able to change the angle by changing spindle speed to avoid the need to keep stopping and starting. This idea was shot down by a few people in the original thread without much ado they said that they thought that vibration and other issues would afflict the device. It actually works very well indeed, the implementation was a bit more complex than I described but it allows much easier actual use when working with shallow beams, in effect the speed control is a remote beam angle control .

So if you want to make one of these gizzmos I would suggest that you fix the pointer to a rod so that you can move the pointer from the axis of rotation outwards and that you can adjust the inclination to an almost vertical angle.


PS Many thanks MG for the quadrant detector link, I was mighty impressed by their price tag, thinking of knocking out a few....

29/01/2014 01:09:38

There are devices called quadrant photodetectors which are now very cheap and common, you can find one in the optical block of a CD/DVD player. As the name suggests the detector is four adjacent square detectors now made in the surface of one IC.. Lets call them a,b,c & d going around the centre. If you electrically add (a+b) but subtract (c+d) then you detect misalignment along one axis, adding (b+c) but subtracting (a+d) gives misalignment at 90 degrees to the first axis.

Using a small rotating beam painting a circle around the quadrant detector gives a constant brightness spot, Misalignment varies the proportion of the rotation that a quadrant is illuminated so we get a modulated signal which can be AC coupled to reduce steady state drift. So we could have two meter pointers, when both were reading no signal the circle would be rotating around the centre of the detector.

The quadrants are around 2mm square in some blocks, it is trivial to display microns with this arrangement.

Before anyone explodes off a high chair, this is a very well known set up with non-rotating sources. The Optical disc player uses a variation to recover height information . The player has a focusing lens driven by a coil actuator. The light from the lens is then sent through a round rod to create spherical abberation, the rod is at 45 degrees to the quadrants.

When the lens is focused on the disc surface the detector gets a round spot hitting all four quadrants equally. When the track is off then the detectors use the axis data to servo the lens to track the pits on the disc.

The focus is performed by adding (a+c) but subtracting (b+d), when the lens is too high the output is positive and proportional to the error, lens too low the out put negative. This is because of the cylinder lens abberation, out of focus the spot becomes eliptical, the major axis twists 90 degrees each side of focus.

This stuff was originally developed by Philips/Sony for the 12" video disc but was then recycled for CD & DVD players. The method of using servo's and quadrant detection is needed because you need micron accuracy to track the pits as they go around very fast on a disc that can go up and down several mm and also have the same kind of eccentricity. An all for ten quid for the player and electronics!.

You can use the rotating source and the quadrant detector to align co-axial shafts. A fixed beam can be rotated into a parallel rotating beam by rotating an inclined glass slide in the beam, that will scan the beam but it will not rotate a shaped beam. No fibers, no time domain measurements


26/01/2014 23:20:16

I do not see why you need to introduce a fibre. The discussion is about rotating a source in air to generate a cone then observing the intersection on a cylinder, cone or sphere target. We are not into precision metrology, we don't need DRO's, we are not into absolute measurements or taking gravitational levels. This is about a bloke in a shed with a poundshop pointer lining up a drill, mill or Lathe.

The sensitivity geometry is simple, the shallower the angle of illumination the higher the sensitivity. For cones and rods a Tan term gets in there so the gain increases very rapidly towards infinity around zero degrees. With a sphere the sensitivity function then includes the diameter of the sphere. Although a ball can be placed over a hole as an alignment target we might not need a ball target too often. A hole can be the target, we can set the pointer to cross the axis of rotation to produce two cones, with points touching, the lower cone can then illuminate a bore.

A point that may have escaped- pointers often have non-round beams and fuzzy edges. However because we are rotating the beam, the defects only produces a wider ring when the cone hits something. Say the beam was a small picture of David Clarke, as we rotated the beam it would then appear to be a series of rings but always rotating around the true axis of rotation. Often the spot is so bright that it appears fuzzy, TURN UP the background lighting then you will reduce your eye sensitivity and the spot will appear tighter. Always better to use pointers in the brightest illumination usable.


PS thanks Sir John for your comments, Others got there before me.

26/01/2014 14:36:05

Just over two years ago in **LINK** the idea of a slant mounted laser was discussed, ChrisS then made one and it went on show at AP on the SMEE stand. Sir John's Dambuster pictures were then posted as a "been there done it way before you" but it is not the conical beam idea but two projected lines.

Thanks John McNamara for posting the link, the video series looks very good- something interesting to watch and learn from.


Thread: Ally Pally show
24/01/2014 00:42:29

My wife and I have been selling in another Hobby market for 10 years, we make everything we sell in my garage workshop by using CNC . We now attend one third of the UK shows that we started at because the smaller shows are just not profitable, so now it's four UK shows per year, not 12. But we now fly to the USA to trade at two shows which cost us half of the UK stand costs and give us 250% increased takings. We also have almost the same experience in F, D and NL however we can drive there!

By going abroad we also help stimulate web sales which are very much cheaper than " UK Show" sales, most of our trade comes from outside the UK now. Like many other exhibitors we are seriously considering pulling out of UK shows, many traders have already realised that the ever increasing UK exhibition charges have priced them out of their local markets. Running a stand is hard work, a two day show is at least a three or four day event for a trader, it costs a lot of money paid in advance. So if you cannot get a small reward then you learn the hard way and don't repeat the mistake. It is not a matter of "rights to business" or any other romantic notion, if you don't earn then the "punters" have voted you out next time. Simple, honest and hard.

Signs of Show decline include the reduced number of trade stands and the increase in seating and free stands to help fill the Hall. It is an unstable state, as the trade stands decline those traders left have to pay much more to give others more free space. Any new traders then face much greater start up costs which stops them from starting! There has been mention of reduced rate stands, this is the quickest way of closing a show down ever devised. Traders talk to each other and belong to associations, if anyone ever picked up that free or discounted stands were being offered then that would close that show if all of the existing exhibitors did not get exactly the same treatment. It would be interesting to hear of any free stands at any show- put us down for 50 stands right away and we will bring some friends.

We see very different conditions outside the UK, the venues are FAR better, you don't need wellies in the toilets and you get a good food choice without feeling that you have been mugged. These half UK cost shows are also growing in size, scope and duration and have a real international dimension. If only UK Organisers were that clever!

Billy and Sue.

Thread: Hot bandsaw........
15/01/2014 21:47:12

Agrre with Neil, sounds like a blunt blade. I've often found that I have used blades quite a bit more than I first thought. Investing in a decent bimetal blade is a very good move, you get a lot more cuts per quid and save time too.

A small cheap drilling vice fixed onto a lump of wood ( sorry non-specific technical term) holds short ends OK and saves epoxy and time. One other point, if the bandsaw is set up well the cut is very predictable so you can go very close to a scribed line with a bit of care. There are quite a few mods on the web, many concern vice mods.


Thread: mini Bandsaw, or mini Scroll Saw ??
06/01/2014 01:18:56

Norman's link is more or less the same machine as I have. Yes it is a bit big but it will cut anything you want with certainty, there are a few improvements that are fairly standard. I stow mine under a high bench. If you want to do a lot of sawing then this is a very inexpensive way to do it even including the bimetal blade that is a very desirable extra. If you can find the space then this is a very good tool for the workshop.

With the blade vertical and mounting a table on the lower guide you have a good vertical bandsaw which can do fine cutting on a broad range of materials.

Although there are always exceptions to any generalisations..... wood bandsaws tend to have rubber tyred wheels, high blade speeds, dust extraction, no blade lube, vertical blade. A metal bandsaw tends to have slower speeds, metal wheels, no dust extraction, often horizontal blade, better machines blade lube/coolant .

My view is that this is about the cheapest reliable way of cutting a fair bit of metal however the Evolution Rage sliding saw is less expensive , takes up less space and has other tricks. Aldi were selling a compact hand circular saw recently which is the lowest cost option and within your budget, When mounted inverted and with a few extra bits this could be a useful tool for light use, Mike Cox reviewed the saw on his website which I mentioned earlier.


05/01/2014 17:17:36


Had a look at your first choice bandsaw, the blades run about 3000 ft/min which is fine for wood but you want 100-300ft/min for a wet bimetal metal cutting blade. There is a useful table of cutting speeds for various metals at:-**LINK** ( as well as a lot of other stuff).

So that little saw would need a reduction of 10 to 40 times to get the blade speed down to the range needed to cut metal reliably with a bimetal or carbon steel blade. Quite a rebuild but if you have some spare pulleys and bearings it could work, the reduction would give a useful torque increase for the small motor.

The real question is if it is worth doing, that depends on how well made the patient is before you start surgery. If the the wheels are well supported and the guides are half rigid then it could be viable if decent blades are available in the size needed. Still a lot of work.


02/01/2014 23:59:48

Hegners go for £500- £1000+ so way out of the range that Russell was talking about. Most scrollsaws use a crank drive at the base of the lower blade holder, sometimes with a parallelogram jointed frame to keep the blade vertical. A few "safe" types use a vibrator which oscillates the blade over a very small distance, these tend not to cut fingers as much as other types!

One other point that did not get mentioned is that if you can run an inverted jigsaw / scrollsaw slowly then you can potentially mount a Swiss file vertically so that you have a mini filing machine, that would fit in with Ian's top beam.

I have found a mini filing machine very useful, someday will get around to making something more perminant than the lash up that gets me out of hand filing these days. The machine works for me, all of the effort goes into guiding the cut line not powering the work.


02/01/2014 19:12:28

I would not think that a scrollsaw would be of much use above 2mm in soft metals, low cost scrollsaws are for 1-6mm or so soft woods, with wider blades you can go through thicker wood very slowly without the blade bowing too much but scrollsaws are not suited for general metalworking. A good bandsaw with a bimetal blade is a very handy machine for heavier use as is the Evolution metal cutting circular saw which is so useful for chopping 5-50mm mild steel, alloy or wood to lenth.

Another option can be found on Mike Cox's most excellent website. Have a look at **LINK**

You can also mount a jigsaw in the same way, if you have a throat plate with zero clearance around the blade you avoid distorting thin sheet during cutting- same trick used with circular saws, use the blade to cut it's own slot.

Happy New Year,


Thread: 3D Metal Printing
07/12/2013 17:03:53

Here's a DIY article and a lot of links **LINK**

Interesting that many people mention guns not the model engineering applications.


06/12/2013 20:06:19

First cheap metal printer is based upon a mig outfit and a deposition platform. Platform runs a bit warmer than plastics models. **LINK** has the details.

Very much work in progress, not Santa-ready yet!!


Thread: Sufrcae Prep of Aluminium
12/08/2013 17:28:38

The reason for not grinding Aluminium is that many people have been injured by trying to grind on a conventional bench grinder. The soft metal very rapidly cloggs the stone then can weld to the job so the stone can shatter and do a lot of damage to the people around the machine. The spinning stone has a lot of kinetic energy that gets released in miliseconds.

Specialists know exactly how to grind Alloys but they do it under carefully controlled conditions which are not available in the home workshop.

The OP is looking to produce Ali blanks for direct disc cutting - LP style. So the requirement is to have the surface locally smooth to idealy well under a tenth of a micron. Milling or turning might not quite do...!!!!


Thread: Why won't this work...or will it?
12/08/2013 16:56:50

Method 2 IS optical wavelenths Michael. For a very long time the metre WAS defined by optical wavelenths. Time measurements present the problem of the variation in velocity of the media, they only work without secondary effects in a vacuum. However there is no need for national standards accuracy on a home machine tool. For a home machine glass scale DRO's work very well, are not that expensive and cope with life quite well.

A cheap way of getting distance readings is to use a modified digital caliper or the ready made digital scales. Or you could do what people did BIC ( before integrated circuits) and use a dial gauge or two.


Thread: Telescoping tubes needed
09/08/2013 20:08:24

Geoff -you have not given much away. All depends on how long you want to go and if there is a head load, 50cm is very different to 5m! Will assume Alluminium - low cost tube is welded so although the outside is smooth you can get an irregularity in the bore. Extruded tube gets around that but not quite so easy to get.

You can still buy imperial tube in inch sizes in 1/8" steps, at 18 SWG it wil always telescope but the more common 16SWG will not telescope. Turning down is not at all practical if you have much to do.

Metric tube is easy to get in 1mm or 2 mm wall, to ensure a fit you need to step 3mm or 5mm unless you have an assurance on the bore. I buy Ali from Aluminium Warehouse who have a very good range of tube and all other kinds of sections, sheet and plate. Their prices are keen too.


Thread: Searching for a "Bench Grinder with Sanding Belt"
02/08/2013 18:04:42

I saw the offer in a local store but did not buy as I already have some linishing gear. For someone starting out it might be useful but we have now two reviews against.

In the past I have found Lidl and Aldi stuff to be very good value, not the world's best but good value for everyday use. They don't quibble about refunds and do give a 3 year warrenty.

Couple of years back I got a small belt and disc sander from Warco. Not expensive but have had to fiddle around lining up bits and replacing the table lock which falls apart. It does ok for the light use it gets but then it did not cost what a RJH Bison cost new.


Thread: Aciera F3 Mill
02/08/2013 17:30:19

Hi Yoram,

Check " my messages" in "My account", have sent you a message.


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