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Member postings for Norman Billingham

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

Thread: Capillary gaps required for silver soldering.
26/07/2020 14:03:37

The capillary gap can be very small indeed. There are published data for tensile strength of silver brazed copper joints with different gaps. The optimum gap is about 1.5 thou which gives a tensile strength of 0.9 GPa (135,000 psi). Smaller gaps give weaker joints by a very small amount, so it falls to about 0.7 GPa (100,000 psi) for a nominally gap-free fit. It’s thought that may be because it’s harder for the molten alloy to push flux out of a very small gap. However, the tensile strength is still 0.34 GPa (50,000 psi) at a gap of 20 thou. The ultimate tensile strength of annealed copper is about 0.2GPa (32,000 psi) so even with a 20 thou gap the joint will still be stronger than the metal. Bearing in mind that the diameter of a silver atom is about 350 pm (0.000014 thou), a gap of 1 thou will be enough space for more than 70,000 atoms of silver.

Thread: 33mm Spanner
26/07/2020 10:12:10

Propane cylinder spanners are 30mm AF, cheap and fairly easily modifiable

Thread: Hearth material
26/07/2020 10:07:24

The compressed vermiculite boards are very good - lightweight and easily cut to shape for odd jobs. The thin boards do become very brittle and prone to breaking. The spun kaolin blanket is also handy stuff to have around for insulation and for odd small jobs.

Both are quite expensive for occasional use. I mostly use a hearth made of standard firebricks which I assemble to suit the job, on top of a Workmate, I got eight of them from Travis Perkins for less than £1 each. Local branch didn't have them and said would deliver - a large truck arrived next day with a neat pile of bricks the only thing on it. That was a few years ago though.

Thread: Q-Tech Collet Chuck
19/07/2020 10:32:25

My VMC mill doesn't have a spindle lock and the ER collet chuck doesn't have spanner flats, so I had difficulty tightening collets especially at the smaller end of their range. The answer was to swap the closer nut for a ball-bearing version (I got mine from Arc Euro). Reduces the tightening torque dramatically and I can get things more than tight enough just by holding the quill pulley with one hand and the c-spanner with the other. I had planned to grind flats on the chuck but there's no need now.

Thread: Basic Electrics
13/07/2020 10:56:31

I think the drive for battery powered tools comes mainly from site safety considerations - low voltages and no trailing leads. Mains powered is hands down better for serious drilling and sawing - though I wouldn't be without my cordless drill/driver.

Thread: Cigarette Papers
13/07/2020 10:47:45

I use the green ones, though not as feeler gauges. The trick I was taught many years ago for setting a milling cutter was to dampen the paper with a bit of oil (or saliva) and stick it to the work then lower the cutter till the paper is dragged off, when you are within 0.001" of the work.

My green ones measure 0.001" + roughly 0.0002, - 0.0000 using a Mitutoyo micrometer.

Thread: Cutting Oil
09/06/2020 10:57:16

If you really want to understand cutting fluids in depth, there's a full account in "Metal Cutting Principles" by M C Shaw - the second edition is from OUP in 2005 and chapter 13 is the one to read - though not an easy bedtime story. Its expensive, though there are (probably illegal) download versions on the web and occasional bargain copies on ebay - especially of the first edition.

Apart from the things already discussed there's chemistry involved, though more so at low speeds in things like tapping and broaching - cooling seems to be the most significant thing in high-speed operations like turning and milling, which is why some operations use blown air.

Shaw also discusses in great detail the different cutting mechanisms in brass and steel. Basically steel is ductile and fails by compressive shear, whereas typical "hard" brasses are brittle and fail by repeated cracking ahead of the tool tip - which is why brass "sings" as it is cut and produces tiny spicules of metal. The process in brass is essentially unaffected by cutting fluid.

Thread: Bending 1/8" Steel Plate
16/05/2020 14:27:31

A lot depends on what your silver solder wire actually is. Silver solders come in lots of grades from "extra easy" (mp 670) up to "hard" (mp 760). The normal braze alloy for model engineering is AG455 which melts at 650. If you use that with EF flux it's pretty much self-indicating - the flux will dehydrate to a white, fluffy powder on heating and turn to a clear liquid when the work is hot enough to melt the braze alloy. So apply flux as paste, heat gently till it dehydrates then as strongly as possible until the flux turns clear, then apply the alloy - use the work not the flame to melt the alloy.

I'd be very cautious about using house bricks for a hearth - they can contain a fair bit of absorbed water which boils and cause bits of brick to come flying off. The compressed vermiculite blocks are good or you can get proper firebricks very cheaply. With half decent insulation, a MAPP torch should have no problem brazing a job like that.

Thread: Percival Marshall gramophone message?
07/04/2020 16:14:20

It certainly still exists - the SMEE archive has a copy, but as far as I know it's not online anywhere. It's occasionally played at SMEE on special occasions.

Thread: What does diamond turned mean?
02/03/2020 12:02:01

I used to do bits of consultancy work with a company which makes intraocular lenses for cataract operations. They were turned to shape from acrylic plastic using a CNC lathe with diamond tipped cutting tools

Thread: Polly Steam Plant
02/03/2020 11:57:56

We teach students on our basic course at SMEE to make Polly. So far I think we've had about 120 made. We use copper tube to make the boiler and just give it a wash through with hot water to remove flux residues after brazing in the end plates. We've never had a problem. It's actually more important to wash thoroughly when you've used soft solder with Bakers fluid flux as in soldering the firebox to the base - chloride residues from the flux can be corrosive to steel.

Good luck with the build

Thread: History of model engineers
17/02/2020 17:04:06

If you contact SMEE you may be able to get hold of a copy of "100 years of Model Engineering" - a history of the Society published by SMEE in 1998 - many of the people you mention were members.

The Society has also recently published a book by Roger Backhouse on Jim Crebbin - readily available

Edited By Norman Billingham on 17/02/2020 17:06:17

Thread: Stuart S50 (Want to cry)
12/12/2019 09:53:23

I had the same problem with the steam chest cover on a 10V. Some of the castings Stuart supply are chilled and glass hard. You can return it to Stuarts and they will supply a replacement. If there's enough metal left it's also possible to soften the casting by heating and then cooling slowly - but I'd just get a new one from Stuarts.

Incidentally the "gold" coating is actually vacuum deposited titanium nitride (TiN) and it can be a mark of very good but also very poor cutters

Thread: Beginners models
08/12/2019 09:28:46

I think a lot depends on what kind of model you have in mind. On our training course at SMEE, for beginners to the hobby, we build “Polly” the first of Tubal Cain’s models. In many ways this is an ideal beginner’s model because it involves a huge range of techniques, sheet metal work, forming and flanging, brazing and soft soldering, turning, milling, spring winding etc, leaving students well set up for whatever they may want to do next. It’s also built more or less completely from stock materials so that mistakes are cheap – and when finished you have a fully working engine and boiler to show off. On the other hand many modellers only build stationary engines, which may never be run on steam, so that they don’t need, or want, to learn the sheet metal techniques. Many people start with something like the Stuart 10V which is a nice model. Its disadvantage for a beginner is that mistakes are expensive – if you make a mistake with a casting you have to order a new one and wait for delivery before you can move on.

I wouldn’t worry too much about scale. It’s easy enough to build small things with big machines – we’ve seen Pollys built with everything from Cowells to Colchester lathes, and from micro to Bridgeport mills,

Thread: New to model engineering - what solder / flux and annealing question
29/11/2019 17:23:51

I help to run the SMEE Polly course, where we teach the basics of model engineering by building the Polly engine. I'd guess we've seen approaching 150 of them built by students over the years we've run the course. Forming that boiler seam neatly in rolled sheet is pretty tricky and we've always avoided it for beginners by making the boiler from 1 3/4" copper tube. Stronger, and very much easier to get a neat and leak-tight boiler. We supply a piece of the tube to our students, but you can use 42 mm plumbers pipe which is a bit easier to find in short lengths - though you have to change quite a few other dimensions to avoid problems.

Thread: Anyone know what is the protective plastic film on brass sheet made of?
24/11/2019 09:58:38

Oh dear - I do seem to have started a hare running here with an attempt to be helpful.

To be clear, I wasn't suggesting burning kilos of plastic, or tons in an incinerator. A piece of thin film about 2-3 mm square held on the point of a pin in a small flame is all that's needed and the risk from emissions is non-existent. Before IR spectroscopy became readily accessible, the flame test was a routine starting point for screening plastics. A version of it - the hot needle test is still sometimes used in heritage conservation, though largely superseded by spectroscopic methods for those who have access to them and can get suitable samples.

23/11/2019 13:22:40

If you want to be sure, strip a bit of the film and put it in a flame. PVC will char and produce acrid fumes, PE will burn away smelling a bit like a candle and with almost no char. Incidentally the gas released from PVC is not chlorine, it's hydrochloric acid. You can double confirm by putting a bit of ammonia solution nearby - the acid released from PVC will produce clouds of white smoke - though you shouldn't need to do this - the difference is very obvious once seen.

Thread: Reilang oil cans
13/10/2019 13:55:16

Would one of these generate enough seal and pressure to lubricate a Myford lathe through those ball-seal oil nipples? If so, which model is best?

Thread: Garryflex Blocks
01/08/2019 13:24:12

You could also look for York abrasive blocks - same thing but different maker. Cromwell tools have them for £4.40 including VAT. Other suppliers too.

Thread: Multi faceted drill bits - really necessary?
03/07/2019 09:22:27

Not sure if it counts as advertising - in which case i'm sure mods will remove, but there is a recent book by Jorg Hugel called Drill Sharpening. It covers all the details of setting angles for cone and four facet drills in great detail and has a CD of spreadheets which let you see the effects of changing setting parameters for yourself. It's only available from SMEE and all profits go to the Society. Not for the mathematically faint heated. A message to the SMEE secretary via the web site will put you in contact.

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