Member postings for John Fielding

Hi Brian,

Yes ATF is the stuff used in power steering and automatic gear boxes in automobiles. And there are several grades of ATF, mineral oil based and true synthetic. I keep it not because I have car which needs it but for pumped cooling systems on our radio telescopes. Mixed 10% with paraffin it lubricates the high pressure scroll pumps inner moving parts well which use the paraffin as a thermal transfer fluid.

Lovely stuff and it withstands up to +400C temperatures! Even makes a good substitute for steam oil in some applications. Readily available in small quantities from motor factors or garages.

Hi Brian,

I wouldn't have thought one necessary for something that small. Look at the Mamod steam engines which use a similar size bore, no rings ever used. They used brass for the piston and liner and apart from the occasional drop of oil when starting would run for years on and off with very little wear. Brass on brass is not a good combination but the choice was driven by cost. The piston and bore were over time burnished to a high polish and the friction was close to zero. As I mentioned earlier, friction in small engines is a major problem. If fitting a ring increases the load significantly then the poor thing is gutless.

If you put a tiny groove, say 1.5mm wide and about 0.5mm deep it will form a labyrinth seal which will be a bit better, it will tend to hold a little oil and condensate etc, but you would be hard pressed to measure the difference. The little loss of piston surface area means the friction reduces a tad but it is so small it is insignificant.

In model IC engines of the compression ignition and glow plug variety very few used rings and the piston speeds of those engines were very high compared to a steam engine. As long as the bore and piston are finished to a good polish then the friction will be low and running improves the surface finish even more. Cast iron when well polished with running has a glass hard surface, but it also has millions of tiny inclusions which hold graphite and the odd bit of oil or condensate, meaning the friction is very low. Bronze and gunmetal don't have this benefit and any loss of lubricant can make them seize suddenly when the oil film is lost.

The real reason why piston rings are fitted to motor car engines using a cast iron liner or block is because of the piston material. Before WW1 when WO Bentley experimented with light alloy pistons in his aero engines all engines used either cast iron or steel pistons. Now steel and cast iron have very similar rates of expansion. If the piston and liner are cast iron then the expansion is exactly the same and the clearance between the two is virtually constant. Steel is very close to cast iron, steel is simply iron with a lot less carbon, so you would expect them to be similar. But aluminium alloy pistons expand at almost the twice the rate as cast iron. So when the engine is cold it rattles around in the bore, but when up to working temperature it closes up the clearance. This looseness causes a knocking noise when cold called "Piston Slap" as the piston is slapping on the bore as it goes up and down when cold. If they overheat then they go tight and they can seize. To allow the alloy piston to change in diameter but still maintain a good gas seal you need another mechanism, ie piston rings made of cast iron. Very few engines used piston rings until about the 1860s, before that they simply relied on a good fit. Early Newcomen engines used a grooved piston with "junk rope" seals soaked in water on the wooden piston. But in those days they couldn't machine cylinders, they were used as cast.

I think one thing we can all learn from this saga is that although one purchases a reputable brand name in good faith, there will always be Monday Morning cars leaving the factory. Agreed it should have been picked up before it left the factory and the selling agent also should have done a full Pre Delivery Inspection, but sometimes things slip through the cracks.

One of the problems is the use of rust preservative gels and waxes the manufacturers use to coat the machines to prevent corrosion during shipping. This needs to be carefully removed before a slide can be assessed for correct adjustment. Hell, on my Taiwanese mill/drill I bought over 25 years ago I am still finding the odd bit here and there when I take a part off the machine. How one is supposed to check slide adjustment when it is gummed up with wax eludes me! So the selling agent probably is limited in what they can and cannot do to check a machine is fit for use. And again a raw beginner isn't expected to know all the tricks someone with years of experience would have, so things do sometimes go pear shaped.

Many years ago I had a friend with a well known 4x4 vehicle which developed an intermittent clanking noise in the rear diff. Despite all attempts to find the cause it came and went erratically. Finally decided to pull the diff out of the housing and inspect. Problem solved, in the bottom of the diff casing was the remains of a 1/4-inch drill spiral bit. It had apparently broken off when the diff casing was drilled in the factory and occasionally would be thrown up from the bottom into the gears. Three chipped teeth on the diff meant an expensive repair job.

I bought a Taiwanese mill/drill machine a while back, about 25 years actually. It has metric dials and it is claimed to be a metric machine. Well, it isn't metric at all.

Every single screw is imperial including the lead screws are 10tpi. One rev of the handle is supposed to give 2.5mm movement. It gives 2.54mm ie 0.1 inch. Thinking something was odd I measured the lead screw pitch and sure enough it is exactly 10tpi.

The table locking screws are UNC and the others are Whitworth.  Actually a good choice as metric threads in cast iron isn't a good idea as the pitch and thread depth is not suitable for these applications.

Edited By John Fielding on 25/03/2016 08:07:43

Hi Rufus,

I beg to differ!

Plastics need razor sharp tools to work satisfactorily and they produce a lot of stringy swarf which makes seeing what is happening frustrating. Some types are also a pig to hold firmly, like trying to hold a lump of jelly!

For learning I would second the others, go and have a rummage through the off cut bins and find some free cutting BMS. Ali as mentioned can weld to the tool tip and then it just becomes impossible to cut well.

Instead of metal try machining some wood, say a few inches off a broom handle, it cost almost nothing and will give you a start before attempting metal. You won't get a good finish but you also won't break the tool if it digs in!

Hi Lee,

Vesconite isn't new it has been around for yonks! The problem is it is one of the best kept secrets in the industry.

I have been using Vesconite for more than 30 years and have used it all over the place. We even used it for clapper bushes on the church bells to replace the ligmun vitae bushes installed in 1920 when the bells were made by Taylors Bell Foundry in Loughborough.

It is a South African product and widely used in the mining and earth moving industry. It outlast bronze about 5:1 under these arduous conditions, and a fraction of the cost. Also widely used in ships stern bushes, it is self lubricating but water helps. Unlike nylon it doesn't swell to any great extent and has a secret ingredient similar to graphite, but they won't tell us exactly what it is!

I wouldn't recommend Vesconite for a headstock bearing, it is slightly pliable, which is great for shackle pins bushes etc but the small amount of sqidgy movement isn't what you would want for a lathe spindle.

Yes Hopper is correct, sticky plunger due to the oil turning to varnish. My old Mercer DTI does that if not used for a long time. I put a few drops of lacquer thinners or benzene on the plunger and hold it so the liquid runs into the plunger bush. A few strokes pushing it in and pulling it out sorts out the problem, until the next time! A drop of paraffin with 10% ATF dissolved in it is a good lubricant.

The use of O rings in square cut grooves as used for cast iron rings is a poor solution. O rings are meant to fit into semicircular grooves so they can roll as the piston slides in the cylinder. A square groove means the ring bunches up against a flat surface and it doesn't roll but gets squeezed out into closer contact with the bore and high wear rates occur. If there are ports in the liner then it gets the bacon slicer treatment as it gets shaved on every stroke!

I have used PTFE square rings, Vesconite rings, bronze rings, dural rings, mild steel and cast iron rings with varying degrees of success. If I had the choice then it would be either bronze or mild steel in a cast iron sleeve liner. For a gunmetal or bronze liner then CI or mild steel is the best, but my 3 1/2" Netta has dural rings and they work fine. Even the D-slide valves are dural and they show almost zero wear if the lubrication is up to scratch.

In a mechanical engineering textbook I read that for steam engines operating at low pressure - ie below 250psi - then pistons with NO rings have very little leakage compared to ones with rings. In fact no grooves and a plain piston works perfectly well as long as the piston fit is correct. Many model aero engines of the compression ignition types never had rings fitted and the combustion pressure in that sort of engine is ten times or more of a steam engine. Piston compressors in fridges similarly have no rings on the pistons.

In my experiments I found that a groove in the piston without a ring works only slightly less well than a piston with a ring, it is a labyrinth seal, same as a piston with a ring. The major difference is in the friction, the piston with a ring has considerably more friction and friction in small engines robs power.

In steam engines the condensate which forms in the bore is an adequate piston to liner lubricant and seal when cast iron is used.

Look at the piston in a Crosby Indicator to see how well it seals, it has a single groove with no ring and it seals perfectly! The condensate fills up the groove and acts like a flexible ring. The friction is virtually zero!

Hi Peter,

Is that the same stuff as Mazak?

Hi Chris,

Welcome aboard, sound like you have acquired some nice bits of kit there. Of course one thing you won't need reminding of with your wood working experience - keep your fingers out of the nasty bits!

Keep us updated on your progress.

Perhaps Matthew could be a bit more specific as to what "soft" refers to?

As a few have mentioned aluminium can be regarded as soft, but some ali alloys are definitely not soft! Same goes for steel, some are easier to machine, but not soft in the normal understanding of the word.

So Matthew could you be a little more specific?

Congratulations!

Looks like a good piece of kit to have. If the original pictures of the miller are anything to go by then the table looked in excellent condition. No obvious dings or other damage, so it has been well looked after. Things like slideways etc can always be fettled, but those generation of machines were built to last. As long as no cracks etc then all it should need is some TLC and it will run for another 50 or so years!

How about "Caveat Emptor" !!

A classic example involved the Brussels Parliament deeming that only metric threads would be legal tender. This caused a huge argument and much taking of sides. The NATO standards for all radio frequency connectors all use imperial threads. When NATO sat down and worked out how much it would cost to replace every rf connector and mating connector it ran into billions of $. The fact that no equivalent metric thread connectors existed and would have to be designed and certified apparently was unknown to the Brussels politicians! Even the Russian equivalent rf connectors are direct copies of the NATO pattern and was due to the fact that during WW2 a lot of American and British radio and radar equipment was given to the Russians. As they became the accepted pattern throughout the world there was no sane reason to change.

Aircraft bolts etc are usually imperial for the simple reason they are stronger.

The very first metric fastener system used in Britain was the BA, introduced in 1884, which is a true metric system, but due to the average mechanical engineer not being au fait with the metric system they were specified in imperial dimensions. The largest BA thread is the 0BA being 6mm in diameter and a thread pitch of 1mm, the same as a metric coarse M6 today. The difference was the metric thread angle is 60-degrees whereas the BA is 47 1/2-degrees. BA threads were based on a Swiss pattern adopted earlier by instrument makers where small diameter fasteners were needed.

As the thread (pun intended) has drifted off into thread length engagement etc it is useful to look at the different thread types used in different materials.

For example, automotive applications where a cylinder head bolt or stud is inserted into an alloy casting. Metric threads are not really suitable where high tensile loads are required, but UNC and Whitworth are superior. I once had a discussion with one of our young mechanical engineering guys who insisted his VW car had metric threads throughout. I told him he was wrong, there are plenty of non-metric fasteners used on those models. I told him to pull out a cylinder head stud and measure it. Sure enough it was UNC but the top bit where the nut screwed on was metric fine.

Another screw type on cars which is not metric is self tapping screws, as far as I am aware there are no metric versions of these.

Hi Ian SC,

That's nothing!

When I was an appie we had a gorilla in the workshop who one day broke a 1 1/2-inch Whitworth die in a handheld die stocks. When the others asked how managed it he sheepishly replied it was a bit tight going on and so he used 4-pound hammer to hit the end of the die stock handle. Needless to say he had to pay for the die and the bench vice which broke under the punishment!

Hi Robert,

The Myford should be able to machine those bits with a bit of faffing around. The wheels although apparently daunting would fit on the face plate and as the gap is quite generous on the Myford could be maybe tackle 10-inch diameter at a pinch. All you need is to set them up to run fairly true with some bolts through the spokes and then centre drill and ream to size. Hell LBSC covered this umpteen times in his words and music. It seems to be a lost art today.

Same goes for the cylinders. Fettle them a bit to remove the blobs and casting flashes with a file, or if lazy use a small angle grinder to carefully knock the bits off which are unwanted, and then bolt it onto the cross slide and stick a between centres boring bar though the core hole and away you go. Use the self act on the leadscrew to get a nice slow traverse and Roberts you proverbial family member!

But I agree that finding an engineering works to do the machining might be a challenge and to find one sympathetic and who isn't going to bugger up the job and cost you and arm and two legs today is more difficult. Rather get to know the local model engineering club, by that I mean join as a member and your small monetary investment annually will be well repaid for all the advice and help you will get. Six heads are better than one!

OK folks. It looks like one of the gadgets sold for sharpening wood saws. I have seen something similar, but woodworking isn't my cup of tea. The round bobbin goodie, which is double ended, is pressed by the knurled screw on the side to hold the saw blade with the teeth pointing upwards. The base was normally cast iron so it it doesn't tend to move around on the bench. The slot is wider than a handsaw because it could also be used for tenon saws which have the thicker spine of a folded over piece of channel section crimped onto the blade. I wonder if there is a makers name somewhere to confirm this ?

I think some folks are missing an important point regarding the differences between steel and copper for boilers. The need to make steel boiler shells thicker is not so much to do with the ultimate tensile strength but more to do with potential pitting and corrosion. Normally water treatment plants are required to ensure the water is of an acceptable standard and often chemicals are added to adjust the local water supply to that which will give the lowest corrosion.

The other point is the tensile strength of steel versus copper. Although for a given thickness of boiler shell wall thickness steel is better than copper the elastic limits are quite different. Steel has a lower ability to "swell" under pressure, which is good as it can withstand higher pressure than copper of the same wall thickness. But copper has a greater elastic limit and can balloon safely under high temperatures and to some extent return to its original form after an over pressure event. Steel on the other hand resists swelling better but once it reaches it ultimate limit tends to rupture.

Now there is also a huge difference between mild steel tube bought for structural and other uses and genuine steam pipe and boiler shell duty. Most steel pipes are rolled and seam welded, which is a potential weak point in the circumference when internal pressure is applied. Genuine boiler tubes and casings are seamless drawn and hence much more expensive. There are nowadays not many steel manufacturers who can supply genuine steam pipes and boiler shell material. I am only aware of one in Europe, in Germany, who can supply genuine steam boiler tubes etc. There may be more but I haven't come across them. I know for a fact that the locos down in the depot locally import their boiler tubes from Germany and they are ten times the cost of locally made welded seam tube.

Welding of pressure vessels is a highly skilled job and in this country (South Africa) may only be undertaken by government certified coded welders, who are few and far between with the necessary ticket. I have two friends who are coded welders, one has the top certification possible the other is one step below so he cannot tackle all the jobs and has to pass on them.

Steel when subjected to repetitive heating and cooling work hardens and stress fractures can appear, it needs to be a very special grade to withstand this arduous duty. Vickers Steel in the old days was the only British steel maker who could make the required plate and tubes. Riveted boiler construction obviates the need for welding but in some cases it cannot be avoided when repairs have to be made.

Lastly, as others have mentioned, copper will outlast steel in boiler applications by a large amount, so if you want to make it and forget it then copper is the way to go. Annual boiler tests will have in most cases to be done but a well constructed copper boiler should have no difficulty in lasting 30 years or more as long if it has been handled correctly and not allowed to run low on water.

My 2c worth!

Hi Jerry,

Thanks for your lucid answer. So it seems the textbook I read had the story correct. They do mention standard cups with calibrated holes.