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Member postings for Howard Lewis

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

Thread: I screwed up!
02/05/2016 20:39:41

My! You are scientific!

I just turned a bit of nylon to size and, typically, bashed it in with the hammer!

Also you have cleaned up everything.

The rollpin hole in mine had been drilled freehand, so pin, gear and shaft only lined up in one orientation.

Of course, when making the new shaft, I driiled the hole square on, so refitting the pin needed a bit more impact force (aka Hammer blows). If you use official spares, the gear will probably act as a guide, so that the holes are more likely to line up.

Like the new plumbing to feed oil everywhere that its needed. Not too much, or it will go everywhere that its not needed, but nothing will go rusty.

Having overcome the problems (self made) with the worm housing, and the time spent retightening the capscrews, blind, everything works as it should, possibly a little sweeter.

If the capscrews on the wormhousing do need tightening, a 5mm Allen key needs to be shortened by about 6mm at the business end, and the long end extended some 60mm or more,.so that although you can not see what you're doing, fingers are not against the bed and tilting the key. Just take a large dose of patience before attempting to tighten the screws, in situ. (You really don't have much option, unless you have the sort of luck that wins you first prize in a multi roll over lottery

So, if anyone else has mangled their BH600 or a lookalike, even someone as nervous as I , with Geoff's advice, can fix it.


Thread: Springs??
29/04/2016 23:02:03

The "unit of springiness" is known as the Spring rate. This is expressed as the force required to compress, or extend, the spring by a set unit of length, such a Pound per Inch, in old money., as as above.

Spring design is quite an art, and can be very frustrating. You design a spring to give the desired rate, and to fit into the space available, but then when you check the stress, it is excessive. So back to the drawing board! When you get the stress within limits, the wire size is likely to be such that the spring is coil bound before reaching the required travel!

You recalculate and everything is now fine, except for the spring rate! And so it goes on, until eventually, if you are lucky, all falls within limits. If not, think about changing the coil diameter or the space into which the spring needs to fit?


Thread: Carburettors!
29/04/2016 22:50:21

The carburretor has been described as a device to deliver an incorrect mixture at all engine speeds.

Fixed Jet

With a single jet, and fixed venturi, the fuel passing through the jet will only provide the correct air/fuel ratio at one engine speed. To expand this range, more sophisticated units effectively put the Main Jet out of circuit at small throttle openings, and take fuel through a smaller, Idling Jet. Again, this is not ideal, so arrangements are made for air to bleed into the fuel stream, to weaken it as the speed rises. The extra air to create the air/fuel emulsion is controlled by the Idling mixture Screw, (A needle valve actually). The idling system, usually delivers air beneath the throttle plate.

As the throttle opens and the air flow through the venturi increase, the main jet comes into play, but the air/fuel delivered is modified by the Compensating Jet, which can admit extra fuel to improve mixture strength at relatively low air flows. As the air flow increases, and the fuel delivery from the Main Jet increases the Compensating system decreases the fuel flow and can admit extra air to prevent the mixture becoming over rich.

Constant Vacuum/ Variable Venturi

The best known exponent is the S U. This uses the depression caused by the air flow through the variable venturi to lift a dual diameter piston which carries a tapered needle, (which is centred in a fixed fuel jet). As the air flow increases, the depression increases, because of a greater throttle opening, and or higher engine speed, so the piston rises, increasing the area of the venturi, and decreasing the depression acting on the jet. To compensate for this, the tapered needle , being higher, increases the area through which fuel can flow. By carefully matching the profile of the needle to the air flow of that particular engine configuration, the air/fuel mixture delivered to the engine can be fairly closely controlled. This has the advantage of providing minimal restriction to air flow, and therefore volumetric efficiency at high engine speeds and large throttle openings.

At lower speeds, the smaller area venturi improves fuel atomisation, and hence mixture distribution, so giving better low speed torque.

The Stromberg version of this, replaces the larger diameter of the piston by a "rubber" diaphragm, which has the advantage of providing an air tight seal; but the disadvantage of having a spring rate, so that the resistance to lifting increases as the diaphragm and smaller piston lift.

Ford also produced a variation on this theme, using a pivoted sector to move the needle in and out of the jet.

In every case, the profile of the needle has to be matched to the particular engine and its air flow

Twin choke, progressive, carburettors are an attempt for fixed jet units to match the characteristics of the constant vacuum units. Some use a mechanical linkage from the primary throttle to open the secondary throttle more rapidly as the primary reaches a certain opening. Other versions, use a vacuum diaphragm to open the secondary throttle.

The opening points need to be carefully set to ensure as smooth a changeover as possible and to optimise performance..

So taking a carb, off, say, a 3.4 litre Jaguar and bolting it straight onto a 1.8 Litre BMC B series will not provide optimum performance or economy. With a suitably matched needle, the performance can be improved..

In the same way, fitting a pair of big bore Twin Choke Webers on to a 850 Reliant engine will improve breathing, but the jets will have to changed to match the air flow characteristics of the smaller engine.

Changing the camshaft to one giving different valve lift, or events, will call for ta change of jets.

A carburettor which is badly matched to the engine will not provide smooth driveability, torque, power, or economy. And, it may make the engine an absolute pig to cold start!

Electronic Engine management, controlling fuel delivery, from the Injectors, and Ignition Timing, gives much better control since the fuel delivery can be adjusted to the required level by feedback signals from the Lambda sensor, which should optimise all engine settings, for emissions and power output.


Thread: What has happened to this die to cause this ?
29/04/2016 21:56:06

The M3 thread is only 0.25mm deep, (Tapping size for M3 x 0.5 is 2.5mm) that is most unlikely to withstand the force needed to drag the Tailstock along the bed. So even with a new die, do use a Tailstock Die Holder, and lubrication. The only force imposed on the freshly cut thread will be that needed to slide the Die Holder along the Arbor, (which will be absolutely minimal).

Cutting a thread with a Die, in one pass, you are removing, relatively, a lot of metal. If you were cutting the thread with a single point tool, you would use several passes, with increasing depth of cut.

Using a handheld Die Holder, and resisting rotation by resting against the Bed, or the Toolpost, may tend to lever the die off the lathe axis, which will not improve the cut at all. The Arbor, mentioned above, allows the Die to pick up and follow the workpiece, but keeps it more closely aligned.


Thread: Tuning
29/04/2016 21:36:01

Production machines are mass produced, and whilst compromising various parameters. it is surprising how much of an improvement can be made by just setting up the engine to specification.

(For many shops, "near enough" is often "good enough"; and some can't even manage that, making quite incorrect settings. You wonder if those folk could diagnose a flat tyre!)

An easy "improvement" is to match the ports, manifolds, and joints so that there is little or no step between them. Be careful in changing the shape of the ports, sometimes an apparent restriction actually improves the flow and Turbulence into the cylinder.

Sometimes, a small change to the shape of the combustion chamber can increase power.

It used to said that a prewar tuner of Rileys, Freddy Dixon, could add 5 mph to the top speed of a car just by stripping and rebuilding the rear axle. he was, effectively, "Blueprinting" the components. He was also an exponent of inlet and exhaust tuning

On naturally aspirated engines, improvements to the exhaust manifolding, will allow the use of a "tuned"system, with bigger advantage, if the pipework is low back pressure (ie Straight Through silencer rather than baffled. This will remove the high frequencies, leaving the pleasant low notes).

But be warned, "Tha gets owt for nowt", tuning the exhaust or inlet system to get ram at one speed, may well damage performance at lower, often half of that, speed.

The same can be said of changing valve events by altering the camshaft. There may be more power at higher revs, but a lot less torque at low speeds. If the power band is very narrow, you will need a lot of gear ratios to keep it on songl

And some engines need some backpressure, especially two strokes. Otherwise you can have worse performance and higher fuel consumption! In an extreme case the fuel carried into the exhaust could eventually explode, and blow apart the exhaust system

Also, tuning the exhaust system may well need revised ignition timing to maximise performance.

Avoid over advancing, as this will raise rates of pressure rise, and probably peak cylinder pressures. Peak maybe just a short "spike" which gives little extra power but can play havoc with gaskets, pistons, and bearings, and in the worst case the crankshaft or crankcase!

Enzo Ferrari once said that the ideally designed race car would fall apart as it crossed the finishing line; but I don't think that we are interested in going that close to the limits.

Also, remember that higher power has to be transmitted to the road, so the gearbox and final drive need to be considered. And having got the machine upto a higher speed, it has to be able to stop, handle and to take corners, so don't concentrate on the engine in total isolation; you are super tuning the complete vehicle.

In every case, you are balancing output against reliability and durability. The original VW Beetle engine was very reliable, (it was virtually impossible to over drive it), but as the capacity and power was increased reliability decreased. Some folk advised that to prevent valve failures, and extensive engine damage, the 1303 should have new exhaust valves fitted every 30, 000 miles. Apparently, the quickest way to break a crank was to increase the maximum engine speed. In my opinion, that was NOT reliable

Upspeeding any engine will decrease the reliability and durability of components, possibly just by extending the running range into the region where components go into resonance, and overstress themselves.


Thread: What has happened to this die to cause this ?
29/04/2016 14:50:32

All the foregoing advice is good. To which I would add,:

Chamfer the end of the rod, to help the die to start cutting.

Use lubricant (Rocol / Trefolex / Bacon Fat - Don't laugh, it works very well!)

Use a Tailstock Die Holder (Make one?) You are asking a lot to ask a M3 thread to drag the Tailstock along the bed. AND the Drill Chuck does not allow the Die to float to pick the rod.. The Tailstock Die Holders will be a relatively slack fit on the Arbor for just that reason.

Commercial Tailstock Die Holders usually have the ability to accept a variety of sizes of Dies.

I made myself a Sliding Tap Holder, to fit the Arbor for the Die Holder, for Tapping. Again, a slack fit to ease picking up the drilling. (Mine uses ER25 Collets).

Making your own tools is often time well spent, since you can make exactly what you want, you learn, and save money, (and in view of your location, time).

Hope that you get things sorted.


Thread: Herbert Cridan lathe
20/04/2016 20:49:36

When I joined Rolls Royce at the Sentinel Works, Shrewsbury, in 1958, CriDans (two models) were still being made there. (A left over contract from the Sentinel ownership days). With the tool controlled by hand stoned cams, they would cut a 1" Whitworth thread, 10 inches long in little more than a minute or so. Machines on test were an obligatory stop when we took visitors around the factory. The swarf came off as a continuous blue wire, until the cam caused the tool to withdraw and return to the starting point for another cut.

They were a special purpose machine, unsuited for general turning work.

The machine tool expertise was then used by R-R to produce special purpose machines for producing jet engine parts.


Thread: Bridges electric drill refurb- thread issue
20/04/2016 20:19:06

Since Bridges is/was an American manufacturer, I would put my money on 8 x 32 UNC.

MANY years ago, pre WW2, Morris used Hotchkiss engines, so they were metric.

The BMC A series engine rocker adjustment screws were 1/8 BSP, when the rest of the car used Unified threads. The earlier side valve engined Morris Minors, used 7/16 BSF wheel bolts. The BMC powered ones were Unified. The handbook made a point of the identification marks.

Pre WW2, C.A.V. started by making Bosch Fuel Injection Equipment, under licence, so metric dimensions were the standard. In the 50s, they bought the licence from Hartford Machine Screw to make the Roosa Master pump as the DPA, (Distributor Pump A) all drawings had to be Metric, but still use Unified threads. So the American Imperial dimensions became odd Metric ones, (1/4 inch became 6.354mm , and so on). BUT, the threads for the Injection Pipes were, like all others, Metric, (often a 14mm  fine thread).

Certain Bristol buses were powered by Gardner engines which were resolutely Imperial, BSF and BSW.

The Bell Housing was retained by 9 off 3/8 BSF bolts and three 3/8 UNF studs.  The Clutch went one better, 12 off 3/8 BSF bolts, to hold it to the Flywheel, but with 5/8 A/F heads!

Leyland drew a line, and all new designs changed to Unified threads, but the engines, gearboxes, and certain other parts were earlier designs, carried over onto the new chassis. So a fitter needed two toolkits to be certain.  Then came the 500 Series engine which was Metric, imagine the confusion when working on the "Unified" chassis, powered by the "Metric" engine, and containing original Whit standard components!

Until recently, engines which had their roots in Imperial sizes were made to Metric drawings, (so few round figures there!) but on engines which changed to use metric fasteners in most places, certain critical threads remained Imperial, because of the massive cost of converting the tightening tooling to suit Metric fasteners. It was only when the new Designs evolved into totally metric ones, requiring new jigs, fixtures and tooling that they became truly Metric.

Remember, that the Continent use threads which they call "Gas", which are actually British Standard Pipe; Whit form threads and all!

My lathe uses metric threads everywhere, except on the Mandrel, that is 2.25 inch x 8 tpi Whit form.

My Mill/Drill with Imperial leadscrews, has a mixture of Metric and Whitworth threads; the latter for the more important ones, funnily enough!

Standardisation, where art thou?


Edited By Howard Lewis on 20/04/2016 20:30:59

Edited By Howard Lewis on 20/04/2016 20:35:15

Thread: Stripped T bolt
20/04/2016 19:53:46

Generally, I am sceptical about oriental materials. They do seem to have a bit of a blind spot over fit and concentricity of threads.

The M8 capscrews that secured my Top Slide were pretty soft and soon replaced by some decent ones, which have lasted well enough still to be in use after nearly ten years, and likely for many more.

I am more likely to be the first to fail!

The suggestion to modify a High Tensile Bolt / Setscrew is a good one, but use good quality nuts with them.

If you can make a "jury" rig to use the lathe, make a neat, and consistent, job of the new bolts by turning, rather than an angle grinder, to maximise the material in the head, (particularly thickness, you don't want it flexing when tightened, and then slackening off; that could be expensive at worst, embarrassing at least).


Thread: Hot workshop
20/04/2016 19:34:52

If possible, insulate the roof and walls. My shop has a black rubber roof, over 12mm ply, 50mm Glassfibre and 12mm ply. (Walls ditto, but 19mm external cladding, no windows). Keeps reasonably warm in winter, (needs minimal heating) and reasonably cool in summer Location: East Anglia, UK.


Thread: C2/Warco lathe Motor Problems
16/04/2016 18:07:00

Am not an expert, (Far from it) but as I understand it, the motor for the C2 is a brushed 300 watt unit, with Pulse Width Modulated speed control. From what I have read, the FETs are likely to have failed.

A friend has just acquired a lathe in a similar condition. Our estimate is that spares to return it to working order are likely to cost just under £200, based on Arc Euro prices.

If you want more info, contact Ketan, he is most helpful, and has provided a lot of info about these machines on other threads.


Thread: Inverter Tripping RCD
09/04/2016 16:13:28

For what its worth.

Our house wiring is still on hard wired fuses. (we avoid blowing them!)

The workshop is fed through an RCD from a 13 Amp socket. The shop is wired with a ringmain, and the VFD is fed through a filtered socket on that ring. Since installation in late 2003, the RCD has never tripped, (My problem is stopping SHMBO switching off , by mistake, the socket that feeds it) nor is any interference fed back into the house wiring, judged by the behaviour of TVs and radios.


Thread: Automotive Automatic Gearbox
09/04/2016 16:01:33

In the old days, trawler engines used a drip feed of water into the induction, when operating at high loads.

Possibly, humidity in the air,(moisture) evaporates in the induction system and by cooling increases air density, and so the mass of oxygen available for combustion. A sort of cheap internal charge cooling. But overdone, can result in water finding its way into the sump and emulsifying the oil.

The Full Load torque curve of a diesel engine is usually mirrored by the Specific Fuel Consumption curve, so the best speed for economy is often Peak Torque speed. Possibly this is the engine speed for maximum volumetric efficiency. Road load operation will mean that the engine is unlikely to be on full load, unless on a hill with a convenient gradient, but can still be running at the speed for optimum volumetric efficiency.

Mechanically governed Diesel engines, having higher compression ratio and miminmal induction restriction were more economical than a petrol engine, plus the fact that fuel was cut off as soon as the engine speed exceeded that selected by the position of the throttle lever.

A Diesel engine with a vacuum governor is a slightly different kettle of fish. It still cuts off fuel on the overrun, and engine brakes because of the induction restriction, but gains efficiency from having less variation in temperature at the Inlet Valve.

Possibly, the best point at which to change up is just about peak torque speed.

Certainly, on a hill hanging on below peak torque is likely to result in a rapid loss of engine speed.

Modern petrol engines, with electronic control, now do the same thing, giving improved fuel consumption. (A closed throttle on a carburetted engine applies maximum vacuum to the idling system and pulls fuel through giving a richer than normal mixture. Despite being a lot heavier, my 2005 1300 petrol gives a fuel consumption nearly 50% better than a 1977 1650 with a carburettor, to prove that point. Having a higher Compression Ratio, and D O H C rather than push rod valve operation helps, despite the pumping losses imposed by the emission control bits.


Thread: Free hobbed worm wheel
09/04/2016 15:16:24

Beware of labouring under delusions of accuracy!

I do not believe Model Engineers who claim to be able to work consistently within "a tenth" or "a micron". Very many commercial shops would not make that claim. A Micron is the sort of clearance found in the Fuel Injection Systems of Diesel engines, often the result of a lapping together the two components.

To give a sense of proportion, a human hair is about 125 microns in diameter, a tenth of a "thou" is 2.5 microns.

We are making one or two offs, not spares for a Lunar Rover.

As JS says, accurate measurement can only be made under standard conditions of temperature and humidity, which are the conditions in the Standards Room of larger commercial engineering undertakings. The Calibration Room is even more closely controlled. In neither room will anything be measured until it has "soaked" to the ambient conditions for at least twenty four hours.

After all, the Calibration Room is where the measuring instruments and slip gauges are themselves checked for accuracy, (and slip gauges have to be accurate to a millionth of an inch). The instruments, there, will very likely be traceable back to a National Standard, such as those held at the N P L at Teddington in UK.

To minimise the effects of expansion, resulting from heat from the hand, micrometers now have insulating pads on the frame. Many measuring instruments are marked "at 68F" or "at 20C" to signify that they are only accurate at that temperature.

In industry, ball and roller bearings are placed on a hot plate for a time, before being placed on the shaft.

If you pick up an automotive piston and immediately try to fit the gudgeon pin, the chances are that it will not enter. Put down the pin and hold the piston in the hand for a few minutes. Then, the pin will be an easy sliding fit.

Gear trains often contain a "hunting tooth", to ensure that the same two teeth only mesh very intermittently, to reduce wear. Even with precision ground gear teeth, backlash and eccentricity will reduce accuracy and repeatability.

In our non climate controlled workshops, we are not going to match the end product of a heavyweight machine very carefully manufactured and assembled under carefully controlled conditions, and costing many more times than our lightweight, mass produced machines of lesser precision.


Thread: Gnome event in Leeds
09/04/2016 12:49:37

The headline made me think that it was a reunion for owners of old photographic enlargers! (AGE showing!)


Edited By Howard Lewis on 09/04/2016 12:49:54

Thread: Special ER Collets
09/04/2016 12:47:25


Length/bore ratio

Just think about pulling sideways on the top of a 1 metre post that is 10cm into the ground. It will wobble!

If you are lucky, the short work won't come out as you cut!


Thread: which lathe
09/04/2016 12:42:29

British made lathes are good, but are probably now so old as to be worn, in many cases, so do check carefully..

Oriental have had quality problems, but later ones seem to be improved. If you can get a Warco BH600, or Chester Craftsman, they are not too bad. Pretty rigid, will swing 12" , (18 in the Gap), Belt driven head, so not too noisy, Norton Gearbox, and the bed is Induction hardened.

Spares are available, if you need them.

The BH600 (There was also a long bed BH900) came in either Imperial or Metric form, the Craftsman, I think, was/is only metric. My Engineers ToolRoom BL12/24 (now 12 years old, not a Tool Room lathe, but still pretty accurate) is very similar, being essentially Metric, but with dual dials. They weigh about 300Kg, and should come with steadies, faceplate and 3 and 4 jaw chucks.

Quite a few lathes, especially the mini ones, come from the SEIG factory, with different livery, or detailed specifications, (Clarke, Axminster, Chester spring to mind).

If you buy new, you have every right to expect it to be right, (if it isn't ; the supplier should put it right / replace / refund under warranty or common law Sale of Goods Act) but buying a secondhand machine, you need to check for wear, signs of abuse, or bodged "repairs".

When a Rodney Milling Attachment was mounted on my ML7, the lack of rigidity became apparent. Maybe I was a bit heavy handed, but two of us could lift the lathe with ease, so it was a lot lighter.

You will always find a job that is too big for whatever you have. But, as I was told once, "You can do small work on a big lathe, but not the other way round"

Hope that this is some help


Thread: David Piddington's Vise
08/04/2016 10:43:00

Some years ago, whilst visiting Pro Machine Tools, at Barnack, I saw what I call an "Infinite Vice" on an Austrian Milling machine.

After returning home, I made one using three pieces of steel, about 1" square (25mm for metricians)

Two pieces had side cheeks (1/4" or 6mm plate) attached to make a snug fit on the sides of the table, and keep things square, drilled and counterbored to take two M8 capscrews going into Tee nuts, to clamp down. One of these, the moving jaw, had a centrally placed dimple made with a small centre drill.

The third piece had the Tee nut facility, but carried, centrally, a 1/2" UNF setscrew with a small ball bearing in the end, to act as the pressure screw. (Any fine thread will suffice. Metric coarse threads are not ideal for use as pressure screws)

In use, the "plain" one was secured to one end of the table, with the work against it, and the second dimpled one brought up to it, but not clamped down until the third piece had been clamped down and the pressure screw tightened onto the moving jaw. Finally, the the second, moving jaw, was clamped using the M8 capscrews and tee nuts.

It did not take long to make, and although not often used, is invaluable when needed.


Thread: Air Compressor recommendation?
08/04/2016 10:13:46

Direct drive air compressors are noisy. Belt driven compressors are quieter, because the compressor runs at a lower speed. Diaphragm compressors are quietest of all, which is why Dentists use them to power their drills.

Mine are direct drive, one (Branded S I F) is claimed to have a 3hp motor, but starts and runs off a 13 Amp socket, without blowing the fuse.

Before putting it into use, I removed the plugs on the reservoir, and sprayed Waxoyl through it, to reduce the risk of rusting. (Catch 22? - NO, I used the HPC for this)

Another, the HPC with a smaller motor, capable of running off a 5 Amp supply, is still functioning happily after more than twenty years.

After use, I ALWAYS drain out the condensate, and leave the drain open. (Recommended by the supplier - a local compressed air equipment specialist). This means that the motors always start up on No Load, except when the pressure falls to the level where the pressure switch restarts the motor. The HPC has a valve on the compressor head to allow an unloaded start, even if the reservoir is pressurised.

At least, any moisture remaining after drain down has a chance to get away.

Don't be surprised if the drain stops after a while, and then restarts. (You are quite likely to see "steam" coming from the valve) As the air expands, it cools; often to the point where it freezes the condsensate. The big 200 Gallon (909 Litre) reservoir, in my bus garage, used to freeze repeatedly during drain down. We used to open the drain tap, and go for a cup of tea, while it spat lumps of ice around!

Both compressors have condensate filters fitted between between the outlet and the delivery connections for the flexible hoses. It is surprising how much water accumulates there during use, and needs to be drained out.


Must learn to check for typos BEFORE posting!


Edited By Howard Lewis on 08/04/2016 10:16:57

Thread: hi new here from ely
07/04/2016 17:24:34

Welcome! You'll find plenty of good advice and info on this forum.

I'm a member of the Peterborough Society of Model Engineers. We cater for almost every interest, as we demonstrated at the Spalding M E Show for the last two years, and will again this year.

Come and have a look at us, next meeting is Monday 18th April.


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