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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: Milling on a Lathe with a Vertical Slide
28/07/2021 06:29:42

You are making progress!

There is light at the end of the tunnel which will bring great satisfaction when everything goes to gether and functions as intended.

Keep at it!

Howard

Thread: Tapers
27/07/2021 19:15:42

You do wonder why different manufacturers deem, or deemed, it necessary to employ different tapers.

I have drill chucks with Jacobs, Jarno, and Morse tapers in the body, Cannot remember if there are any with B series tapers, would not be surprising if there were one or two!

It would be more understandable if there was am aftermarket to be captured, but drill chuck arbors tend to be "fit and forget" items rather than high volume turnover parts, like car brake pads.

Maybe it is a desire to be exclusive. Elsewhere we have Morse, B & S, R8, and International tapers, and the collets with Morse, 5C, ER and Autolock, to name some. Each with its own specific advantage, in grip, or ease of breaking that grip.

Some have been produced by a specific manufacturer, for a particular purpose, at that time, whether need or exclusivity, just like screw threads, or gears!..

Howard

Thread: To paint, or nor to paint.
27/07/2021 18:48:03

A friend won a Gold Medal and an other very well respected trohy with his model

But you should have seen what it looked like after being steamed, fortunately unpainted..

The superb paint job covered the singe marks, and went a long way towards winning the prizes.

If you don't mind an unpainted model acquiring any sort of patina, leave "as is"

So the choice is entirely yours. If others don't approve, TOUGH.

Your model, your choice.

Howard

Thread: Valve Run Out Gauge
27/07/2021 18:37:47

I mmade a bvad approximation that a valve would be open for about 180m degrees.

The longer the open period, the less time spent on the seat to rid the heat collected, which makes life very difficult for the Exhaust. The Inlet, on a naturally aspirated engine does pass ambient air (If it has not acquired too much heat during passage into the cylinder through the induction tract.

On a turbocharged and intercooled engine, the charge is probably at 150'C by the time that it reaches the valve!

But this is relatively cool compared to exhaust temperatures of 650'C and upwards under full load rated speed conditions.. And these are for commercial engines, not tuned for racing or rallying, where specific outputs can be doubled, although at the expense of life probably.

(Ferrari's ideal racing would, he said, disintegrate as it passed the chequered flag! ).

And all valves expose a large area, to collect the head, to heat during combustion, so cooling is importance.

And who knows what shape the valve seat takes under F L R S conditions!

Howard

Thread: Help with surface plates in Derby
27/07/2021 18:21:59

There is a sequence for lapping a surface plate absolutely flat, but involves lapping two others together and using the result to lap the final one.

Very much an iterative process, obtaining an improvement at every stage.

So neither quick nor easy.!

Full marks for aiming for the best that you can get with the facilities available. Go for it.

A machine tool needs to more accurate / precise than the work that it is required to produce. Tolerances and clearances, may be minute, but they build up into quite sizeable figures. 0.0005 on a shaft and 0.0005 on the bush in which it runs will give 0.001 clearance. Do that on the location of the bush in the Headstock, and on the Headstock / Bed locations and things start to look less than precise!

Howard

Thread: New Chuck won’t screw on
27/07/2021 18:11:45

Brian,

The "standard" Myford Mandrel thread is 12 tpi BUT 55 degree WHIT form not 60 degree Unified .

The 12 tpi Whit form dates back to late ML lathes manufactured in the late 1940s (The early MLs used 7/8 x 9 , 7/8 BSW, before moving to 12 tpi, The Series 7 launched in 1947 used 1 1/8 x 121 tpi. )

Even the Taiwanese lathes available until, at least 2004 used Whit form threads for their chucks, (Mine is 2 1/4 x 8 tpi WHIT form! )

Howard

Thread: Running needle roller bearings
27/07/2021 18:01:02

If the shaft bis soft, it is possible that the rollers will brinell the shaft, when subjected to a repeated cyclic load.

In one instance the ratio between shaft diameter and roller diameter meant that the cyclic load was applied in almost exactly the same point every time.. The shaft suffered, and the design had to be altered.

Howard

Thread: Valve Run Out Gauge
27/07/2021 17:21:48

Often, in industry, to avoid having to lap valve to seat, there is a slight, about 1/2 degree, difference between valve and seat angles, to give a line contact for an initial seal.

Although this means that there is absolutely minimal area to conduct away heat while the valve is on the seat, the two hammer into greater contact, to provide the area for heat transfer and a longer leakage path.

At 4,000 rpm the valve spends very short periods of time on the seat anyway. About 1/4 of a millisecond each rev of a four cylinder four stroke!. So probably a lot of the heat is conducted away up the stem and into the guide. via any oil film. Maybe, the oil from the valve gear helps to cool the end of the stem.

Makes you realise that valves have a pretty tough life, and yet, thanks to the materials, survive for an INCREDIBLY long time..

Howard

Thread: More Q's about surface finish.
26/07/2021 09:11:26

Michael. I think that we both were cast in similar moulds!

But you will agree that once we get into the wavelengths of light, the units are physically VERY small.

Have you never been troubled by Newton's Rings in glass mounted slides?

Not even sure if we are actually differing, let alone disagreeing.

Howard

Thread: Myford Gear Spacers
26/07/2021 09:03:48

In this instance, the Myford lathes , and many others, were manufactured to Imperial dimensions, using Whitworth form threads for almost everything,.

In industry, Imperial spares and Taps and Dies were kept for repair and maintenance well into the 80s , because that what even fairly recent machine tools required.

In 1971, I was sent on a course dealing with the change over to Metric.

Changing a complete product over from Imperial to Metric dimensions is no mean undertaking.

I've seen it happen; new composite drawings with non integer metric dimensions alongside Imperial dimensions, replacing the original Imperial dimensioned ones, for every part, before the new product made to sensible Metric dimensions is introduced, having been made to the new Metric drawings.

And then there are the implications for the aftermarket and spares supply. Not unknown for components to be damaged, in the field, by trying to fit non matching components together...

Count up the number of individual components in your car engine,.

That means a new drawing, jigs, fixtures and tooling as well as measuring equipment needed for every single component..

Morris were not unused to Metric dimensions, having used Hotchkiss engines in the early 30s, although the rest of the car was Imperial..

IIRC the Morris Minor did not change from Whit form threads until the BMC A Series engine replaced the Morris side valve unit, in about 1954. This meant that even the wheel fixings had to be changed, with a service bulletin warning of dire consequences if the two standards were mixed..

This was one of the reasons for Unified hardware being marked to distinguish it from Whitworth form fastenings, with circles on nuts and nicks on the hexagons of bolts and setscrews, if identification was not forged into the heads.

The Bristol RE and VRT buses, of the late 60s and early 70s, were a fitter's nightmare. The chassis was to Unified standards, but the Gardner engine was still Whitworth.

Leyland had the same problem. The Leopard was to Unified standards, but incorporated some parts which dated from the Tiger Cub, or the PD3. The 0600 and 0680 engines were Whitworth standards, but chassis components were Unified. Sometimes it was uncertain which came from where. For instance Brake adjusters were interchangeable, but the adjuster hexagons were not!. So eventually, In service, it was possible to find a Whit hexagon on one wheel and a Unified on the other.

And when the Metric standard 500 Series engine was introduced onto the Leopard chassis, you can imagine the confusion!

Hence reluctance to change from one standard to another.

Howard

Thread: Valve Run Out Gauge
26/07/2021 08:19:19

If the guide is worn, the datum point will not be consistent, so the results are likely to vary every

Taking a ridiculously extreme example, using a 6 mm pilot in a 1/4" guide will never give consistent and repeatable readings!.

These devices were used to check freshly machined, and unworn components.

In high volume production, this is a means of checking that components have not been mislocated by swarf trapped under the component, or that the tooling or machine has not deteriorated.

Howard.

Thread: Myford Gear Spacers
26/07/2021 08:08:36

My comment was not meant to be snide.

In this case working to metric dimensions does not really matter.

In other cases where closer fits are required, working to metric units could cause problems, in having to work to minute portions of a millimetre.

The unit used is immaterial, just select what is easiest, and most appropriate.

Don't take 39.394 inches when offered a Metre!.

There may be problems finding a 6.354 mm reamer, when plenty of 1/4" ones are available, if you take my point?

Howard

Thread: More Q's about surface finish.
26/07/2021 08:01:07

Michael,

Unless power cross feed is used, even with a skilled operator, the groove spacing is likely to vary slightly, and that assumes that the power cross feed is absolutely uniform in its operation, as is the speed of rotation of the workpiece.

Since we are discussing wavelengths of light, we can, I think, afford to be a little pedantic in those respects.

As you say a matter of interference and diffraction causing an optical effect. (note the partial mspectrum visible in places.

Howard

25/07/2021 21:48:21

It may well be an optical effect, relating to the wavelength of the colour visible in each band and the physical sizes of the grooves on the surface of the material. A result of the light being reflected minutely different distances, to cause interference patterns..

Howard

Thread: OMT microscope - restored
25/07/2021 21:41:28

When you are trying to check to those levels of accuracy, the instrument and the gauge block need to be left to soak to ambient temperature, without touching for several hours. 24 hours was the minimum when I was at work.

Those levels of precision are for temperature and humidity controlled Calibration Room conditions.

Rather than checking the instrument with Gauge Blocks, it would have been used to check that the Gauge Blocks were within calibration!

For £65 and your time and effort, you now have a measuring instrument which probably cost four figures or more when new!

OMT were high precision Industrial quality instruments, used in our Standards Room and Calibration Room

You have done very well to restore it such good condition!

Howard

Edited By Howard Lewis on 25/07/2021 21:43:28

Thread: Valve Run Out Gauge
25/07/2021 21:31:40

Such gauges were, and probably still are regul;arly used in industry.

Basically it is a pilot which is a tight fit in the valve guide, and bears on the end of it for axial location, which carries a DTI bearing on the valve seat.

Rotating the device will show the high and low spots (Eccenticity ) in the valve seat. Sometimes a basic handle is provided to facilitate rotation.

Rather than being available commercially, such things are usually bespoke items, made in the Toolroom of the factory concerned.

So, it looks as if you have just found another job on the Round Tuit. (Design and make a valve seat concentricity gauge. Two if Inlet and Exhaust valve guides are at different levels, or have different bores )

Howard

Thread: New Chuck won’t screw on
25/07/2021 21:23:22

With regard to run out of the chuck in either plane, unless the thread is integral with the chuck body, this will be determined by the backplate.

The OD should be a really snug fit in the register in the chuck. (ANY clearance will reduce concentricity. )

The front face of the backplate should be skimmed to clean up, to ensure that is as square as possible to the lathe Mandrel axis.

If we are still pursuing absolute accuracy reliance has to be placed on the jaws holding work absolutely parallel to the register in the chuck body.

The threads will provide a location in the form of two long tapers being brought together..

Howard

Thread: Myford Gear Spacers
25/07/2021 21:07:16

I would ,not expect to find any Metric threads or dimensions on elderly British or American machines.

The Myford ML1, 2, 3, 4 and 7 Series changwheels were all 5/8" bore, with Whitworth form (BSF or BSW ) fixings, to match all the other Imperial dimensions. (If you can call BA Imperial! )..

Metric threads possibly might have only crept in on the very last Super 7s, or Sigmas I suspect.

We may work in Metric now, but they didn't start, in most cases, until after 1971 when the slow changeover to Metric began.

Howard.

Thread: Corbetts Little Jim Lathe restoration - newbie needs advice
23/07/2021 17:11:29

Being pedantic, am not thrilled at the prospect of Metric Leadscrews on an otherwise Imperial machine, as a permanent solution.

But you have done a great job in making the lathe operational again, and very neatly..

Now, possibly could it be used to make the new Imperial Leadcscrews for the Cross and Top Slides?

But, before the days of graduated dials, craftsmen used their skills, with a six inch rule, plain callipers, and pencil marks, to turn things precisely to size, so in practical terms it may not really matter..

Howard

Thread: Mc Donald Model tractor
23/07/2021 16:54:32

Fred,

It will be an awe inspiring exhibit when it comes.!

Do let us know when that will come about.

Howard

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