Machining before CNC/WW2 tech
 

I've recently been in awe at WW2 technology and the massive piston aircraft engines, it got me thinking how were things like centrifugal compressor wheels for turbos/superchargers made back then. All compressor wheels today seemed to be machined by CNC.

How did they machine such complex surfaces back then? I can't figure it out and it is annoying me.

Many thanks

Skill and measuring in huge quantities!

First the scientists and technologists would decide exactly what was needed, and what shape and material the part should be, then huge ranks of highly skilled draughtspeople would prepare technical drawings and blueprints, then the engineers, foundry men and machinists would make parts as per the drawings, each one with huge quantities of skill and measurement!

You should never under-estimate human skills, but conversely you should never loose admiration for the incredible work done by previous generations, without modern facilities. In my opinion there is no better example of this than the Antikythera Mechanism.

I am a non-engineer, but for a year, and what a year, 1969-70 I worked I production control at what was then called Marshall of Cambridge Engineering Ltd. Machine shop work went from thousands of small parts produced on capstan lathes, many of WW2 vintage, to nc work on the droop nose and visor for Concorde, other than the first aircraft. A small team at one end of the production office wrote the programmes for the punched paper tape, and designed the machine tool heads that were, ISTR, made by a firm called Marwins. One hole in the wrong place and £12.000 (at 1969 prices!) worth of alloy down the pan. We also did work on attenuation panels for the first generation RB211 (the one they tried to make with a carbon fan). It was all exciting stuff, and I sometimes wonder where I would have finished up if I had stayed there. Years later, as a sqn ldr, I was an usher at the BoB Memorial Service in Westminster Abbey, and as I was showing the then Sir Arthur Marshall to his seat in the Air Force Board seats, he looked at me and with a grin said "Didn't you used to work for me?". Good memory, as I was well down the food chain at MCE.

Wander00

A little after your time at Marshals, around 1971-74, I was a maintenance engineer for a large American computer maker. One of my customers was Dowty-Rotol at Gloucester.

They used the computer to write the programs that were punched out into the paper tape, that were used on Milwaukeematic Machines. At this time they were producing components for Harrier undercarts.

To avoid the extremely large expense of the tools moving in the wrong direction, the cost of the damaged tool was likely to be more than the material, they always tested a new program on a block of wood!

Having learn't just enough about NC and in an earlier incarnation having worked on Beverley's, and being very aware of the reliability problems of the Bristol Centarus, this all made me wonder if today we could build the last of the big piston engines to a level that would give them the reliability of my Japanese motor car?

In particular I would love someone to build a Napier Sabre with modern CNC machine tools.

There is always something to learn on PPRuNe

Have a look, it is astonishing:

Have a look, it is astonishing:

At first the supercharger on the Merlin isn't such miniscule as the turbineparts in modern automotive turbochargers: http://upload.wikimedia.org/wikipedi...percharger.jpg
The parts for the Merlin supercharger aren't machined but casted. However, before casting a model has to be made, but this is done in simple materials wich is able to form easily. Additional, pattern makers are on the limit of artists/sculpturers and the modern CNC-milling of such parts have almost choked this fine craft to death.
Personally I find it very impressive when looking at the transmissionbars between the piston and wheels on steamlocomotives: All is handcrafted, but the fitting is perfect though rather complicated :-o
http://youtu.be/6HzRrmn_ZUc (at 0:45!)

Called "Pattern Makers" in the UK.

I am in such awe of the people that could make a mold for something so complex as the supercharger, how would people even draw the blueprints for objects like that since they are so kind of 3 directional, it must've taken forever to sculpt the mold.

Wander00, I worked on Marwin Maxitrace machines at Strand Road in 1970, they were 1/4 in. magnetic tape controled then. I was at Marshalls in 2008 and noticed they were still using the identical machines. Strand Road dissappeared years ago:{

Marshalls always seemed to make machinery last - extracted every ounce of value out of a piece of kit

Ze Bedie:
 

Thanks for correcting!
I have edited the text to 'pattern maker' now and You might wish to delete Your answer for not to look foolish ;-)

maxitrace
 

I've worked where the welding-robot had been modernized with a modern harddrive instead of the antique 1,44Mb floppy-disc. However, the processor couldn't handle all that information and the harddrive had to be sectioned in 1,44Mb parts :-o
Its not only in the homeoffice-corner the electronics evolve too fast and some day short in the future will CNC-milling be just as difficult to comprehend as the mold/cast, because 3D-printing have taken over!

Pattern Makers often used Jelutong, a dimensionally stable soft wood with very close grain which allows it to be worked to a reasonable degree of accuracy.

Does anyone know how they manage to measure and make things like the compressor wheel. It is a part with so many curves it seems impossible to not only draw but impossible for someone to get such complex curves correct or so many blades. I would be forever grateful if anyone could explain how engineers and machinists/pattern makers etc dealed with such complex surfaces?

Such mechanics was mostly created during experiments and not calculated to seventh decimal like expected by digital design today.
It could be quite interresting to have the effiency valuated against a modern CAD design with same measurements!

To me, the model might have been made by two dishes with curved ribs mounted evenly around but mirrored and thereafter layed together.
The major issue will be the balance but that should be the easiest part to weight out - On the model as well as after the cast!

The beauty of the french curve maybe - but how did they draw a french curve without a french curve?

http://www.isomars.com/productpic/d5...1a5a42e558.jpg

In a similar vein, how do you make a more accurate machine tool using one that is less accurate?

How were the propellers machine back then? Metal ones obviously

As a young lad doing my O-level Metalwork, that question did my head in ... how on earth did Henry Maudsley perfect his first precision screw cutting lathe from less accurate tools?

Machining before CNC/WW2 tech
 

I was a Vickers-Armstrong apprentice at South Marston, Swindon starting in 1961 and remember being told that many of the machine tools were WW2 era, (when it was originally Short Brothers). Some of the great British manufacturers of that time were on show, Ward, Dean Smith and Grace and Colchester lathes, Alfred Herbert and Cincinnatti milling machines plus the many other odd machines that made up the two large machine shops turning out at that time, very high quality aeroplane parts. Saw the early implementation of CNC with MilwaukeeMatic and Marwin machines and it was obvious to me that it was going to be that way for the future of production engineering, but never envisaged for one moment the effect computers were going to have in later years.

Ah, yes, machining back then was an art.

One company made the housing for an equipment out of pieces of balsa wood glued together to establish the best shape before using that to generate a precision casting.

Many parts were cast by the lost wax method and then finished by hand.

I can recall making a replacement part for our home ice-cream scoop (quite complex with gear teeth on it) by filing it by hand.

One of our first apprentice exercises was to file a rod of arne (very hard steel which work-hardened much harder) by hand to an exact inch in length and exactly square. Amazing just how accurate that had to be so that a set-square placed on end and side did not show the faintest glimmer of light. I was first out of our course to finish, exactly right, dead square, absolutely perfect, but, as Mr Derek Wilkinson was quick to point out, exactly 1.100 inches long. I spent hours getting that down to the required 1.000 inch.

There were a lot of cunning techniques for making better and better machines. In fact, one of our tasks was to make on a really grotty old lathe jobs which the better lathes could knock out in seconds. That sorted out the men from the boys!

One of the most spectacular jobs I had to do was to machine a great ingot down on an Ormerod shaper. This had a to-and-fro action, and, if you came in carefully from the side you could work up to enormous cuts taking great swathes of metal off, which when dosed liberally with cutting oil, left great smoke trails across the model shop. The next lad took over from me and enquired what cuts to take. I told him I'd been doing half an inch by fifty thou. Didn't expect him to start right in the middle of the workpiece. The shaper drove the tool clean into the piece, the Ormerod stopped dead with a broken carriage, and took the workshop floor up like a good-strength quake. :E

Continuing the thought long back one ends up with the tool version of the hen and or Egg paradox: The hammer or the anvil! ;-)

What a great thread. And great stories of handworking to great precision.

However, I hope it's not too churlish of me to bring up Sir Stanley Hooker's story about how the RR Merlin drawings had to be totally redrawn to Packard's standards - as used in motor car production.

Could it be that British manufacturers, with far cheaper labour costs, were actually too dependent on the hand skills of its labour force. Later, when labour costs rose, the companies concerned were slow to change the manufacturing culture and so many jobs went away.

Redrawing
 

The world was bigger at that time and actual it's as late as after CAD/CAM and the web that drawing spec's have been finally internationalised. The Packard/Merlin story shows only that Packards management managed to favour their methods of drawing and producing - Maybee it was reasoned well (by american state of art series production) or maybee it was a matter of hard negosiations wich Packard might have been better suited for or maybee it was a pure political decision :-/

I recall from 'Guy Martins Spitfire' that the production of the plane first came into beat after being supervised by the former Morris Boss, this even though the production of the plane was crucial for the RAF and with that, the country!
Planning and leadership is nonplusultra and lack of that might have been the fate of the later british industry :-/

Isn't it true that before the Packard Merlin, there was a Ford plant in the UK that had to build Merlin's to tighter tolerances than RR used?

This was because Ford used unskilled and semiskilled staff where RR used 'skilled' fitters who made things 'fit'.

I once bought a 12" steel rule at a surplus goods store.

Very handy for some layout work I was doing - until some of my projects didn't fit together just right.

Then I happened to read the fine print on the scale - it was a patternmaker's scale, 1/4" to the foot LONGER than standard, to compensate for metal shinkage as the casting cooled! :ugh: :{

I can recall where the Americans had to convert Merlin blueprints to decimal fractions.
Despite both countries using the inch measurement system, the Americans had long ago changed to decimal fractions for ease and simplicity in engineering work - whereas the British still stuck with fractions.
So a Merlin blueprint would state [1 1/16"] whereas the Americans needed it to state 1.0625".

As far as the machining of early turbines for superchargers went, many lathes and hobbing and milling machines were set up with additional jig-holding drives, that moved the component as it was machined, thus enabling complex curves to be machined.

Gear cutters and hobbers are the classic machines for producing involute curves on gear teeth. Once you see a machinist who has gear-cutting skills in action, you'll see real skills with machine tools and calculations.

Wikipedia - Gear Hobbing

I think the principle with screw cutting is that you start with a lead screw that is fairly good, and use a compliant follower (say, cork) that averages over several turns to cut another lead screw that is better than the first.

Somewhere I have seen what must be a simple explanation of this, but I can't find it on Wikipedia under Maudslay or Whitworth.

machining
 

centrifugal compressor wheels.
I am not familiar with machining these items but they were probably done as Onetrack suggested on specialist lathes and other machines. I am sure I have seen photos of early ones where individual blades were set in slots in the backing disc.

More accurate machines
One way to make more accurate machine tools is to hand-make more accurate components and fit them together into a new, more accurate, machine. Then you are able to use that prototype to build your better production machines.

Templates were often used to check progress. So you machine a bit, check against the template, then machine a bit more. Accurate and relatively fast.

Seiran, have a look at the work of Model Engineer enthusiasts. A lot of traditional skills are maintained by these hobbyists and many of them are very proficient.

I ran a medium sized machining co. From the late 80's until the early 2000's. We had around 60 machine tools.
The co. had been in operation from the late 40's and had examples of the history machining from 1920's capstan lathes through to the (then) latest CNC's
Man has always been ingenious.
I would think that from pre WW2 to the advent of NC (C omputer came later) the technique for machining intricate shapes would would have been hydraulic copy - a stylus followed a 2D model of the desired shape and controlled a hydraulic ram (no lead screw). It was accurate enough to produce tolerances suitable for bearing fit. We still occasionally used hydraulic copy up to the time I left. It was 100% reliable, unlike CNC.

The precision of modern tools isn't due to the digital programming as much as the invention of extreme fine electronic measuring devices to control the tooling!

Indeed, plus the ability to do time-based critical movements - which have been back then just not possible on pure mechanical ones (say, pre NC).

When I did my degree in mechanical engineering (mainly about surfaces) we've been put into a non-(C)NC workshop for three months to learn that three axis exist even outside computers :p (early 90s). Students later on
didnt had that and they really had struggles about it - full 3D visualization
wasnt available yet.

CNC saves time, not clue. :cool:

The greatest advances in modern machining are to do with cutting-tool technology.
In the old days, carbide tools were cutting edge, but they were limited in speed and loading - and many materials had to be ground because they couldn't be machined.

Todays tooling technology is absolutely amazing, with astonishing speed and loading abilities, that enable fast machining of items that formerly had to be ground.

NURBS - Non-Uniform Rational 'B' Splines. Or that was what was used in the 1980's when I was an area manager for Computervision.

What a cracking Thread,

to add just a little, Ford Motor Company manufactured Merlins at Trafford park during ww2, and it seems they were easily serviced when compared with RR built Merlins.

See my earlier post #27.

This was because the parts were interchangeable. The RR ones were individually 'fitted' by craftsmen.

henry crun
Your post reminds me of two of my apprenticeship jobs.

We were given a fist sized lump of steel from the foundry and had to carve it to a one inch cube, scraped flat - no machines allowed, only hand tools.

When we had completed that to the training managers satisfaction, we were given an even bigger fist sized lump of steel from the foundry. This time we had to carve it to a one inch thick by four inch square plate, scraped flat, again no machines. Then we had to cut a one inch square hole dead centre of the plate - we were allowed to drill a half inch hole in the plate, using a hand drill. Then the previously made cube had to fit the square hole we had cut in the plate - every whichway!

We learned how to use hand tools and measuring the hard way.:)

Compass Call, great post, it reminded me of the old test which was given to itinerant shipbuilders wanting to work in the Tudor royal docks. The test for an adze (a curved horizontal axe held in both hands brought down from over the head to ground level) was to cut and point a small stick about the size of a match in as few blows as possible, then drive it unbroken into a plank with one highly accurate blow with the back of the adze.

Skills accumulate and mature over centuries, but get wiped out over a generation by bean counters and politicians!