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Machining before CNC/WW2 tech

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Machining before CNC/WW2 tech

Old 31st Mar 2015, 09:26
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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
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Old 31st Mar 2015, 12:02
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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.
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Old 31st Mar 2015, 13:12
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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.
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Old 31st Mar 2015, 14:44
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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.
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Old 31st Mar 2015, 17:44
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There is always something to learn on PPRuNe
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Old 31st Mar 2015, 18:24
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Have a look, it is astonishing:


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Old 31st Mar 2015, 18:25
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Have a look, it is astonishing:



?rel=0" frameborder="0" gesture="media" allow="encrypted-media" allowfullscreen>
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Old 31st Mar 2015, 19:19
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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!)

Last edited by Flybiker7000; 1st Apr 2015 at 09:14.
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Old 31st Mar 2015, 20:33
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casting-modellers
Called "Pattern Makers" in the UK.
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Old 31st Mar 2015, 21:27
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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.
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Old 31st Mar 2015, 22:42
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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
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Old 1st Apr 2015, 06:08
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Marshalls always seemed to make machinery last - extracted every ounce of value out of a piece of kit
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Old 1st Apr 2015, 09:17
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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 ;-)
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Old 1st Apr 2015, 09:25
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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!
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Old 1st Apr 2015, 10:21
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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.
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Old 1st Apr 2015, 11:57
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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?
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Old 1st Apr 2015, 22:26
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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.
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!
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Old 1st Apr 2015, 22:47
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so many curves it seems impossible to not only draw
The beauty of the french curve maybe - but how did they draw a french curve without a french curve?

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Old 2nd Apr 2015, 02:50
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The beauty of the french curve maybe - but how did they draw a french curve without a french curve?
In a similar vein, how do you make a more accurate machine tool using one that is less accurate?
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Old 2nd Apr 2015, 05:40
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How were the propellers machine back then? Metal ones obviously
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