Machining before CNC/WW2 tech
Coppula eam se non posit acceptera jocularum
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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?
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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.
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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.
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.
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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.
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.
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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 :-/
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 :-/
Last edited by Flybiker7000; 4th Apr 2015 at 20:23.
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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'.
This was because Ford used unskilled and semiskilled staff where RR used 'skilled' fitters who made things 'fit'.
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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!
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!
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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
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
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In a similar vein, how do you make a more accurate machine tool using one that is less accurate?
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 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.
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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 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.
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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
(early 90s). Students later ondidnt had that and they really had struggles about it - full 3D visualization
wasnt available yet.
CNC saves time, not clue.
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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.
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.
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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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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.
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.
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See my earlier post #27.
This was because the parts were interchangeable. The RR ones were individually 'fitted' by craftsmen.
it seems they were easily serviced when compared with RR built Merlins.
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.
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.
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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!
Skills accumulate and mature over centuries, but get wiped out over a generation by bean counters and politicians!