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Machining before CNC/WW2 tech

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Machining before CNC/WW2 tech

Old 2nd Apr 2015, 10:33
  #21 (permalink)  

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Originally Posted by India Four Two View Post
In a similar vein, how do you make a more accurate machine tool using one that is less accurate?
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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Old 2nd Apr 2015, 16:32
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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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Old 2nd Apr 2015, 20:08
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Continuing the thought long back one ends up with the tool version of the hen and or Egg paradox: The hammer or the anvil! ;-)
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Old 2nd Apr 2015, 20:42
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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.
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Old 2nd Apr 2015, 21:15
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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 :-/

Last edited by Flybiker7000; 4th Apr 2015 at 20:23.
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Old 2nd Apr 2015, 21:44
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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'.
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Old 2nd Apr 2015, 22:50
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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!
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Old 3rd Apr 2015, 00:01
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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
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Old 3rd Apr 2015, 08:40
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In a similar vein, how do you make a more accurate machine tool using one that is less accurate?
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.
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Old 3rd Apr 2015, 09:42
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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.
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Old 3rd Apr 2015, 13:25
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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.
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Old 4th Apr 2015, 20:42
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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!
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Old 4th Apr 2015, 21:17
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Originally Posted by Flybiker7000 View Post
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 (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.
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Old 5th Apr 2015, 01:34
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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.
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Old 5th Apr 2015, 02:59
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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?
NURBS - Non-Uniform Rational 'B' Splines. Or that was what was used in the 1980's when I was an area manager for Computervision.
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Old 5th Apr 2015, 14:24
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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.
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Old 5th Apr 2015, 15:39
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See my earlier post #27.

it seems they were easily serviced when compared with RR built Merlins.
This was because the parts were interchangeable. The RR ones were individually 'fitted' by craftsmen.
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Old 5th Apr 2015, 21:43
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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.
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Old 6th Apr 2015, 07:05
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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!
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Old 6th Apr 2015, 08:57
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Hi Compass Call

At the Railway Museum in Darlington there used to be (don't know if still there) similar early 20th C apprentice test pieces made with hacksaw, cold chisel, file and scraper only, but the square was instead a 5 pointed star.

Having just about mastered the 1" cube, I applaud their skills.
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