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ISO Photo of Merlin V12 Machinist Setup

JLeather

Cast Iron
Joined
Jul 28, 2009
Location
Ijamsville, MD
I recall years ago running across a thread here on PM with interesting photos of old machinist shops. One of them was a setup from ~1943 showing some sort of tracer mill set up for machining Merlin V12 impellers. This was my desktop background for years, and thanks to a computer crash I lost it and cannot find either the photo or the thread where I found it originally. I know it's kind of a long shot, but does anyone on here remember the thread and/or the photo?
 
Maybe this is the one you are looking for ?

https://www.practicalmachinist.com/...er-old-fashioned-way-304104/?highlight=Merlin

I clicked on the picture to see what would happen and was sent to this site that might be better to download from should you want to.

https://ia800307.us.archive.org/2/items/C-1945-10126/1945_10126.jpg

I also remember seeing the picture and found it here.

https://www.practicalmachinist.com/vb/search.php?searchid=24398371

Maybe someone will know if the same picture can be found on another site in a better format.

Regards,

Jim
 
That's the one! Thanks Jim. I don't think that was the thread where I originally saw it, but that link to the archives seems like the same, and it's definitely the same picture.
 
That photo has been featured here on a number of occasions as Jim has listed; and so it should, it's a wonderful photo with so much going on.

The rotor/impeller would have been an experimental model that NACA were working on; as far as I know, production impellers were mostly as-forged, with only the essentials machined before balancing.

It would not have been possible to make the hundreds of thousands of impellers that were used in WW2 on such setups.

The scale of production of wartime material was staggering. Consider just the B-17, of which over 12,500 were produced; that's over 50,000 engines/superchargers, not including spares/replacements.

Extrapolate that kind of statistic into all aircraft produced and "hundreds of thousands" might be a low estimate.

Precision aluminium casting & forging was well-understood by the time WW2 arrived.
 
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Plannerpower’s comments got me thinking, or rather looking at books, and finding that the Rolls-Royce Merlin supercharger impellers were of a much simpler shape than that being profile milled in the 1945 photo. As plannerpower says, the one in the photo was probably experimental.

In the RRHT book ‘The Merlin in Perspective’ by Alec Harvey-Bailey, drawings show that the main part of the Merlin impellers had straight radial vanes, while at the inlet the vanes had a curved profile. The change in profile was achieved using separate components, carefully married together (different materials, too). This is well-shown in a photo in an excellent article by Calum Douglas (link below), which also explains why the engine makers at that time favoured vanes that were predominantly straight and radial over more efficient shapes.

Compressor Impellers - Straight or Curved Blades ? A historical perspective...
 
The link was very interesting, Asquith, particularly the clear photo of the impeller;





The un-machined areas are clearly visible.

Rolls-Royce referred to the steel section as the "inducer"; quite a neat piece of engineering itself, welded-up from forged/machined sections I guess.

The whole assembly was balanced on "knife edges" to a limit delightfully described by R-R as "0.1 dram = .0625 ounce".

(My copy of the engine manual says that, but on-line calculators give 0.1 dram = 0.00625 ounces).

In the single-stage system of the Merlin II it rotated at 22,330 rpm at the normal engine speed of 2600 rpm.
 
Jn the RRHT book 'The Rolls-Royce Crecy' there's a photo of one of those 'inducers' (rotating guide vanes) for a Crecy engine, and the caption describes it as 'conically turned'. ?

From the RRHT book ‘Rolls-Royce Piston Aero Engines – a designer remembers’ by A. A. Rubbra:-

The The Merlin’s predecessor, the Kestrel, didn’t have the 'inducer' (rotating guide vanes). Rolls-Royce had started using superchargers on the V-12 Eagle in the 1920s, but they were very inefficient. Arthur Rubbra was packed off with a supercharger to RAE Farnborough, who had the brains and the apparatus to investigate. Long-short, efficiency improved from 37% to ~70% under the guidance of James Ellor of the RAE (Royal Aircraft Establishment).

Attempts were made to lure Ellor to America, with the offer of considerably more money than the RAE could pay him (they were a government department with fixed salary scales). The Govt dept, anxious to retain his skills, suggested that Rolls-Royce make him an offer, and there he went, in 1927. During WW2 he was one of three leading R-R engineers sent to the USA for the unenviable task of liaising with Packard on production of the Merlin. He was there from 1940 to 1944.

Now, to Bristol:-

JD 2020 Mercury 1.jpg 1. JD 2020 Mercury 3.jpg 2.

These photos show stages of production of a Bristol Mercury supercharger impeller, which starts as a nickel steel forging. It seems that the main product of radial engine makers would have swarf.

Photos from ‘Aero Engines’ published by Newnes in 1937. The Mercury went into production in 1927, and it looks as though the profiling machine might have already been an antique then!

Bristol were already using the curved guide vane supplement in 1927 on their Jupiter engine superchargers, but strangely it doesn’t seem to have been used on the later Mercury (ref photos in aviation adverts link below).

From having partially free-standing vanes, Bristol went to fully shrouded impellers. Advert No. 13 at the top of the link below shows a ‘Forged light alloy impellor machined all over, dynamically balanced’.

Classic British Aviation Industry Advertisements 1909 - 1990
 
I'm a bit slow posting this but this will be a bit of a follow up to Asqith's last link to the Bristol Hercules super charger so there will be a bit more of the same thing but from from more recent times
A few months ago Karl Kjarsgaard shared a link on this Facebook group Plane savers about a supercharger blade from a Bristol Hercules engine for a Halifax bomber that had been damaged when something got into it while it was running .
I couldn't find the post there since I'm not on Facebook but here is a picture showing the damage
https://static.fundrazr.com/media/0b2b87de621b4626afa1753e57231c8a_large.jpg
and one showing what it should look like
https://static.fundrazr.com/media/0b93baabf8a3439ca79fc801d39eaa9a_large.jpg
He posted some videos about changing it out .
This was the first one
https://djcb52oh54rte.cloudfront.net/249fb13ab57b1c68415a711ae6a1af53.mp4
You can see more of the process in these links
Bomber Command Museum of Canada Curated Public Group
You have to scroll down a long ways in the link below to get to the April 10th update for the start of the story .
https://fundrazr.com/profiles/halifax-57-rescue-canada
I have posted in other older threads about the work Karl and his team at the bomber Command Museum of Canada are doing to try and build another Halifax bomber for Canada
https://www.youtube.com/watch?v=D26bOxCOKuI
I'll look over the other links I was trying to sort out and perhaps add some more later.
Regards,
Jim
 
Sorry if this is a bit off topic. I don't know too much about machining, but I am trying to learn as much as I can.

I assume those are two tracers for machining x and y? Also, the vertical spindle on that big Cincinnati seems dinky, and the cutter seems long and thin.

I just saw a Cincinnati that may be the same size for sale near me.
 
mjr,
The Milling head is not original to that machine .
It was mentioned in post #18 here,https://www.practicalmachinist.com/...er-old-fashioned-way-304104/?highlight=Merlin that it is an M head from a Bridgeport that I think at that time were sold to be adapted to a number of different machines .
You can see more of the heavier type made by Cincinnati in post #41 of this thread
https://www.practicalmachinist.com/...ioned-way-304104/index3.html?highlight=Merlin and the base slightly newer base machines can be seen in the book link.
Regards,
Jim
 








 
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