When did gunmakers “standardized” their gun parts for all their guns to have the same specs?

Most of British industry used first-angle orthographic projection for drawings in those days. It caused American industry some confusion and in a least one case forgings were produced for the 20mm Oerlikon with the lump on the wrong side.
By the 1970s our technical drawing teacher had us doing it both ways as British industry was still changing over.
Somewhere in my photos of the papers I researched in the [British] National Archives a while back about seeking producers in USA was a statement to the effect, "Don't go to the New England gunmakers. There's too much of the old world craftsmanship about them. Go to the automobile industry, they understand mass production, and interchangeability."

 

The information comes from Sir Stanley Hooker, himself, he was the chief engineer on the supercharger and later went on to be a key figure in RR jet engine development. In his autobiography, "Not Much of an Engineer," Sir Stanley relates the following anecdote:

"In my enthusiasm, I considered that Rolls-Royce designs were the ne plus ultra, until the Ford Motor Co. in Britain was invited to manufacture the Merlin in the early days of the War. A number of Ford engineers arrived in Derby, and spent some months examining and familiarizing themselves with the drawings and manufacturing methods. One day their Chief Engineer appeared in (Merlin development head Cyril Lovesey's) office, which I was then sharing, and said, 'You know, we can't make the Merlin to these drawings.'

"I replied loftily, 'I suppose that is because the drawing tolerances are too difficult for you, and you can't achieve the accuracy.'

"'On the contrary,' he replied, 'the tolerances are far too wide for us. We make motor cars far more accurately than this. Every part on our car engines has to be interchangeable with the same part on any other engine, and hence all parts have to be made with extreme accuracy, far closer than you use. That is the only way we can achieve mass production.'

"Lovesey joined in, 'Well, what do you propose now?'

"The reply was that Ford would have to redraw all of the Merlin drawings to their own standards, and this they did. It took a year or so, but was an enormous success, because, once the great Ford factory at Manchester started production, Merlins came out like shelling peas at a rate of 400 per week. And very good engines they were too.”

Total Merlin production at Ford’s Trafford Park factory was 30,428.

Ford (UK) began work in early-1940, this is about the same time that Ford (US) originally committed to build 9,000 Merlins. Ford (US) backed out a few months later, and in June 1940 a example engine and the drawings were turned over to Packard. These drawings would have been the same drawings Ford (UK) had just insulted in front of Hooker and Lovesey. Packard would have been in the same boat as Ford (UK), in that a redrawing of the R-R prints was in order.

The Trafford Park in Manchester began delivering engines about the same time as Packard, summer of 1941, even after being bombed during its first week of operation. The Merlin was built in five places, Rolls-Royce's factories at Derby (82,000 engins), Crewe (26,000) and Glasgow (23,500), Ford's plant at Trafford Park, Manchester and Packard's plant on Grand Boulevard, Detroit (55,500).

 

I think you may be right, but maybe not completely right.

I just started looking into this and only have the one previously mentioned source in my procession. Searching for additional information online I have come across this topic. I will keep looking. So far this is what I’ve come up with.

The story related by Hooker appears to be more accurately an example of an insulting impertinent remark being parried with a not wholly accurate in detail insulting remark. Hooker after all was not a participant in the project to set-up Ford production, just someone who happened to be in the room. It is hard to believe R-R parts were all required to be hand fitted during assembly. That would cause an enormous problem with spare parts supply. I have seen mention of R-R parts being used for repair in the field on Merlins not manufactured by R-R. Wouldn’t those parts have to have a common specification unless mechanics were hand-fitting in the field. Was hand fitting of parts to a Merlin in the field by mechanics who just months earlier were not mechanics really expected? Difficult to believe.

I still haven’t seen anything to indicate Packard had to create new drawings due to R-R having too loose of tolerances. Seems the type of drawings used was more about what was needed for a specific manufacturing system than a problem with the tolerances.

It would be great to see a comparison of manpower, time, output of the various Merlin producers. Looking at total numbers produced does not provide enough information as to which manufacturing system was the most efficient at producing Merlins.

In this thread there has been comment about problems with licensed manufacture of firearms in the United States. What about international licensed manufacture of firearms. Anyone know about drawing problems with the foreign manufacture of U.S. designs and vice versa?

 

1) Rolls adopted Ford's modern production methods after 1941, and greatly increased production rates. The three R-R plants matched Ford's production monthly numbers (All this is from Hooker's book).

2) Robert J. Neal writes in Master Motor Builders, a tome documenting Packard's non-automotive engines that "the British did not specify tolerances and fits, and Packard had to take parts from an existing engine and make measurements to determine these specifications as best as they could, using engineering judgement where necessary."

This notion is also reflected in the March 1946 issue of Flying magazine, which includes a retrospective on the powerplant by Paul H. Becker titled “Mass Producing the Merlin”:

“It took the war to prove that the aircraft engine is not that complicated micro-micro-inch construction problem peacetime talk has made. It is larger, lighter-per-horsepower and has more parts than the automobile engine. But, it can be made with the same ease, relatively cheaply, and on a similar assembly line.”

Later: “The secret of the this low-cost, high-production manufacturing is the assembly line. Rolls-Royce manufacture[d] a 'fitter’s' engine with parts being brought to the unit under construction on a bench. If the part doesn’t fit, it is machined until it does meet required specifications.

“An American assembly line reverses this procedure. A conveyor belt brings the engine to the parts which always fit for by American methods all parts are made so precisely that they are always interchangeable.”

(I have seen this type production in the UK. In assembly a gas turbine, where US production would measure and assemble a shim stack to pre-load a bearing, the Brits would take a single oversize shim over to a lathe on the assembly floor and machine a single shim to the measured dimension. When I asked about this, I was told, ". . . it's no problem, the repair shops have lathes too . . .")

3) From a British mechanic with experience with their design philosophy - "It seems the original RR Merlins were balanced and blueprinted type engines. I have worked on factory Jaguar engines which had multiple different fit pistons in cylinders that were all standard bore. They were not interchangeable. I have balanced and blueprinted engines fitting parts to the minimum clearance. Pistons were knurled for the best fit to a particular cylinder. They were not interchangeable."

4) The Hispano-Suiza HS404 20mm cannon, the 40mm Bofors, and the 20mm Oerlikon all had to have the drawing package redrawn by the US manufacturers to eliminate hand-fitting and parts serializing, with varying degrees of success. The later two worked very well, the HS404 went through four variations (M1, M2, M3, M24, and Mk 12), but never quite achieved the desired reliability. More recently (early 1970s), when the US Navy bought the Oto Melara 3in/76 Compact rapid fire mount, spare parts from Italy had to be hand fit by the Oto Melara field team, until FMC took over the contract, and began to supply replacement parts. On the flip side, when the US bought the MAG-58 as the M240 back in 1977, the drawing were redrawn in accordance with MIL-STD-100 (but still in metric units), but the tolerancing was adequate for universal interchangeability.

 

Thank you for your excellent reply! You have saved me much time and probably the cost of a couple books in a search for answers.