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How would you handle the problem that almost most every machine tool in the Packard and other factories were in inch configuration? Almost every machinist out there worked in inch, and had nothing but inch micrometers, dial gauges, calipers, indicators, last words and so on. It was already hard enough to get small tools. For some things it was so bad, that the government put the word out to amateur radio operators to turn in every electric meter that they could, so that they could be repurposed for the war effort.To me the biggest stupidity that both the US and Aus engaged in during ww2 was the total redrawing of imported designs. Packard wasted untold manhours redrawing all the Merlin blueprints to US standard when it would have been far simpler to train the production staff to read and use the RR drawings. These were all new hire staff and had to be trained in reading the US blueprints so sticking with the UK prints would have been easier and faster and have no chance of the inevitable conversion errors that arise when converting mm to US inches etc. Likewise training their draftsman to work with the RR drawing standards would have taken a minute fraction of the time taken to redraw every blueprint.
Whose production staff?Packard wasted untold manhours redrawing all the Merlin blueprints to US standard when it would have been far simpler to train the production staff to read and use the RR drawings.
How would you handle the problem that almost most every machine tool in the Packard and other factories were in inch configuration? Almost every machinist out there worked in inch, and had nothing but inch micrometers, dial gauges, calipers, indicators, last words and so on. It was already hard enough to get small tools. For some things it was so bad, that the government put the word out to amateur radio operators to turn in every electric meter that they could, so that they could be repurposed for the war effort.
Whose production staff?
Did Packard make everything in house or did they subcontract items?
At one point Allison had over 800 subcontractors, granted a number of them were suppling washers, nuts and screws. But places like Maytag (washing machines) were suppling Aluminum casting to Packard, (small stuff, not engine blocks).
Most engine companies subcontracted things like valve springs and even valves. US had several different carburetor companies, that supplied everybody. Same with magnetos/ignition parts.
A large number of drawings would have to be redone in order to give them to the subcontractors.
It makes sense for Packard to do the drawings so all the American suppliers would be on the same page.
Yes Packard will have had many subcontractors and in some cases redoing a drawing for a subcontractor would make sense but when a valve spring for example is a round metric measurement, or even to two decimal places, and made from wire that is a round metric measurement, again even to two decimal places, then using purely metric numbers makes more sense that fartarsing around in inch to five decimal places or n/128ths. The biggest problem with Packard using a Brit drawings is not the metric measurements, where used, but the projection angle and in many cases that does need a new drawing unless the subcontractor is purely working for Packard, as many were.
Sheet metal gauges are different for steel or aluminium.dH used a lot of metric measurements in their engines as well, presumably because it is far more precise than inFerial measurements are. Other Brit manufacturers also used meteric so dH were not alone on that. There is only one dimension called a mm but there are multiple inches and other inferial measurements and you need to know exactly which of the many measurements with the same name they are using
For example many inferial users talk about n gauge material. Here are just a few of the gauges in use in ww2. For a good example of how confusing these can be note the lines that say
Birmingham Gauge for Sheets and Hoops. (See Birmingham Gauge).
Birmingham Gauge. Abbreviation: B.G.
Not to be confused with the Birmingham Wire Gauge.
View attachment 700273
This manual alone has another two and a half pages of different gauges in common use in 1Sheet metal gauges are different for steel and aluminium.
The other big problem is that you would have forced machinist to spend a lot of their own money to change over to metric. Until much later in the war, when various production lines started the mass hiring, the companies did not supply the individual machinist with the small tools required for the job. One supplied their own scales, calipers, micrometers, dial indicators and so on. A journeyman machinist at that time, probably had a year's gross pay in tools in his box. Very few could afford to suddenly have to duplicate 50% of his box in one shot.
There were two big problems....For the machine tool manufacturers, only a tiny fraction, if any of their products were metric at that time. When you're scrambling to get machine tools out the door, you don't want to add to the mix having to convert part of your production to run metric in parallel to your existing lines. By revising the designs to inch standard, it means being able to use the tooling you have on hand and getting production up much sooner. Lead times for new machines were in area of 6 months or more. My grandfather's company changed over from making pumps to parts for anti-aircraft guns, rifles, tanks and howitzers, all in a matter of days.
Been working on restorations too, since 1979, and in aircraft manufacturing since 1986. Rarely have I ever run into fractional drawings for machined parts. See lots of them for folded and flat parts such as tabs and brackets, but mostly with wood components.
AutoCad has made designers stupid at times. Specifying a dimension to 4 decimal places drives production costs way up. Combine that, with then specifying a tolerance table that is too tight for what is actually being built. I've seen stuff designed to 4 places, get a 3 place tolerance and then have the assembly drawing tell you to hand fit to the location.
Error avoidance starts at the design level, but continues right to the production floor. Because so many unskilled people were being brought to the production lines, many companies had to train them up first. To help minimize production losses to defects, there were often 100% QC checks against calibrated check tools, master gauges or fixtures. A fresh trainee could insert the gauge into the requisite feature, or the part in the fixture and it met spec or did not. Look at some of the wartime production films and you see the inspection work.
Except that nowhere in the US was wire made in " round metric measurement", or valve springs, or pretty much anything!
All of it was in US Inch standards - which was close... but NOT the same.
Did they really?Things like valve springs were made to the RR requirement so either they made the wire to spec in the US or they imported the wire or the finished product from the UK using reverse lend lease
Not directly related to the Mosquito, but the problem with the US built Hispano cannons, at least as I understand it, was that most of them had an excessively long chamber that tended to cause light primer strikes. The French versions had the issue even at times it seemed, but for sure the early British and a lot of US built ones did, possibly due to conversion between metric to customary measurement. The Brits realized the issue and on the Mk2 versions incorporated a shortened chamber, as well as a Martin-Baker belt feed mechanism to replace the drum, and other changes that BSA did. Other than belt feed, the US didn't fix most of the problems until the M3 and M24 versions (based on the British Mk5 version).Did they really?
I understand that International Harvester did a poor job of manufacturing Hispano 20mm cannons. Packard designed and built engines. At some point, if Rolls Royce specifications made to sense to them, they could ask themselves what material they would use if it were their part.
"What would I call up if that were my valve spring?"
The Packard engineer probably would be right.
Is that issue so obscure that experienced eingine designers at Packard not see it?But then the spring would not be interchangeable with the RR spring as it would not fit the keeper and base ring perfectly and I pretty sure the requirement was that Packard and RR parts must be totally interchangeable.