5" speedo trip reset retaining screw-er wot size?

Howard

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I remember reading a story a few years ago that during the latter part of WW2 when Rolls- Royce and Packard were both building the Merlin engine Packard sent over to Derby a drill so many microns thick with a look how clever we are, Rolls Royce sent it back with 3 holes drilled in the shank.

I bet they could have put a blob of weld on a 1.4 mm screw!! :)

H
 

TouringGodet

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I remember reading a story a few years ago that during the latter part of WW2 when Rolls- Royce and Packard were both building the Merlin engine Packard sent over to Derby a drill so many microns thick with a look how clever we are, Rolls Royce sent it back with 3 holes drilled in the shank.

That's funny, over here we hear the same story but the other way around.
 

mercurycrest

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That's funny, over here we hear the same story but the other way around.

The way I heard it, "they" (your pick) sent it back drilled and tapped along with a set of three taps and a die...
But, I seem to think it was Germans vs Allies in that version.
Cheers, John
 

ogrilp400

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I recently contacted a very skilled instrument repairer and constructor about the threads in a chronometric speedo. He told me that all the threads are metric, based on the french jaeger design. I have just machined up two screws for the face and they are 2mm x .45, not a standard screw series, hence me having to machine some up. Yes it can be argued that the BA series is metric based but not pure metric. So I would be looking at a metric diameter to start with.
 

1660bob

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Well, I tried a 1.6mm screw as a last option and the diameter is perfect but, as expected, the small pitch difference soon halts its progress after about 1-2 turns (pitch is .35mm as against .30 of the 1.4mm screw).I tried to,er,Ahem,gently persuade it, but damaged the thread on the screw, luckily my ham fistedness did not affect the trip shaft which does indeed seem to be hardened (bodgerproof?).Would be interesting to see how an 11BA tap fits, I`m convinced now that what it is ........Bob
 

1660bob

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Update: I managed to get some 11BA taps via Fleabay, not dear. and found them a perfect fit in the trip shaft, the pitch is 0.31 as against 0.30 for the 1.4mm (or the other way round, I forget) but so close as to be negligible.The 11BA is a good close fit in the shaft whereas the 1.4mm is horribly loose.Perhaps my trip shaft has been "rebored" in the past with an 11BA tap but it looks as if my best model engineering skills are about to be tried out- i will make a screw to fit- no miller so ingenuity and a ground down junior hacksaw blade for the slot...... Cheers, Bob
 
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