5) Calculations before computers

My Maths in the 1960's

In the training school and at college we learned how to "Screw Cut" on the lathe. One would check the size with an appropriate nut, which worked but was it right?

In the R&D workshop precision was the thing and that meant maths. To check a screw thread you put three small wires in the thread two at one side the third opposite and measured over the wires with a micrometer.

Two formulae had to be worked on one to calculate the best wire size, then you got 3 twist drills from the stores. Then you used the actual drill size in another formulae to calculate the desired measurement over the wires.

Oh BTW one also had to look at the VP book (Vickers Process) for thread truncation etc. Something I had not learned of before.

http://www.threadcheck.com/the-three-wire-method-of-measuring-pitch-diameter/technicalinfo/

OK I could do it, I passed O Level maths but how I just can't remember. Here I am now 50 years later with a calculator, a computer, a spreadsheet, the internet and it is all so easy.

The only aid I had then was 4 figure log / trig tables. Square Root = Find Log using table divide by 2 then find the Anti log 

Working on the Jig Borer in the Wind Tunnel,  say two meters long and to three places of decimals required more than 4 figure tables. So we had a 7 figure log tables and the super calculator of its day the Brunsvega, a mechanical calculator.

To calculate a square root in a simple right angle triangle calculation  (Pythagoras) John and I would have a race. One would use 7 fig logs the other the Brunsvega. Up to five minutes later one of us would have an answer.  The method is described here It was based on the formula that the sum of the first n odd integers is n squared.

Why oh why didn't  the draughtsman put the dimension on the drawing? Because he did not know how we would set the work,  that was the planners job.

The planning sheets that we received just said, "Make complete" we were paid top money and on shift pay (+ 20%) but the planner was paid more to write "Make complete"!

The drawing office also had the same type of thing but they had 12 fig logs and their calculator had motors!

One job of note was a checking fixture for the Rolls Royce RB 211 jet engine. We had  a RR inspector with us we worked the maths he checked it we set the machine he checked it. Then we could drill the hole!

I left BAC 1971 and worked for a petrochemical instrument company. Initially any maths were done using a slide rule. Then a new desktop electronic calculator arrived, just a calculator not a computer with nixie tubes not LEDs but it did do square roots. 

The graphic above shows a flow meter control cone and represents about three years of my work in the1970's. Two hundred coordinates were required and all had to be calculated on the new calculator, written down and given to the lathe operator to machine. 

Today creating the graphic and the calculations will take less than 15 minutes. My how things have changed. MS Excel is thought by some to be an accountants tool, which of course it is. Engineers however should now think of Excel as their trusty calculator. 

These pages now continue with a description of the various departments of the factory.