Hi Compass Call

At the Railway Museum in Darlington there used to be (don't know if still there) similar early 20th C apprentice test pieces made with hacksaw, cold chisel, file and scraper only, but the square was instead a 5 pointed star.

Having just about mastered the 1" cube, I applaud their skills.

Compass Call

Over the years variations of this have been and are still used.

It was used by the RAF for Boy Entrant and Apprentice trainees in the aircraft trades.

I was pleasantly surprised that when my son was training at Witwatersrand Technicon for his National Certificate in Jewellery Manufacture and Design, they used a very similar, albeit much smaller, exercise.

The common thread is that you are never have the 2 pieces in your hand until you try to fit them together.

At my old School in the late fifties, our metal/wood work masters asked us to plan, draw and make a working model of a single cylinder engine from wood, with gear driven cams to work side valves, in the cylinder head box, they promised if we could do it within term time , the next term we could make one from steel, we all had a portion that needed to be done with correct measurements so they mated with the other sections and we overcame alsorts of problems, not only on the size and bore but in working out how to make the gears with angled teeth so as to operate smoothly, it really tested us, but we just managed to finish it in our Autumn term, we all received a headmaster award for that wooden engine, but when asked not many of us wanted to then go on to a steel replica, then we found out the lathes were not big enough to do what was needed and so sadly the project in steel was abandoned, our Wood and metal instructors were ex military and ex RR , so they then gave us lumps of mild steel and a measurement to make a cube to fit into a hole we had to make in a flat piece of 1/4"thick steel plate, now at 14/15yrs old that really tested us.. but that taught us much about files and filing.. I don't think they do that now..!

. . . And often plain knowledge too :-(
Some swedish indland lake-fishers got a very old wooden box with rusty items in their net - and the archeologists went crazy: It showed to be a craftsmans toolbox from the first millenium-change.
In Scandinavia is amateur experimental archeology a widespread branch and when copying the hammers in the box they found that they had so much punch and precision :-o
My brother in law is carpenter and lets no chance of testing hammers he come past get spilled, hence he knows that it's not obvious that modern hammers do have punch and precision as his hands experience it and the one wich do never must be unattended!
The viking carpenter had probably had his words with the blacksmith about the tools, where my inlaw must chose between houndreds of seria-produced 'items'. Development?

an able demonstration of the difference between accuracy and precision ....

Profile machining
 

Plus propeller operation details: https://www.youtube.com/watch?v=65sdTFdj5VU

I did my apprenticeship with BAe in the 70's - as a rule the best became toolmakers (pattern makers).

Plenty of guys there then who were 25 year + veterans of their trade - great skill sets, great days

AS

Nowadays a Bastard File is one that disappears into cyberspace just as you've almost finished working on it.

As an apprentice I helped on a couple of projects which involved making spiral and involute flutes on shafts these were done by linking either a rotary table or dividing head to a milling machines feed mechanism so that they rotated as the bed of the mill moved along. Working out the ratio between them to get the correct end result was a complete nightmare but we eventually got the required locus, I think that was the posh word for it. I also learned to chisel keyways in machine shafts. ;)

Yeah machining the propeller seems too easy these days but how did they do it before CNC/NC?

The Halton Apprentice test piece was so famous, that a model of it became their "memorial".

Sounds similar to some mentioned (I wasn't a Halton Brat, so don't know exactly what had to be done (I'm sure someone will tell us!!))

http://rafhalton77thentry.org.uk/wp-...e1-150x150.jpg

During the later part of my Boy Entrant training, some of us fairies had to share a billet with some oily Riggers!

These guys all seemed to have kept their test piece and from memory they had been given a piece if 1 inch thick mild steel plate. They had to make it a 3" square, then put a 1" square hole in the centre.

A separate piece of mild steel had to be made into a 1" Cube.

The 1" cube had to fit into the 1" hole, any possible way, with not more than a 1 thou gap.

We fairies, played around with 'dominoes' of brass, ebonite and paxoline. All soft materials where it was dead easy to take too much off with one swipe of a file.

Actual pretty simple and just like this wooden shoes: http://youtu.be/gUDHPiJXkyU - 1:1 after a model/pattern!

Amazing, thank you so much!

But how did they make the 1st propellor perfectly, to enable it to be used as the master on the copy lathe? :suspect: :confused:

Skill ....same as those 17th century carpenters who produced immaculate woodwork which would be difficult to replicate today, or the stonemasons carving perfect statues hundreds of years ago.

Some people are just incredibly F#$king talented

AS- I'll go with that, but IMHO in UK we are very poor at recognising that talent, and more importantly, ranking it with academic achievement

The British attitude towards engineering and manual skills was amusingly highlighted to me a few years back at an orchestra concert in London, using instruments I had designed and made. After the concert the conductress brought the borough's Mayor and his wife to meet me and see the new instruments.

They were polite and enthusiastic and said it was "absolutely mwarvellous, mwarvellous " to see a new design in use. After a few question the Mayor's wife asked who made them, I replied that I did. Then she said "Yes, but who actually does all the metalwork for you?" "I do". Her expression changed to disgust, she said "Oh, so it's manual labour" and they turned promptly and left. Clearly I had instantly been demoted from "Designer" to "Grease Monkey" in her and her husband's opinion. I could hardly control my laughter.

Thanks ian16th

I just knew someone here would come up with the answer! :ok:

A propellarblade is an array of wing-sections, differing in thickness and incline as the speed through air is higher at the end than close to the hub.
The cross section is rather easy to calculate for each 1/4" and likely ist possible to cut out the same sections in 1/4" wooden plate and stack them all together, whereafter the 'digital' surface is smoothened to 'analog state' with sandpaper!

Actually I think the RC-guys makes wings in the same manner, just with styrofoam :-/

It's the same as shipbuilding there they made a drawing of half a hull then reversed the profiles to get the same shape on the other side.

There are if you look for them Profiles of aerofoils designed and tested by the RAE in the UK and NACA as was in America.
Somebody would sit down and work out the theoretical profile that should work and then they would draw that profile using standard drawing methods usually third angle projection. From this sections would be be taken at stations along the propellor and a jig made up with negative profiles which would allow for the twist in the chord to be included and a master blade would be made which would fit into this jig.This blade would then be used as a pattern to carve the next set of blades. These then would be tested to see if the actual performance matched the theoretical figures, the blade would then be tweaked until the desired performance was obtained and this would then be used on the aircraft.
Tis an arcane art but they've pretty much got it knocked these days. Not like the days when Sir Stanley Hooker joined RR and improved the performance of the superchargers by a large amount with a simple change to the shape of the rotors.