JB Atoms

Doug wrote: I believe Mills engines used hardened pistons and cylinder, and because of this were virtually impossible to wear out. A modern example of this set up is the very high quality Peter Burford 0.3cc engine. This explanation on his web site states that a small variation in hardness is enough to prevent galling. See www.peterburford.com.au/construction/
Doug

Thanks Doug, Mr Burford is a man after my own heart and has me drooling over some (all?) of the machines he has!
Certainly the Indian Mills have not been hardened anywhere!
Boz, General engineering practice is that Ball races can be hard outer, hard balls and hard inner because there is no slippage between surfaces. (Paradoxically using too good a grease (Molybdenum disulphide for example) encourages slide, leading to the rapid demise of the race)
Where you have two surfaces with differing speeds it is normal in the motor industry to fit a dissimilar material as a carrier, bronze or white metal are examples. The thinking is that the softer material picks up any impurities in the oil, these impurities (grit etc) could cause galling elsewhere in the machine.
As Mr Burford says, a difference of 7 Rockwell hardness's is enough to stop galling (pick up) and I still don't like the idea of running steel on steel!

I love it! Everywhere you look there are more examples! It must be remembered that some things that are normal today are only possible with modern lubricants.
The piston ring/cylinder example is cheating a bit, the ring is very hard (try expanding one too far some time) and the cylinder is very soft (relatively speaking) otherwise you would never be able to re-bore. Mr Burfords' 7 points of Rockwell would appear to hold true. The problem with testing for Rockwell hardness is that the test damages the part, and I don't have the facilities.
To continue


This is the EN30B ready to turn, why is it coloured you ask? All types of steel have an international colour code, normally painted on the end of the bar stock. Once the bar stock end has been cut off it becomes the Storemans job to paint the code down the entire length of bar!
Most damage in factories is caused by incorrect steels being fed into the system!

Cutting steel is always a compromise, surface speed too fast and you burn the cutting tool, too slow and your tip loads go sky high and the tip chips and abrades. The above pic is .5mm coming off at about 300ft/min, you can see the heat is coming off with the chip (the swarf is blue) the spiral is the spring cut as I rapid return from the last cut.


Here I've doubled the feed rate in an attempt to get the chip to break. This is a cheap Chinese machine, the spindle speed has dropped and the chip is no longer curling, answer, more horse power, I don't have any. (It's 1.5Hp, belt drive)


The material turned down the the outside diameter of the crank web, our first objective.

Second objective is to go down to close to shaft size. But first compare with the finished article.


Then down to shaft size, plus a bit.


I've left about .2mm (8thou), I hope this will be enough for lapping.

At this point I'm worried about the shaft pushing away from the cutter and becoming taper so I've decided to centre the end so I can use a running centre.


I will then thread the end 2BA while I still have the advantage of the thicker shaft.


I always make a drawing for posterity, my Engineering master at school would have had a fit! But at least I know what it looks like!

Of course as you get older it can take a while for the penny to drop! The reason there is a stud in the nose as a prop driver is because the shaft is so hard! The shaft is like glass so the separate stud is used because in any accident the crankshaft would break!
The manufacturers intended to have all surfaces glass hard to reduce friction and enhance life, personally I don't think they've gone the right way about it, and certainly the reviewer in the article was not overly impressed. He battled to get one engine to run consistently and the other took a long time to approach consistency and higher revs. It got so hot he had to pour raw fuel over the crankcase to cool it down!
A brief word about terminology, hard is not necessarily strong, tough is not necessarily hard. Hard and tough together is good, today we can surface harden a tough material using a coil driven at high frequency. When we pass a shaft through the coil the surface heats up and we then quench immediately using a ring of fluid jets. This gives us the best of both worlds, a glass hard outer with a tough inner as support. We can even control the degree and depth of hardness by adjusting frequency, current, speed of pass, and type of fluid used for quenching.
If we want to get really fancy we now have steels that must be heated in an oven containing an inert (specific) gas and held within 5^o of a specific temperature for a specific length of time Using todays methods we could make model engines that will literally last for ever, running on a breath of oil, or no oil in the case of a petrol engine. The only problem would be, we couldn't afford them!

It's not an option at the moment, perhaps John (OT) can do it when he's older. I don't know how this material will react to heating and quenching, at the moment after finish lapping it's .03mm larger than the sample, any 'pull' in the structure will mean it will no longer fit.
To continue, threading after first checking the thread is correct.




finish lapped with the driver taper machined.

and ready to part off, not a job I enjoy, it needs a really rigid machine because the tip is so wide at 3mm

Now the shaft is size we have to take care not to damage it. This is a split block in a 4 jaw chuck, the hole is about .0005" under size so we can grip the shaft without hurting it.


And with the shaft blank in place.


And make sure it's running true.