Quality Billet crank

I always thought that Young's modulus was about load and extension. Ductility and fatigue life come into this. 4140 is a nickel chrome low alloy steel, probably 70 TSI un heat treated and 90 TSI quenched and tempered. If it has few inclusions it would be unlikely to break when made into that crank. Safety factors are related to the 0.1 % proof stress - in this application it is similar to aircraft landing gear.
Do you agree that is a weld holding the flywheel ? if it is going to break that is the likely position.

acotrel said:

Do you agree that is a weld holding the flywheel ?

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I think we need some details of how that 'one piece' crank was actually made.

Having a weld there would certainly kill the one piece claim,
and that would then be a weakness in about the most stressed part of the crank,
which would make a nonsense of the one piece = strength claim.

Could a large spark eroder carve out that shape, and still leave something useable ?
Could a plasma cutter or even an oxy assist in carving that shape and leave something useful... ?

This photo should clear up and question about it being machined. Of course its machined - its billet.

How did they machine the flywheel ?

Yep, Thats fully machined! Just the product of modern CNC. Just look on you tube that a 7 axis can do.

Nice looking crank, Jim. Please post more details when you can.

Ken

All steels have pretty much the same modulus" Not really.... try bending High speed steel :!: I bet a crank made from HSS would be good..not sure how it would be machined :lol:

X-file said:

john robert bould said:

will it flex?

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It will flex as much as any other steel crank made in the same thickness.
All steels have pretty much the same modulus of elasticity. If the crank is made of stronger material, you can flex it further before it breaks.

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john robert bould said:

All steels have pretty much the same modulus" Not really.... try bending High speed steel :!: I bet a crank made from HSS would be good..not sure how it would be machined :lol:

X-file said:

john robert bould said:

will it flex?

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It will flex as much as any other steel crank made in the same thickness.
All steels have pretty much the same modulus of elasticity. If the crank is made of stronger material, you can flex it further before it breaks.

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Sorry John,

but like X-file said, pretty much all steels really do have roughly the same Young's Modulus (Elastic Modulus E), somewhere between 200 to 210 GPa at normal temperatures, including most HSS alloys as well as the usual high end crankshaft steels like 4340. I found some specialty steels, including some HSS, that are up to maybe 230 - 240 GPa, but that's not really a big difference, and some of those alloys have other properties that would make them less suitable for crankshafts. You do see huge differences in tensile strength between different alloys, but we were talking about flex (bending), and that's determined by the modulus, not the strength.

I had a design engineer from Boeing try to convince me that we should make a Commando crankshaft from titanium (ti design was his specialty). which has about half the modulus of steel. When I pointed out the Commando design with no center or outrigger bearings, he agreed that wasn't a good application.

Ken

according to the latest classic racer magazine,mick hemmings is offering one piece billet cranks for Norton and triumph motors,they are being manufactured by a well known company in the car racing world, but does,nt state which company,my guess would be cosworth, contact mick for details. chris

I don't think a titanium crank would be very good. For one thing it would be too light, and another unless the journals were chromed or similar a regrind would always present problems achieving dimension. The other thing about titanium is that it can reduce in dimension dramatically if any hammering occurs. Interesting about the capabilities of CNC machining. I would have thought the same problems would exist if you had to machine around the corner into that flywheel.

Well, Cosworth is just across town from Mick, but there are quite a few other companies who produce components for the F1 industry in the UK.
In fact its quite a long list. My guess would centre more on people like Arrow, who are very amenable to short runs and one offs (at a price), and already do quite a bit of bike stuff.

Cosworth is a bit of a conglomerate these days , likely not their thing , unless your a Sheik. E before eye .

Just a guess , but TVR is a limited volume outfit with a engine manufacturing plant .

That's been machined all over and I don't think it was done on a CNC machine because the finish where it hasn't been ground isn't good enough. It's a nice job but the tell tales that suggest it wasn't CNC machined are the tear marks on the surface finish of the inside faces and the fact that the blend radius between those inner faces and the 'throw' for the big end isn't a true radius when you look at the 3rd picture down.

I'd be a lot more impressed if it was made from a forging because if that's been made from a billet it's got too many stress point on it. If I'd been making it for myself I'd have been polishing out all those machining marks and smoothing out all the rads with a small die grinder and abracaps but when someone else is paying for it the additional costs would probably push it over the limit.

I've spent a lot of years machining complex components and that's a good piece of machining but if the manufacturer was going to start producing them on even a moderate scale (maybe a batch of 20?) I'm pretty sure by the time they got to the 5th one it'd be a lot nicer.

Great photos, thanks for taking the time to post them jim.

Andy_B said:

That's been machined all over and I don't think it was done on a CNC machine because the finish where it hasn't been ground isn't good enough. It's a nice job but the tell tales that suggest it wasn't CNC machined are the tear marks on the surface finish of the inside faces and the fact that the blend radius between those inner faces and the 'throw' for the big end isn't a true radius when you look at the 3rd picture down.

I'd be a lot more impressed if it was made from a forging because if that's been made from a billet it's got too many stress point on it. If I'd been making it for myself I'd have been polishing out all those machining marks and smoothing out all the rads with a small die grinder and abracaps but when someone else is paying for it the additional costs would probably push it over the limit.

I've spent a lot of years machining complex components and that's a good piece of machining but if the manufacturer was going to start producing them on even a moderate scale (maybe a batch of 20?) I'm pretty sure by the time they got to the 5th one it'd be a lot nicer.

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No it is not CNC. It does not have to be machined to a smooth polish in the flywheel area because steel cranks never break there. The only place they break is at the PTO shaft and the radius on the outboard side of the right side journal where all the power is being applied - and this only happens to hollow bolt up cranks with sludge traps. Its NEVER going to break where the journals join the flywheel.

No one makes a forged crank for a Nort and I doubt that will ever happen.

Look at the polish and the .090" radius at the base of the PTO shaft - you can't get better than that. Also look at the polish and .090 " radius on the sides of the journal - its perfect. This is a solid crank and its not going to break at the journal - that happen's to hollow bolt up cranks with sludge traps because they are weaker.

What makes this crank special is that its one piece and only weights 23 lbs. And its affordable. Make an absolutely perfect polished crank and no one is going to pay the absolutely perfect polished price. Check out another one of these cranks below and take a close look at the finish.

My comments weren't meant as a criticism; some were suggesting it wasn't a one piece crank or that it had been done on a multi axis CNC and I said it hasn't and I've no doubt that it's a one piece crank.

Once you get into the realms of forged crankshafts the costs are so high that nobody would bother even looking at one and the only way it'll ever happen is if someone owns both a Norton and a small forging company and wants to make it because they're bored and don't care about what it costs. Anybody out there in this position? 8)

I honestly think it's a good bit of machining and it's only because I've often got too much time on my hands that I suggested it might be worth polishing the rads with Abracaps because it's what I'd do if it was mine. I don't know who machined it and whether or not they're looking at doing a small production run but I'm pretty much convinced it was done by someone with limited access to modern machines but a lot of years experience behind them which is why they managed to machine it in the first place and why the surface finish shows signs of tearing which means it wasn't rattled off at high speed on a CNC.

I used to finish machine multi stage turbine rotors on a manual centre lathe and we had to turn them then polish them using emery tape lubricated with oil to float any debris away then finally finish using wet/dry paper lubricated with paraffin because the surface cracks generated by grinding caused long term damage even though they were invisible to the eye. Ok, a turbine rotor runs at a hell of a lot higher speed than a Norton crankshaft but if you've got the time why not aim for the same levels of finish? I'd also prefer to burnish bearing diameters rather than grind them but I'm awkward like that :wink:

Andy, The flywheel is machined around the corner around the weight on the side opposite the journals. How would you achieve that, if you were making the shaft ? I can't get my head around the length and shape of the tool needed to do that. Dave Nourish's shafts were simply a billet with straight cuts to the journals, and the exterior cut to a triangular shape to give bob weights. This one has the flywheel interior machined and it is circular. It is a lovely piece of work, however I cannot imagine how it is machined into that shape.

You could do it with a concave end mill of the right diameter with an extended shaft, and a rotary table, but it would be really time consuming and tedious. A multi-axis CNC mill could do the same much more efficiently, but Jim already told us that this was not done on CNC equipment. I'm looking forward to hearing the details eventually.

Ken

Me want. :lol:

i guess the internal finnish is "Rough" because the lack ofg ridgity of the long 90degree tool used to get around the corner. it took some "hogging out" thats for sure...ask me to make one from solid...i would CNC the bulk away for speed,,then finnish with a 90 cranked tool the remove that material around the corner... problem is the 90 tool would be long so small cuts only. That interal finnish is tipicial of lack of ridgity.

acotrel said:

Andy, The flywheel is machined around the corner around the weight on the side opposite the journals. How would you achieve that, if you were making the shaft ? I can't get my head around the length and shape of the tool needed to do that. Dave Nourish's shafts were simply a billet with straight cuts to the journals, and the exterior cut to a triangular shape to give bob weights. This one has the flywheel interior machined and it is circular. It is a lovely piece of work, however I cannot imagine how it is machined into that shape.

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