Billet Vs press-together crankshaft

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J.A.W.
J.A.W.
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Joined: Mon Sep 01, 2014 4:10 am
Location: Altair IV.

Re: Billet Vs press-together crankshaft

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The new press-together crankshaft shown below may be of topical interest.
(To see how it works directly, scroll vid across to ~2:05 mark):

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J.A.W.
J.A.W.
95
Joined: Mon Sep 01, 2014 4:10 am
Location: Altair IV.

Re: Billet Vs press-together crankshaft

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Mudflap wrote:
Tue Oct 06, 2020 10:24 pm
Greg Locock wrote:
Tue Oct 06, 2020 9:40 pm
That Ferrari F430 one is interesting. Notice how the counterweights are symmetrical for each throw? That's an old, and not especially efficient trick, to avoid having to do FEA and stuff. Basically treat each throw as a single cylinder engine. For a production engine your aim is usually trying to minimise the maximum load in the mains, and you can normally get a solution that achieves that with less mass for a given load by considering the crank as a flexible whole. FWIW it was about 2 kg on a straight 6.
It's funny how technology has evolved. When I started in the late 90's we used spreadsheets to calculate crankshaft bending loads as you say i.e. treating the crank as a statically determinate beam. We had simple frequency domain in-house codes to work out torsional loads and the FEA was done one HALF throw at a time.

Nowadays we just flush an entire crank through commercial multi body dynamics codes and fatigue solvers and it spits out factors of strength. It's probably twice as fast but when it goes wrong it can take days to debug.
Here's how R/R engineers did it for their V12 cranks - back in the day - via mental computation,
(courtesy of your ol' buddy Calum, scroll down the page): https://www.calum-douglas.com/design/
We are standing on the shoulders of Giants. So wash your feet.

Greg Locock
Greg Locock
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Joined: Fri Jun 29, 2012 11:48 pm

Re: Billet Vs press-together crankshaft

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It was one of those techniques that sort of got mentioned at uni, but the level of nitty gritty involved was never fleshed out. The handcalcs for main bearing loads at one speed and throttle opening were a day or so, for each counterweighting strategy. Incidentally if you are really into historical crankshaft design read Torsional Vibration by Kerr-Wilson.