Thread: Turning a crankshaft

Originally Posted by joe greiner

Instead of "swinging for the fences," admirable though it may be, try using a design with less offset (1/2 piston stroke), so that there's some continuous long grain throughout. The original design relies on cross-grain bending strength, which is very low in almost any timber. In fact, building codes in earthquake and wind territory forbid reliance on cross-grain load paths for lateral resistance.

The crank journals can also be made larger diameter to provide overlapping of the cross section to achieve continuous long grain. For an operating replica, the deviation from "reality" could be reduced by making the piston rod ends in thinner rings.

Cheers,
Joe

Very good point Joe, quite obvious when you think about it .

how about a piece of cypress pine WITHOUT a great big split in it. Looks like this is why it fell apart on you.

Brendan, there were a few hairline splits in the piece when I started turning and I was hoping that they were only surface checking but these opened further as I progressed. I'm not upset, nor surprised that it fell apart. I was just having a play around to work out how to tackle the job once I found a more suitable piece of timber.

They say steel's pretty good.

Anyway, it's a VW design.

No wonder it bombed ;-}

Next step oval pistons?

Elm is highly split-resistant.

Originally Posted by rsser

Next step oval pistons?

I've got a Honda oval piston in a box somewhere.

Yeah, IIRC they ran some bike race engines with them.

That's pretty cool, GJ. Fun playing with stuff like that.

As for turning air, no probs. The nice long scar on my left fore finger reminds me however that the air does tend to stop at some point, and it can be abrupt

Cheers,
Dave

And one experience is enuff? ;-}

Originally Posted by rsser

And one experience is enuff? ;-}

For any normal, rational person, yes. dunno if I will learn that quickly though