Turning a crankshaft

[Grumpy John]

After turning a crankshaft at groggys last Sunday I thought that it might be fun to have a crack at something more realistic. I searched the internet for a drawing of a crankshaft and came up with this.

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Using a vernier I roughly dimensioned the drawing.

I located what I thought would be a suitable piece of timber and cut it to length, mounted it between centres and did a test cut at each end to make sure it would turn to size.

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I then roughed out to the largest diameter and marked the position of the 2 large diameters and using a useless* 6mm parting tool I turned them to size.

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I then turned a 40mm spigot for the Escoulen cup chuck.

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I then mounted the blank in the Escoulen chuck and marked the position of #2 main bearing and turned it to size.

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I marked where the 4 pin bearing diameters were located and removed some excess weight to help minimise vibration. I also marked the corresponding points on the chuck body.
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Time to have some fun. I offset the chuck 25.5 mm and adjusted the counterweights as best I could. There was still some vibration (note to self, make some extra weights to bolt on to the counterweights), but I could get the lathe up to ~350 RPM without shaking everything to pieces. If you look closely at the chuck you can see the offset. I then turned pin dia. #2.

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Pin #4 went without a hitch, but it was obvious by now that I had not chosen a very suitable piece of timber for this project as there were a few splits developing. After barely touching the tool (the useless* 6 mm parting tool) to the timber the whole thing fell apart :doh:.

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Things I have learnt from this project:
1. Cypress Pine is NOT suitable material for making a crankshaft.
2. don't do the offset in one hit, sneak up on it in 5mm increments.
3. The Escoulen chuck is good fun if you're not scared of turning air.

I would love to have another shot at turning a crankshaft, but this time with a more suitable blank. Can anyone recommend a suitable timber for this project. I'm thinking one of the dense desert timbers i.e Gidgee etc., but you don't usually get them as big as 95mm dia.



*Sorry Jeff, I couldn't help myelf :p.

[artme]

Better for it to fall apart there than after being installed in the vehicle!!:D:D:p:p

[RETIRED]

Merbau.

[Grumpy John]

Merbau.

What about glued together strips of Merbau decking. And you can be more verbose if you like or even if you don't like :p :D.

[RETIRED]

What about glued together strips of Merbau decking. Not recommended. And you can be more verbose if you like or even if you don't like :p :D.Hmmm. :shrug::D

[China]

Jelutong

[Ad de Crom]

John, for practising for the fun as you are doing, I would recommend as startingpoint to use a rectangular beam of merbau or meranti. Only this stuff creates a lot of dust, which is not so nice, so be aware of that.
Have fun. Ad

[Ed Reiss]

gonna' build a wood engine to go with it ???

[hughie]

gonna' build a wood engine to go with it

watcha gonna use for oil BLO ? :U

[Manuka Jock]

watcha gonna use for oil BLO ? :U

and run it on turps :p

[tea lady]

I've got a 100mm aquare post of merbu you can play with if you like. (Not laminated. ) I'll take it to 's tommorow. You can pick it up from there whenever.:cool: (It was an off cut from something else. )

[Grumpy John]

That's very kind of you Anne-Maria :2tsup:.

[tea lady]

That's very kind of you Anne-Maria :2tsup:.:cool: Actually quite nice to have something I can give to someone else for a change.:U

[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

[Wilco Flier]

Maybe hard maple?

[Allen Neighbors]

Gutsy Bloke, GJ. :D When you get the whole thing finished, I want a short ride in it. :D

[Grumpy John]

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 :doh:.

[brendan stemp]

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

[Grumpy John]

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.

[rsser]

They say steel's pretty good.

Anyway, it's a VW design.

No wonder it bombed ;-}

Next step oval pistons?

[Woodwould]

Elm is highly split-resistant.


Next step oval pistons?

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

[rsser]

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

[Ozkaban]

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 :oo:

Cheers,
Dave

[rsser]

And one experience is enuff? ;-}

[Ozkaban]

And one experience is enuff? ;-}

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