# Experimental Crankshaft



## dvbydt (Nov 25, 2010)

I cannot claim to be much of a model engine builder, I have reconned more fullsize ones, but I'm constantly amazed by the skill, patience and perseverance of the builds on here. In stevehuckss396 thread on the Small V8, I suggested that it might be possible to machine the crank in a big bore 4 jaw chuck. Nobody said "thats how I do it", so it's been bothering me and I had to try it. The advantage is that you can do all the heavy cutting close to the chuck, lestening the probability of chatter. 

My 6 ins 4 jaw has a bore of 1 3/4 ins so, there is enough to offset the crank. Not trying to make a crank for an engine, just try out the principle. Material to hand was CRS 25mm dia. The crank has 6mm offset, so on the mill I drilled one centre and 4 offsets. All other sizes are 6mm for webs 10mm for journals, with the end mains 12mm.

This is how it turned out, with some photos of the method. (I hope - haven't posted photos yet.)


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## dvbydt (Nov 25, 2010)

And some more photos :-


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## dvbydt (Nov 25, 2010)

So, what did I learn?

The main journals are under 0.075 TIR of the centre line, should be easy enough to get true but it would probably have been best to leave a final cut on them to be done between centres.

Use a stress relieved steel.

Time per journal was about 15 mins each - getting the journal centred, roughing out from the back, then a finish cut from the front.

OK now is the time for someone to say "Ian, have a look at this thread!"


Ian


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## Lakc (Nov 25, 2010)

The force is strong with this one. :

You try, and learn something, and the next time your a little bit smarter. Good job.


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## stevehuckss396 (Nov 25, 2010)

If I had your equipment that would be the way to go. My lathe has a 3/4 bore so i am stuck trying other methods.

Next time you try an experiment like that let me know and i'll send over a blueprint!! :big: :big:

Great job!

Steve


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## gbritnell (Nov 25, 2010)

Ian,
Have a look at this thread.
http://www.homemodelenginemachinist.com/index.php?topic=5673.0
gbritnell


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## dvbydt (Nov 26, 2010)

Steve,

The lathe is a 12 x36 with a VFD and the speed was 550 rpm. Like I said in aaiveprevios post - If you lived nearer, no problem.

One question you might be able to answer, why are all the model V8 crankshafts cross plane types like the ones used in cars? All F1 V8 engines are single plane and it would be much easier for the model maker to make them.

George,

I like it! Makes things a lot easier. With a lot of people now having access to CNC mills, thanks to Mach3, if they also have a 4th axis, could they not produce crankshafts almost to size on the mill, then just true them up on a lathe. Or am I being a bit naive?

Ian


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## stevehuckss396 (Nov 26, 2010)

dvbydt  said:
			
		

> One question you might be able to answer, why are all the model V8 crankshafts cross plane types like the ones used in cars? All F1 V8 engines are single plane and it would be much easier for the model maker to make them.



I think it's just a case of "we model what we know". That's the way they made them so that's the way I make them. This way everything is like the V8's I worked on in my hot rod days. Familiarity!


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## gbritnell (Nov 26, 2010)

Absolutely it could be CNC'd. It's just if you have a pretty elaborate CNC machining center.
[ame]http://www.youtube.com/watch?v=E1Fj1j8Sg1g[/ame]
George


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## dvbydt (Nov 27, 2010)

That vid is real eye candy! and to think someone gets paid to look after that machine.
I was hoping perhaps there had been an attempt to do the rough milling work with a cnc dividing head and a vertical mill. Don't hold your breath, I WILL NOT be trying that experiment anytime soon. (Mmmmm - let me think what I need is a nema 23 and .................)

Ian


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