forged crankshaft

[Russell FurzerParticipant @russellfurzer50760]

I am making the OB Bolton triple.

I realise that making the crankshaft in bits and cobbling them together is one route forward (and perhaps full scale practice).

I had originally planned to machine the crank from a MS round bar but am a bit appalled by the prospect of making all that swarf out of stock.

I now wonder about using a 1.5 x 0.5" bar, cutting the crank webs out in the same plane, rough turning the main bearing parts of the shaft then heating and twisting the bar to give the crank offsets, then finishing the machining in a routine manner.

Anyone tried that?

[Russell FurzerParticipant @russellfurzer50760]

[John McNamaraParticipant @johnmcnamara74883]

Yep it is quite common in industry

**LINK**

Regards
John

[John OlsenParticipant @johnolsen79199]

I'm pretty sure it has been written up in the ME, although I can't remember when. It is certainly not uncommon to twist a flat blank in model sizes, and was done in full size steam practice too. Professor Chaddock many years back suggested using a milling machine to remove as much as possible of the stock, with the shaft mounted between centres. I have done this a few times, including making a shaft for a Stuart Triple from one piece, including all the eccentrics. A two throw shaft for a Double Ten went from a three pound blank to a three ounce shaft.

For larger shafts you can make a pattern and have it cast in Spheroidal Graphite iron. I did this for my Leak Compound, which greatly reduced the amount to be machined away.

Back when I used to write for Model Engineer an article of mine about milling crankshafts was published.

John

[JasonBModerator @jasonb]

Different type of forging to what John has linked to but it should be possible

As the shaft has been roughed out you would need some form of jig to male sure it remained in line end to end as you twisted it. There may also be a tendancy for the twisted section to become a little shorter so allowance would have to be made to O/A length to compensate, a few practice pieces would be needed.

Heat would also need to be quite concentrated in the area of teh crank pins so Oxy torch rather than using a blacksmiths forge.

Edited By JasonB on 26/02/2014 08:04:05

[Author]

Posts