Crankshaft design

[ray jones 1Participant @rayjones1]

I am in the proces of constucting a Gardner O 1/2 scale engine. The engine is 2 inch stroke x 1.375 bore. The crank shaft is, diameter 0.5" ,. overall length 10inches .

The drawings just say, " crankshaft, from solid or fabricate./ steel."

My questions are,

1/ What type of steel would you recommend to use..

2/ Which would be the best option for construction, machine the item from solid or fabricate in sections.

I would welcome any suggestions and advice . thank you

[ray jones 1Participant @rayjones1]

crankshaft material options

[JasonBModerator @jasonb]

I've done it both ways on similar size engines.

From solid you can either use round bar or to reduce waste cut from flat bar. The main advantage is there is no risk of the joints failing but it takes longer to machine. This is the write-up I did on my slightly larger 1/2 scale domestic's crank

If building from solid then I silversolder the joints followed by drilling them for pins which are peined over into CSK holes, once filed off ther are all but invisible and you just see a ring of solder where it has filled the chamfer around the shafts like this one . With it pinned there should be little chance of things moving.

Most times I just use ENIA, you could go with the precision ground version of for something a little stronger EN3 or EN8

We do have someone on here that has built the Gardner but he does not post very often, maybe he will see this and say what he used on his.

[Ian S CParticipant @iansc]

Just finished a new crankshaft for the Stuart Turner S6, the old one had a slight wobble, I tryed straightening it. I made the new one from a bit of scrap that I had to machine down to a workable size, it machined well, the bearing jornals are as machined, no polishing required. No wobble. I,v got to the stage where I can't tell how low the pressure is that it stops running, the water trap on the compressor blows off around 8 to 10psi. Really pleased with the new crankshaft.

On my hot air engines, I fabricate single over hung cranks, but if I require two cranks on the shaft, I usually machine it from solid, the first of this type of crank that I made was fabricated, but I did'nt like the clean up(did'nt know about pickeling), and not long after instalation , it failed, that was back in 1991, and I saw it in the junk box the other day, The motor it was for is still going strong, on its second crank(third)shaft, wore the first one out. Ian S C

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