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machining billet crankshaft using KT dividing head

Great project !

Shows guts.
I´m not qualified to offer advice, but would appreciate pics..

Steel is the same strength and rigidity weather hardened or not. No ?

Does someone know if they actually need to be hardened ?
And why ?

Im purely asking out of curiosity.
Afaik with pressurised oil, its essentially a free running hydrostatic bearing, with no contact apart from start-up.

Any info is appreciated, as are any links.

You never fully harden a crankshaft.........it cracks and then breaks. Manufacturers will zone harden and do surface hardening at the journals by induction hardening, shot peening and nitriding. A crankshaft will be continually torsionally flexing. The choice of material and heat treat is critical. Material choice is driven by fatigue strength more than any other factor. The best advice I could deliver is "Don't re-invent the wheel!" The ICE has sustained continuous development for 120 years. Use what has been proven to work. Use 300m, 4140, 4340 or other equivalent CrMo alloys. Also, even these alloys come in different qualities of purity. Be careful and get certs when ordering your material.
 
Nice looking job Cuttergrinder, and a LOT of work (I know I've made several large model 2 cyl steam engine cranks)

As they say in my adopted county ''keep you a troshin bor'' :)
 
Update on the crankshaft project

A little update my crankshaft project. I left stock all over and then had the crankshaft heat treated and stress relieved. Now I am semi finishing it in the lathe. Here is a picture and also a short video of the crankshaft turning while centered on 2 of the rod journals. I cant figure out why I feel dizzy. Lol

Billet crankshaft centered off 2 of the rod journals - YouTube
 

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  • john deere crankshaft after hardening.jpg
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Well that's a thing, a fricken thing of beauty.

Very nice work so far and best of luck finishing it.
 
Interesting project, commendable effort.

Question: how are the counterweight sizes determined and how accurate do they have to be? It seems like a very complex thing to calculate, as you've got the rod portion going side to side, and up and down, and some fraction of the rod weight changes sides on the crank throw centerline itself effectively adding to and subtracting from its own weight imbalance. Meanwhile the piston only goes up and down. Or did somebody just WAG it and then finish by trial and error?
 
I turned some large cranks in the past. I believe something like 12 inch throw for a stamping press.One of the most stressful jobs I have ran in the lathe.always think before you made a move and make sure you were clear of the throws.
 
I did some research and from what I can gather, since the rods and pistons are very heavy in a diesel engine to get them hold up, there is just not enough room in the motor to make the counter weights the ideal weight. So I just made them as big as possible and still get the crank to spin in the block and miss the bottom of the pistons. An original john deere crankshaft has no counter weights at all on the 2nd and 5th cyl to make the crank easier to manufacture and the other ones only have 1 counter weight but the engine only turned a little over 2000 rpms. We are planning to spin this engine up around 6,000 rpm. Here is a poor picture of the crankshaft sitting in the block but I think you can still see that there just is not enough room to make the counter weights any bigger. I could drill holes in the counter weights and press in slugs of heavy metal like Mallory but it would be really expensive.
 

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  • crankshaft in block.jpg
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Beautiful project.
How did you cut the angles on the outside of the throws? They almost look turned, but obviously they can't be.

192753d1488678464-machining-billet-crankshaft-using-kt-dividing-head-john-deere-crankshaft-after-hardening.jpg
 
I machined those on the mill while the crankshaft was being rotated with the powered dividing head. I used a tapered cutter that I made that held 5 apkt carbide inserts. I still need to finish these since the crankshaft ran out about .090" after the heat treat. I am planning to use a universal horizontal mill and the dividing head arrangement to finish them using a long endmill by swiveling the table around to the proper angle.
 
Interesting project, commendable effort.

Question: how are the counterweight sizes determined and how accurate do they have to be? It seems like a very complex thing to calculate, as you've got the rod portion going side to side, and up and down, and some fraction of the rod weight changes sides on the crank throw centerline itself effectively adding to and subtracting from its own weight imbalance. Meanwhile the piston only goes up and down. Or did somebody just WAG it and then finish by trial and error?
Something I found pretty interesting asking around about this a while ago, you can just neutral balance the crank and flywheel on an inline.

On his six there's two pistons at top (or bottom), two coming down, and two going up at any one time, they're all balancing themselves out, provided the pistons and rods are the same weight, and the rods have the same weight distribution big end/small end.

When you have a vee motor then you run into more complex balancing.
 








 
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