Quality Billet crank

I was wondering if 4130 is ever made in billet or bloom instead of bars. I've been thinking of making a Nourish style crank which has the triangular bobweight in the middle and not a full circle flywheel. The machining would be much easier and cheaper. - Cut out a rectangle and go from there. It would probably get away from the problem of the inclusions in the centre of the barstock

Deets55 said:

Same here, still have my first slide rule. Bought my first calculator in 1973. All it did was add, subtract, multiple, and divide. Cost $100.00.
But then there was Polish Notation (H.P.?) I think.

Click to expand...

There still is. On my HP I use every day.

acotrel said:

I was wondering if 4130 is ever made in billet or bloom instead of bars. I've been thinking of making a Nourish style crank which has the triangular bobweight in the middle and not a full circle flywheel. The machining would be much easier and cheaper. - Cut out a rectangle and go from there. It would probably get away from the problem of the inclusions in the centre of the barstock

Click to expand...

Not sure what you mean by bloom. In the US the term usually refers to sponge iron, which you certainly wouldn't want to use for a crankshaft. Similar problem with the term billet. Used to be it meant a square or rectangular chunk of metal, whether cast, forged, or rolled. If you're asking whether 4340 is available in plate, from which you could easily make flywheels, the answer is yes. It is commonly available (at least in the US) in plate, sheet, tube, wire, and bar form. You can buy squares and rectangles of 4340 plate in thicknesses from fractional inches up to at least 6 inches, usually in annealed condition.

Ken

6 inch plate would probably be big enough to rough out a Nourish type crank. I'll have a search to see if anyone carries it in Australia. The problem is that most of our engineering industries are essentially low-tech these days. I cannot think of an application here, which would require anything other than barstock in 4130. I've often thought about making another billet crank, however the possibility of the sulphide inclusion in the middle of the bar has always put me off the idea. With a piece of very thick plate, the risk would be greatly reduced. Over the years I've seen a lot of sulphur prints done on the end of steel bars, the inclusions are almost invariably there, and they would be where the mainshafts end up in the finished crank.
About the Nourish crank - I've been wondering whether there is an advantage in having the circular flywheel. The Nourish simply has a big wedge shaped bob-weight in the middle. A friend of mine has one in a 750cc Triumph - it seems to work OK. It's an expensive exercise if the crank ends up being useless.

Billets, slabs and blooms :

http://www.globalspec.com/learnmore/mat ... abs_blooms

What have you guys made cranks out of ?

acotrel said:

Billets, slabs and blooms :

http://www.globalspec.com/learnmore/mat ... abs_blooms

What have you guys made cranks out of ?

Click to expand...

4340 VAR is pretty common for custom crankshafts in the US. In the UK the steel of choice used to be EN40B. As far as I know, all the ones for motorcycles are machined from a large lump of round bar. The vacuum arc remelt process seriously reduces the amount of contaminants in 4340, making a very clean steel. I've never heard of anyone worrying about sulphide inclusion as an issue. You can buy 4340 double, and even triple remelt bars, complete with certificates of compliance to very tight aerospace and military specs. The lump I had, that comnoz turned into a crankshaft for his bike, was from a double melt bar, with a vacuum induction melt, followed by a vacuum arc remelt, called a VIM VAR process by Fry's Steel, where I purchased it. I think it was certified to MIL-S-8844 CL1. You can find the spec online, and look at the limits on inclusions and sulfur content, if that is of any interest to you.

If I'm missing something here, so are all the companies manufacturing shafts and gears and such from 4340. It just doesn't look to me like you gain anything from starting with plate instead of round bar. More important is to choose the right quality of material. I misread your post and thought you were thinking about just making the flywheel out of plate, which seemed like a reasonable plan, and has been done by a number of folks already.

Ken