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Old 02-06-2016, 06:40 PM   #11
grizelli
 
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I like it! My crank is a little more difficult because each cylinder has 2 opposed pistons, and one lags the other by around 15 degrees, so none of the crankpins are in line with any of the others - picture here of the first one maybe shows this a bit. In spite of this, loctiting all the webs to a single shaft would certainly help alignment and straightness.

Thanks a lot, you've given me plenty to chew on. Time to start making more swarf :-)

Cheers
Martin


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Old 02-07-2016, 04:21 AM   #12
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I just happened to be working my way through a pile of old MEW's rescued from a shed demolition job (no, I got there too late for the good stuff).

Issue 35 has a very good 11-page article on "Machining model crankshafts - materials, tooling and methods" and would be well worth rounding up a copy if you can.

It covers assembled and cast and one-piece machined crankshafts.


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Old 02-08-2016, 08:23 PM   #13
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Many thanks, I'll see if I can dig up a copy. I am currently deciding whether to go down the 'machine solid bar between centres', or the 'fabricate with lots of bars which are then mostly sawn off ' approaches. Plenty of other bits to work on which I decide.

Thanks again
Martin
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Old 04-21-2016, 11:11 AM   #14
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If you want to create an artificial crank, you can use a process of metal forming to as the forging process. In forging, a hot chunk of rolled cast iron is placed between heavy dies having the pattern of a crankshaft. The metal is squeezed into the crank's basic shape by applying extreme pressure from a forging press. The simplest crank forging dies are arranged in a single plane, which produces a crank forging that, has all the crankpins in one plane. To index the crank throws at 90 degrees, the raw forging is twisted to offset the journals in two planes to create the final raw crank blank.
You can use an improved forging process which includes forging the crank in two planes, so that all the journals are pressed into their final configuration. It eliminates the need to twist the crank to index the journals.
By using this method you get fewer internal stresses in the forging, as well as an improved grain flow in the cast iron. Crankshafts made with this type of tooling are called as non-twist forgings. Tooling for a non-twist forging is more complex and less durable than that for a simple flat forging. There is more excess material to be machined from such a blank to create a finished crankshaft. You can produce crankshafts forgings in huge volumes which are naturally gravitated to the lower cost and higher tooling life of a flat forging. These high-end non- twisted cranks can be easily used for many engines.
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Old 04-22-2016, 03:16 PM   #15
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Thanks for that, Cynthia. Unfortunately, even the last 60 years spent in all aspects of mechanical engineering has not yet persuaded me to invest in a massive furnace and a set of drop-hammers - oh, and of course, a building to put them in. I suspect that it might be overkill for the single model engine that I'm building, but thanks for reminding me of a process that I first learned about in 1963 when a flying piece of red-hot slag off a drop hammer hit me just below the eye


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