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jdunmyer
12-04-2005, 01:05 PM
My buddy & I are building 3 model engines, using Debolt Machine casting kits. The crankshaft is shown as a 5-piece buildup or optionally, a one-piece outfit, machined from the solid. OAL is 14", all shafts are 7/8" diameter. Having never done one of these, we have had to do a bit of head-scratching.

Our planned procedure is to make the throws, including the hole for the crankpin, but NOT the hole for the shafts. Press the throws and crankpin together. Have a friend TIG weld the assembly. Bore the throws in one setup in the B'Port, sizing for a shrink fit. Heat the throws and slide the shafts in. Hope that it ends up being straight, attempt to straighten if not.

Does this sound like a plan that's likely to be successful? Would we be better off turning it from the solid, using the procedures outlined in some old message threads? (I did do the search thing here)

Mcgyver
12-04-2005, 01:47 PM
as a five piece built up crank, its obviously 1 throw. I've made a number out of solid, from 1 to 3 throws, and the trick is to turn the cranks first, and then duct tape in place an accurately made spacer between the webs.

if its a single throw, you can saw it out of a piece of flat stock - really reduces the material to remove vs from round.

on this page http://www.users.bigpond.net.au/cowiepeters/
there is a good description of a built up crank and the force calculations on the required press fit and material. its also one of the nicest metal working sites on the web imo.

If you are machining afterwards, perhaps welding is ok, but then again one of the benefits of a built up crank is avoiding machining a large crank


[This message has been edited by Mcgyver (edited 12-04-2005).]