crankshaft

[refinery mike]

I had this plan to build a 4 cylinder boxer engine. and it was a brilliant plan,,,,,until ,,, well does anyone have any suggestions on building my crankshaft. I was just taking a little roughing cut.
And yes i do resemble "Crankshaft" in the funny papers.

[gcarsen]

Practice makes perfect, probably not what you want to here! just think, it will take less time to get this far on the next one!!
When I was taking shop class in High School. I built a 2 cyl steam engine with a double throw crank. took 3 times to finally get one crankshaft to come out.
the first one just fell in half while in the lathe, I mean literaly fell apart into 2 pieces. wrong kind of matl that finally fatigue broke,
the second one, while milling the flats on the side. I left the wrench on the drawbar. started up the mill, bang! wrench hit, lossened and backed of the drawbar, the insert cutter fell out of the spindle, caught the crank between the throws and bent it,,, only thing hurt was my pride and my now scrap crank. never did that one again!
third time I got it right. My old shop instructer still talks about that project 25 years latter. how many high school kids can say they turned a crankshaft. took the engine into my first job aplication and was hired into the aprenticeship basicaly on the spot.

[Rick]

Built a crank for the Kozo (original shay) three throws, 6 eccentrics. One very important step was to add temperary stiffeners in the throws that you are not machining, These were closely fit spacers with bolts thru them to clamp each side of the throw as to make it a more of a solid piece and not give it any room to colapse or twist. Then lots and lots of light cuts with a large helping of patience.

[refinery mike]

Temporary stiffiners , now that makes sense. i can picture it. Thank you thank you thank you and i will work on that patience thing.

[hammermill]

i think most folks who have tried a crackshaft have had the same learning curve mike, i used nuts,bolts and supper glue to hold things on the last steam engine project.

here i one example

http://www.homemodelenginemachinist.com ... ic=5234.30

[gaston]

use steel and counter weights while turning. Looks like you were trying to make it from "soft metal" , don't think that will work too well

[wally318]

Just an observation.
From what I can see, the crank looks to be out of aluminum,
which won't be anywhere as rigid as a steel one.

[stevec]

i think most folks who have tried a crackshaft have had the same learning curve mike, i used nuts,bolts and supper glue to hold things on the last steam engine project.

Hey hammer, dontcha think that's what Mike's trying to avoid?
Thanks for the link, that was cool.
Steve

[refinery mike]

no it was steel, but the spacer thing is what i needed. i could actualy see it bend a little when i tightened the tail stock on the crank. no wonder it got loose. I guess it was the flash that made it look like aluminum. Thanks again you guys always come through for me.

[coal miner]

Here's another way that kept the webs of the crankshaft in line . Single throw , but the spacer was a .0005 interference fit and held in place w/ some wire for safety . Turning between centers .





And finished .

[Fender]

What type of steel were you using? Might be easier to make with an alloy which has greater strength, but still machinable with hss, such as 4140 pre-hard.

[Harold_V]

What type of steel were you using? Might be easier to make with an alloy which has greater strength, but still machinable with hss, such as 4140 pre-hard.

I'd also suggest the use of Stressproof. It's not available as flat bar, but it would be easy enough to make it from round stock. It has wonderful machining characteristics and more than adequate tensile strength.

Harold