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Crankshaft


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  #1  
Old 12-16-2007, 12:01:25 AM
Jerry B Jerry B is offline
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Default Crankshaft

Can A Small Crankshaft About 1 ' Long , Be Maded Out Of A Slid Pice Of Metal On A Lathe Jerry B
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Old 12-16-2007, 12:36:46 AM
J Dayman J Dayman is offline
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Default Re: Crankshaft

It can but it takes a lot of patience. Start with a flat bar blank the thickness of the crank webs, and mark out the plan view of the crank on it plus say an extra inch each end. On the ends, centerdrill accurately at both the centres of the main shaft and the journals. Bandsaw out the excess material, leaving the extra inch on at each end to keep the centers. put the bar in the lathe on the main shaft centers and turn them, again leaving the extra inch at the ends. TURN VERY SLOWLY and take very light cuts. This part is where it takes patience. if you go too fast you will hear a KA CHUNK and the crank will be airbourne. After the main shafts are done, take the crank out and put it back between centers but this time mount it on the journal centers. Turn the journal, again go slow. After doing the journals and cleaning up the sides of the crank webs, take the shaft out and cut the extra inch pieces off the ends.

At this point breathe a big sigh and get a cold drink of your choice - you earned it.

I've done a few cranks this way, it's not all that much fun, but it can certainly be done by anyone who has done some practice experience on their lathe.

Hint - use only hot rolled steel, and anneal/normalise it well before starting (heat to red and slow cool a few times in sand or ashes). If it is not annealed the crank could spring out of true while you are turning it, and you will have a wobbling unit rather than a dead true crank. Cold rolled steel has a lot of internal stress from the rolling and will spring real bad if big chunks are cut away.

Good luck, Jeff
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Old 12-16-2007, 05:12:30 AM
Roger U Roger U is offline
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Default Re: Crankshaft

The more roughing out of material before you start tuning the better if you happen to have a milling machine then you can remove metal very close to the finished size. When you start machining larger crankshafts from solid then it is best to use a steady when turning the mains as the crankshaft can flex even with light cuts Roger
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Old 12-16-2007, 11:40:12 AM
Tim Christoff Tim Christoff is offline
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Default Re: Crankshaft

On all the cranks I've done I will lay the crank out on the flat bar stock, I always use stress proof steel, then cut out most of what is not needed in the crank throw. Put this in the lathe and turn to final size. Take out, and then expoxy a scrap piece of steel in the throw to keep it ridge as possaible, put the crank in the mill and take out all the excess material on the main shaft on each side, put back in the lathe, turn one side to finish size, take out and turn around, chuck up this time and turn the last main to finish size. With practice, you can turn a 1 cyl crank in less than an hour this way. I did a 2 cyl crank in about an hour and 15 min once with this method and it turned out great.

Tim Christoff
Basehor Ks.
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Old 12-16-2007, 02:13:39 PM
peterR peterR is offline
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Default Re: Crankshaft

I have just fabricated a crankshaft for a 2 hp Bulldog using 1.375" precision ground steel for the main journal and 2"x1" steel for the webs. The big end was turned from a larger piece of steel to create the shoulders. Bore holes in the webs for both journals (clamp both together and bore together to ensure complete accuracy). Shape the webs to the required profile. Assemble checking squareness and all measurements then clamp to a piece of flat steel to retain settings.

Drill 5/16" holes through each web and journal (4 holes) then insert 5/16" steel pegs (longer than required).

Set up on mill and mill keyways then mark each joint so it can be reassembled the same way.

Strip down then clean and degrease the journal steel and holes in the web. Scrape grooves inside each hole to help with later distribution of braze Apply brazing flux and reassemble ensuring all joints are the same as drilled. Check squareness and measurements.

Heat and braze, the flux drawing braze into each joint. When cold cut through main journal between web with a hacksaw and tidy with a file. Trim pegs. Tidy with file/grinder to desired shape. For the smaller open crank engine this method is plenty strong enough.

Photo shows finished article. If you need more details send me a message.

Peter
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Old 12-16-2007, 06:57:41 PM
Kelly Tytlandsvik Kelly Tytlandsvik is offline
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Default Re: Crankshaft

Here is photo of a Crankshaft being made for a MODEL B Ford engine. The fellow is going to try to set a land speed record for its class. It is whittled out of one piece. Not exactly model engineering but the same idea.

Kelly T

http://www.smokstak.com/gallery/file...icture_233.jpg

http://www.smokstak.com/gallery/file...icture_235.jpg
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  #7  
Old 12-18-2007, 11:11:04 PM
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Wayne Grenning Wayne Grenning is offline
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Default Re: Crankshaft

Kelly - That is very impressive! Wow
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Old 12-19-2007, 01:33:46 AM
Kelly Tytlandsvik Kelly Tytlandsvik is offline
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Default Re: Crankshaft

It is nothing compared to the rest of the work they are doing but that could be a thread all of its own. But I can't give all their speed secrets away!

Kelly T
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Old 02-12-2008, 10:28:32 AM
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putputman putputman is offline
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Default Re: Crankshaft

Tim, what kind of stress proof steel do you use? I have use 1144 but it is only available in round stock locally. That is just too much material to remove.
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Old 02-12-2008, 10:55:18 AM
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Forrest A Forrest A is offline
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Default Re: Crankshaft

Here is a picture of a couple small cranks. The small crank has 1/16" diameters on throw and journals. The larger is a 3/4 inch stroke with 1/4 inch journals and throw. Single crank pin cranks are easily done with just a four jaw chuck and center in the tail-stock. A hack saw or mill can be used to remove large amounts of material before turning final diameters. The large crank is hot rolled steel (stress proof) where as the small crank is 12L14 which will be heat treated.

Forrest A
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Old 02-12-2008, 01:00:45 PM
Tim Christoff Tim Christoff is offline
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Default Re: Crankshaft

The stuff I use for the cranks is cold roll that has been stress relieved. I can't tell you the name of it because I don't know, a good friend of mine's father gets it for use and it is in round stock form. What I will do is put it in the mill and use a 3 bit flycutter at around 3200 rpm and just plow off 250 to 375 thousands at a time across the full surface. The chips will fly all over the place and are very hot but it only takes a few min to get it down to the right size. I called my friend to find out the number and he didn't know what it was but will ask his father the next time he talks to him.

Tim Christoff
Basehor Ks.
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