Any Tips For Machining A Small Cast Crankshaft?

I had a thought, which is always dangerous. My thought was that if I can get the shaft machined to within, say, 15 thou of the final dimension I could use a file to get the rest of the way.

Unfortunately, this material is quite resistant to filing! I have filed CI before, and this does not behave like I would expect (given my limited experience).

The photo below shows my attempt at smoothing the surface with a file. I used about 30 strokes of the file to get this.

Crankshaft after filing.jpg

The surface has not changed in appearance.

I then tried some medium grit 3M emory cloth. That did nothing to surface (no photo, sorry).

The set up is certainly stout enough to get something of a result from filing and/or abrasive cloth.

The lathe filing and sanding were done at around 300 rpm. The file was sharp, and the emory cloth was new.

Thank you for your help.

Cheers,

Tom
 
sounds like it's seriously hard if a file won't make much of a mark on it. You probably have too much flex and vibration to use carbide at the speed it wants, and HSS will probably just rub. What does HSS sound like in the work - squeaking and howling? Or producing chips? I'd agree that the live center tip is a long long way out from the tailstock - it certainly doesn't look like a normal live center. Perhaps try a dead center with the tail stock quill retracted as far as possible? How much material do you have left to take off? Is it a small enough amount to use a dremel rigged up in the toolpost?

Also, even if you do get all that done, how are you going to turn the center journal?
 
Ok if I am way out of line please tell me as I am very green, but why are you trying to do this between
centers why can't you chuck one end in a 3 jaw as close to the cam as possible then turn and do the other half? Seems to me that would be a much more stable.
 
The shaft finishes at .375, sticking out four inches needs some sort of support. A dead center would supply a far better right end than that long a live center. Just grease it (lead pencil graphite would do) and turn it reasonably slow. After all, you got all day.
 
Kenny G said:
Ok if I am way out of line please tell me as I am very green, but why are you trying to do this between
centers why can't you chuck one end in a 3 jaw as close to the cam as possible then turn and do the other half? Seems to me that would be a much more stable.
Click to expand...
Kenny,
3 jaw scroll chucks are usually not perfectly centered for the entire range that they grasp. Independent jaw chucks, like many 4 jaw chucks, can be centered pretty accurately but it might take a little while, which must be redone every time it's removed and replaced. In fact I'm not sure you could ever remove and perfectly replace something from a chuck.
Working between centers it's very easy to remove and replace and return to exactly the same center.


Steve Shannon
 
The casting they supplied you looks very rough, if the file won't cut it probably was chilled and hardened. I built a #1 years ago and the crank machined nicely without the bridge between the mains. Didn't have a small lathe at the time that would hold decent tolerance, so it was done on the 17 inch Summit with a 12 inch 3 jaw holding a centre.
IMGP1200.jpg

Greg

IMGP1200.jpg
 
Steve Shannon said:
Kenny,
3 jaw scroll chucks are usually not perfectly centered for the entire range that they grasp. Independent jaw chucks, like many 4 jaw chucks, can be centered pretty accurately but it might take a little while, which must be redone every time it's removed and replaced. In fact I'm not sure you could ever remove and perfectly replace something from a chuck.
Working between centers it's very easy to remove and replace and return to exactly the same center.


Steve Shannon
Click to expand...

Steve thanks I think I understand, but it only raises more questions in my mind but will try to ask in a different thread so as not to hijack this one
 
Could it need to be annealed prior to turning to relieve internal stress.
This might reduce vibration and let it machine cleaner.
 
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