Any Tips For Machining A Small Cast Crankshaft?

[ogberi]

Try vertical shear tool, ground from HSS. Low cutting pressure, excellent finish, but low metal removal rate. Easy to grind and resharpen, though.

 

[stupoty]

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.

Centers should be one of the most secure holding meathods as it's possitively locked in every direction.

The amount of flex in the work piece is somthing else though.

Stuart.

 

[Billh50]

I would do what Billy G suggested and use a follower steady rest. But you might also try something that sometimes works. The reason I asked if that was tape is because I have used rubber strips in the past to absorb vibrations. I wrapped the part tightly where I was not machining and secured it with a staple. It did make a better finish.

 

[tomw]

Overhanging the tool 1/2 of its length is probably not beneficial, but what do I know?

I noticed that as well. I was mainly pointing out the rubber wrapping he used as a vibration damper.

What does HSS sound like in the work - squeaking and howling?

High pitched squealing. I get chips, but it certainly doesn't cut very deep. If I try a 5 thou cut, I might remove 2 thou, and not evenly.

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?

I have tried a dead center, and I have tried to have less stick out. The odd looking live center is Sherline's way of making an adjustable tail stock. The non-adjustable tailstock is the one part of this lathe I don't like.

I need to reduce the diameter 60 thou total on both ends and the central rod journal. That is a lot of grinding.

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.

Wow, that looks like a really nice crankshaft! Your set up doesn't really look much different from mine, except for the larger machine.

If the casting has been chilled and hardened, can I heat it up to anneal it? Will that work on CI?

Thank you all for your help.

Regards,

Tom

 

[TommyD]

Personnaly, I think Matt the muppet and a few others identified the problem, vibration caused by an off-center weight on a thin, long shafh. You have to dampen the vibration and the follower rest or a steady rest would probably go a long ways in curing it. Once that is solved you might try carbide again.

 

[tomw]

I just spoke with Matt at PM Research. He said that it sounds like the piece never got annealed. He said that sometimes happens. He will be sending me a new crankshaft in the mail.

Thank you tons for your help.

Tom

 

[f350ca]

I think that will solve your problem Tom. If another one is on the way you could try annealing the old one. Heat it up in a charcoal barbecue and let it cool in the ashes. Nothing to loose.

Greg

 

[mattthemuppet2]

neat, it'll be good to hear how the new one turns. High pitched squeaking and squealing is a sure sign of the tool rubbing and not cutting. Probably there was enough flex that every so often the work and tool flexed down, it bit off a piece and then everything sprung back up to keep rubbing.

 

[34_40]

We used to turn brake drums & rotors at the shop I worked for. There was a wide thick band of rubber for the drums and a narrow thick band for the rotors.

Without wrapping the part to be cut, the sounds and finish would be awful. Make your ears bleed bad!! and the finish would be erratic almost "jumpy"..

 

[Sandia]

Tom, glad to see you got PM to send you a new casting, I was going to suggest that. When I turned the crank on my Redwing engine, I used carbide and I also set the tool height a little bit below center, which helped a lot. The crank journal is the part you need to get really smooth. I also wrapped my casting with tape and it helped some with the chatter but not a great deal.
Keep us posted on the new casting they are sending you, hopefully that will help you solve your problem.