Fish Bellied Con Rod

[Phil PParticipant @philp]

I have a connecting rod to make which is "fish-bellied" and radiused at both ends. It is 6.75" between centres.

I have a few ideas of my own on the steps needed to make it, but would welcome any thoughts on the fish-bellied portion.

Unless someone knows better I am going to make a sheet steel template and disconnect the leadscrew on the cross slide, so it can follow it in a similar fashion to the taper turning attachment with probably a counter balance weight to keep it in contact.

Any ideas ??

Phil

[Phil PParticipant @philp]

How to make ?

[JasonBModerator @jasonb]

The usual way is to roughly divide the length into three, the centre is left parallel, left and right ends turned to a slight taper and then blend the three with a file.

Have a look at this post of mine about crowning a pully/flywheel its the same method.

Depending on the radius at each end you may get away with a round nose tool or it can be done will a ball turner set to turn concave like this, the ends are then machined to the rectangular section

J

Hopefully Andrew Johnson will see this as he has just posted the machining of a couple of conrods with a template follower on TT, I won't steal his thunder and post the pics here, he can do that.

 

Edited By JasonB on 06/11/2012 19:02:41

[Anonymous]

Indeed I have seen it. Here's a picture of the long taper (about 11.5" long) on the connecting rod being machined:

The taper is being cut with the aid of a hydraulic copy unit. The sheet steel pattern and follower can be seen bottom right. It is essentially the same idea as mooted by Phil. A couple of caveats I'd add are: one that the hydraulic copy unit has variable stops, so the workpiece can be reduced in a series of steps, rather than one go. Second, as the copy unit is at an angle to the lathe axis it can follow the pattern at right angles to the lathe axis to clear the big end, even though the feed is still engaged. However, I see no reason why the method suggested by Phil will not work.

Here's a picture of the two finished connecting rods:

Regards,

Andrew

Edited By Andrew Johnston on 06/11/2012 22:11:22

[Harold Hall 1Participant @haroldhall1]

You ask for ideas Phil, you may like therefore to look at my method which is an extension on Jason's idea. See here for the details.

Harold

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