Fish Bellied Rods

I’d originally planned to ” fishbelly” (a new Nerb?) the slide valve pushrods,  then changed my mind and today did it anyway!

I stripped down the push rod assemblies and mounted in the lathe.  If you wind back through the blog far enough you will find I had centre drilled the rods for the purpose of creating the fishtails and I’d made a little fixture for holding the rod at the chuck end of things.   The short rod I can almost get half the rod before  I run out of travel,  the longer rod I’m about 1/2 inch short.  For the longer rod then,  I end up with a flat in the middle.    For both rods the shaping is finished with coarse emery tape with the lathe at full speed,  then cleaning up with a 400 grade emery and brasso,  followed by 800 wet and dry and brasso etc.

Here is the rod re-assembled and with the eccentric strap cleaned up.  Looks much better.

As an aside,  you will have noticed that I’ve now acquired a quick change tool post (QCTP to those that know about these things).   To be honest not sure of the value it adds,  thought it is handy for fine tuning tool heights.   It isn’t as quick as spinning round a four post tool holder in my view.

A bit of fun…

I’ve decide to add some fencing to the engine stand to give some perspective.  Great Grandfathers engine does this quite effectively,  so simple to follow the theme.

First off,  I cut four lengths of 1/4 square bar to 50mm length.    Then mounting one in the lathe started to think about how to shape a ball end to the post.   After a bit of messing about with a file,  I remembered a UseNet post from Workshop Master Stevenson.    The method is to take a piece of gauge plate and drill a hole in it the diameter of the ball you want.  Countersink until you get a sharp edge then saw through the hole.   Grind to appropriate profile,  harden, temper, grind a bit more and there you go:

I didn’t have any gauge plate 😦  so I used a piece of EN3B flat.  As you can see,  it works a treat.   The profile isn’t right yet as the form tool (which is what this is) is flat topped,  which isn’t right,  I don’t think,  so  abit more fiddling with the grinder and this should be great.   At least it saves buying or making a ball turner.   Thanks JS.

Here you can see how I’ve used my biggest countersink to create a cutting edge in the diameter of the hole.  It’s not profiled correctly yet,  but did produce a decent result first off.   The underside is all a bit scaly from the heat treatment.

Someone will post to let me know that you can buy fence posts from the model shop.   If I had done that,  I wouldn’t have learned how to make a form tool – and that’s why I make most of my own stuff.   I could have bought the bevel gears too,  or gone the whole hog and bought a ready to run engine from Stuart but I would have been a lot poorer in cash, knowledge and skills if I’d done so!