johnsmachines

The connecting rods on the Trevithick dredger engine were wooden, presumably to save weight.  I used to do a lot of woodworking and still have radial arm saw, bandsaw, thicknesser and planer, etc, and too many scraps of wood and left overs from previous furniture projects.

The con rods are 16x10mm and about 320mm long.  Lignum vitae was recommended by Tubal Cain, and “hard wood” by Julius deWaal.  I looked through my piles of offcuts, and eventually settled on West Australian Jarrah.

There are 2 con rods, but I cut enough sticks for 4, just in case.  One was immediately rejected due to a split.

Jarrah is hard, remains stable during machining, is dark and becomes darker with aging, and is relatively resistant to rotting and warping with water.  In Oz it is often used for outdoor decking.  The figuring tends to be quite wavy rather than straight, so very sharp tooling is required to avoid teatouts.

Using a shell end milling cutter to make the end rebates.  It is really sharp and heavy, and quite scary to handle.  But does leave a beautiful finish.

I try to avoid machining wood on my metalworking machines.  The dust gets everywhere, and if not removed attracts moisture, and rust.

But, the metalworking machines are far more accurate, so that is what I used after the initial roughing cuts.

Next was the metal U shaped metal strips to hold the bearings at each end.  I chose brass, because I had some 2mm sheet, which was the specified thickness, and I imagined that it would be easier to machine and bend than steel.

This is my bender, with a test strip of annealed brass.  I made this bender last year to bend copper pipe, and my advisor, Stuart, suggested using it to bend the brass ends for the Trevithick.  So I turned up some aluminium cylinders and a brass pusher to the appropriate diameter, leaving a 2mm gap for the brass strip.

Worked like a charm.

I will make the bearings before I trim the U strip to final length.

So that all went very nicely.

Hang on.  There are 2 connecting rods, with 2 ends each.  I need FOUR U pieces, not TWO.  Shit.

No time to make the other 2 today.  Got to get home to clean up before visiting my hearing specialist.  Should see a brain specialist too.