Trevithick Boiler End

by John

The first part to be made for the Trevithick dredger engine is the domed end of the boiler.  It is formed from copper plate which is 3mm thick.  first a circle is marked out, then bandsawn from the copper plate.

I decided to make a wooden form.  Fortunately I have a CNC lathe (see earlier posts about the CNC conversion of a manual lathe), so drawing the profile and generating the G code using Ezilathe was, well, easy.

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CNC’ing the wooden form for the boiler end plate.  The roughing steps.  Carbide tip which has been sharpened to a cutting edge, suitable for wood.

This is the final roughing cut, and starting the finishing cut.

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CNC turning.  Light sanding required to remove the fur.  The wood is European oak.  Central hole for a locating pin.

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The oak form was attached to a red gum block which was held in a 6″ vise.  I have already commenced shaping the copper disk here.  The copper is cramped to the oak form after annealing, and gradually hammered to shape.  Tapped rather than hammering.

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My “forge” is a few fire bricks in a steel shell, and a roof of steel to help retain the heat.  The torch is fuelled with propane.  It was originally a weed flamer, used to burn serrated tussock.

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Red heat was achieved in 90 seconds.  This is 600 degrees centigrade.  copper melts at 1084c, so there is a good safe margin.  I quenched to cool, for speed.

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This welder’s clamp proved to be the most effective method of holding the copper disk to the form.  I fitted  copper and  brass heads to the tapping hammer to minimise the chance of “bruising” the copper.

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Progress

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About 10-12 heating-hammering cycles in 1.5 hours to get to this stage.

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Getting close.  I will finish it tomorrow.  Might wash up before cooking dinner.