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Wood and Metal Beam Engine - Part 3

Nigel Taylor

This was my sketch for the main crank bearing supports. I considered brass blocks attached to the tops of the horizontal beams but thought this would not be that strong a solution.

The A frames would allow me to tie the upper and lower beams of the frame together and so add some lateral stiffness to the main bearings.

I decided that the main bearing supports should be formed by steaming wood around into an A-frame. In order to bend the wood I made myself a bobbin to fit into the soldering iron that would allow me to form the wood around a tight radius. A brief page on doing this is available in our glossary Steam Bending Wood

This image shows the three jigs for the flywheel bearing supports and for the piece that fits in and strengthens the A-frame.

The top curve of each piece was bent by wetting the wood and using the hot iron, being careful not to bend the wood too far as I wanted to maintain a positive outward spring whilst the frame was within the jig.

A close up of the A-frame showing the layered wood.

The outer layer is walnut, then a layer of ash, a layer of bog oak (nearly black) and then an inner layer of walnut.

The larger nails were strategically placed so that some pressure could be applied using the wedge as each layer of wood was added.

Once all of the layers of wood were in place and the wedges firmly home I locked up the workshop for the night so that I would not be tempted to look before it had all set.

At the same time as making the A frames for the main bearings I made this A frame to fit within the upright.

There is quite a mix of wood here and the engine may end up a bit of a mish mash of colours, techniques and materials - oh well.

A close up of the insert into the upright.

The horizontal spreader was made from bog oak and was glued in place with quite some pressure being applied from the frame.

The bearing support frames now removed from the jigs with the holes drilled in the upper fillet to take the main bearings.

The spreader holds the frames prior to being assembled into the main frame of the engine.

The main bearings are small ball races that are 6mm ID and 10mm OD.

The supporting wooden pieces were turned from what I believe is lignum vitae - this came from one of those old round rulers (23mm diameter, 224mm long and weighed 113g - this works out as a density of 1200kg/m3). Great to turn very accurately.

This shows the bearing block from the other side.

The hole through the wood is 8mm diameter so as to give a good clearance for the shaft.

The wooden blocks were pushed into the A frames and glued with PVA. Note that the blocks were turned so that the grain ran at 90 to the wood in the A frame.

The outer A frame was cut into the main frame, however, I decided not to cut the A frame itself as thought this would weaken the support too much - you can clearly see from this view that the A frame sits half into the main frame.

The crankshaft is only roughly turned at this point and was used to check the alignment of the bearings to the main frame.

I aligned the frames by first fixing one of the frames and only once this was set did I then cut the joints for the second frame and then glue in place.

The main A frame was reinformed with two pieces of steamed and bent walnut and then sanded to a finish.

The top bearing was machined and reamed to take the centre pi of the beam. The picture shows the beam assembled and the A frame varnished.

The next job is to finish the crankshaft with the crank, flywheel fixing and the eccentric for the valve gear.

Back to Part 1, Part 2 on to Part 4, Part 5, Part 6, Part 7

If you have made a similar engine and would like to share your experience we would love to hear from you - ed.