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Harold Hall

Workshop Projects

Crankshaft 34/35

At this point I am going to deviate from the novice approach and rather than use the method proposed on the Stuart drawings, to detail a method that is much more satisfying to complete. The difference is that the simpler approach is fabricated whilst the method I am about to suggest is made from one piece of steel. The one making the engine can chose which method to adopt as the fabricated version needs no more detail than that given on the drawings, the one piece method will though give greater satisfaction.

 

Cut a length of 1” x 3/8” steel 3-3/8” long, carefully file the ends and centre drill both ends as follows. If though you prefer your crankshaft not to have centre drilled shaft ends when finished start with a length of 3-7/8” so that they can be machined away at the final stages. Mount the length of material on the top slide, packed up to  centre height, and with a centre drill in the drill chuck position it such that its larger diameter just touches the materials rear edge. Traverse the saddle so that the workpiece is clear of the centre drill and then, using the cross slide, move the part 5/16” plus half the centre drills diameter and centre drill the end of the workpiece. Traverse the cross slide by a further 3/16” and centre drill once more. Remove the workpiece, rotate, refit and centre drill the other end similarly, Photograph 61.

 

Tip

If working between centres is a new technique to you a major benefit of the method is that the part can be removed, replaced, perhaps turned end on end and concentricity is maintained perfectly. Heat thought is developed and the part will expand so the tailstock needs resetting periodically. If you do not have a rotating tailstock centre it will also need lubricating to minimise the heat generated at the centre itself.

Stuart 10V steam engine machining
Stuart 10V steam engine machining
Stuart 10V steam engine machining
Stuart 10V steam engine machining
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61

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62

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63

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64

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Fit the Catch plate, or a faceplate with a suitable driving peg, and both headstock and tailstock centres and place the workpiece between these using the central centre drilled impressions. If you do not have a suitable driving dog for this size of material drill a hole, say 5.3mm for an M5 screw, in the eventual waste material near the end and fit a short length of steel to provide the drive.

 

Machine the outer edges reducing the width to 13/16” and thereby also producing the curvature as shown on the drawing. Only doing it just past the  position for the webs, Photograph 62. I say “as shown on the drawing” but the radius produced will be 13/32”, the drawing calls for 19/32” but this is of no importance.

With that completed, mark out the position of the webs, both inside and outside, similarly the width of the shafts and rough cut just outside these marks to minimise the machining necessary.

 

Do not though take out the portion between the webs at this stage but drill a 6mm diameter hole to assist with the eventual opening up of this space, Photograph 63.  Ensure you drill the hole in the correct place, that is nominally in line with the shafts, or it may be a case of start again.

 

Return the part to the lathe and turn the shaft to 19/64” at this stage and face the outer face of the web, Photograph 64, remove, rotate and repeat.