The Shipyard ( Dry Dock ): Builds & Questions > Steam
Marcher Build
IanJ:
I have started a Marcher steam Engine with the intention of fitting it into a relatively small boat. So far, I have drawings and after encouragement from George (ooyah/2) have completed the crank shaft which I view to be a crucial part. Given a shaft and big-end journal size of 1/4" such an off set gives an overlap that complicates the fabrication of the crankshaft, hence the need to machine from one piece.
The photos shows the sequence that I adopted, I am sure others may have alternative approaches. Photo 1 shows the 3/4" bar faced and centred, then transferred to 'v' blocks to mark out the off-sets of 7/32, 90 deg. apart. Subsequently centres were drilled and the opportunity to mark distances between webs. Before mounting between centres I took the opportunity to remove a lot of material whilst held securely in the 3 jaw chuck before mounting between centres. It was necessary to leave bosses at either end to accommodate the centres. The greatest difficulty was getting cutting tools into and between the crank webs. Using such small tools means very small cuts and feeds and slow progress! Once the big end journals and web faces are finish the boss at the ends can be removed in conjunction with taking the shaft to its final dia., as the final photos shows. Let's see what other challenges lay ahead and the build continues!
Ian
xrad:
First, great job. Nice crank. But it looks like your centering holes are off compared to scribe lines?
How do you mark both ends of rod in exactly the same location for the two offset centering holes(with one end in the chuck)? If rod was on a flat plate and a line scribed at each end through dead center(parallel to plate)...then roll rod 90 degrees and scribe a second line through dead center at each end...... then another scribe done 'x' distance from center(this time without rolling rod)parallel to plate on both ends...then rolled another 90 degrees and final scribe line done on both ends 'x' distance and parallel to plate... the marks would be pretty close at both ends....
ideas?
IanJ:
Hi,
I am very pleased with the end result. First all I believe that the camera angle is giving a distorted view of the scribed lines and the centres. Regards scribing the lines; first step face and centre drill the bar at both ends. Remove from lathe and mount and clamp on 'V' blocks resting on surface plate. (1) Scribe line thro centre height at both ends. (2) Set surface gauge to 'off-set distance and scribe a further two line parallel to the first two at each end. (3) Release clamps and rotate 90 deg. with the aid of a square off the surface plate. (4) With the surface gauge at the same setting scribe a further two line at 90 deg. to the others. You now have two off-sets marked at either end same distance from the centre. (4) With the aid of sight glass centre pop the centres and whilst still clamped within the 'V' blocks drill the centres. Given than the centres in the lathe (dead centre, head stock end and Live centre at tail stock end) are in alignment the the shaft will be tuned parallel. Hope this explanation helps with what I did.
Regards
Ian
xrad:
Thx for reply Ian. Yes, it is a nice smooth looking crank. Any need for counterweights while turning?
steamboatmodel:
A very good job on the shaft, I think I would have gone with a fabricated one.
Gerald.
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