Machining, boring stuff

Willem Buys turning the bearings

Since we are full speed on to getting the diesel installed, the prop shaft demanded attention. Francois van Wyk at Vortex engineering got working on the shaft itself and the hub, finishing it with three M6 grub screws. I need to weld up the hub and propellor now, and if it does not come out well I will ask David to work his magic on it.

I asked Willem Buys to take a break from his goldsmithing to turn up the bearings from high molecular weight poly-ethylene. My little Unimat just could not grip the pieces, but Willem did a fine job. It took me a while to get a universal joint to fit on the flex joint. The one I got was, of course, inevitably, imperial, so I have to shim a 25.4mm yoke to a 25mm shaft. And all the ship plate is in thousands of inches. I could not get imperial grub screws, only bolts, which would work for the moment. 6mm key bar will work on a 6.2 keyway, I hope. If only the USA could get to honour their commitment to Napoleon...

Marking the thrust collers

Rounding the collars

The thust, in reverse gear, will be taken by a collar, which I turned up in the little Unimat. It was fun making two up from flat bar cutoffs. Rounding it was tedious, but boring the inside was a challenge. I can only fit a 10mm drill in the chuck, so from there to 25mm was going to take a long time. I tried the little boring bar that came with the Unimat all of 40 years ago, but that was slow and blunted quickly. A little lateral thinking ensued: a drill bit is a boring bar, isn't it? A 7mm 'cobalt' drill bit, sharpened and set at the right angle did a great job, producing the longest steel shavings I have ever seen. Tapping the 6mm threads for the grub screws with my cheapo chinese tap did not work, but a new tap from Cosmo worked a charm.

Boring bar?

I know the bearings and stuffing box will give rise to comments, so an explanation. The bearing at the propellor end could have been an old-style cutless bearing, if I could find one. However, several engineering people suggested either PET or HMWPE. Both should be water lubricating, although both have rather bad expansion rates when they run hot. A pump rebuilder told me they replace bronze bushings on industrial pumps with HMWPE. Vesconite claims to do stern bearings for oil tankers from their product. So I will try my way. Refitting is always possible.

Drilling the holes for the grub screws

The stuffing box, again, would be rather expensive to import, while the HMWPE cost relatively little and was not too difficult to work. I could find very high quality gland packing, used in indistrial pumps, but have to buy 8 meters, while I will use maybe 500mm. A pump rebuilder suggested I follow industrial practise and use oil seals instead. I plan to try, as shown in the photo, and fill the gap between with a suitable marine grease. The sea-facing seal has had its spring removed, which might reduce its lifespan to ten years.

New tap works better

But if the outboard parts arrive, I intend going sailing in the next week or so, just to try out the modifications we have made.

Stuffing box/stern gland, showing oil seals

Trial fitting of shaft. It will be cut to length once we get it all to the
boat and installed.