A few months ago, before planking had progressed very far I decided to drill the hole for the shaft assembly of stern bearing, tube and stern gland while it was easy to clamp some packers on which to bolt the bearings that would support a boring bar that I was able to borrow from another boatbuilder mate. I began by working out where the shaft centreline would be located on the inside and the outside and drilled with a 3/8” long series drill bit from each end. The photo below shows that the holes were just slightly misaligned in the middle of the approximately 2’ (600mm) of sternpost and deadwood but there was a clear line of sight through. I increased the diameter of the hole by using incrementally larger drill bits until I had a clear hole larger than the diameter of the 1” boring bar, about 1 1/4” diameter, but not quite straight. The second photo shows this hole with a string line through it which enabled me to work out where the bearings for the boring bar needed to be placed. I set up the bearings outside and inside. Here's a couple of shots of the inside with the boring bar fitted through the bearing. The boring bar has several alternate holes to locate cutters of tool steel held in place with grub screws. These are adjusted to cut a required diameter. For ease of cutting and to help keep the boring bar true, it is best to select a diameter that will only remove about 1/16" at a time, and incrementally increase this with each succeeding pass. The boring bar needs to be removed to check that the tube will be a sliding fit, not a loose fit. Once happy with the main diameter, each end has to be bored out a little more to allow for the bearing and gland which are of a larger diameter. These also need to be a sliding fit. The whole assembly can then be dry fitted to check it will all work. I will not be fastening and bedding this in until later. The whole procedure is in this YouTube video. Archives April 2018
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AuthorIan Smith, Boatbuilder (ret'd) Archives
January 2024
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