Stern Tube Hole

Work on this was mentioned in an earlier post. At that time there was a pilot hole all the way through the skeg and keel. Over a period of days I have slowly fitted the block to the inside of the keel and extended the hole through it. A selection of twist drills on the end of a long extension took this hole out to 32mm. At the end of this the hole was about 5mm off the centreline inside the boat. A boring bar was used to open up the hole to about 46mm for the stern tube.

Bearing blocks were set up at both ends of the hole to carry the boring bar that would finish the job. At the outer end I made up an aluminum bush to be a good fit in the pilot hole and to the boring bar. Here's a photo of the bar in place and the timbers that will support the bearing block.

At the inside end the pilot hole didn't allow the boring bar to be centered. This photo shows the 32mm pilot hole with the lines showing where the final hole should be. The bearing block with its 25mm hole was screwed to the support as far to the left as the pilot hole would allow. When the hole was large enough to allow the boring bar to be moved over the bar and inner bearing were removed and the pilot hole in this supporting timber made larger. Then the bearing block was reattached with the bar lined up accurately on the centreline. The final arrangement of this inner bearing is shown clearly in the last photo below.

Now the boring bar is supported at both ends the cutting can begin. One photo was taken when the hole was close to the final diameter and it shows the cutter clearly. The hole was opened out in steps from 32 to 46mm, each step removed about 1mm of timber. After the first few steps the inner bearing was moved to the centreline. The other photo shows the battery drill that turned the bar - fortunately I have 3 batteries for this drill but there were still pauses while batteries were recharged. Very cruel to the drill but it survived!

There was a problem about halfway through the hole where it passed through the 3 layers of plywood. The cutting tool handled the oregon in the skeg and the block inside the hull but had trouble with the glue lines and interlocking grain in the plywood. The is resulted in a hole that was a couple of millimetres smaller in this middle section. Advice from a friend led me to reshape the cutting edge of the tool and then to hone it to a very sharp edge. This solved the problem and there is now a nice parallel hole ready for the stern tube.

The hole is about 780mm long and nicely centred at both ends. I will leave the bearings for the boring bar until the stern tube is fitted using the boring bar to line it up while it is glued in place.