Rounding the Mast
I fabricated a marking tool to mark guidelines on the square mast. Then the electric hand plane was used to remove unwanted material. It is a great tool and worth the investment, especially if you are as lazy as I am.
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5/16" holes prove to be to large for pencils, so I used 1/4" holes and twisted the pencils through forcefully. I just used threaded bolts on the outside, and kept my thumbs on top of them as I was marking.
Then the electric plane was used to change 4 sides into 8, then 8 into 16.
I then sanded by turning a sanding belt inside out and using my own power to sand. It worked very well.
Next Step
Do some final filling and sanding on the mast. Then apply spar varnish.