Monday, 25 November 2013

oddity 3


The latest oddity is boring out a plastic plumbing fitting to accept a brass drain fixture for a sailboat. Seems that, in the winter, the contents of the flexible drain pipes freeze and pop off the brass fixtures. The new plastic fittings are barbed, and so should hold the flexible pipe more securely when used in conjunction with screw-type pipe clamps.

I am somewhat concerned about the differentials in expansion co-efficients of the plastic and brass. Since they will expand/contract at different rates, I bored the plastic fittings slightly oversize to allow for the use of flexible silicone as an adhesive.

The job forced me to create a mandrel out of thick wall PVC tubing to hold the plastic fittings. What was really needed was a core inside the tube/mandrel to keep it from distorting in the 4-jaw chuck. As it was, the white (possibly nylon?), plumbing fittings had the most annoying habit of peeling off thin sheets from the interior which would wrap around the boring bar and threaten to rip the whole assembly out of the chuck. The grey PVC would generate wispy strands that would either float around or ball up at the tip of the cutting tool.

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