Thursday, September 24, 2015

Casting a new handle for a bilge pump.

The cockpit sole is removable, but not easily, so the pump can't go on the sole, nor under it.

I need it somewhere I can get at it while sailing, so I can pump and sail. Ideally on either tack, but that's asking a lot.

And sadly I bought a whale urchin, without a removable handle.

The pump will sort of fit in under the benches, but the handle sticks out. The original handle comes across the body of the pump... Not the direction that I needed.

 Annoyingly the 2 pivots are different sizes, you can't reverse the handle.

But since I have a furnace for casting aluminium or bronze, I measured up and made a new pump handle. Obligatory warning here, liquid aluminium is going to mess you up something special if things go wrong. If you want to play with molten metal, you need to do a lot of learning. if at first you don't succeed, perhaps foundry work is not for you...

I used a hot wire cutter to make up the shape in expanded polystyrene (sorry no photo). This has a sprue of polystyrene attached, and it gets coated in plaster except for the very top. It's placed in sand with the sprue sticking out the top. You pour in the molten aluminium and it vaporises and replaces the polystyrene. Let it cool and you have an aluminium widget the exact shape of the polystyrene. I drilled holes for the pivots, and drilled and tapped a hole for the handle.
The handle is made of wood, with a 10 mm stainless bolt screwed up inside it with the had cut off afterwards. Drilling a 75 mm long hole up inside it is a bit fiddly.  I don't have a drill press so this was all done by eye.
The whipping helps reduce the chance of the handle splitting in use. The thread is 10 x 1.5mm so quite course, and it goes through 25 mm of aluminium, so it should be plenty strong. 

This is how it looks now.  I need to build a small platform under the seat to hold it just in the right place for the handle not to hit anything at either end of it's range.

If I polish it up, a lot of work, it will come out shiny and silky to the touch. I will probably get things working and then decide not to bother polishing it. A little metal paint may well suffice.

I could have bought a handle, and the pivot, but that would have cost silly money for something that I made up in an evening. Since it's solid aluminium, even with my less than perfect casting skills, it's vastly stronger than it needs to be.

It's not perfect, but it pumps just fine.

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