Lead in the centerboard

[Clem Freeman]

I've made a mould out of plywood so I can cast a piece of lead to put in to the centerboard. My first attempt was reasonable but contained large air bubbles trapped at the bottom. Anyone done this before and have any tips?

[Anthony Huggett]

Hi Clem,
      I (for one) would love to know how you did this.

How did you melt the lead?

Did you make a positive or a negative mould? i.e. did you pour the lead into a plywood box, or use the plywood to make a dent in casting sand? If the former, the latter might be the answer.

I think if I were going to try a plywood box for casting I'd use a horizontal box, with a top with a reasonable sized hole for the lead to pour in, and small holes in each corner for the air to squirt out. A real pro mould would have a tapered hole for the lead to go in, to minimise the burr that will be left which you would need to file off.

Any chance of some pictures?

Anthony

[Steve Joyce]

Hi Clem,  is the centreboard on the 17 a single piece of thick ply,  or do you need to laminate it up yourself?  On the 15 its a single piece,  and although the instructions refer to putting lead in,  they all seem to refer to making the board up, rather than it being already in one piece.  Although I haven't really thought about this too much yet,  I was thinking along the lines of a golf club weight,  drilling out a hole with a forstner bit and dropping in pennies of lead chopped out with hole saw,  and sealing up with epoxy.
My whole centreboard thing has been a bit of a trial. Its about the only part of the kit that didn't fit together well.  I will update my build post with the latest.

[Clem Freeman]

Anthony,
I made a flat open mould out of ply and that is probably where I went wrong. The ply seems to have stood up to the heat pretty well, just a bit scorched. Mark 2 will be as you suggest with an upright mould where I can pour the lead in at the top. I melted the lead in an old saucepan on a camping gas stove. Not sure when I will get around to the next attempt as I was only trying this as the weather was to bad to get the S17 out of the garage to work on.

Steve,
The S17 centreboard is made up of 2 laminates of ply which have had hollows routed out. You could just lay the scrap lead in but I thought by moulding the lead to fit I could maximise the amount I could get in.

Clem

[Jeremy]

My guess is that the bubbles were probably caused by the ply outgassing, or not being totally dry.  I cast a lead keel bulb many years ago, out in the garden, by making a mould from concrete cast around a shaped polystyrene foam master.  Having been warned of the dangers of damp causing gassing and a possible explosion whilst pouring, I lit a fire around the mould and baked it for an hour or two to burn the polystyrene out before pouring the lead in (it was a lot of lead, around 500lbs or so of melted scrap).  I melted the lead in an old cast iron cauldron over a charcoal fire, but it too four of us to tip the lead into the mould, via a feed runner made from a bit of old cast iron guttering.

I've heard of people making smaller lost foam castings using plaster of paris as a mould, over a bit of carved foam.  If gently dried in an oven you can apparently just pour the lead directly on to the foam so that it vaporises as a the lead is cast.  Extruded polystyrene foam (the pink or blue stuff) is best, as it can easily be carved and sanded to shape.  I'd think that the same technique might work for making a shaped insert for a centreboard.

Jeremy

[gerald turner]

Anthony,
I made a flat open mould out of ply and that is probably where I went wrong. The ply seems to have stood up to the heat pretty well, just a bit scorched. Mark 2 will be as you suggest with an upright mould where I can pour the lead in at the top. I melted the lead in an old saucepan on a camping gas stove. Not sure when I will get around to the next attempt as I was only trying this as the weather was to bad to get the S17 out of the garage to work on.

Steve,
The S17 centreboard is made up of 2 laminates of ply which have had hollows routed out. You could just lay the scrap lead in but I thought by moulding the lead to fit I could maximise the amount I could get in.

Clem

Wotcha Clem!'Tis Gerald here,Maybe it would be better to make a mould out of plaster, would need to be done in two parts with a pattern made out of scrap wood,I say this because I had a notion of making a Model yacht which would need a lead bulb.

Why not ping John Perry, he can advise

[Clem Freeman]

I'll give the plaster of paris a go and report back.

[Anthony Huggett]

Whilst waiting for the epoxy to set on the inverted hull I turned my thoughts to how to cast the slug. I'm going to try the lost polystyrene method, with a plaster mould. Pouring the hot metal destroys the polystyrene former, allowing the metal to take it's shape. The advantage of this is that the plaster mould can be in one piece, but is destroyed as you get the slug out. This is fine, since I'm only going to make one slug, assuming everything works correctly.

I got some half-inch polystyrene (4.99, Hobbycraft), cut it (standard hacksaw) and sanded it (80 grit) to fit the CB cutout.

Next I got a suitable container (old seed tray, lined with cling film), and some plaster of Paris (3.99, Hobbycraft). I learned that it is important to mix the plaster of Paris in small amounts. It kicks really quickly and I wasted about 0.75 kg at the first attempt. I put some in the tray to form one side of the mold, inserted the foam and a sprue, and coated the other side. In theory (according to me) the plaster does not need to be all that thick. I'm going to stand it in common or garden sand to support it when I come to do the casting - the sand should hold the sides in.

Having read tales of what happens if hot lead hits water, casting will be after everything has had a week to dry. Will keep you posted. Meanwhile I'm waiting for it all to dry then I can scrape the plaster off the floor.

Sorry if this read like an advert Hobbycraft.

[Clem Freeman]

My attaempt with plaster never really got started. I made the mould much to thick and gave up waiting for the plaster to dry. Instead I used a pice of scrap ally sheet and made a shallow tray which I poured the moulten lead in to. I used an old saucepan and a camping gas stove to melt it. It was then just a case of pouring the lead until I had the right thickness.

[Anthony Huggett]

Clem,
         Thanks for letting us know how you did it. I'll try that if this attempt fails.

          I didn't fancy the open mould because I thought there might be scum or some such on the top, which I would then have to file. 

           I have a couple of weeks before I will have time to do any more, so the mould has plenty of time to dry out.

Anthony

         

[Anthony Huggett]

Here's the action of the lost polystyrene casting experiment.
The plaster mould has thin walls, so the first job was to bury it in builder's sand, padded out with spare bricks around the outside.  I rammed the sand down to make sure it was firmly packed, working 2 or 3 inches at a time. I used about 2 bags.

[Anthony Huggett]

Next job was to clean out the sprue (funnel shaped hole where I was going to pour the metal). I used a soldering iron, which showed me how the polystyrene would react to the head of melted lead. I also used a drill to remove some unwanted bits of plaster. I also used the drill to attempt to create some vents at the top - a minor mistake, as it turned out. See lessons learned ... . With the sprue cleared I used a vacuum attachment to clear out as much polystrene and plaster of Paris as possible.

[Anthony Huggett]

Now the fun part. I'm using a portable cooker because my wife (who took the pictures) wouldn't let me use the kitchen hob. £14.99 Halfords+ gas at about £2.30 per canister. I used less than one canister of gas. The saucepan is an old stainless one (free from Mum).  Rather than use new lead (Cheapest roll from Wickes is over £60) I talked nicely to a local builder who gave me enough scrap lead. I was pleased to see it soften and start to melt - there was a crust of oxide which I mostly lifted off with the ladle (£2.50, Morrisons) leaving a nice pan of shiny molten lead.
To minimise the hazard I transferred the lead using the ladle, rather than attempting to lift 6 kg of molten metal whilst wearing welding gloves (Screwfix, £3.99).

[Anthony Huggett]

And the result?

It was very easy to chip the plaster of Paris off the lead with a bolster chisel.

I had to hacksaw off the sprue, and file off one or two extra knobs near the sprue. I think this was where I tried to make sure the sprue was clear into the polystyrene of the mould with a drill. Where I drilled air vents the vacuum didn't get out all the plaster of Paris - resulting in a couple of small indentations at the top where the plaster resisted the lead. The lead shrank slightly on cooling and is an easy fit in the CB cutout. I might just need to file a bit more away (or wet emery) to make it fit snugly - it's slightly too fat I think (by less than a millimetre). 
 

[Anthony Huggett]

Scrap now disposed of.