Strong casting alloy? And machining something else

[Jonathan Webb]

Hello, I'm investigating the possibility of casting an unavailable piece for my boat that is badly worn. I've cast a few simple things and thought it might be simple enough to cast at home. It's about 100cm/4" and takes a fair amount of load, especially when the boom slams across accidentally... Any suggestions as to a suitable grade of aluminium to cast - AB2 has been suggested in an international group I'm in and it looks suitable, but as always, sourcing small quantities is not so easy (ebay usually delivers - at a premium) - any idea where I could try for a kilo or two of something suitable? Many thanks.

 

[Pete.]

There is no way in hell I would cast one of those from ally at home.

I might be tempted to fabricate one from steel or even weld up the wear grooves and set about filing it back to shape but an ally casting - no way.

 

[Newlands]

You could get one cast in bronze. In the distant past I made up some patterns for a few boat fittings and sent them off to Classic Marine. It wasn’t horrendously expensive - something like £80 for four rudder fittings. I wouldn’t trust a home-cast aluminium fitting. Your other option would be something fabricated from 316 by your local friendly Tig expert, or a look round Beaulieu Boat Jumble for a secondhand fitting if you fancy a day out and the risk of spending much more on a load of other old tat!

 

[Munkul]

Machine one from stainless steel? Turn the centre hub in a lathe, and the excircled diameter. Use plasma or something to rough out the rest of the shape, and grind/file to finish. Would take a couple of hours at most, and be far stronger than casting an alloy one.

 

[Pete.]

You could get one cast in bronze. In the distant past I made up some patterns for a few boat fittings and sent them off to Classic Marine. It wasn’t horrendously expensive - something like £80 for four rudder fittings. I wouldn’t trust a home-cast aluminium fitting. Your other option would be something fabricated from 316 by your local friendly Tig expert, or a look round Beaulieu Boat Jumble for a secondhand fitting if you fancy a day out and the risk of spending much more on a load of other old tat!

I like the casting in bronze idea.

 

[brightspark]

I like the casting in bronze idea.

that would be best but would need to make a new pattern up or fill the existing worn part and use that as one . it will be fractionally smaller due to shrinkage but its negligible and decent bronze a lot harder than ally

 

[500e]

Had one Break on our small Albin Viggen not a happy experience, in a heavy blow boom came over BANG boom went to max and hit the rigging hard enough to put a mark in it.
We made another out of SS as @Munkul suggested.
Had to jury rig a sheet to boom to get into Falmouth.
Do not think of casting one, Fab out of SS.
With that much ware how is the rest of your rigging ?, our fitting showed no wear at all just went bang under the sudden snatch load.
We had just replaced all standing rigging as per Insurance and both us and the rigger had gone over all fittings, so it was not neglect

 

[Newlands]

I’m sure I’ve seen these fittings just made from a piece of stainless strip - about 4mm thick and 35 or so wide with three suitably sized holes. They have a slight bend in them to suit the angle of the topping lift and mainsheet. Since the topping lift is slack when you’re sailing, the fitting can swivel as you go through the wind and the boom swings (assuming that you drill a suitable clearance hole for the centre fixing bolt).

 

[500e]

Just out of curiosity whats the pin like ?
That's what we did made a plate out of 18/10 SS (A4) with a few extra bits to clear the sail foot tension screw
If my memory is correct the bit that broke was integral with the boom plug, and the shackle slid around in it, the whole part broke and it included foot tensioner.
Do not make a cast one.

 

[awemawson]

3D print it in PLA and have it 'lost wax PLA' cast - I had some stuff done this way in bronze by Abbey Castings (they advertise on the Home Workshop sales site) and came out superbly.

 

[graffian]

There is a foundry in Hurstpierpoint that cast bronze and aluminium.

 

[Jonathan Webb]

OK thanks. I get the message. I did say I was investigating the possibility.... Getting one made from stainless is one of the options, although having no lathe I can't just knock one up :-(
Incidentally, I have bronze in the form of my old propeller (in VGC, no dezincification, changed due to engine swap).
For my enlightenment, just looking up propeller bronze & Propellerpages.com mentions Nickel Aluminium Bronze. which has a pretty similar composition to AB2 - why the "no way cast it in ally"? Looks like an ideal candidate, but it seems not - why's that? Thanks.

 

[Jonathan Webb]

I’m sure I’ve seen these fittings just made from a piece of stainless strip - about 4mm thick and 35 or so wide with three suitably sized holes. They have a slight bend in them to suit the angle of the topping lift and mainsheet. Since the topping lift is slack when you’re sailing, the fitting can swivel as you go through the wind and the boom swings (assuming that you drill a suitable clearance hole for the centre fixing bolt).

Yes. that's the obvious route and I've seen that... As I'm starting out casting (small arty things ATM) I thought it looked like a simple piece to try, but I appear to be wrong!

 

[Jonathan Webb]

3D print it in PLA and have it 'lost wax PLA' cast - I had some stuff done this way in bronze by Abbey Castings (they advertise on the Home Workshop sales site) and came out superbly.

Investment casting seems to me to be a bit overkill for a piece this simple?

 

[Jonathan Webb]

Just out of curiosity whats the pin like ?
That's what we did made a plate out of 18/10 SS (A4) with a few extra bits to clear the sail foot tension screw
If my memory is correct the bit that broke was integral with the boom plug, and the shackle slid around in it, the whole part broke and it included foot tensioner.
Do not make a cast one.

Pin (and gooseneck) are in good shape. Actually, mine's not as bad as this but has some wear. There are a number of people with this problem and I was looking for a solution. Out of interest, this was cast AFAICT, why is it not castable?

 

[Jonathan Webb]

Had one Break on our small Albin Viggen not a happy experience, in a heavy blow boom came over BANG boom went to max and hit the rigging hard enough to put a mark in it.
We made another out of SS as @Munkul suggested.
Had to jury rig a sheet to boom to get into Falmouth.
Do not think of casting one, Fab out of SS.
With that much ware how is the rest of your rigging ?, our fitting showed no wear at all just went bang under the sudden snatch load.
We had just replaced all standing rigging as per Insurance and both us and the rigger had gone over all fittings, so it was not neglect

I'm going through all my rigging ATM. Mast is down. Stainless is tricksy stuff, it can look fine... Swaged fittings have a high fail rate when new, then the rate settles down then rises again later with age. I think there's a term for it but it escapes me. Making one out of stainless bar seems the best option but I'm still intrigued as to why not cast? I wasn't talking about melting pie dishes...

 

[Newlands]

Incidentally, I have bronze in the form of my old propeller

It’s highly likely that your prop is actually brass rather than bronze, unless it’s really old. Although brass is pretty useless in salt water, they get away with it for a prop because it’s pretty chunky, and if it fails it does so slowly and visibly, rather than catastrophically like, say, a keel bolt.
But back to the aluminium - I personally wouldn’t cast one because of the likelihood of porosity and therefore weakness. I used to sand cast small odds and ends for work, all non-critical stuff (garden ornaments etc) and although we had de-gassing chemicals etc we lacked any real temperature control. As a result some of the stuff we knocked out would have been chucked straight back in the melt if it was for any serious application.

 

[Jonathan Webb]

It’s highly likely that your prop is actually brass rather than bronze, unless it’s really old. Although brass is pretty useless in salt water, they get away with it for a prop because it’s pretty chunky, and if it fails it does so slowly and visibly, rather than catastrophically like, say, a keel bolt.
But back to the aluminium - I personally wouldn’t cast one because of the likelihood of porosity and therefore weakness. I used to sand cast small odds and ends for work, all non-critical stuff (garden ornaments etc) and although we had de-gassing chemicals etc we lacked any real temperature control. As a result some of the stuff we knocked out would have been chucked straight back in the melt if it was for any serious application.

Thanks for explaining it, much appreciated. FWIW, the prop is probably 48 years old - medium old...

 

[brightspark]

It’s highly likely that your prop is actually brass rather than bronze, unless it’s really old. Although brass is pretty useless in salt water, they get away with it for a prop because it’s pretty chunky, and if it fails it does so slowly and visibly, rather than catastrophically like, say, a keel bolt.
But back to the aluminium - I personally wouldn’t cast one because of the likelihood of porosity and therefore weakness. I used to sand cast small odds and ends for work, all non-critical stuff (garden ornaments etc) and although we had de-gassing chemicals etc we lacked any real temperature control. As a result some of the stuff we knocked out would have been chucked straight back in the melt if it was for any serious application.

the only temperature control needed is use an infrared thermometer on the melt in the pot for min temp and dont over cook it

 

[Newlands]

only temperature control needed is use an infrared thermometer

I know, and we didn’t have one.