Producing brass casting patterns

[EasternO]

Are there any relevant instructional websites or videos on building brass patterns for casting in pewter out there or on here? I can't find any with my search terms. Whole wagons would be ideal, but a general overview would be fine. Thanks.

[Camperdown]

Casting whole wagons?

 

Don't know of any videos, but there have been some articles in MRJ over the years.  The crucial thing, AIUI, is the curing temperature of the rubber mould taken from the brass master, from which the wax copies are made, to be sprued together for investment casting.  The rubber curing temperature dictates the type of solder that can be used in building the master.

[Happy Hippo]

If you are casting in pewter, you will not require to use the lost wax method of casting.

 

I'm sure that Pewter can be successfully cast in the normal RTV type moulds used for white metal.

 

So you can make your masters out of any suitable materiel such as plasticard.

[EasternO]

Thanks above, but to clarify:

I'd like to build brass patterns of wagon parts to cast (RTV) in pewter or another 'white metal'.

I won't be casting whole wagons in one piece, but parts of wagons to solder or fix together some other way.

Apologies for the confusion in the way I worded my question.

 

What I've learned so far, which is critical before you start making patterns, is that most cast metal materials can shrink once cooled, typically by around 3% but can be more or less than this. So, to start the ball rolling on instructionals, I would have to decide which material I would like to cast my wagons from so I know how much larger I would have to make them to account for shrinkage. This is critical.

 

Second, do I make a whole wagon of parts or, if the wagon is symmetrical, do I just make an end and a side and make two castings of each?

 

There are many suppliers of parts, but would it be best to produce my own in case one of the suppliers goes out of business? I'm thinking about the obvious things like wheels, buffers, couplings, etc.

 

Also, what sort of fidelity is achievable with RTV or any other casting process? For example, could I include intricate hinges or pin chains into my patterns or are these better added when building the model?

 

It's these sorts of questions I'd like answered, so seeing someone do it, or reading about it, would give me a better understanding of the process.

 

Thanks

[david.hill64]

Few people these days would go to the trouble of producing a brass or metal master from which to make moulds for whitemetal or pewter. The cheapest route is to produce the master by 3D printing and then use that to produce the moulds. The same method can be used for producing lost wax casting moulds for brass/nickel silver but here you have to use low ash resins. You don't need to worry about shrinkage of whitemetal but should allow 3% for brass.

 

All the casters I know use vulcanised moulds as the cold cured ones have insufficient life. You can get good surface detail representing hinges etc.

 

I have just spent £125 on a master for a loco backhead produced by 3D printing. if I had paid a commercial rate to have a master produced by traditional machining processes it would have cost at least 10 times that much.

[Pebbles]

51 minutes ago, david.hill64 said:

Few people these days would go to the trouble of producing a brass or metal master from which to make moulds for whitemetal or pewter. The cheapest route is to produce the master by 3D printing and then use that to produce the moulds. The same method can be used for producing lost wax casting moulds for brass/nickel silver but here you have to use low ash resins. You don't need to worry about shrinkage of whitemetal but should allow 3% for brass.

 

All the casters I know use vulcanised moulds as the cold cured ones have insufficient life. You can get good surface detail representing hinges etc.

 

I have just spent £125 on a master for a loco backhead produced by 3D printing. if I had paid a commercial rate to have a master produced by traditional machining processes it would have cost at least 10 times that much.

I would be grateful if you could clarify whether items produced on a home 3D printer can in fact be directly used to produce vulcanised rubber moulds.

[david.hill64]

37 minutes ago, Pebbles said:

I would be grateful if you could clarify whether items produced on a home 3D printer can in fact be directly used to produce vulcanised rubber moulds.

If you mean 'can home produced resin printed parts be used as casting masters in vulcanised rubber moulds' then yes, provided you have the correct resin. The production of the rubber moulds requires a vulcanising machine. Vulcanising is usually done at about 150 degrees so you need a printing resin that is stable until at least that temperature.

[EasternO]

4 hours ago, david.hill64 said:

Few people these days would go to the trouble of producing a brass or metal master from which to make moulds for whitemetal or pewter. The cheapest route is to produce the master by 3D printing and then use that to produce the moulds. The same method can be used for producing lost wax casting moulds for brass/nickel silver but here you have to use low ash resins. You don't need to worry about shrinkage of whitemetal but should allow 3% for brass.

 

All the casters I know use vulcanised moulds as the cold cured ones have insufficient life. You can get good surface detail representing hinges etc.

 

I have just spent £125 on a master for a loco backhead produced by 3D printing. if I had paid a commercial rate to have a master produced by traditional machining processes it would have cost at least 10 times that much.

Thanks David, that's very interesting and exactly the sort of information I was after.

 

Did the £125 include CAD or was it just the print? I can design in 2D fine, but not so much 3D.

[Scorpio7uk]

6 hours ago, david.hill64 said:

If you mean 'can home produced resin printed parts be used as casting masters in vulcanised rubber moulds' then yes, provided you have the correct resin. The production of the rubber moulds requires a vulcanising machine. Vulcanising is usually done at about 150 degrees so you need a printing resin that is stable until at least that temperature.

I would also add that quite a lot of pressure is involved in vulcanising as well so do not make your masters out of anything brittle and you would be best to arrange the part in the mould so that it can take the pressure - 'flat' rather than 'end on'.

 

Jeff

[david.hill64]

17 hours ago, EasternO said:

Did the £125 include CAD or was it just the print?

Everything.