advice on casting needed

andrewnummelin
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advice on casting needed

Postby andrewnummelin » Fri Jan 22, 2021 5:12 pm

There are a couple of few components that I wish to make and it has been suggested to me that brass casting may be the way to go. This technique is one that I have never tried and know very little about.

For etching there are design guides by some of the suppliers (Hollywood Foundry, Mastercut, PPD, ...) - do any casters publish similar guides?

I've taken a brief look at Shapeways ( https://www.shapeways.com/materials/brass ) but the minimum dimensions for their wax printing route are too thick.

I believe that with brass casting it is normal to start by making a master from which a mould is made. I'd like to know the requirements for making such a master. (I tend to think in terms of plastic injection moulding where one would start by cutting a mould - a technique way beyond my capabilities and not appropriate for a making a small number of items.)

My initial wishes are for some difficult lampirons and footboard supports but I'm also wondering about other rolling stock iron-work.
Regards,

Andrew Nummelin

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Winander
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Re: advice on casting needed

Postby Winander » Fri Jan 22, 2021 6:04 pm

Andrew,

I have seen in lists of materials for 3D printing, one that appears to indicate it could be used to produce patterns for moulds to be used in casting - the property was described as one that burns out with very little ash.

This could potentially speed up development because it bypasses the lost wax process because the pattern is left in the mould and burnt out.

I can't find the original thing I read but this site discusses the technique https://learn.colorfabb.com/3d-printing-investment-casting/

HTH
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nigelcliffe
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Re: advice on casting needed

Postby nigelcliffe » Fri Jan 22, 2021 7:04 pm

I've been 3D printing to metals using Materialise in Belgium. They work like Shapeways, but offer different materials. Their stainless steel product is much higher resolution than Shapeways. I've used them for driving wheels for the 2mm Scale Association. Needs a bit of care to keep the cost of items from running away.


My father-in-law used to own a precision engineering casting business. Retired from it best part of 20 years ago, he was casting from 3D printed investments back then (producing bits for aero engine R&D and F1 car makers, who were starting to use 3D printers). I have a handful of cast iron 2mm scale loco wheels, derived from injection-moulded plastic investments, done as proof-of-concept.

Traditional investment casting (lost wax) starts from making a mould and pouring wax into it.
The mould can be formed by surrounding a master pattern using a flexible (rubber) compound.
The wax (investment, it is lost) is then poured into the mould. When set, the wax is removed from the mould.
The wax is coated in a ceramic (typically a slurry), firing the ceramic and melting out the wax.
Then pour metal into the ceramic mould. Break off the ceramic, clean up the metal, and the object is produced.
To make it efficient, multiple wax pieces are placed on a "tree" or sometimes attached to a "brick slab", so the ceramic and metal stages produce a lot of items, rather than one. For some stages, a vacuum during wax or metal casting is applied to assist flow.

One can injection mould wax, but that's expensive to make the injection mould tool - good for very high numbers of items, not so good for low volume. One can 3D print into wax-equivalent compounds, which avoids the mould making, but tends to cost a bit more to produce the 3D print.

There are a fair number of investment casting firms around. Some serve the jewellery trade, others engineering. For most model making jobs, jewellery casting is more appropriate. They often publish guides to producing the investments (waxes), and most are geared up to work from 3D CAD and 3D printing methods.


- Nigel

Jeremy Suter
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Re: advice on casting needed

Postby Jeremy Suter » Fri Jan 22, 2021 9:42 pm

Hi Andrew
Talk to the horses mouth ring up David White at Slaters they do there own waxes and send them on to the Jewellery Quarter to have them lost wax cast

Basically you need to make a master which is 3% bigger than the finished product because you are in effect casting it twice once in wax and then in metal. The metal shrinks by volume so is not and exact science. I recommend going to Slaters they have produced some excellent stuff for me.

Making the masters its best to sprue them up so that the fall of metal is as much as possible on a downward flow and the masters should be able to stand the vulcanisation process which cures at 180degree and 40psi Although ask David if he can do silicon cold cure moulds, which you could make the masters out of plastic.
Last edited by Jeremy Suter on Sun Jan 24, 2021 3:20 pm, edited 1 time in total.
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Terry Bendall
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Re: advice on casting needed

Postby Terry Bendall » Sat Jan 23, 2021 9:17 am

Nigel has given a very helpful summary of what is called lost wax casting which is a very old technique used in jewellery and silversmithing. The traditional way of making the mould is to use Plaster of Paris. Hold the wax mater in a suitable container, pour the plaster around the master and when it is set, melt out the wax. The molten metal can then be poured into the mould. When the metal is cool, break away the plaster. The process is obviously only suitable for a one-off job.

As a variation, a mould can be made in MDF wither by hand or by machine and CNC machines are good for this. It is really only suitable for fairly simple shapes. You need a mould that is in two parts so either half the shape must be cut into both parts or it must have one flat side. If a MDF mould is used it is only really suitable for casting low melting point metals such as pewter.

If using a plaster mould it needs to be dried out. Brass melts at a fairly high temperature around 850 - 950 degrees C, depending on the exact composition so care is needed as well as suitable PPE. You also need to be able to heat it to the required temperature which is usually done in a crucible furnace. It is possible to build such a thing and there are model engineering books that describe how to do so.

Terry Bendall

davebradwell
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Re: advice on casting needed

Postby davebradwell » Sat Jan 23, 2021 9:25 am

I've always used Slaters, too and I'll add a few comments to Jeremy's recommendation. As with all castings, large chunks should be avoided as they will sink but 0.3 wire can be cast in sensible lengths and edges can be tapered below this. Sudden changes in section are bad, too. A great advantage of their process is they will include cores so that, for example, you can get a chimney with a correctly shaped hole down the middle or a dome that's just a thin shell and more easily soldered but the principle can be applied as required.

If you are going to need sub-masters to produce quantities of a component then this is an extra stage and double shrinkage must be added. In contrast to Jeremy's experience, Slaters have always sprued my components for me as the process involves experience of getting enough metal to flow into the mould. On the other hand, by doing your own you can avoid a feed onto an awkward part of the casting but Slaters have knowledge of our components and this would be rare. I usually add a few notes to express my preferences.

Do a sketch of what you are trying to do and discuss it with David W - you'll soon get the hang of it. Although I had designed a number of castings and mouldings in my past the rules are quite logical and mainly concerned with getting the master out of the mould. I think cold cure moulds have a different shrinkage but it's just one of the things to agree on.

DaveB

andrewnummelin
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Re: advice on casting needed

Postby andrewnummelin » Sun Jan 24, 2021 3:03 pm

Gents,
Many thanks for all the very useful advice - I'll be following up on this next week.

However, don't expect rapid feedback on the results - my current project is on assembling some etched coach sides that I believe I have had since the early 1980s that are being glazed with material that must have been bought before April 1973!
Regards,

Andrew Nummelin

nigelcliffe
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Re: advice on casting needed

Postby nigelcliffe » Sun Jan 24, 2021 5:35 pm

Just to add, there are techniques for DIY metal casting using a focusing furnace inside a domestic microwave oven. It's in the "moderately dangerous" end of home techniques, so think hard about the risks!

I got onto the technique by a jewellery making friend, who's been using the technique for melting glass beads as part of the things she makes. An internet search will bring up various details of the glass furnaces, and from them finding discussion of metal casting with the same hardware isn't too hard.

No, I haven't tried it myself, and were I tempted, I'd only try outside.

- Nigel

billbedford

Re: advice on casting needed

Postby billbedford » Mon Jan 25, 2021 12:12 pm

nigelcliffe wrote:Just to add, there are techniques for DIY metal casting using a focusing furnace inside a domestic microwave oven. It's in the "moderately dangerous" end of home techniques, so think hard about the risks!


The main risk being that the domestic authorities are not going to be very happy about it.....

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Guy Rixon
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Re: advice on casting needed

Postby Guy Rixon » Mon Jan 25, 2021 1:40 pm

Can one get a microwave with a remote control, so that it can be operated from minimum safe distance?

Enigma
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Re: advice on casting needed

Postby Enigma » Mon Jan 25, 2021 4:28 pm

Guy Rixon wrote:Can one get a microwave with a remote control, so that it can be operated from minimum safe distance?

Plug it into a long extension lead - and get a friend to set the controls...........................

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Winander
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Re: advice on casting needed

Postby Winander » Mon Jan 25, 2021 4:47 pm

Back on topic, although the diversion was certainly amusing, I have been ferreting around our website and found a list of where to get useful items https://www.scalefour.org/links/wheretoget01.html. The item Aluminite caught my attention, but a search on the supplier's site failed to provide results. Their site, however, contain products that enable DIY casting and, at the very least, may provide the opportunity to prove a master.
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nigelcliffe
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Re: advice on casting needed

Postby nigelcliffe » Mon Jan 25, 2021 5:04 pm

Enigma wrote:
Guy Rixon wrote:Can one get a microwave with a remote control, so that it can be operated from minimum safe distance?

Plug it into a long extension lead - and get a friend to set the controls...........................


My jewellery casting friend uses a Tesco-cheapest microwave for this work, because it was cheap, and has a very simple rotary timer. She keeps a posher microwave for the kitchen.
Turning on itself isn't a direct risk, its being able to turn it off if something goes badly wrong. Which is where a decent extension lead, with easy access to the plug and socket, is one thing to consider.


- Nigel

billbedford

Re: advice on casting needed

Postby billbedford » Tue Jan 26, 2021 8:46 am

I found this video yesterday, which may be useful as a starting piont

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Jol Wilkinson
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Re: advice on casting needed

Postby Jol Wilkinson » Tue Jan 26, 2021 10:15 am

I would suggest that the best and safest option is to make the master patterns and send these to a casting company.

The attached (not very good) photo shows the cylinder/slidebars/motion bracket for the LRM LNWR Jubilee. The cylinder rear plate/piston rod gland/slidebars are a one piece N/S casting. I made the pattern this from brass components using a Unimat lathe. The components were soldered with 220 and 188 solder. The crosshead/piston rod and the cylinder front covers were made the same way. These were sent to David White at Slaters on behalf of John Redrup at LRM for casting.

When I designed the LNWR Teutonic for LRM I followed the same approach but omitted the piston rod from the casting, instead providing a hole in the casting to take a piece of .9mm N/S rod as it is stiffer and has a better finish for a polished part

Jubilee slide bars.JPG


I believe that the costs involved breakdown into the cost of creating the silicon rubber mould, the casting process cost and the cost of material by weight. Once the mould cost is covered, the item cost is relatively small.
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andrewnummelin
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Re: advice on casting needed

Postby andrewnummelin » Wed Jan 27, 2021 11:49 am

billbedford wrote:I found this video yesterday, which may be useful as a starting piont

Indeed interesting, and enough to convince me that, for my needs, contracting out rather than diy will be the way to go.
Regards,

Andrew Nummelin

andrewnummelin
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Re: advice on casting needed

Postby andrewnummelin » Wed Jan 27, 2021 11:54 am

Jol Wilkinson wrote:I would suggest that the best and safest option is to make the master patterns and send these to a casting company.

The attached (not very good) photo shows the cylinder/slidebars/motion bracket for the LRM LNWR Jubilee. The cylinder rear plate/piston rod gland/slidebars are a one piece N/S casting. I made the pattern this from brass components using a Unimat lathe. The components were soldered with 220 and 188 solder. The crosshead/piston rod and the cylinder front covers were made the same way. These were sent to David White at Slaters on behalf of John Redrup at LRM for casting.

When I designed the LNWR Teutonic for LRM I followed the same approach but omitted the piston rod from the casting, instead providing a hole in the casting to take a piece of .9mm N/S rod as it is stiffer and has a better finish for a polished part

Jubilee slide bars.JPG

I believe that the costs involved breakdown into the cost of creating the silicon rubber mould, the casting process cost and the cost of material by weight. Once the mould cost is covered, the item cost is relatively small.

Thanks, this may well be the way to go with another project on my list of thing to do one day!
Regards,

Andrew Nummelin

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Hardwicke
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Re: advice on casting needed

Postby Hardwicke » Tue Mar 02, 2021 4:31 pm

Have you thought of contacting Alec Tiranti's? Their London shop is closed due to covid (it's quite small) but their Thatcham shop is open for orders and advice.
https://tiranti.co.uk/
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SteamAle
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Re: advice on casting needed

Postby SteamAle » Wed Mar 03, 2021 11:15 pm

Andrerw
If you have not got sorted with a caster yet cspmodels.com could help you out.
We do casting for a couple of 4mm kit manufacturers, one of whom posts on here on a regular basis.
Philip

andrewnummelin
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Re: advice on casting needed

Postby andrewnummelin » Thu Mar 04, 2021 6:15 pm

Thanks guys for the suggestions that I shall now follow up (having just been thwarted in my plans to order some gearboxes and motors this evening).
Regards,

Andrew Nummelin


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