I was wondering if anyone has had any experience with cold casting brass components and what are the pros and cons of it compared to traditional methods. I am also wondering how to identify what the make up (in terms of the metals used and in what ratio) of a brass part is, I seem to recall someone on here mentioning a company that does this. Here is a photo of one of the parts I may want to reproduce.

I am not aware of any way to "cold cast" brass.

There are metal repair epoxies which are filled with metal powder. These can be used to repair small areas of wear to bring a part back to it's original dimensions. But they do not have the strength of the base metal.

Here is one;

http://www.devcon.com/products/products ... 20%28BR%29

These are quite expensive, a one pound can is about $90.

You could in theory make a rubber mold from an original part, then mix up this repair epoxy and fill the mold. But, the mixed epoxy is quite thick and you cannot just pour it into mold. And it will not have the tensile strength (bending) that brass would.

Your finished part would likely break if you twisted it.

These are made to fill in worn areas only where tensile strength is not an important factor.

Brass melts at approx 1600 degrees F, there is no way to cold cast it.

They can 3-D print metal powders into a porous metal part. These printing process typically glue metal powder (dust) together at room temperature. Then the porous part is heated in an oven which evaporates the adhesive and binds the metal powder together. These are typically used for decorative purposes (jewelry, art work, etc.) because they lack the strength of a solid metal part. They might work in some cases, but I would not recommend them for anything that is going to be twisted/pulled/torqued when in use.

Your photo looks like a foot rest bracket, or luggage rack, or something that is going to have a substantial load on it from time to time. The epoxy or 3D printed parts will break (in my opinion).

You could braze together some basic shapes (cylinders and bent rods) out of brass and then file them down to the shape you want. That could work for a few pieces.

Short of sending off samples for lab tests there is no way to tell from the color alone what is in your existing parts. Most brass looks yellow, there are "red brasses" that have more copper and less zinc. Older parts may suffer from zinc leaching out which can make them more orange in appearance.

Kevin.

Could you make a pattern, or use one of these as a pattern and have them cast at a foundry?

You could get a 3-D scan of these parts and turn it into a CAD model. This could be used with a 3-D printer to make a wax pattern. A foundry could use these to make a plaster mold. Then molten brass could be poured into the mold giving you a solid/strong brass copy of the original.

The 3-D scanning and 3-D printing technologies could help to make copies of these parts, but it does require melting brass at 1600F to get final strong useful parts.

Cheers, Kevin.

https://en.wikipedia.org/wiki/Lost-wax_casting

There's been articles in Model Railroader/RMC about lost wax casting.

Maybe here you could make a rubber mold from your original, remove the original, seal the rubber mold but for an entry to pour in melted wax, cool, cut away the rubber mold, then make a ceramic mold, melt the wax out then pour in your brass.

good for a one up copy.

I've never heard of a "cold casting" process that will give you the results you want.

For a one off-copy this doesn't appear to be a particularly difficult part to reproduce as a sand casting using the original as a pattern. (That's likely the process used to make the originals.) For multiple parts, I would make a new split pattern copying the original in an RTV mould and cast one or more polyurethane duplicates as casting patterns to simplify the moulding process.

Note that the reproduction castings will be a few percent smaller because of the shrinkage of the metal as is cools. Looking at your parts, this may be an issue if hole spacing is critical.

I see one hole in all of your originals is badly worn. If that is what needs to be corrected, boring the holes on a milling machine, making brass or bronze bushings, and silver soldering them in place would be my first choice for a relatively easy fix. The repaired part shouldn't suffer any loss in strength over the original part.

I would find a local foundry that does bronze in sand molds (at least here near San Francisco Bay, brass has more air pollution issues than bronze, and is not genially an option) and talk to them...

Option 1, have a pattern made by a professional...

Option 2, using your part make a pattern using silicon molds, then resin casting, cutting and adjusting as needed... following the foundries advice... I have had some success addressing shrink by using "high fill" spray on automotive primers...

In my experiance, trying to reinvent the wheel is more complicated than using the tech used to make it in the first place... But sometimes that tech is hard to find... but by finding it you are both making a part and preserving the craft.

Randy

This is a tempest in a teapot. A quick Google search for "cold casting" yields a host of information about the use of metallic powders in a polyurethane or epoxy binder to cast "metallic" items. This is in NO WAY a process for manufacturing objects for actual use. The process is to make visually attractive, precisely modeled objects good for looking at or as components for more complex objects, even operating, but just for looking at. The resin binders do not have anything like the required strength to make a practical working object.

Shapeways will do cast brass parts directly from a wax print of your 3D model. Since they are printing, rather than casting, the sacrificial wax part, you only need to take into account the shrinkage of the brass itself (not the wax as well). They are vague about shrinkage rates, but 2-3% should be in the ballpark. Certainly far closer than sand casting from an existing part!

https://www.shapeways.com/materials/brass?li=nav

If you're only looking for one or two parts, this will probably be competitive with having them made via cast wax sacrificial parts.

Steve Hunter

Cat tail Foundry in Penn. They cast parts using original pieces as the pattern all they time. Also try asking on Alloy Avenue

http://www.alloyavenue.com/vb/forum.php

I thought Cattail was an iron foundry?

I know for a fact that several railroad/trolley museum shops do their own casting of things like this--if not in-house, at least locally. I've seen the shop guys at the Baltimore Streetcar Museum walk in with pieces just like this that they've reproduced themselves. I've even cast a few things like this myself using sand form casting--reproduction plates, small parts, etc.

Hint: In sand casting it's difficult to reproduce holes such as what you see in your bracket, so don't even try. Take the sand out of the hole along with the original/pattern, come out with a new piece lacking the hole, and drill out the proper size yourself, then round off the edges of the new hole as needed.

They do a lot of iron but also do aluminum, brass and bronze

In regards to type of brass, back in the good old days a lot of what was commonly referred to as "brass" was actually bronze since it can be very difficult to distinguish between the two. Sort of like the receivers on the 1860 Henry repeating rifles - they were commonly called "brass frame" when in reality they were gun metal which is a bronze alloy. Another example are the intake and water manifolds on a big T-head engine I am working on. They are referred to as "brass" but are actually bronze since it was intended for marine service. (even the 500 lb crankcase is bronze)

About the only way I can tell which is which is by the machining properties. The old rule of thumb is drilling into bronze will produce crumbs, brass produces strings or swarth.

Terry wrote;

"About the only way I can tell which is which is by the machining properties. The old rule of thumb is drilling into bronze will produce crumbs, brass produces strings or swarth."

I have machined quite a bit of brass and bronze, and in my experience they both produce "crumbs" or "chips". The strings or swarth come from the steel and stainless steel metals which have a stronger tensile strength.

I have several metal lathes with many years of use and none of them have "strings" of brass/bronze in the chip pans underneath. They have lots of strings of steel in the chip pans.

One of the tasks while making heavy cuts in steel parts is managing the "strings" of cut metal so they do not clog up the cutting area. There are guides in the old text books about how to grind a lathe tool bit to include a "chip breaker", these helped to break the steel cutoffs into smaller chips.

Cast iron also produces lots of "crumbs".

In my experience Brass "squeaks" when it is machined, it makes a high pitched sound when you cut it. Bronze is more quiet. Steel "groans" when you cut it.

Cheers, Kevin.

A picture is worth a thousand words:

From my 1942 Southbend: Brass "Crumbs" on the left, Bronze chips (some call it strings - In hindsight swarth would not be the appropriate term) on the right.



Hope this helps,

Best regards,
Terry