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View Full Version : Get Me Started in Brass/Bronze Casting?



Fasttrack
03-18-2011, 10:23 PM
I've been doing some google research on backyard metal casting. Someday, I'd love to get into casting iron, but I'm not ready for that yet.

What I do want to do is cast a bunch of brass gear blanks. I've got pounds of scrap brass (mostly from old plumbing fixtures). I thought I could use this to make my gear blanks. These gears are for an orrery, so they don't need to have any special mechanical properties. They just need to be shiny. :)

I've looked into building a waste oil burner (which I prefer over propane) and I think I can design a decent furnace.

What I'm not sure about is what to use as a crucible and what I need to do as far as actually casting goes - do I need to add flux or anything to the pot before I start melting the scraps? Do I just let it melt and then skim it?

Can I use steel for molds? I'd like to cast several duplicate gears, so I thought I'd make a die out of steel and then pour into the steel if it's possible. Do I need to preheat the mold slightly before casting? I don't want to inadvertently braze my mold together, either, though.


I dunno. Where do I start learning??

Black_Moons
03-18-2011, 10:37 PM
Heres a place I read a lot at: http://www.backyardmetalcasting.com/

Have not yet started doing any casting, other then messing stuff up with my oxy/fuel torch :)

Waste oil seems like a good idea.. they sure leave enough of it outside the local auto store.. :P
The most popular waste oil designs seem to use a propane preheat so that burning the oil is dirt easy once the foundry reachs a decent temp.

Brass will bind very well to steel.. See: brazing.
I don't think steel would make any kinda remotely useful mold. Maybe for melting the brass in, but thats about it.

Reenforced plaster of paris I think can be used for brass molds. Theres also types of plaster designed for higher temps..

From what iv read, you are really better off finding a real foundry supply place and buy the real foundry refractory material and molding sand/plaster/whatever, then trying the verious online recipes. Brass melts at like 1100f, Not much withstands these kinda temps!

Even the cheapo guys online seem to agree that the real refractory material is much better then homemade, especialy at brass (or higher) melting temps.

Note this is really not something you should just 'try' before reading a WHOLE lot. A tiny bit of moisture can turn into a steam pocket that violently explodes under molten metal, Spraying molten metal everywhere. The pot you melt the metal in (crucible) can crack and dump material, You might accidently dump it yourself. Molten metal + concrete = explosion.
Molten metal + any moisture = explosion. Etc etc. Nasty stuff. Lots of safty percautions to read!

Wear proper gloves (I would assume welders leather gloves would be an absolute min acceptable), Leather shoe covers (More welding equipment.. but im sure foundry stores would have similar or better), full face shield (Likey gonna have to be plastic, but at least it should stop small molten splatters from hiting your face), and safty glasses (Double protection!)

Long tongs are also often used to move the molten metal around. its not something you wanna be near. Molten brass boils off zinc. You may need to add zinc.. And be ware the fumes. Get brass too hot and the zinc violently boils off suddenly...

Consider foundry work to be as big as subject as machining, Except 10x more likey to explode in your face leaving you with lifelong scars and/or blindness, And approch it as such. Cautiously. with much research.

Tony Ennis
03-18-2011, 10:40 PM
I recommend you start with Aluminum, not brass.

portlandRon
03-18-2011, 10:43 PM
If you look halfway down the page there is a section on casting
http://www.homemodelenginemachinist.com/

CCWKen
03-19-2011, 12:13 AM
Red brass (plumbing fixtures) is too soft for most gears. Gears are usually made from the bronze group. I would save that red brass for ornamental castings and/or for practice. Also, I wouldn't use steel or iron for a crucible. Iron will contaminate the melt. Best to use one of the ceramics or the graphite type. Study up on the procedure because you can ruin a new crucible real quick.

Dale Lusby
03-19-2011, 12:51 AM
Aluminum melts at 1200 f and brass/bronze/copper melts at 1600-2000 depending on the metal. Melting aluminum is pretty easy and can be done with charcoal and a blower. I've successfully melted copper once but it wasn't too good on my refractory. I can't say for sure on the steel mold but it might work. I used a simple steel crucible made from 1/4" walled pipe which held up decent with the copper but I wouldn't use it if I were doing too much. I would start with aluminum to get your feet wet and then move to brass. The fundamentals are the same but you'll need a furnace that gets up around 2000 to melt the brass. My neighbor has been working on a Yates American mortiser and it has cast beveled gears that aren't machined but simply cast. Quite impressive casting to make accurately. You might make a gear that you could use in casting sand to make impression and then machine for finished look.

If you decide to go with aluminum melting you can pick up pottery kilns for cheap and they are easy to use and probably safer than the waste oil. Plus you might be able to use for heat treat oven.

+1 on backyardmetalcasting.com

knedvecki
03-19-2011, 01:12 AM
There is a book published by Tab books, authored by C. W. Amons?? on casting bronze, one on aluminum, and I think one on iron.

macona
03-19-2011, 01:55 AM
We did some bronze and aluminum casting when I was at techshop. We were using furnaces that ran off of natural gas, propane works as well. Simple designs really.

You could do the gears a couple different ways. Make up a positive pattern figuring in shrinkage and cast in sand. We use petrobond. You will get pretty good detail from good sand.

You can make sets of copes and drags from plywood.

Bronze and brass will not stick to cold steel.

There are still some pics on the old techshop flickr page here:
http://www.flickr.com/photos/techshoppdx/page11/

Also a pic of us pouring bronze:

http://farm5.static.flickr.com/4088/5055969331_ac9ea2ee46_z.jpg (http://www.flickr.com/photos/67292116@N00/5055969331/)
IMGP2247 (http://www.flickr.com/photos/67292116@N00/5055969331/) by macona (http://www.flickr.com/people/67292116@N00/), on Flickr

Dr Stan
03-19-2011, 01:40 PM
As others have mentioned safety is of extreme importance when casting metals. You're dealing with very hot materials and if water is accidentally introduced you get an explosion since the water to steam expansion ratio at normal atmospheric pressure is 1600:1.

If there is a tech school, college, or university nearby where you could take a casting course it would be well worth your time. There are some excellent resources from http://www.lindsaybks.com/ including a reprint of the US Navy's 1958 Foundry manual. I especially recommend this one as I've used it.

One more thing. If you have access to coal it burns hotter than charcoal. I too built a backyard foundry using a hot water heater lined with fire brick, coal, and a couple old HVAC squirrel cages for air input. Also built the lid from fire bricks I shaped into pie sections and held together with a steel band.

Richard Wilson
03-21-2011, 12:40 PM
We did some bronze and aluminum casting when I was at techshop. We were using furnaces that ran off of natural gas, propane works as well. Simple designs really.

You could do the gears a couple different ways. Make up a positive pattern figuring in shrinkage and cast in sand. We use petrobond. You will get pretty good detail from good sand.

You can make sets of copes and drags from plywood.

Bronze and brass will not stick to cold steel.

There are still some pics on the old techshop flickr page here:
http://www.flickr.com/photos/techshoppdx/page11/

Also a pic of us pouring bronze:

http://farm5.static.flickr.com/4088/5055969331_ac9ea2ee46_z.jpg (http://www.flickr.com/photos/67292116@N00/5055969331/)
IMGP2247 (http://www.flickr.com/photos/67292116@N00/5055969331/) by macona (http://www.flickr.com/people/67292116@N00/), on Flickr
Is that a cardboard box you are pouring into?
Richard

mackme
03-23-2011, 08:55 AM
Here's where you need to start http://www.bodyscape.net.nz/bronze-casting-tutorial.htm

PeteF
03-23-2011, 04:31 PM
That looks like a good resource. I love the use of the BBQ tongs :D

Weston Bye
03-23-2011, 05:17 PM
I got the book - It's pretty good, easy to understand. I plan on doing some casting this summer.

Rich Carlstedt
03-23-2011, 05:47 PM
Probably the best overall view of casting is covered in a book by Tim McCreight called "Practical Casting"
http://www.gettextbooks.com/search/?isbn=9780961598402
It is sort of aimed at jewelry or precision casting, but covers the range available

The backyard casting books by Terry Aspin are good.
I have done Aluminum ,Bronze/Brass, and Iron, and each differs in the approach.
Safety cannot be preached enough, as when you get hurt, it is serious !
Cast Iron at 3,000 degrees takes no prisoners !

But there is nothing that gets the heart beating faster than picking a part out of the sand, after hours of work.

Doing a gear is tough, unless you just want the blank. Thats OK

Rich