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View Full Version : Casting and Foundry Casting (making) clasps



Balsanu Gabi
05-13-2014, 2:30 PM
Hi to all,

I need some advices to make this kind of clasps. I know I can buy some of them, but I need a very large one (40mm long). What need to know is:
- can I make that at home?
- recommended material?
- recommended process?
I have made some from acrylic (2 pieces connected with small grub screws), but I need to have a production time. I also try to make a mould from RTV and try to cast that clasps in resin. Failed, probably because of lack of air sprue or something else. Thatís I am trying to have a pro opinion.

Thank you for your time
Gabi


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Charles Wiggins
05-13-2014, 3:18 PM
I have no idea what you have access to, but if I were going to attempt to make those in production at home I would look at sand casting with greensand. I'd make a model out of something fairly durable to pull the molds from and make sure that all of the edges were rounded and have draft (http://www.afsinc.org/about/content.cfm?PreviewContentItem=23297&RDtoken=53822&userID=12674).

Looking at your photos, It seems likely those were sandcast. I'd try aluminum first. It's a good compromise between strength and low melt temperature.

There's lots of information on getting started with backyard casting here (http://www.backyardmetalcasting.com/), including how to make greensand (http://www.backyardmetalcasting.com/greensand.html). He's got a book for sale, but you can find plenty of info online:

http://foundry101.com/new_page_7.htm

http://www.instructables.com/id/Backyard-Metal-Casting-and-Homemade-Forges/

http://www.myhomefoundry.com/

Cheers,
Charles

Balsanu Gabi
05-13-2014, 3:44 PM
Hi Charles,

Thank you for links (I've read all of them already). I was thinking at different approach. I saw some videos with making little soldiers toys. I can source some that material but I need to know:
- that has enough strength for that clasps;
- can be couloured;
- mould can be from;
- recommendation on somebody who can make that mould.

Thank you
Gabi

Shawn Pixley
05-14-2014, 2:30 AM
That looks like it is at or over the size for centrifugal casting with hobbyist scale equipment. Assuming you have a broken arm casting setup and kiln, you need to calculate the mass of casting material needed including sprue. At 200 gms you'll have problems casting it. It can be dangerous flinging molten metal around at that mass. Above that scale you'd want to consider vaccuum casting. If you insist on casting, I'd agree with Charles on sand casting in aluminum. There is a nice book titled, "How to Cast Small Metal and Rubber Parts" by William A. Cannon that explains homemade Sand Casting.

To me, If you are making only a few, I'd consider fabricating it from solid brass, bronze or aluminum.

As I read your second post, it sounds like you are leaning towards casting in resin with a metal mold. If you are not making the mold yourself, it sounds like this would be prohibitatively expensive. Depending upon the strength needed, you might consider metal clay.

Charles Wiggins
05-14-2014, 12:36 PM
Hi Charles,

Thank you for links (I've read all of them already). I was thinking at different approach. I saw some videos with making little soldiers toys. I can source some that material but I need to know:
- that has enough strength for that clasps;
- can be couloured;
- mould can be from;
- recommendation on somebody who can make that mould.

Thank you
Gabi

Gabi,

If you are talking about going to resins instead of metal I am afraid I would be of no help.

Balsanu Gabi
05-14-2014, 3:28 PM
Hi Charles,

I want to cast that in metal (I dont know which is more suitable). I said I try resin, but I failed. Any advice is good. In a meantime I will buy some aluminium sheets and I will make that clasps. I need to find out how long it will take.

Thank you
Gabi

Steve Menendez
05-19-2014, 2:49 PM
For a relatively simple shape like the pieces shown in the photos, I believe there are more efficient processes than casting. It looks like some bar stock and a milling machine (or even a drill press) might be a better option than casting unless you are going to make very large quantities, in which case, a commercial foundry is called for.Obviously, castings have certain advantages when it comes to large volume production (permanent molds), creating complex shapes and internal passages, but those parts look pretty straightforward.My 2 cents (as a Metallurgical Engineer)Steve.

Steve Menendez
05-19-2014, 2:54 PM
Hmm, something funny is happening with the formatting of my posts. Paragraphs and hard "returns" are not working.Steve

Steve Menendez
05-19-2014, 3:20 PM
I think I have the paragraph thing figured out.

It's difficult to tell from just a photo, but appears that the original pieces may have been die-cast in a permanent mold. This kind of process is very popular with aluminum/magnesium or aluminum/zinc (pot metal) type castings.

They may have also been tumble-polished for a shiny surface finish.

Steve.

Balsanu Gabi
05-19-2014, 4:12 PM
Hi Steve,

I dont have a metallurgical knowledge but, I look on YouTube at many vids about pewter castings. I believe that is the process. I need to find a mold maker (for that rubber molds) in the UK ir elsewhere to make that mold (I will have a master made from acrylic or aluminium).
Any help on that?

Thank you
Gabi

Steve Menendez
05-19-2014, 4:59 PM
You might have good luck talking to a commercial foundry, and asking who does their patternmaking work. If you are committed to having these parts cast, as opposed to machined, you will need to have some good contacts in the foundry business. It will save you money and hassle in the long run.

On a small scale, I have seen people use old brake drums (like from a small truck) as the cope and drag for a mold, then make their own matchplate type pattern (half in the upper drum (cope), and half in the lower portion (drag). Then, you would need to cut in a pouring spout and sprue. For a small part like you have shown, a riser is probably not needed. This is only viable for very small scale parts production.

From my professional standpoint, I would still recommend a milling machine or drill press. If you can make satisfactory castings in a non-industrial setting, then congratulations. However, there are many obstacles to making castings efficiently.

Steve.