Custom-molded weights!

Custom-molded weights!

Postby WillYart » Fri Mar 29, 2013 6:30 am

Today I brought some cars up to NMRA standard weight (for TT scale, 3/4 oz. initial weight + 3/8 oz. per inch of car length).

To avoid lead poisoning (I have a small child), I chose a lead substitute of increasing popularity: Bismuth, 86% the weight of lead. It is a metal, basic element (#83 on the periodic table). Unlike lead it is quite non-toxic, you can eat it with no problems. Someone sells it on eBay for $22 for 16 oz, free shipping. It looks and feels kind of like lead, but internally it's rather crystalline, kind of crunchy when you crush a small piece with a pair of plyers.

Anyway, the stuff came in rough 2-3mm spheres, not compact enough to hide in sufficient quantities on, say, a small flatcar with no load. So, I decided to melt the stuff and mold it! Fortunately it melts at 271.5 °C, 520.7 °F, which was very convenient, easy to accomplish on the stovetop.
as it came in the mail.jpg
Fig. 1. Some Bismuth as it came in the mail

I created the mold by routing a correctly dimensioned space in some wood and lining with heavy foil (affixed with thumb tacks and white glue)
mold.jpg
Fig. 2. The mold.

Melting it was achieved quickly and easily over an electrical burner. (The second batch melted in a small metal cup rather than the frying pan!)
Melting.jpg
Fig. 3. Melting.


finished weight.jpg

Final product (underside of flatcar before mounting the chasis, which hides the weight). Super glue and Silicon calk affixed the chasis to the weight and the rest of the car.
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Re: Custom-molded weights!

Postby ConducTTor » Fri Mar 29, 2013 2:43 pm

Very cool. I've saved an ebay search for this as I can see many uses for it when it comes to adding weight.
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Re: Custom-molded weights!

Postby Richard-B » Fri Mar 29, 2013 4:59 pm

... another way might be to just bind the metal pellets together with casting resin.
Not quite as dense... but no melting!
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Re: Custom-molded weights!

Postby WillYart » Fri Mar 29, 2013 11:12 pm

Ah yes, and to trim the weight a little I did use a technique of that sort, but with 50% white glue and just a little sprinkle of dish detergent to break the surface tension, as here (attached).

Untitled-2.jpg


I'm glad this was of interest to some folks.
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Re: Custom-molded weights!

Postby ConducTTor » Fri Mar 29, 2013 11:43 pm

WillYart wrote: a little sprinkle of dish detergent to break the surface tension


Can you elaborate please? I'm not sure what this means :(
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Re: Custom-molded weights!

Postby WillYart » Sat Mar 30, 2013 5:52 am

Oh I mean the water in the glue/water mix normally sits on top in droplets and refuses to settle in between the crevices. That is an effect of the high surface tension of water - the same effect that allows water spiders to sit on top of the water.

So when gluing ballast, or in this case weights, the trick is to add just a tiny bit of liquid dish detergent to the glue/water mix. The detergent breaks up the surface tension so the water no longer stays in droplets, and instead diffuses everywhere it needs to go.

In my case, this has worked out nicely; the glue has dried and the weights are firmly affixed. I have used this technique with ballast in the past after hearing about it somewhere.

Here is a reference on using soap in water, it is also called "wet water". http://www.model-railroad-infoguy.com/ballast.html

Another variation on the theme is to spray with soapy water, then apply the glue mix.
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Re: Custom-molded weights!

Postby ConducTTor » Sat Mar 30, 2013 10:19 am

Gotcha thanks :wave:
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