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Discussion Starter · #1 ·
I've been casting my own urethane tires at home for a little while now, and the last time I visited the supplier of the ingredients, I picked up some mix for a hard plastic. I figured I might able to make some mirrors or other small parts that often go missing. I also have four of the BWA heavier motor mounts, really nice pieces. I recall Al telling me it was very expensive to make another batch of these, and each item was also fairly pricey because of the waste involved.

So then I got thinking, I wonder if it's possible to cast a version of the BWA mount with plastic. The answer is yes, sort of. I made a standard version, but it's not very strong, so I doubled the thicknesses, made another mould and the thicker version might just work, although it is still not as rigid as the brass version.

Now I'm wondering if I could get stronger plastic, or resin, or maybe add some metal filings to stiffen things up. Here are some shots (not very good, sorry about that), of the first version and its mould, the real McCoy and the second version with mould:





I'm not convinced this is worthwhile but I'll never know unless I try.

Randy
 

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Good idea .... Why not use glass reinforced epoxy resins? Different resins have different quality's. Ribs cast into the part may work with what you have now just adjust the molds. Good luck let me know how it works for you.
 

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Interesting
I'd recommend adding cast in bracing if you need extra stiffness.
It is common practice to solder a brace to metal U brackets joining the lower rear legs of the bracket, this could be cast into the resin equivalent.
A triangular braces each side at the rear would help.
A web at the base of the moulding would also add stiffness.
Obviously the design has to leave clearance for the gear.

(It is common practice to redesign resin replacements of metal parts to make best use of the material's very different properties. a direct copy of the metal part in resin is all too often not stiff enough.)

How is the resin U bracket intended to attach to the rest of the chassis?
A metal U bracket would normally be soldered in, and the wire or plate used would provide additional stiffening for the U bracket.
If you are planning to glue the resin bracket to the chassis, it would be a good idea to design in a good sized mounting areas for the glue.
 

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If you want to go the route of cast resin bracketry, my advice would be to include the whole chassis...you'll get greater stiffness and avoid the issues of weakness where you mount to the bracket itself. Also...you can capture the motor rather than screw mount it as with metal. I agree that including glass or metal filings will add strength...but only if they are tiny and well distributed. I wouldn't rely on that though (it's ok as an added bonus), focus on a balanced chassis design instead. My 2 cents. I'll be happy to discuss this in more detail if this approach interests you.

John
 

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Discussion Starter · #5 ·
Thanks for the advice gentlemen, I'll continue fooling with it as I get time. Al's mount was originally designed for narrow chassis' and has holes in the rear to slide chassis rods into. This combined with a similar front axle mount provided the ability to quickly build a brass chassis for open wheel cars. It is a very nice design really.

Randy
 
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