Re: Model brake component size comparison to prototype


Schuyler Larrabee
 

Ralph, I believe that lost “was” is, except for unique individual items made by artists casing in silver or gold, no longer used for mass production of parts like model railroad brake gear.  That has become a “lost plastic” process, where many plastic parts are glued together in a “tree< which is then inserted into a can of wet plaster.  When dry the plaster cylinder is heated to get the plastic to run out, and then brass is poured into the middle of a spin casting machine, which forces by centrifugal force, the metal into all the voids in the plaster cylinder.  After cooling (and shrinking) the plaster is broken away and the parts harvested.

 

I presume that the plastic used has a lower melting temperature than that used for injected molded parts from metal dies.

 

I have received lost plastic parts that still have plaster on them.

 

Schuyler

 

From: main@RealSTMFC.groups.io <main@RealSTMFC.groups.io> On Behalf Of Ralph W. Brown
Sent: Saturday, April 04, 2020 1:34 PM
To: main@RealSTMFC.groups.io
Subject: Re: [RealSTMFC] Model brake component size comparison to prototype

 

Hi Tim,

 

My understanding is that the sacrificial material used to make the molds for casting is, as the name of the process implies, wax, which melts and is absorbed by the mold when it is first heated leaving the void later filled with molten brass or other casting metal.  I doubt plastic detail parts made by Cal-Scale or others would or could preform the same function, although I suppose they could be used as “masters” for casting the sacrificial wax patterns, copyright issues notwithstanding.

 

I suspect there are others here who are more familiar with the process and could provide a more detailed description of the process.

 

Pax,

 

 

Ralph Brown
Portland, Maine
PRRT&HS No. 3966
NMRA No. L2532

rbrown51[at]maine[dot]rr[dot]com

 

From: Tim O'Connor

Sent: Saturday, April 4, 2020 9:15 AM

Subject: Re: [RealSTMFC] Model brake component size comparison to prototype

 


As I recall, all Cal-Scale detail components were OVERSIZE because they were used
for lost wax casting! In that process the plastic parts are for the molds and are
destroyed in the casting process, and the shrinkage produces parts that are closer
to scale.

Or am I wrong? :-)

Tim O'Connor

========================================

On 4/4/2020 9:00 AM, Lester Breuer wrote:

A comparison of several manufacturers’ model brake component measurements to Westinghouse prototype brake component measurements prepared by George Toman was sent to me for my use.  I asked George to share his measurements comparison on my blog.  If you are interested in the  comparison measurements, they are now available on my blog I have to share photos and writeup of projects on my Minneapolis & Northland Railroad Company. If would like to take a look please do at the following link:

 

http://mnrailroadcab100.blogspot.com/

 

Lester Breuer

 


--
Tim O'Connor
Sterling, Massachusetts

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