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Sidewall of my Sn3 pilot model.

Sidewall of my S-scale pilot model

MAKING THE MOLDS



    DURANGO and GUNNISON Roundhouse in On3!


    I'm taking digital pictures of my progress on the O-scale roundhouse models as I go and posting them here on my web site. It's more a scapbook than it is a well organized essay at this point. Perhaps later when I have the time- Note that this is a work in progress and not all sections are posted at this time.


        Durango Roundhouse Kit Page    

        Index    

        Introduction    

        Durango Prototype    

        Gunnison Prototype    

        Drawings    

        Durango 2006 Convention    

        Constructing the Patterns    

   

      Mold Making    

        Casting Hydrocal    

        The Floor Plan    

        Constructing the Base    

        The Inspection Pits    

        Fitting the Parts    

        Coloring Brick and Stone    

        Building the Roofs    

        The Engine Doors    

        Final Assembly    

        The Boiler House    

        Foreman's Office and Crew Room    

        Additional Details    

        Turntables    

        Gunnison Notes    

        The Pilot Model Display    



! LET'S MAKE SOME MOLDS !

    With the patterns complete we now move on to making the rubber molds. I'm using Dow Corning HS II RTV base with the Clay catalyst, which is a very strong and flexable silastic moldmaking rubber. Since I have already composed an article on mold making I will direct you there:  
  Crow's How 2 - Mold Making  

Durango rounhouse construction.

The new rubber is very flexable.

    Here's a look at some of the new molds I've made. That green sort of growns on you. After 20 years some of my original 3110 RTV molds are finally breaking down. Subjecting them to an alchohol wash (de-bubbling agent) didn't help. I'll be more careful with the new ones. The HS II requires vacumm de-airing in the process. 3110 does not. The HS II is very stong and flexable.

Durango rounhouse construction.

When complete the patterns are sealed with Scalecoat Sanding Sealer.

Durango rounhouse construction.

The patterns do not have to be glued down to the base but there's a risk of them shifting out of place and/or breaking.

Durango rounhouse construction.

Here's a series of parts that will all be on the same mold. I've glued them to the plywood base.

Durango rounhouse construction.

Be sure to fill any openings underneath the patterns with putty, wax or other.

Durango rounhouse construction.

Petrolum jelly is used as a releasing agent on the patterns and boards.

Durango rounhouse construction.

Simple dams are built with stripwood. I'm leaving a 1/2" wide boarder around each piece and about 3/16" of thickness.

    I'm using Dow Corning's HS II silicone rubber for these molds. It's softer and more flexable than the 3110 I've normally used. The HS II requires more careful measurement and vacuum de-airing which the 3110 does not (though its recommended). We'll see how it goes. Of course there are a number of choices and brands. This is just what I use for Hydrocal casting.

Durango rounhouse construction.

HS II RTV rubber base and Clay Catalyst.

Durango rounhouse construction.

One scoup of rubber base is about 100 grams.

Durango rounhouse construction.

The rubber and catalyst is carefully weighed out for the 10:1 ratio.

Durango rounhouse construction.

Once mixed the HS II rubber is vacuum de-aired to eliminate bubbles.

Durango rounhouse construction.

The rubber is poured into the mold box.

Durango rounhouse construction.

Just a little more.

Durango rounhouse construction.

The mold box is vigorously tapped to help any trapped air bubbles rise to the surface.

Durango rounhouse construction.

In order to get a perfectly smooth back on the new mold a sheet of styrene is placed over the rubber and then a flat board followed with some weight. I'm using a drill press vise for this.

Durango rounhouse construction.

In the morning a stack of molds for the Durango rounhouse are ready to have the patterns removed.

Durango rounhouse construction.

Here's that sheet of styrene being removed.

Durango rounhouse construction.

We have a nice flat back.

Durango rounhouse construction.

The excess rubber is trimmed off.

Durango rounhouse construction.

The new mold is gently pulled away from the pattern.

Durango rounhouse construction.

Being careful not to damage the pattern.

Durango rounhouse construction.

Almost have it.

Durango rounhouse construction.

Now we can reproduce those parts.

Durango rounhouse construction.

On some larger pieces I do not glue them to the board. Some rubber may migrate underneath the pattern. Before removing the pattern from the new mold the excess can be simply removed with your thumbnail or a razor.

Durango rounhouse construction.

Here are the inspection pit side walls.

NARROW GAUGE RESEARCH CENTER

Durango rounhouse construction.

Here's the research library for the Durango roundhouse.

Durango rounhouse construction.

Some sketch notes.

Durango rounhouse construction.

The laser computer desk.

Durango rounhouse construction.

We're using Corel Draw to run the laser. Looks like the roof panels for Gunnison'e extended stalls are on the screen.

Durango rounhouse construction.

Durango rounhouse.

Durango rounhouse construction.

Durango rounhouse.

Durango rounhouse construction.

Durango rounhouse.

   

   

   

   

   

    Next section:     Casting Hydrocal    

   

O SCALE LISTS


    Limited Run - O Scale    

    Future Kits - O Scale    

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  C. C. CROW     P. O. BOX 1427      MUKILTEO, WA   98275   USA