I have been thinking about attempting to make double hung windows and doors using the resin casting method. There are a million posts in this category so I thought it best to ask for help. Latex mold? You guys are the experts. I have one each of the door and window I want to use as masters. They are like brand new and have no details on them that would appear to prevent using a mold. I thought of using evergreen strips but too time consuming and the cost where casting I can go into a production mode and make as many as I feel like. If this is not feasible I will have to go to Colorado Scale Models again…
Mike it all depends on how many undercut areas your going to have and how much detail you are going to have on your windows as to what material you want to use for your molds and if you will need to make single or two part molds.
Double hung windows present the problem of the upper window section is closer to the outside of of the window than the lower section which in real life allows the lower section to slide up past the upper section. In modeling however this present a problem making a mold that would allow this kind of detail to be present in the final casting. Usually in these cases you will have to make a two part mold. Using a two part mold is more difficult to make and you run the risk of having anoying air bubbles that leave hollow areas in the window mullins.
The easier and simpler way to make the double hung windows is to actually make two seperate molds. This would require the cutting up of a couple of windows to get the masters you would need to make your molds from.
If you don’t want to cut some windows up to do this then you can make the individual parts, which is not that difficult.
First you need to make one of the window sash sections, These will be the upper and lower windows sections. just remember that they over lap in the middle of the window, so you will need to take this in to account when you make the sash section. Once you have this done, make a mold of it and then you can cast up the window sash sections.
The second thing you need to do is make the master for the window frame and trim boards around the window. Use your master sash section as a guide to make sure that the frame fits around the sash with no gaps. Make a mold from this master and then make the castings. If you use the same RTV to make both molds and use the same resin to make the castings, then any shrinkage in the castings will be the same so all the parts fit together like they should.
You will then need three castings to make your windows.
1 Window frame with trim boards.
2 Sash sections to glue into the window frame. Remember one sash section will be in front of the other and will meet in the middle. Using the two sash method allows you to glue them in place to make the window look like it is open (i.e the bottom half raise up some.)
So my recommendation is use RTV to make your molds, Use Polyester resin for your castings. Your two best places to find the casting and mold materials is Tap Plastics and Micromark. I like the Tap Plastics casting resin as it is water thin and and you get almost no air bubbles. Look for thier Quick Cast resin
If you use RTV for your mold and polyester resin for your castings, then you should not need any mold release for your fist 50 or so castings. after that I would use some mold release as the natural slipperiness of the RTV starts to break down and some castings can stick.
If you use a Polyester based mold material, you MUST use a mold release for every casting you make or they will stick to the mold.
The above method is what I will be doing to make the windows I need for a Station I am about to start building as Grandt Line and Russ Simpson does not make the style used on the Rio Grande Western Station at Cumbres Colorado.
I hope this helps out for your window making.
Dan Stuettgen
Houston Narrow Gauge nut.
Denver & Rio Grande Southern