I've only tried to cast one propeller so far and it worked alright for a first attempt. I used the props from the old AMT A-20 for the Y1B-17 project and needed to come up with spares. Here is a photo essay on how I did the mold.
First I built up a clay base that encompassed just the blades, then constructed the sides of the box. You'll be able to see why I tried it this way later:
The balance of the moldmaking process is exactly as the little wheel project at the start of this thread:
After the mold was fully cured I made my first pour. Since I was learning-as-I-went I decided to do the pour in a "sandwich" method. The mold with the front propeller is face-down on the table and the other half is ready to lay in place immediately after the resin is poured. It's important that you have everything ready to go so that the resin won't start cooking off before the back half of the mold is laid in place. Mix the resin and carefully pour it into the blade and hub recesses:
Next, take your "deaerating/bubble-busting" tool and see that all the hub details are filled with the resin.
Now lay the male half of the mold into the female and press it down slowly to allow excess resin to ooze out of the mold seam. It's a matter of experience how much resin it'll take to fill the mold but not make a big mess during this step. After the resin is fully cured you can remove the male half of the mold and pop out the freshly cast propeller. If you use the sandwich method you'll end up with a bit of flash to trim as in this example. Notice the remnants of clay on the blades? This is the first piece that I poured from the virgin mold and it picked up some little bits of clay that I didn't get:
Give it just a half-hour or so to fully set up and then trim the flash carefully from the part and you'll have something like this. A couple of small voids are visible on the trailing and leading edges in a few spots. These are where tiny bubbles of air were entrapped during the deaerating step:
I learned that you can cast knife-edged prop blades with a fair amount of success by using this method. I haven't yet tried to use the pour-stub method on a prop and don't know how it would work without a vacuum chamber. I would think that you would have to have a vent or pour stub at each of the blade tips to get the resin to fully fill the cavities. If you are only doing a small run of a few props I tend to think the sandwich mold might be better. An alternative that some of the professional casters use is to pour the blades and hub as separate parts for later assembly.
Incidentally, the RTV I used on the propeller is the Bare Metal brand stuff. It is really easy to work with and seems to be pretty durable.
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). When you poured the resin parts there would be an opening with no tape bump or membrane.
