Warbird Information Exchange

As I said on the B-17C/D thread, people who make molds and castings professionally are going to roll their eyes at my crude moldmaking methods. That being said, I've used these techniques for years and had great success.

I decided to make a mold of a nice 1/48th scale narrow chord propeller a while back, and here is a rundown on my methods. I invite anyone else to share their ideas and experience on this thread so we can all learn from WIXers experience.

First you'll need a box to pour the rubber into. I use plastic signs and cut out pieces the size required for each job. After making the base of the box I used modeling clay as a 'bed' for the prop to lay in. I built up the clay to seal the back side of the blades and hub so that no rubber would work between the plastic and clay. Here I'm working the clay around the blade to get a tight seal:


This is the complete box ready for RTV to be poured:


The two-part RTV I used is leftover from when I had a resin casting business, but Hobby Lobby has an Alumilite RTV that gives good results. It's a little pricey to buy in the small quantities that hobby shops sell it in--I purchased mine in 5-gallon lots way back when.

The next step was to pour the mixed RTV into the mold box. I am showing this bomb trailer dataplate as an example so you can see the method I use to keep from getting air bubbles. I pour a small quantity of RTV on the subject and use an acid brush to carefully fill all the crevices and cracks with a film of rubber, making sure not to have any entrapped air bubbles.

After applying a thin film to the entire part I then pour enough RTV to make a good, solid mold--usually 3/8 to 1/2 inch thick is enough.

Now it's a matter of letting the RTV fully cure before the next step. In the case of making a two piece mold, disassemble the box and very carfully remove all of the modeling clay without disturbing the master part in the RTV mold. This will leave you with the female mold half and master still together. I then make a "key" in one corner of the mold so that the two halves will always match up when using the mold. Next step is to lightly coat ALL the rubber that will lay against the male mold half with Vaseline so that the halves won't stick together. Now the box must be reconstructed so that you can pour the male side. Mix up a small batch of RTV and pour it into the box on top of the prop/mold/vaseline. Here is the result after curing:


I let the finished mold open to the air for a day or so to allow for full curing, and then resin can be poured. I use Alumilite resin and have always had good results with it. Mix the two parts (this step requires pretty fast action because of the short pot-life of the resin) and pour a small amount into the female mold half. Then I use a pick to carefully, but rapidly, remove any small air bubbles around the hub bolts or anywhere else that may entrap air. Next, pour enough resin to fully make the part and put the male mold half in place. Use a bit of pressure to work the resin around, and then wait for it to cure.


After curing, open the mold and remove the part. There is sometimes a small amount of flash to trim, as in this example, but the more of anything you pour the better you get at judging just the right amount of resin to dump in at the start.


And this is the first prop I poured. It's got a couple of little flaws that I'll correct as I gain experience with this particular mold.


Scott

Very nice. Thanks for the pictures. That's something I've been meaning to try for a while now.

Ryan

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Aerial Photographer with Red Wing Aerial Photography currently based at KRBD and tailwheel CFI.
Websites: Texas Tailwheel Flight Training, DoolittleRaid.com and Lbirds.com.

The horse is prepared against the day of battle: but safety is of the LORD. - Prov. 21:31 - Train, Practice, Trust.

excellent article Scott. I thought about posting this when I first read that you were doing this, but there can never be too much information for somebody wanting to learn to mold.

You make it easy for casting simple parts.

Here is one I wrote a few years back:

Casting for Beginners

You don't need to vacuum or pressurize with this process. And it has a few links for materials.

The only thing I can think to add, is to not mold and cast existing kits. Molding and casting parts for personal use is okay. Recasting is bad.

And Lego's, they aren't just for kids when it comes to mold making.

Smooth-On used to have a beginners kit that cost less than the Alumilite one, but you only get to order it once.

Cozmo's linked article is exactly what I hoped would happen when I started this thread. Anyone who wants to make parts at home should read it!

Heed his advice about recasting parts. When we had our business making update body parts and other detail pieces for Na$car modelers back in the nineties we were always careful to NOT steal stuff directly from a kit to repop. Imagine my consternation when we showed up at a contest and one of my "competitors" had obtained some of my stuff and copied it, repackaged it, and was selling MY parts for more than I did! So.....don't do the same with your favorite Tamiya, Monogram, etc. parts to start up a business with--I know how it feels to see my hard work pirated.

Scott

I figured that is what you were aiming for. Its always good to have different ways of doing the same thing. Different processes work for different people.

I know what you mean about seeing something you spent lots of time sweat and thinking to produce getting ripped off by somebody just taking your work, ripping it off and selling for more than you do. It just about killed the garage kit figure cottage industry.

What hurts almost as bad is spending just as much time building what you think is the perfect kit...and nobody wanting it. But I was building those three for me anyway. And learned how to photo-etch while doing one of them.

Yup, I had a similar thing happen. I collaborated with another caster and had a really nice series of Hudson bodies from '51 to '54 ready to start marketing. The then-current owner of the Hudson marque let me know that they would NOT appreciate me selling any Hudson stuff without them getting their royalty payments. End of project. I did build some for a Museum and several friends got a copy or two for their own collections, but I wasn't about to fight a legal battle over my hobby. I still have the molds (about $300 worth of RTV) but they'll never see the light of day.

On a related subject, have you ever built a vacuform or resin model, taken it down to the hobby shop, and heard "Monogram/Hasegawa/Tamiya just announced a styrene kit of that!!!!" That's what happened with this Falcon F-89J:


Scott

Heh, the Star Trek Reliant. Waited about four years after the movie to make one. I just knew AMT/ERTL would make a kit. Got tired of waiting. The kit came out just after I finished it.

I had better luck than you did with Hudson. For a customer, I modified a simple kit I had into a vehicle Timeline had for one of their role playing games. They were happy and sent me drawings of some of their other stuff.