Have Mold Now What? - RC Groups
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Oct 07, 2007, 11:10 AM
Come out swinging
sporter's Avatar

Have Mold Now What?

Here is the next section of my mold making methods. When we left off, we were here. https://www.rcgroups.com/forums/showthread.php?t=534484

We spoke to the materials used in the previous thread.

Once I have the female molds, I want to make male presses for these. The press ends-up like a matched die set, or injection plastics mold set, with male and female molds with built in tolerance to establish the part thickness. I use a hard material, not silicone.

As the pictures show, I start by laying a film into the mold. I use blue masking tape for it's great ability to make curves. Teflon tape works also, see McMaster Carr. Do this in front of the TV, because the more time you take, the better the molds. More layers of tape will establish larger tolerances between the matched molds. Trim to the top of the cavity. Wax and heavily PVA the tape before the next step.

Next, I build a dam and pour casting material in. Let cure and open it up.

The tape may or may not stay in the cavity, but clean it off with WD-40 or something.

I do this for both mold halves.

Now I have a matched mold set. See photos of what parts look like out of the mold. Use oak strips and C-clamps to press the mold together while it cures. Open, trim flashing, and join. There are tons of threads about joining.

The best thing about making molds this way is I can control the final part thickness. I can establish areas of the part which stand taller. For example, if a zone on the part requires more cloth layers, I can thicken this part by adding more tape. Larger tolerances between the male and female molds allows thicker layups. Again, I can control all of this, based on how I tape the female mold. Molds like these do not require vac. pumps, and allows for production quantities of parts, since every part is the same, inside and out. I can use thick weave cloth because making tight turns is not a problem. As the molds are being compressed, the mold shelfs touch before the the male/ female tolerance is met. The shelf grabs the cloth before the mold is fully compressed (500-800psi). This means the cloth is under tension as it cures, which is good for strength.

Last edited by sporter; Nov 20, 2008 at 11:00 PM.
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Oct 07, 2007, 12:22 PM
infopimp's Avatar
Do you need to use so much extra fabric? I just ask because it looks like almost another fuse's worth will be trimmed off. Lookin' good!
Oct 07, 2007, 07:13 PM
Registered User
Interesting method.

Can you give some more information about the number of layers of tape needed for a given weight of cloth?

I'm curious if this could be done using Hydrocal. My first suspicion is that the plaster mixture might get under the tape before it sets. I know it wouldn't be as tough, but for cheap one off parts it sure is nice.

Oct 07, 2007, 09:52 PM
Come out swinging
sporter's Avatar

Two to three layers of blue masking tape is good for about 1 layer of 5.8oz carbon cloth. I use 1 layer of tape for thin glass parts. You could figure the thickness of masking tape, and compare that with the thickness of your weave. Or, since it's so easy to do this, just make several male presses, varying the tape layers when casting each one. I have 3 different male presses for the top half of my pod mold.

Oct 08, 2007, 08:18 PM
Registered User
Ward Hagaman's Avatar
Sean, I am impressed at your willingness to share your techniques--Thanks!

Oct 09, 2007, 12:15 AM
dougmontgomery's Avatar
I drool to have the patients to make a mold that great-thanks for sharing Sean.

Oct 11, 2007, 09:52 AM
Chuck 'Em and Chase 'Em
Fly2High's Avatar
can you give us a materials list for the complete construction of a mould from malle plug to completed mould?

Can you also go over how you make the plug?

This was very kind of you to share your knowledge and photos with us. thanks. It is much appreciated.

Frank N.
Oct 11, 2007, 12:31 PM
infopimp's Avatar
Don't be cheap ( ), $35 will get you a wealth of information on how to build a plug and then molds:


I learned a lot more from the above DVD than you could probably learn over the forum... not disrespecting Sporter, just saying... sometimes a picture is worth a thousand words, but a video is worth maybe 100,000.

This DVD doesn't show how to do a wet-join of fuse halves (in the mold) but was more than worth the price, IMO, and is brought to you by the same firm who do the legendary Phil Barnes DVD an absolute must-have.

/off soapbox
Oct 11, 2007, 12:44 PM
Registered User
motorhead's Avatar
Sean, have you ever had to polish the mold after it was made. I used Repro on a mold and after having to fix it, it would not polish out very well.

Oct 11, 2007, 01:15 PM
Chuck 'Em and Chase 'Em
Fly2High's Avatar

Been there ddone that many, many moons ago. I purchased them long ago. Now I want to see what other ideas that are available. I am not a fan of the hydrocal method eventhough it works well. I have used the same basic techiques Terry taught me to make fiberglass molds.

Unfortunately, the mold is only as good as the plug and I have a hard time keeping the foam plug from getting dings and dents.


Thanks for the suggestion though. Due to the Phil and Terry DVDs, I was able to build a few Super Gee IIs.

Thanks Phil and Terry!!!
Oct 11, 2007, 05:36 PM
infopimp's Avatar
Oh great.... and sorry! Just wanted to make sure you weren't missing out on those... there are a core part of my viewing diet these days. Maybe others reading will benefit?

Well... now back to watching sporter do his 'thang.
Oct 11, 2007, 09:36 PM
Chuck 'Em and Chase 'Em
Fly2High's Avatar
I do not know if you ever get to speak to the great ones - Terry and Phil but they have on many occasions been at contests I have attended as well as contest hosted by my club. Both are great guys. Once in a while when you here them talk shop you realize that their skills have progressed beyond what is shown in those videos and they are always looking for more ways or ideas to use. I have also been fortunate to speak to Aradhana (ASK) and talk about building technique. He is also another great guy with phenomenal skills at building (He gbuild the LightHAwk and LightSpeed at RCBuilder - lot of good ideas found at his site regarding plane building/assembly).

Those videos are a great starting point and will get you able to actually build planes but it is discussions like this that help you to add new and innovative techniques to ones repitoir.

Anyway, infopimp, thanks for the suggestion. I hope other will follow it as I have. They are standard watching for myself before I venture into a new project too.

Oct 11, 2007, 09:42 PM
Chuck 'Em and Chase 'Em
Fly2High's Avatar
If you read the Super Gee threads you can pick up other ideas as well in the hand launch section.

For example many guys use Mold Max 30 to cast a plug once the mold is done and use the silicone plug to press the fabric into the mold. For 2 layers of 1.7 oz kevlar and one layer of 1.4 glass, no tape spacer is needed. The rubberyness of the plug seems to conform to the mold easily.

Again, just a different way I have come across. I have seen Sporter's work and always marvel at how fantastic it comes out. I can now see why - fantastic molds that seem to be made with extra care and great technique.

Sporter, we all envy and appreciate your talents and thank you for sharing your ideas.
It is guys like you that keep this hobby alive.
Oct 12, 2007, 09:34 AM
Come out swinging
sporter's Avatar
In terms of polishing the mold, after some time, I try not to... with any urethane. I started using a tooling resin as a surface coat followed by the urethane fill. In this case, post production polishing works well.

The male press molds do not need to be perfect, since they form the inner surfaces.

Frank...For plugs, I use different materials, from clay to wood to epoxy. I prefer a material that can be polished though.

I think the most important concept to take home from this expose' of my methods is the tolerance control with the two-part molds and the idea of pre-tensioned layups.

Dec 19, 2007, 05:15 PM
Registered User
Sean, thanks for your threads on moldmaking so far. Very interesting reading. I've read each thread more than once, and keep going back to them. Great stuff!

Your comment in your "Have a Plug, Now What?" thread:
Originally Posted by sporter
I do something completely different than a joggle gasket, so I can't comment. There a several ways to join the halfs, well documented
got me wondering exactly how you join pod halves. Wet seaming? Dry seaming? Some other method?

Ya know, if you posted a "Have Pod Halves, Now What" thread, then it'd be like a boxed set!

Anyway, thanks again for the great information.


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