Rtv Molds

[Bassman755]

I am looking for some information on RTV molds. I have been looking at buying alumilite RTV molding material. What I was wondering is if I would be able to do a 2 part mold with rtv and how. I have tried a 2 part mold with POP and it worked out fine but I was thinking that I would like that rtv a little better. Any info would be great.

[Piscivorous Pike]

I am looking for some information on RTV molds. I have been looking at buying alumilite RTV molding material. What I was wondering is if I would be able to do a 2 part mold with rtv and how. I have tried a 2 part mold with DIY An Instant 1/2 Rd RTV Silicone Mold For Under A Buck.

Here is an example in post number 152 of that thread. The flat bottom of the mold is all water catalyzed RTV sealer, clear.

]

But here is where I differ. From the sprue down one side I cut the fully enclosed item out of the hardened RTV.

click this thumbnail picture for a bigger view to see the mold better.

What I have is a clam shell. I pour in or inject at the sprue . The mold is held closed by rubber bands or tape. In my case I put a puck of pop in the bottom of a long narrow tumbler. Cast the mold. Cut the mold open from sprue to 2/3 down on the jerk bait. I removed the puck and can put the empty rtv mold into the tumbler, I put a shorter stopper in the bottom of the tumber. I cut a hole in the bottom to allow venting . I put the rtv mold back into the tumbler and the taper of the tumbler closes and holds the mold closed. I can inject it. That is why I have it vented at the bottom.

The mold does not have to go back into the tumbler, tape or bands will hold it closed. From now on I think I will use the triangel style mold.

Once the plastisol cools I can open the clam shell style mold and remove it. Essentialy the flexible rtv on the side not cut acts like a hinge.

The advantage you see is you can do this in one casting, split the rtv with a razor blade or exacto knife and you have a two piece, or clam shell full round mold.

Boy I wrote this in a hurry, hope it make sense. The tutorial is longer and explains more. Its coming, maybe a couple to three weeks.

[Bassman755]

Wow! Thats alot to take in. I will definitely be looking forward to your tutorial. Thank you for the info. Most of it makes sense but with me being pretty new at this there is some that didn't. Every little bit of info helps though. Thanks Pike!

[Bassman755]

Ok I have another question. How would I go about degassing the rtv mold step by step?

[Piscivorous Pike]

Ok I have another question. How would I go about degassing the rtv mold step by step?

I suggest Google and read all the art forums. You will find people used the hand pump sold to bleed brakes. Those too only get 25 inches of mercury. Get some you tube on it too. btw- Smooth on says you have to have 29 inches to degass their products. I found that not to be true.

RTV that needs degassing will say by the manufacturer, most do. It will swell with foam to 1 and 1/3 original volume at least so leave some room. I have a seal a meal with a marinade tank. I measured how much RTV I needed both by calculating it, smooth on has wizards to help with that, and my using a mock up and measuring the volume with water. The spec sheet told me that 25 cu. inches is a pound of 27T. This will help:

http://www.convert-me.com/en/

I used a digital scale which cost $14 from harbor freight.

I put the RTV in the vacuum container and ran the seal meal until it stopped foaming. Then i mixed in the hardener and did it all over again.

Another trick on video from www.tapplastics.com/ shows bombs away on video. Fix a funnel or plastic disposable cup way above the mold and pour into it. A pencil size hold in the cup will let the RTV out. It will streatch into a thin stream and this removes any more stray bubbles.

The stuff I used had a 45 minute pot life. That is why I degass with out the hardener first then again with hardener, that gets it degassed with enough time to pour slowly and by bombs away method.

Another thing is call the manufacturer. Smooth on told me that 27t and oomoo was not good for making baits. Take what they say with a grain of salt. TU folks been using oomoo for a long time. I used 27t because it is almost clear.

Secondly it is the cheapest. Half of what oomoo cost and oomoo is got the other brands beat. I will continue to use smooth on.

Smooth on has on the oomoo page videos. The candle making by Martha Stewart is a must see. I learned a lot and that is what inspired me to come up with a new twist on the old tricks that have been floating around TU .

The gallon cost delivered a $100. By no means is this a way to make cheap baits. It is a hobby and fun, entertainment cost money. So keeping that in mind oomoo is the easiest to use even if it is twice the cost of 27T in the gallon.

BTW. a quart doesn't go far. That is why husky uses old rtv chunks and rtv silicone sealer as filler for the space not in contact with the model. I think it is a good trick.

I am now using a triangular shaped mold. I am using the corner of wall and floor of boxes i make with hot glue and shiny cardboard packing boxes. The peak is the top. So I make the mold upside down . I can thicken the base by adding the water catalyzed rtv sealer. After setting I cut in the peak cross wise for a sprue and slice it long wise to open the clam. The mold you see above also lets me make 3 color laminates. The advantage to the clam is it cam make a full round very easy once the mold is made.

My last rtv mold has vanes so thin the plastisol will not flow through them so I am waiting on my third injector. I tried my adaptation of Vodkaman's vacuum injection but there is three chambers in a Javallon which I copied and they harden and fill before all three are full with vacuum method of injection casting so it will take hand portable injection to work correctly.

[Bassman755]

Thanks for the info pike. It will surely help.

[t-billy]

I've been buying my rtv from aeromarine on ebay. $89 a gallon + shipping. Good stuff. I don't degass. I use the bombs away method. Only I dont bother cutting a hole in my mixing cup. I just carefully pour from slightly above waist hight. The silicone stretches into a very fine stream popping all the bubbles. Just take your time. It is easy to keep a steady stream do to the consistancy of the silicone.