Help With Mold Making Materials
5 replies to this topic
Posted 11 February 2010 - 04:57 AM
I am confused with all the options for silicone rubber. Alumilite has their quickset, high strength 2, and high strength 3. Smooth-on has Mold max 10, Mold max 20,...., Mold max 60. I am going to assume that the two companies have fairly similar performing products but what do all the numbers mean? I want to make mold of some baits I have carved out so that I can play with cutting the joints in different places and things like that.
Any help explaining these products would be greatly appreciated.
Posted 11 February 2010 - 08:52 AM
If you check the Alumilite and Smooth-on websites, they have product descriptions that you might find useful, and there are some pretty decent instructional videos on the web if you dig a around a bit. Like you, I'm just starting out in mold making, so I bought both the pourable stuff and some silicone mold putty to experiment with. One thing's for sure - none of that stuff's cheap.
Posted 11 February 2010 - 10:10 AM
I called smooth on Monday with the same questions. They gave advice contrary to what some do on TU. They did not recommend oomoo 25 or 30 because they said it was too soft yet so many on TU are very happy with oomoo 25. They recommended shore hardness 30 and above to prevent tearing. For soft plastics they recommended Mold Max 30.
But I am cutting the rubber like a clam to remove the model so I needed translucent RTV. The second bonus for translucent T27 is the price. Oomoo 25 or 30 is $145 a gallon , T27 is $85 gallon and $15 shipping! $100 bucks to make a $4 lure I can buy. I think this is the best price on anybody's RTV that I found. But price was not the issue, translucency is and Johngreer.com also makes a similiar clear product.
Now the other problem is mixing. oomoos can be mixed 1:1 by volume the others are by weight ratios, you need a good scale. I got one from Harbor Freight, $15.
Next problem is air and gasses. Oomoo is degassed you mix and pour good to go from the bottles. The other products you must degass which takes a vacuum pump and chamber otherwise bubbles weaken the mold and make pits where the cavity is. Smooth on said it had to be 29 inches of mercury vacuum, 25 would not work.
I searched the net and found many folks that used brake bleed tools and a home made chamber out of a jar. These worked fine.
I tested some brake bleeders, they got only 25 inches. I also tested my vacuum food sealer. Lucky me, it also pulls 25. Harbor Freight sells a venturi vacuum pump that you run from compressed air, on sale this week $12, it pulls 28.3 inches.
After a mild degassing if you pour from a great height in a thin stream to the egde of the container you can do a decent job of getting the bubbles out that way. Youtube videos on that btw.
Another sytem is the corollary to this. In lieu of a vacuum let the mold set up under 60+# pressure in a pressure container as that will surpress the entrapped gas and from what I read it is better than degassed RTV. Harbor Freight sells dozens of compressors.
I decided the translucent T27 was best for me. I could see in it to cut it. Shore was 27 between 25 and 30 at which TU members found to be OK and I trust I can degass with my food sealer.
I am anxious for it to get here. I think I devised a new method not exactly used to make molds on TU before. I was able to run my idea and process to a couple TU members for peer review and we all think it is worth a try. I will let you all know what happens very soon.
I will disclose one trick to it here. When we make 2 piece molds we usually make two indexed pieces, some aluminum 2 piece molds have hinges. If you cast the RTV totally over your model you need only to cut down one side of it to release the model. The RTV is pliable enough that this clam shell will give the same results as a hinged mold because you can flex it open on the uncut side. Cutting it out is why I want translucent but if I placed pins or thin stiff leader wire into the model as index points I could also find my start and stop points to cut it out of an opaque color RTV.
Call your favorite manufacturer and ask them and see what you get. Then spend 4-5 hours on google. The answers is not clear.
Edited by Piscivorous Pike, 11 February 2010 - 10:13 AM.
Posted 11 February 2010 - 04:50 PM
Thanks for the info PP. Looking forward to seeing your new method.
Posted 12 February 2010 - 12:35 AM
It just seems hard when you start cause of all the differant rtv. Lets make it simple use a rtv that is 25 to 30 in shore hardness. It will work for your needs now. If you want a two piece mold use a 30. If you want to use the one piece mold method use a 25 ,this is more flexible and easier to get the piece out of the mold. I do not need to see through my one piece mold to cut them open cause I use two dowels for my pour spouts and index my cuts from there. I split it with a razor till i can get my master out. When i close it up again it goes back to an almost seamless split. As for degassing that is dependant on the time you have to work the rtv after it is mixed. If it is a short time degassing ia a waste of time, it is just to hard to pour when it starts to set up. And I do use a food saver to pull my vacumn. My best friend is pressure to the tune of 30 psi. Now I know you are thinking BIG BUCKS,no harbor freight has a pressure pot for paintingthat will work with a few plumbing fittings. If you cant get pressure do your self a favor and try this,Before you pour in the box put a coat of rtv on your master especially on the bottom. Them pour from a height so air cannot be transfered in your pour. The reason for this is that bubbles will rise from the bottom and get trapped under the bait and you will end up with bubbles on that side forever. With the coat of rtv the chances will deminish drasticly. I have so called wasted some rtv in my time and this advice comes from experiance. To make it even easier try tap plastics blue rtv it is easy to use and without any other choice it is easy to pick the right one. I use this one cause there is a store close. One thing i would watch out for is schringage, this not your friend. This comes from fillers and not good for what you are doing. As for quantity I have always bought it by weight not volume so I do not know what a gallon looks like. This goes for resins to, fillers are not good and if they say it is the some but cheaper it has some type of filler to make up the differance. Hope this does not make things worse. Frank
Posted 24 February 2010 - 03:51 PM
Rick from Smooth-On, I will be logging in time to time to see if I can help...
The pour method is good to try and eliminate bubbles... we are currently working on a white platinium silicone rubber that does not need to be vacuumed, 1:1 mix ratio and has good physicals called mold star but it isn't yet available... keep an eye out... in the mean time a very good rubber is sorta-clear 18 http://www.smooth-on...1134/index.html
also we have a good resin used by some lure makers called feather lite http://www.smooth-on....php?cPath=1162 custom lures: http://www.smooth-on...=135&cPath=1162
Mold Max 30 is a very good choice for making rubber molds and does very well without vacuum and pressure pots... just use the pour method described in this thread...