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Hard baits (Plaster of Paris Molds)
9 replies to this topic
Posted 26 December 2007 - 12:23 AM
I'm new to 2 piece mold making and am hoping to find the cheapest way to make them.
I've searched the archives and it looks like no one uses plaster of paris molds for hard baits. Is it possible to make a 2 part plaster of paris mold and then pour in alumilite to make plastic baits? I'm using RTV right now but was hoping there was something cheaper to use. Also what is the best method/ratio to thin down plaster.
Thanks for your time,
Posted 26 December 2007 - 12:25 AM
My only guess would be that when the mold is coated with epoxy that the mold will lose some of the detail. I'm just hoping to get a basic/simple shape and then add detail to the body when it is out of the mold.
Posted 26 December 2007 - 11:56 AM
If you want to pour baits, don't take short cuts. Cheap is not the best way to go. Its only a waste of money getting where you want to go and you will get very discouraged along the way.
Do a search on the net for all the resin and mold making sites. Study there
tips and watch their videos.
Donot use Featherlite from smooth-on, it is a terrible product that gets
hard in the can.
Get some Alumilite RC-3, its a 2 part mix, get some Microballoons, its added to make lure float. Make you some good silicone molds. You will be on easy street if you start out right,
I know from experience.
Posted 26 December 2007 - 11:49 PM
I guess my question is why it won't work in theory. I know the alumilite gets very warm when its in the mold but shouldn't a 2 part epoxy hold up to that kind of heat?
I know the rtv molds are more flexible so maybe that has something to do with it?
Posted 27 December 2007 - 12:11 AM
The general rule is soft pattern, hard mould. Hard pattern, soft mould.
I tried several times to use Plaster of Paris for hard foam castings, it was a disaster!
The best mould material for alumilite is probably RTV. But you are concerned about the expense. I suggest you try the Plaster of Paris, but don't use your valuable, irreplacable master for the test.
Make a temporary master, but prepare it as you would your regular master. It must be sealed and finished smooth. It must be none porous, so the Plaster of Paris has nothing to grip on to, maybe a coat of epoxy or something similar.
Do several tests, removing the master at different time periods. Try after 30min, 2 hours and over night. Removing the master early is the easiest, but you run the risk of damaging the surfaces of the casting as the plaster is still very soft.
If you are casting hard in hard, it is vital that the master is not die locked, in other words, you must be able to pull the master straight out of the mould with no twisting. For the same reason, deep flat sides should be avoided, too much surface friction, stopping the master withdrawal.
Search for information on sealing your Plaster of Paris moulds, there is a ton of it, also search release agents. Without a release agent, you might as well save yourself some time and throw the Plaster of Paris powder straight into the bin.
Best advice? Stick with the RTV.
Posted 27 December 2007 - 06:40 AM
I didn't say it wouldn't work. But, I will say if your master model has any
undercuts you wil not be able to remove it from a Plaster of Paris mold. You will
destroy the mold doing it, no matter how long you let it cure.
Posted 27 December 2007 - 11:36 AM
I have tried plaster many times in the past and it will work.......about once! Even if you harden the mold in the oven and coat it with Devcon it will crank along the edges after a casting or two. Take the advice of Coley.....it's the only way to go.
Posted 27 December 2007 - 02:46 PM
in my country to obtain an ( almost ) unbreakable Plaster of Paris we add adhesive , it is some kind of acrylic resin called "aracet" , it is white and it can be thinned with water ... sorry but I don't know the USA version for it
Posted 27 December 2007 - 03:13 PM
I believe PVA (elmers) can be used in the same way. I did a quick web search, couldn't get the translator to work, but it looks the same.
Posted 27 December 2007 - 07:37 PM
We used to mix Fixall with milk to make it stronger and to make it stick to the floor when we used it for floor patch. The white glue probably does the same thing. I know I've mixed carpenter's glue in drywall topping mud when I didn't have all purpose taping mud, which has glue in it, and it worked. It also dried hard as nails and was a b**** to sand!