Plaster Patterns

[mtuckf]

I have a MaxNC 10 Closed Loop desktop mill and it has been a pretty decent machine. I have been cutting primarily machinable wax. I would like to "extract" a male plaster pattern from a CNC machined cavity in wax. Does anyone have any experience doing this? I have tried numerous lubricants and nothing works. As soon as the plaster dries it does not want to eject from the wax cavity. Should I be using something other than wax? Should I create some type of ejector pin?
Any help from those experienced would be greatly appreciated.
MT

[cadcam]

Try getting the lube that the Wax investment foundrys use.
you will have to find a local foundry and ask what they are using unless one of the other members can give us a name.

[wms]

MT,

Try these:


http://www.freemansupply.com/index.htm

They have molding supplies and should have a release.


http://www.epoxi.com/main/home.asp

They should have an Urethane wax release.


http://www.gypsumsolutions.com/resul...%20prototyping

Look for the "Rayite" product. Not a wax but some neat stuff.

[vacpress]

we use vaseline whenever we want plaster to seperate from something. brush it on in a very thin layer, otherwise your plaster pattern will get vaseline impressions in it.

we have also used waxes. even.. i think its "johnson wax" from the hardware store may work. i woud try petrolium jelly though. it always works on plaster

another option is to make your molds reverse, and make molds off of them out of something that plaster will release out of easily - like rubbers.

[kenlambert]

hobby lobby carries PVA it is a mold release i use it for all my molds . you spray it on and let drie then make your part . when it dries it is like a sheet of saran wrap and is water soluable

[mtuckf]

What a fantastic forum. Thanks for everyones helpful information.
I will do my best to contribute to this forum when I can help others.

[castguy2003]

First off, I am assuming you are incorporating "pattern draft" on you model. If so I would use a two part release. Paste wax as a first coat, polished when dry followed by a thin coat of urethane wax release available from Freeman Supply.

[mtuckf]

I incorporate good draft on all my CAD models for machining, but thanks for mentioning castguy2003. I have found that a thin layer of vaseline worked great. I also found it best to let the plaster set for a few days and completely dry, when I do this, it pops right out.
Thanks again for the great posts.

[Arnie]

Another way, if all else fails, is to make an air release mould. Of course this does not compensate for undercuts or lack of draft. Also, a release agent is still necessary. Use canvas tube fixed to chicken wire with cable ties, arrange the tube to be an inch away from your mould surface and have one end of the tube closed and the other end hanging out. As the plaster begins to set, cut off the loose end, jam your airgun in the hole and gradually turn up the pressure with your other hand on the regulator. Go from zero to 5psi when the plaster is just discernably warm and increase pressure by 5psi every 30 seconds. If it blows up, do it again but this time go easier on the pressure increase. The best plaster for this technique is ceramic press die plaster but I have done it with other grades such as pottery slip-casting plaster.

[vacpress]

another tip, although i have never tried it:

my very experienced synthetic materials professor told us he has made a vaseline\rubbing alcohol solution and sprayed it on with refillable aersol cans.. they are like 2-5$ and can be used 10 or 15 times he said.. so its a very cheap mold release compared to the 7-15$ per can of PVA.. harbor freight has them. just have to have an air compressor to refill them..

i may try this next time i have to cast alot of something

[ToyMaker]

Seems like if the custom made release compound goes through an aerosol can orifice it ought to flow through an air brush.
And because I already have one it would save a couple bucks and a trip to HF, er, wait a minute - I need a trip to HF . Maybe this isn't such a good idea .

robotic regards,

Tom
= = = = =
NASA recently sent a number of Holsteins into orbit for experimental purposes.
They called it the herd shot round the world.

[High Seas]

I've been using an airbrush to spray the PVA on the molds. You can get a cheapie at WalllMart. The PVA works great using these - you can get the refill cans too - or else use a small compressor!
And on the Plus side- you get yet another HOBBY - OH BOY -- more toys - less time.