It would have been helpful to know the size/complexity of the objects being cast.

Acrylic melts at 250F. Pewter melts at 240C. I don't see a great match here.

Polypropylene doubtful, or CPVC, maybe. Teflon, for sure, if you can get it.

thanks lynlynch

I am talking about small objects, imagine a 30 mm dia circle engraved at 2 to 3 mm deep to make earrings and badges etc for school prjects. The total amount of pewter would be very small.

OK, maybe it will work. Why don't you give it a try. Let us know.

Hi all

Well the answer is yes you can cast into acrylic using Pewter. My first few attempts are not perfect but promising and probably suitable for their intended use please have a look. Thanks for all the comments.

http://s567.photobucket.com/albums/ss116/pj3ns3n/

Nice job! My hat's off to you for your creative thinking.

Don't be a stranger.

You can try high-temp epoxy resins, which stand temperatures as high as 600-700 °F (315-370 °C). Epoxy can be cast and then machined and is increasingly used for prototype-scale plastic injection moulds.

Just try googling "high temp epoxy resins" (Be aware that shipping by plane is not available due to flammability).

Thanks for this fernandotossa. It doesn`t sound cheap though. In education thats often the limiting factor. Would bondo , car body filler work?

I think you should try and see. Maximum working temperatures are usually rated for normal service, so epoxy putty perhaps could stand a few castings. Adding some metallic filler, like aluminum powder (or filings) may also help withstand higher temps and dissipate heat (many heavy-duty, gray colored epoxy preparations actually include Al powder).

GA

You beat me to it.

I am assuming that he needs to make more than one each time, then silicone is the best!!! Fully re-usable.

Thanks aurizon

Yes I`ve seen that did quite some searching myself. One of the reasons I want to try acrylic is we have plenty of it and it engraves well. I`m not really making castings from copy moulds.

you can of course, mill the master in acrylic as a negative relief and then create the silicone mold to cast your objects with the milled aspects exact copies of the original, and the silicone's flexibility will allow for easy removal.

Hello aurizon,

This site sounds promising!

GA to you Sir.

bb

I don't think bondo would take the heat, but it might. I would suggest the high-temp version of JB Weld. It can be used for repairing engine parts, exhaust systems, etc, so it can take the heat. It also molds well and machines well once set.

You can find it at any auto parts retailer or locate a retailer near you online at http://jbweld.net.

Mill up some fine grained hard wood; OR

Get some pottery clay, slice or roll it very thin on some wax paper or foil, cut it a bit over size, and then press your pattern into it - extract the pattern; and then dry the clay in a lowish heat fry pan.

It will give you kind of soft molds - that could be reused almost infinitely - but if they get dropped / broken, just add water and you can remake them into a heap more molds..

I'd use a slightly oily release on the pattern - a level teaspoon of wax with only a few drops of oil in it - and then thinned out with perhaps 50ml of turpentine or kerosine and brushed or wiped on.. just to make a slightly greasy release from the clay.

Dirt cheap, non toxic, reusable, temperature resistant, fully recyclable molds.

Thanks Jammit

I too have considered clay but I want something quick non messy and for use with CNC CAD/CAM router so geometric patterns or text can be cast.

it looks like you are CNC milling a subtrate to mold into (MDF vs Acrylic) . I might suggest you upgrade to polycarbonate (one trade name is PlexiGlass ) but all have the same higher heat capabilities, (melt at 500*F or so) so might be more useable for you.

Plexiglass is acrylic. Polycarbonate is Lexan.

I don't think that this is a CNC project.......once you have made an original shape on CNC, seal it well and use it as the master to make a silicone mould.

If size is important (when is it not?), then make the master 5% or so (experiment a bit!!) larger as some metals shrink on cooling......

or:-

I wonder if there is a hard wax that can be shaped with a CNC machine and then used in a "Lost Wax Process"....?

Just a thought......

Best regards.

Andy

I want it to be a CNC project because in school design is about creating not copying and we have access to good CNC and 2D design tools. I have tried Plaster see link. With better substrate and better engraving tools I think the finish would improve. Imagine a class of 25 all different designs making a one off product speed is the key.

Pewter pendant ist attempt

Thats what happens when you don't give full details up front, we go off on tangents.....thats what has happened here....

For shapes as you have shown, if you used CNC to make a 2 part alumium mould and heated it up to around 200°C first and made sure that the mould is fitted with a large capacity "funnel", this is what forces the molten metal into every crevice under the weight of what is in the funnel.........

Aluminium will not stick to the metal you are pouring (almost nothing other than glue will stick to alumium, it will also shed the heat well and cool down quickly, which it is why you need to warm it up first to make sure that the molten metal reaches every corner before solidifying.

A few air holes are also a good idea as well, but not too big, 0.5 mm max I would say.....just to let the hot air exit quickly, the metal will not flow through really small holes......

Out of order Andy the details I gave were ok if you read them.

I must have forgotten, sorry!!

NP