Plaster Mold Questions

Discussion in 'Lost wax casting' started by Sirgei, Jun 2, 2020.

  1. Sirgei

    Sirgei Copper


    I will try to describe what I want to do as detailed as possible.

    I need several items made of Copper and of Aluminium for an engineering project.

    Main copper items are 2 cylinders. 1 inside another.

    Outer cylinder 120mm wide and 300mm long
    Inner cylinder 90mm wide and 300mm long.
    Wall thickness no more then 3mm

    The following is not yet 100% confirmed, but I hope it is understandable enough for my questions.

    First: I glue a cylinder out of paper. Using wall papering glue and ordinary A4 sheets. I have tested and wax doesn't stick to paper.

    I tested a bit of wax on paper and it didn't stuck only wetted it. To make sure It doesn't wet the pater – paper tube on the side that is touching hot wax would be covered with transparent heavy duty scotch tape. 2 such cylinders with a gap of 15-20mm between them would make basis for the first wax cylinder.

    Would look something like this.

    Second: After wax sets I very gentry uninstall paper tubes. I place the wax tube into a wooden box that is dismantled. And pour Plaster to fill outer cavity. After plaster sets, I dismantle that box and put the whole block into a stanless steel pan onto metal supports inside pan. Then heat it. Wax cylinder melts and floats away. This would leave a perfect or near perfect round cylindrical hole. Any surface impressions can be sanded off with a fine sand paper.

    Would look like this before wax is melted away
    Third: I make 2 smaller paper cylinders. Outer paper cylinder would be build up with layers until it fits tight into the plaster hole.

    Inner paper cylinder would be about 15-20mm smaller in diameter.

    I set them into box and fill wax into gap between them.

    Then make another set of 2 cylinders 10-15mm even smaller then first set and fill that with wax as well.

    After it is finished I pour plaster into gap between 2 wax cylinders. And again heat it up to met wax away.

    The goal is to create 2 plaster molds. Outer mold and inner mold.

    To save plaster, inner mold's wall thickness would be no thicker then 10-15mm. Outer part is a hole inside solid block and inner part is a plaster tube that fits inside first one.

    Inner part after all wax walls are melted away would be smaller then needed. The gap between inner and outer would be 20-25mm .

    So, I build up the inner later by again using a paper spacer.

    But this spacer would be covered with Aluminum foil on the inside surface that is facing plaster to prevent sticking. That space would be 3mm thick. I just place spacer onto the inner tube. Make sure it is perfectly centered and pour plaster into gap between spacer's inner surface and outer surface of the inner plaster tube.

    After this is done it should look something like this:


    To support the inner plaster part that be thinner then outer one – the inner space would be filled with casting sand.

    My casting and is made from a mix of 40% clay and 60% play pit sand. That inner sand filling would also house the pouring channel.

    I pour into that channel nd then it flows into 3mm gap between 2 pieces.


    So, here are my few questions I couldn't find answers for

    When I was trying to make a coal-fired foundry using plaster/sand mix and galvanized steel bucket – after plaster set it stuck to the bucket like if it was glued. To get plaster out I had to chisel it piece by piece. It had even stuck a bit to the surface of stainless steel pan I was mixing it with

    QUESTION #1-Do you think that poured Copper would stick like this to the plaster surfaces of the mold parts? Because I really don't to chisel inner mold like that. It would damage the tube.

    Only way to prevent sticking that I have read on Russian forum, was just before pouring wet the surfaces of the molds that are facing hot metal and stick a thin layer of sand onto them. Then metal would be contacted to the sand layer after water evaporates to steam. Minus-it would create rogue surface. With gap of only 3mm I don't think tht is is possible

    I have read several times that plaster needs to be totally died before it can be used. But if dry is totally, it looses structural integrity and easily collapses.

    QUESTION #2-Would filling of large amount of casting sand inside inner mold and possibly outside as well re-enforce plaster and possibly prevent collapse before metal cools?

    I also read about plaster mold needing pre-heating. I don't have any oven. I can only pre-heat it using stainless steel pan on the BBQ oven fired with charcoal.

    Question #3-If dry the mold as much as possible, but not pre-heat before pouring would it still be possible to perform the casting?

    And also

    Question #4-Would the first 3 questions also apply for Aluminum?


    About my project those things are for.

    Project is with rebuilding an item from patent by Nicola Tesla. I have tried to see if off the shelve copper tubes would do, but none of the sizes on ebay fit the sizes that are required. There are other sizes sold by a metal merchant, but he only deals wih licensed trade. So, I got a choice. Give up on the project or try making them myself.

    My own experience is with casting Lead, Tin and Zinc. I casted those into molds made from that ype of casting sand I described. MINUS with using sand is that item needs a lot of polishing after and sand cannot provide sharp details like plaster can. I have made tests with making such mold out of casting sand.
    While outer part can be made more or less easy - the inner part I couldn't make with high enough precision and sand tends to collapse

    That is about it

    I really hope I can find answers here.
    Thank You in Advance

  2. Jason

    Jason Gold Banner Member

    You wanna pour at less than 3mm? What you need dude is a lathe, not a casting project.

    I miss AA.:(
  3. Sirgei

    Sirgei Copper

    Not less then 3mm. 3-4mm thick.

    Lathe is no way. I am out of options here. Try this or ditch whole thing.
  4. Sirgei

    Sirgei Copper

    This forum is my last place to find some answers.

    Make to order is impossible. Price is expensive beyond reason.
    Lathe is also impossible. It costs thousands of pounds.
    No room to put it in.
    I have experience only with wood working lathe, not with metal one

    This way works r give up project I been trying to get off the ground for 4 years.
  5. Jason

    Jason Gold Banner Member

    3-4mm is pretty damn thin, especially for a beginner!. I cant see how you can cast this without at least some bit of machining.o_O Maybe one of the old heads might have a better suggestion.:(
  6. You realize that any copper alloy that can be cast will have a small fraction of the electrical conductivity of pure copper. It may be easier to get some 3mm annealed copper sheet rolled into a tube and the seam TIG welded.
  7. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Those tubes are not good candidates to be cast. You should buy annealed copper sheet of the alloy you desire, make yourself a slip roll, roll the tubes from the sheet, and TIG weld (or hire someone to) the seems, finish as desired.

    You could also buy copper tube most near the size you need, cut a section out to resize it and TIG weld the seem. You may need to work and true up the diameter depending upon the accuracy you need.

    Either will produce a far better result than you could ever hope to achieve with the casting process you describe. Sorry don't mean to be negative but chances of success for first time caster with that object and materials is almost nil, even for an experienced caster with the best materials and equipment.

  8. DavidF

    DavidF Administrator Staff Member Banner Member

    I'm with this suggestion also ..
  9. Sirgei

    Sirgei Copper

    I already looked at this option. Price for this job is the same as for the other one I mentioned.
    TIG welder leaves a seam on the surface. To grind it down and polish brings the price to thousands of pounds again.

    I came here to ask questions, but instead of just answering you are all telling me to go and do it the other way.
    The way that is impossible for me to do. Because of the costs and because those shops that are located locally would not deal with members of public. Only with licensed trade.

    Dear forum members. Would you please be so kind and answer what I asked straight or tell me to go away and don't bother.
    I have looked at all options before I came to ask questions here.
  10. Peedee

    Peedee Silver

    Sergie, there are no laws in the UK that prevent you getting the materials you need or even having the part made for you, whoever is quoting you thousands probably doesn't want your business. I know a business in Suffolk that would machine those parts but, quite honestly, I'd be reluctant to make the introduction. People here are trying to help and you have stumbled on a very large knowledge pool and some very clever people.

    Shall we start again? What are the requirements for conductivity, I understand this must be something to do with EMF given your past comments or am I way off?
  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Sirgei, you came here and asked questions about a casting process you dreamed up for a specific part. The advice you have received from knowledgeable people skilled in the art is your scheme would not be succesful and the part was not practical for casting. You lack both the knowledge and ability, this much is obvious not subtlety. Instead of being rude and making an ass of yourself what you should be doing is thanking us for guiding you in a manner that avoids a colossal waste of your time and money. So in your terms, don't bother. If you want to go away that's up to you and depending upon your future behavior, possibly me.

    Rotarysmp likes this.
  12. Sirgei

    Sirgei Copper

    I am sorry if anything I said sounded rude. My friend who told me to go on google and look for this forum told me this:

    ''When you join you just describe your process and ask questions simply and you get answers. No strings''
    I did just that, but the responses weren't not what friend said it would be.

    Let me tell you something about myself

    My name is Sirgei Borisov
    I am originally from Republic of Belarus. Belarus had suffered a a lot from the explosion of Chernobyl nuclear plant in April 1986.
    This had given me several illiness. They are for life, but not terminal. One of them is mild mental health disorder.
    It makes me nervous. Especially if I am under pressure over something.

    I live in a consul property. I don't have a car. Never had it and can never have it.
    Suffolk is just as far from me as moon is from you.
    I get most of the things from ebay.

    In the past, I have had some experience with people here, in Newcastle Upon Tyne. The kind of experience I wouldn't wish to anyone to have. It is very very hard for me to engage with people 1 to 1.

    For the room for project I have a garden and a shed. Also a room in the house I live in.
    I have 2 projects that kept me sane over the years.
    But now to complete them I need certain items.
    Local metal shops showed me astronomical prices or the door

    Give up is not an option. Not for me.
    I came here to try finding some answers I couldn't find else where.
    What would you suggest I should do?

    Thank you
  13. rocco

    rocco Silver

    Sirgei, I pretty much agree with what's been said so far, I don't think your plan is viable and you'd be wise to consider a different approach but I'll address some of your questions directly anyways:
    First, with a proper dried plaster or investment block mold, the mold material sticking to the casting is not an issue as the mold material softens up and disintegrates when exposed to water, you'd be able to rinse the casting clean. That said, the plaster MUST be completely dried and baked to drive off any moisture or the casting WILL fail, structural integrity concerns aside, incomplete drying of the mold is simply not an option. What happens with an improperly cured mold is the remaining water in the plaster vapourizes during the pour and the resulting steam will create major defects in the casting. One of the reasons for using commercial investment materials is they maintain their structural integrity when dried to greater degree than a home-brewed plaster/sand mix will.
    Casting sand as reinforcement would be of some benefit, far better would be to embed reinforcing materials in the mold material itself.
    As for as not preheating, with such a thin and tall section casting, it's likely your metal will freeze before completely filling the mold and the thermal shock of pouring very hot metal into a cold mold might well further compromise the structural integrity of the mold.
  14. Peedee

    Peedee Silver

    OK, so you need 2 copper tubes, one of which is 120 outside dia by 300mm long the other 90 outside dia by 300mm long both with a wall thickness of 3-4mm.

    Copper can be a bit of a problem with oxides, I'm not sure what the Tesla patent/device is you are referring to but the purity (as Kelly mentioned) may cause you issues, even if a cast was possible.

    You would need a super hot mould (using proper investment plaster not pop) and a vacumn to even get close to pulling it off.

    How was the original made (assuming you are copying an existing design)

    Edit: Or what Rocco said ;)
  15. Sirgei

    Sirgei Copper

    I research things that are regarded as pseudo-science. Except known things as AC power, generators and such that Nicola Tesla had invented, he also has several other patents for inventions known as Tesla Flying Machine, Earthquake Generator, Atmospheric Electricity and so on.

    One of them is a thing called Tesla Hair Pin Circuit.

    Tesla Hair Pin Circuit is EMF transformer. Sort of. It consists of 2 Solid copper rods set 2-3 feet apart from each other on the wooden base.
    2 high power capacitors are attached to the bottom of each rod. 1 Capacitor per each. Spark gap used to vibrate 2 copper rods.
    I have a friend who had tested this set up and it works to a degree.

    Now we need to replace 2 rods with 2 copper cylinders. Spark gap goes inside inner cyclinder.


    Outer cylinder 120mm wide. his size not yet fully set, but it has to follow specific harmonics.

    120mm wide
    300 mm long
    max 4mm wall thickness

    Inner cylinder 90mm wide
    300mm long
    max 4mm wall thickness

    In the cylinders, a series of holes would be drilled.
    At an angle of 45 degrees

    Outer cylinder is 7 rows down 16 circles around = 112
    Inner cylinder is 8 rows down x 16 circles around = 128
    Total 240 holes.
    Hole size can be determined later how big they can be so structural integrity is not compromised

    What I describe here is a remake of Hair Pin Circuit by another inventor in the later day.
    I have found 1 metal shop here who almost agreed to make them, but they wanted me to tell them what the items were for.
    I have honestly said exactly what for. He just laughed and said I go with my wacky trash some where else.

    Does this answer your question, Please?

  16. Sirgei

    Sirgei Copper

    Thank you very much for the answers.

    What kind of reinforcement would you suggest, please?

    I did not planned to try full casting first.
    First, I plan to try it on a cup sized item.
    But here the bottom part would be casting sand.
  17. Sirgei

    Sirgei Copper

    Thank you for the straight and honest answer.
    I have read every reply here and solutions you proposed are not possible unless I find a shop who would do it for a reasonable price.
    As you know we got a COVID-19 pandemic going on right now.
    1 Shop had offered me design to order. I given them dimensions for it and they said this design is invalid. On the question why design is invalid he said that they do not work with design that is provided by the clients. They only work with what their own designer had created.

    When I was talking with designer he tied to convince me that what I need it be is not what I want it to be. Or that it needs to be what he thinks it needs to be. After 1h of hangling designer told me to go away. That I am unreasonable etc etc etc I refuse everything he said and so on.

    Then he said that finalizing designs would cost £8-00 each item on top of manufacturing. And then he said they don't work with Copper at all. only with steel. When I sked him what was he trying to do this past hour he said ''i was trying to convince you what you really need. Metal used is not important all proper engineering works are made from Steel and steel-based alloys''
    So, that is how it ended.
  18. Peedee

    Peedee Silver

    6" round stock would run you around £1000 just in materials if you were machining it from blank.

    Have you attempted to melt and cast copper yet? I mean this in the nicest possible way but it can be a steep learning curve for the reasons already mentioned.
  19. Sirgei

    Sirgei Copper

    I have not as I already stated above.
    Before trying full sized tube - I intend to try casting a goblet about the size of 1 pint beer jug. As I do have a worry about casting gap being too thin, my biggest worry is metal sticking to the mold.

    Hopefully, answer that other member gave above would sort out that.
    Russians are such people who give up only as a very last resort.
    And I too cannot give up without at last trying

    Hence why I joined this forum in order to ask questions to increases the chances at last a bit.
  20. Peedee

    Peedee Silver

    You are in the right place for help. Get your first pour done and let us know how it goes

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