Investing a complex shape

Discussion in 'Lost PLA casting' started by theroundbug, Nov 8, 2021.

  1. theroundbug

    theroundbug Silver

    Hi all have a few questions here that I hope you'll be able to answer before I possibly waste expensive ultravest.

    I am vacuum casting a hollow object (a pipe) that has holes about 1/8" diameter at differing heights. Can I just sprue this up and fill the flask like normal and let the vacuum pump do the work to fill any trapped air with investment? Or do I need to do something special to fill it completely? It's going to be sprued from the base of the chamber so the investment will have to flow in from the bowl, carb and then down the mouthpiece. Also I'm not sure if the investment will be strong enough for it to stay put from those inlets? Do I need to nail through it?
    IMG_7371.jpg IMG_7370.jpeg
     
  2. DavidF

    DavidF Administrator Staff Member Banner Member

    Your certainly challenging things that way...

    Best bet would be to cast the bowl portion separately from the pipe, then press the two pieces together.
    On the stem, you'll either need to put a small piece of wire through it or some fiberglass strands from some woven roven..

    I'm going to get some beer and popcorn, this is going to be entertaining :cool:
     
  3. theroundbug

    theroundbug Silver

    I can’t cast the bowl and stem separately as I have other designs that have artwork that flows along that seam. It needs to be cast as a single piece.
     
  4. DavidF

    DavidF Administrator Staff Member Banner Member

    Think you might have misinterpreted what I'm saying...
    When I say bowl, I mean the funnel looking part...
     
  5. DavidF

    DavidF Administrator Staff Member Banner Member

  6. theroundbug

    theroundbug Silver

    I see. I have no way of welding that piece on if it were separate. If I did something like that it would have to be friction fit or something. I am contemplating something like that for a traditional tobacco version. Same design but a wooden cylindrical bowl is press fit into the pipe, with no carb.
     
  7. theroundbug

    theroundbug Silver

    Another idea is to fire a clay bowl in place after casting, since part of the patination process involves heating the pipe up to around that temp anyway
     
  8. DavidF

    DavidF Administrator Staff Member Banner Member

    Press fit should be doable imho...
    So I'm guessing that this version burns something other than tobacco?? ;):eek::eek:
     
  9. theroundbug

    theroundbug Silver

    It can burn whatever, I've just been having people who frequent smokeshops (where they sell glass pipes) ask me to make a metal one, so this design is for that market. The one with a wooden bowl would be for tobacco only
     
  10. mytwhyt

    mytwhyt Silver

    I don't think you could cast it with the bowl in place.. There's absolutely no support for the investment core.. How will it retain it's position when the wax melts.. Cast in one piece without the bowl it stands a pretty good chance.. An investment with fiber glass would be strongest.. Bumping it when it taking it out of the oven, might cause the core to shift.. What metal are you casting..
    I once made a pipe out of a pork chop bone.. Sterling silver bowl and mouth piece.. 40 years ago, Meant strictly for burning the devils lettuce..
     
  11. theroundbug

    theroundbug Silver

    Without support pins the investment would still be connected to the core through the bowl, carb hole, and mouth hole
     
  12. DavidF

    DavidF Administrator Staff Member Banner Member

    That's just so wrong, on so many levels...:D
     
  13. mytwhyt

    mytwhyt Silver

    With so little connecting area at each end, it wont support that much core.. Without the bowl the larger connecting area has good chance of keeping the core in place.. Once fired, regular investment has little strength.. It's porosity must be contributing to that lose.. In a steel flask that porosity becomes a plus..

    I made that pipe for a friend, I never smoke pipes. Although I did when I smoked broad leaf tobacco. Stopped that shit, it's really bad for you.. My friends knew if pestered enough, I'd make whatever they wanted.. I still have the knife I made for a good friend.. I just did the handle, it was his blade.. He died before I could return it to him.. I know a jeweler is barely tall enough to take the foundry ride... But then, I did sand casting to make the things I needed in aluminum.. At 79, the molds are getting to be just to damned heavy.. The up side to being a jeweler, I can still sit and work without heavy lifting.. Ah, the good old days.. How sad it is that these are the good old days for the children...
     
  14. theroundbug

    theroundbug Silver

    I can drive pins through in various places. That should hold it good. I can't weld a seam but I can tack a pinhole
     
  15. DavidF

    DavidF Administrator Staff Member Banner Member

    I would not pin it, not on a first attempt anyways...
    I would run a piece of wire through the stem area length wise like a spinal cord. Even if the investment breaks into a bunch a vertebrae the "cord" will hold them together.
    Another thing that works well is to pull some strands of fiberglass out of some 24 Oz woven and run them through the stem...
     
  16. Zapins

    Zapins Gold

    The issue is you can't get the ceramic shell to dry inside the deep stem.

    Maybe a plaster based mold might work? They don't need to dry to solidify.

    Would be easy to make if you could weld it.
     
  17. mytwhyt

    mytwhyt Silver

    He mentioned ultravest in his first post, so I think it'll be plaster.... Pinning it will mean pins left on the inside.. You could use pins of the same metal, still pins left inside, but no pin holes..
     
  18. DavidF

    DavidF Administrator Staff Member Banner Member

    Plasticast has proven itself to be better than the ultravest, and ultravest fg when investing pla prints... just mix it on the thick side...
    Putting a pin through the side of the stem area is certainly going to create a point of failure.
    Pinning is usually done to support larger cores with thick cross sections in larger objects that are cast hollow and not in long thin cores...
     
  19. theroundbug

    theroundbug Silver

    Updates

    First attempt was a simple test - a proof of concept - to see if this might work. I used plaster/sand since I didn't want to waste real investment. I think it would have worked if not for a bad gasket on my machine not allowing vacuum to the flask. With a (essentially) gravity pour I got most of that first print out. The carb hole did not burnout properly, and the inside of the stem did not invest past the pin I nailed through it.

    I revised the design to be much smaller and thinner. The first test proved that even if successful, the resulting pipe would be comically heavy. Nobody would ever want to smoke out of such a device.

    The new design consists of a "bowl/body" and a "stem" that press fits into the body.

    While vacuuming investment I ran out of vertical space in my flask sleeve so I had to cut off the vacuum prematurely to prevent an overflow mess. This resulted in the body not fully investing.

    The 5 inch stem with 1mm walls and a 4mm inner diameter invested and cast perfectly. It all cast perfectly, actually. I just didn't get a good pull on the vacuum to pull out the air inside the body.

    I will try again - this time grouping bodies and stems separately, so as to allow for more vertical space of the investment bubble to rise for the body patterns. I also will try a thinner mix. I went with 40/100 this time around. No cracks, I think I'll try 41 or 42, which will allow the investment to naturally fill the bodies before vacuuming.
     
  20. DavidF

    DavidF Administrator Staff Member Banner Member

    How about some pictures?
     
    Tobho Mott likes this.

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