Think This Process Will Work?

Discussion in 'Investment casting Block method' started by 0maha, Oct 2, 2020.

  1. 0maha

    0maha Copper

    Hello everyone! First real post here. Hope I'm in the correct sub-forum!

    I want to put together a process to make parts like this:

    [​IMG]

    Been giving this a think for a while, and what I've settled on is a vacuum assisted investment casting setup. Or at least that's what I think I've settled on. That's why I'm here. I want to see if you think this will work.

    The main concern is maintaining a high level of detail on the parts. I want them to be as "clean" and accurate as possible.

    My thought is to cast these two at a time, back to back, with sprues and vents that look like this:

    [​IMG]

    [​IMG]

    Then that goes into a rectangular flask like this:

    [​IMG]

    Thoughts? Ideas? Advice? I hope I've done a good job explaining the goal here!

    The rectangular flask is built around the idea of wanting to (a) minimize the amount of investment I use on each part and (b) being able to get more than one flask into the burnout kiln at a time.

    I saw videos from David ("thehomefoundry") where he's using a similar vacuum assist setup. What kind of pressure are you drawing on your setup?
     
    Last edited: Oct 2, 2020
  2. FishbonzWV

    FishbonzWV Silver

    Welcome Omaha,
    Impressive renderings.
    I know nothing about block.
    Good luck!
     
  3. DavidF

    DavidF Administrator Staff Member Banner Member

    As much as I can. I don't have a gauge on it to see. I just make sure the flask is sucked down tight...
    Are you going to be able to cut those castings apart once poured??
     
  4. FishbonzWV

    FishbonzWV Silver

    My thought was...better try one of them first to get the process dialed in. That looks quite complex to be doing two at a time.
     
  5. 0maha

    0maha Copper

    What vacuum pump are you using?

    The cutting apart is a good question. My goal is to be able to do these two at a time, but it's tricky. I'll try them one-up at first and see how it goes.
     
  6. DavidF

    DavidF Administrator Staff Member Banner Member

    For the vacuum assist on the flask during the pour is just a harbor freight 3cfm. But its a bit small for when mixing the investment..
     
  7. Al2O3

    Al2O3 Administrator Staff Member

    I realize you are probably trying to minimize the flask volume and investment required to pour a pair but that would be a real pain to degate. Also, I'm not a practicing investment guy, but why not run the sprue to the bottom on the side of the two parts, feed the two at the bottom, vent the top, and connect the two castings to each other at convenient places on the perimeter for strength and stability? This way you could have about the same spacing between parts and flask volume, but it would be much easier to degate/cut them apart.

    Best,
    Kelly
     
  8. 0maha

    0maha Copper

    Interesting idea. Being totally new to investment, I assumed I wanted to fill from the top and vent from the bottom. You're saying go the opposite direction. I'll put together a couple of renderings later this afternoon and see what the group thinks.
     
  9. 0maha

    0maha Copper

    Played around with things a little bit. Here's a slightly modified version of the original setup. I think the new layout will make de-sprueing easier.

    (I stripped all the detail out of the model to make it easier to play with the sprues, which is why it looks all mottled and crappy...)

    [​IMG]

    [​IMG]

    [​IMG]

    Here's one with one of the models removed, so you can see the sprues better.

    [​IMG]

    I guess that's where I'm at.

    Anyone see any reason not to give this a try?

    I'm trying to be fairly deliberate and thoughtful about this, since it's going to take some doing to get setup to actually test this. I'm going to have to make the special flask, make the vacuum chamber, and I still need to get a kiln. I'm hoping to avoid going down a dead-end if that's where this is heading, but I'm pretty much to the point of concluding that there's not much more to do other than give it a try and see how it works out.
     
  10. DavidF

    DavidF Administrator Staff Member Banner Member

    You don't need vents if your using vacuum assist.
     
    OMM likes this.
  11. OMM

    OMM Silver

    Isn't that a no brainer. I think you've shown this at least a dozen times. Didn't you use the vacuum assist on your thinwall cup, spoon and tea cup plate? Or was that Kelly?
     
  12. DavidF

    DavidF Administrator Staff Member Banner Member

    That was Kelly...
     
  13. 0maha

    0maha Copper

    That's wonderful news. Thank you! Will make things that much simpler.
     
    DavidF likes this.
  14. Aaron M

    Aaron M Copper

    Hi,

    It appears you don't have much of a feeder in the gating. That's a big piece, you're going to have to feed it otherwise you will have cooling pulls throughout the part, probably in the middle thin section trying to feed the inner and outer sections.

    You don't appear to have any undercuts, maybe need a little draft on the edges, why not just fine facing sand and petrobond? You have enough mass, plus a lot easier.

    Good luck.
     
  15. Jason

    Jason Gold

    He would never get the resolution with sand casting compared to solid block investment. Looking at the very first picture on this page, he's seeking jewelry quality I think....
    I see he has put this thick sucker on a diet as the photos progress. The back is hollowed out and that's a smart idea. For a beginner, solid block is probably easier than shell. Much less to go wrong.

    I don't see it on this page, but Omaha, what metal is this thing going to be cast in???
    Next question, how are you getting this part into wax???? Will you print this thing and take a mold of it in silicone to create the wax?? If so, have you a plan for dealing with crappy print lines??
    just food for thought.
     
  16. 0maha

    0maha Copper

    Exactly right. I did a few tests with aluminum in petrobond, but quickly abandoned it. Maybe I bailed out too early, but I don't think I've got any chance of getting the resolution I need going that way.

    My vision at the moment is bronze, but I want to be able to use aluminum also.

    Yep. In fact, this week I've been working out some details trying to figure out a good process for making the molds. The initial attempt was to create a huge block of silicone. That worked, sort of, but used a ridiculous amount of rubber, and I don't think it's going to make for a good wax mold since it's so floppy.

    The new effort looks like this:

    [​IMG]

    The reverse side looks like this:

    [​IMG]

    That test failed in a few specific ways, so I never got to molding the other side of the piece. The idea is to end up with the two pieces of plywood (I've actually converted to MDF for the next test) that then get bolted together for alignment and the wax mold made from there.

    As for the print lines, I'm giving them a good smoothing (22o to 400 to 1000 grit sandpaper) before making the molds.
     
    Tobho Mott likes this.
  17. Aaron M

    Aaron M Copper

    Hi,

    Sand it with water and dish soap, lowers the fuzz from PLA, prime it a few times with krylon white primer, don't use a high build type. Then normal sand it, smooth as glass, krylon makes a product called "triple coat clear glaze" something like that. Three coats of clear in one, it should be perfectly smooth. Smooth On Moldstar 30 will work well for this, gallon kit, maybe it's 2 gallons, not the quart kit, next size up. you can get it from Reynolds Advanced Materials, don't do amazon less quality. Make sure it's at least 1" thick top and bottom so about 3" total thickness. Uses normal mold methods, plus you can put some of the gating in then, makes life easy.

    Moldstar is a platinum cure silicone. Sulfur causes it NOT to cure, just makes goo, watch the clay too (Sargent Art Plastilina Modeling Clay from amazon). Rustolium contain barium sulfate, even if it's not listed on the SDS, so it will not cure and you will have wasted considerable time and effort and nothing will get the goo off your mold without ruining it. If you do end up using rustolium, the people at Reynolds will tell you the tin-cure version of the silicone that is compatible.

    I use moldstar 15 and 30 and get really good results. 30 is a little stiffer and will give good detail, neither of these require degass or vacuum. Mix well, let them sit on the bench for 20 minutes and then pour.

    If you have any questions let me know.

    Thanks
     
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  18. 0maha

    0maha Copper

    Things are starting to feel like they are coming together. Latest attempt gave a far better result than the first time.

    One of the challenges is I need a water-tight seal between both the 3D print and the table (actually, a piece of very heavy, 75 gauge plastic sitting on the table) as well as between the frame and the table.

    On this most recent go-around, I tried using rubber cement. Only worked sort of. Next effort I'm going to try using a hot glue gun, and an x-acto knife to clean up any squeeze out before pouring in the first batch of RTV.

    The other thing I did wrong was add too much thickener in step 2. Should have used half as much.

    My idea is that the first layer of un-thinned RTV will fill in the small stuff, then add layers of thickened RTV from there. Do you think two thickened layers is enough.

    Last, I don't think pre-printing the mounting holes is a good idea. I'm going to take another run at it without the holes. I can drill those later.

    I'm using 74-30 RTV that I got from US Composites. Is the Moldstar 30 essentially the same thing?

    [​IMG]
     
  19. DavidF

    DavidF Administrator Staff Member Banner Member

    I use clay to bed mine down. Easy to work and clean up.
     
    0maha likes this.
  20. 0maha

    0maha Copper

    I'll try this with the next one.
     

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