Casting trilobites

Discussion in 'Lost wax casting' started by Robinson-Foundry, Nov 18, 2020.

  1. I’ve been working on getting this trilobite cast in bronze. I started by sculpting the trilobite in blender. I used the fossil shown here as a reference:

    https://tresorsdutemps.com/index.php/produit/fine-flying-trilobite-hollardops-mesocristatus/

    Im happy with how the model turned out being that it’s only my second attempt at sculpting in blender. This one took roughly 20 hours.

    The model was printed on my resin printer and I just finished making the silicone mold.

    I’ll be using Suspendaslurry and boiling out the wax. Fingers crossed that the boil out goes well.

    231D846E-BB96-4C9A-BA42-C4D13676460E.jpeg 89F36282-42A1-4AE5-8E53-F980BB6278FC.jpeg 61ED908B-EBC5-4443-86E4-E8163C693509.jpeg B3E27805-76B3-44DF-BFD7-BD47C7A9FD06.jpeg 1CFFC267-971E-4842-8BBA-64A5B332A70C.jpeg
     
  2. Jason

    Jason Gold

    Looking great! It's hard to tell the scale of this thing.. How long/wide is that? (I'm guessing 6inch long and 3wide) ???
    Now let's talk about this boiling out thing that some clown told you try...:cool:

    Thickness is going to be key here! You need this thing to be about 3/8" thick for best results. You can get it thinner, but this is your first go so stick with me on this one and get fancy later!
    You can add thickness to the back with wax sheet if you have to and no one will know. I would sprue this thing like this. All shaded area is wax sprue, feeders and a vent at the top.
    That vent at the top goes to the top of the wax pouring cup. Yes I know the angled feeders are pointed UP which is bassackwards of what is normal, but this is because when you boil out, the wax MUST flow UP and out the cup! After you boil the wax out, leave it sit overnight and dry out. Once you have everything else ready, stick it in a kiln and run it up to around 1700. When the bronze is ready, stand this thing up in a metal container or in a hole in the ground and pour your bronze in nice and steady until the cup is full. You will wait 25mins and then you can break it open. A lot of the shell will crack off as it cools. The bronze shrinks, but the shell doesn't. If you wanna roll the dice, add a second bug looking thing to the other side of the main sprue. Speaking of sprue, I would shoot for 3/4" square main sprue and 3/8" feeders and maybe a 1/4" vent up to the cup. If this is your first time melting bronze, your biggest issue is going to be heating the bronze to the right temp. Get it too hot and your surface finish will suffer. Get it too cold and you might not fill. This is the reason I advocate 3/8" thick for your bug. Thicker pieces are poured cooler around 1800. Thin stuff needs 2100 to flow through thin areas. You might even try a dry run with some generic shape on a sprue with a feeder and vent back to a pouring cup. You'll be more comfortable when you pour this thing for real. Rehearse everything before turning anything on. KNOW where all tools are and look for anything that could trip you up. When a shell is cooling on the ground is not the time to look for your pouring shank. (been there)

    Back to boil out. If you make this thing too thin, there is a good chance you won't fully boil out all the wax. This is where it gets fun. I've seen my pieces start smoking in the kiln during burnout before pouring, cracked the lid for a peek and WOOF! BIG FLAME in the kiln as the O2 hits that wax! Not a big deal, just close the lid. Microcrystalline stinks to high hell when you burn the shit. When you boil out. Be sure you have a ROARING BOIL before lowering in your piece for dewax. Then plan on keeping that boil going HARD for about 10-15mins. You should see the wax come flying up the sprue and the wax pouring cup will go floating away. You've seen the video. I recommend you do slurry, fine silica, slurry, fine silica and then 6 layers of slurry and course silica. DO NOT SPEED DRY THE FIRST COAT! Allow a full 12hrs before adding your second layer. Layers 2-8 can be done after about 3-6hrs per layer. Those can be speed dried with a fan blowing onto the shell. It takes me on average 3full days to coat a wax with ceramic shell. Then a day for dewax and FINALLY I can pour pretty much the following day. Please try to stick to the plan I wrote here. This way, if shit goes sideways on you, it will be easier for me to help troubleshoot. Take shortcuts next time will ya?

    This process is slow, but almost as good as solid block investment. Remember, there is actually 2 stages of getting the wax outta that shell. The first is DEWAX where most of the wax is gotten out and is done by fire, boil out or an autoclave. Next comes BURNOUT, which rids all organic material and remaining wax and that is always done in the kiln or a fire and brings the shell to pouring temp. Keep this straight and you'll be fine.
    20201118_213307.jpg

    20201118_213853.jpg
     
    Last edited: Nov 18, 2020
  3. Jason

    Jason Gold

    IF you find cracks AFTER you boil out which you will see upon close inspection, you will need to patch your shell. Mix up some slurry with some fine silica kinda thick in a jar and paint the area with a chip brush. Let dry an hour and repeat a couple more times to build up a bandaid over that crack. I get cracks in my pouring cup usually because I don't get the shell thick enough during dipping. SO I have to conscientiously make myself thicken up the cup. If you have any questions during this, try to stay in this thread and I'll keep a close eye for them. Even after doing this quite a bit, I still always pass my sprue job in front of the peanut gallery to check my work. Better to wear a little egg doing dumbshit than have a failure after all this work. An extra set of eyes is always worth it at this point.
     
  4. Zapins

    Zapins Gold

    I agree but will add that the first 2 shell coats should air dry with no fan then coats 3 to 6 or 7 can be done with a fan and courser grain sand.

    Also while Jason's spruing will work I'd flip the middle 2 sprues upside down so the metal can't flow into all of them at the same time without filling the bottom sprue first. You should sprue items with 1 path for the metal to enter and 1 path for it to leave. If you let metal splash down the main sprue and give it the option of going straight to the bottom 2 sprues and the middle 2 pairs then the metal wil spill into the bug from 3 levels and can trap air or cause turbulence and break the details off the inner layer of shell.

    Bottom feeding and allowing gas to escape from a vent in the top let's metal fill from 1 path (bottom to top) this forces out air and reduces turbulence.

    This spruing idea becomes much more important in very thin or highly detailed castings.
     
    Last edited: Nov 19, 2020
  5. Jason

    Jason Gold

    It's been my experience zap it doesn't take a detour half way down the main sprue. It fills the bottom first, starts filling the mold from the bottom until it reaches the next one. That's when the backwards fill could take place. Never had a problem so far. Besides, he has a vent at the top so no chance of a void.

    If he flips the middle two the other way, wax wont float out during boil out. You would be asking all of it to float out through one 1/4" vent. Not gonna happen.
     
  6. Roy Carter

    Roy Carter Copper

    Hello Jason, attempting a reply and picture uploads on this site. First is with pouring cups and 3/4" gates. Second is with addition of 1/4" vents and first slurry/sand coats. Thanks Roy Carter
     

    Attached Files:

  7. Roy Carter

    Roy Carter Copper

     
  8. Roy Carter

    Roy Carter Copper

    Need to give credit to Eric at lunarburn studios for splendid pouring cup concept. Roy
     
  9. Jason

    Jason Gold

    I've seen his cup. Works great for light stuff. But if you ever really load up a tree, don't trust it. You'll only drop one once and will cry!
    By the time you get 7 or 8 layers on, things start to get heavy REAL FAST! You'll see what I'm talking about. Don't trust it, always keep a hand under it!

    These were real heavy to rely on a wax joint!
    20190611_012303.jpg
     
    Last edited: Nov 20, 2020
  10. Roy Carter

    Roy Carter Copper

    Fair warning taken. Three of the items are light strips. One is heavier and I will be careful in handling it.
     

Share This Page