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Thread: Help with investment casting small intricate parts

  1. #21
    The 500 degree RTV silicone sealant is drying - no idea if I used the right one because it's not red like in your picture, I may try another product from Home Depot. Otherwise looks like the stuff is coming together.

    vacuum-rig.jpg

    The thermocouple from MIFCO accepted the K-type connection from DINICO. No idea if this actually works yet, will double check against the laser reading.

    thermo.jpg

  2. #22
    Moderator DavidF's Avatar
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    No flange on the small flask??
    A calm sea does not make a skilled sailor....

  3. #23
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    The thermocouple from MIFCO accepted the K-type connection from DINICO. No idea if this actually works yet, will double check against the laser reading.
    Stick it in ice water, and also in boiling water. That should give you a good idea as to accuracy. Be sure to adjust the temperature of boiling water according to your altitude above sea level.

    Also, those Mifco thermocouple probes have thin wire in them. Don' overheat them or you will melt the wire. (Don't ask me how I know.) It's not a risk if you are only melting aluminum, but with bronze you can get there if you are not careful.

    Richard
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  4. #24
    It took me a while to set this up including getting all the parts and re-building after mistakes, but I finally poured this weekend. The definition is way better, and more repeatable. I tried to follow the advice on pouring at a lower temperature (3-4 minutes wait after last charge melts), and I think that also made a difference. After all that, however, and I am still coming up short on surface quality. Does it look like a result of poorly controlled mold/pouring temperature?

    First model:

    first-cast.jpg

    first-cast-detail.jpg

    Second model (notice there is small spot inside the "cross" feature that somehow turned out smooth:

    second-cast.jpg

    Wax models:

    cast-flasks.jpg

    Casting:

    cast-rig.jpg

    cast-rig-working.jpg

    [EDIT]

    Looks like the pictures were downsampled & compressed by forum software, see another post with high-res picture here if needed: https://hackaday.io/project/19830-el...-metal-casting
    Last edited by 01binary; 05-28-2017 at 05:32 PM.

  5. #25
    Moderator DavidF's Avatar
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    couple things i see. Looks like incomplete burn out for starters, but the main thing is the sprue size is way way to big. The flask temp should be at 500f for the pour, this is especially important for aluminum.
    Your main sprue only needs to be about 3/8" and the ingate about 1/4".
    parts should look more like this....
    A calm sea does not make a skilled sailor....

  6. #26
    Senior Member Zapins's Avatar
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    Did the thermocouple controller end up being accurate? Did you buy the digital part on the website?

  7. #27
    I couldn't get the thermocouple to work. I double-checked compatibility, but both the probe and the pyrometer are K-type. Nothing wrong with the contacts. It was showing 74F when the temp outside was in fact around 70. As soon as I put it in the melt, it started freaking out and eventually settled on "HI".

    Here's the pyrometer again, K type: https://www.amazon.com/pyrometer-Ann...ords=pyrometer

    Here's the probe again, K type: http://mifco.com/shop/pyrometers/rep...rmocouple-tip/

    Today I also got a second pyrometer, also K-type, and still not working. It's getting 20F-22F reading inside a 300F kiln, outside in 60F ambient, and in the fridge. I cut and re-exposed the contacts, then attached again. No difference.

    http://www.ebay.com/itm/261685822329

    ---

    Today I am repeating the experiment, this time making sure I have 500F flask temp. I have a manual kiln, and I am starting to suspect that temperature fluctuates enough to destroy the inside of the molds since I have no way to control how hot it is inside other than opening the lid if it gets too hot and turning the heating coil pots to a "lower setting". I measure every 10-15 minutes with the laser and adjust.

    DavidF: I tried to make a smaller sprue & gate, but the wax bends/fractures and doesn't hold the models if it's thinner than this:

    models2.jpg

    I assume you are buying your wax sprues pre-made? I could try that route, but the cost might get prohibitive since I have 300 parts to cast, so far made 20 attempts and 0 progress.

    https://www.riogrande.com/Product/Bu...-12-dia/700020
    Last edited by 01binary; 05-29-2017 at 07:18 PM.

  8. #28
    Senior Member HT1's Avatar
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    Quote Originally Posted by 01binary View Post

    The thermocouple from MIFCO accepted the K-type connection from DINICO. No idea if this actually works yet, will double check against the laser reading.

    thermo.jpg
    Please do not use the thermocouple loose here is my setup, It is incredibly simple, 1/2 inch electrical conduit bent to a 90, slot the end so it will crimp, clamp the thermocouple in place with a hose clamp, the electric (handy box) has a receptacle in it so I have an easy way to connect the thermocouple leads to the to the plug for the multimeter... it is basically a 2 dollar electrical junction block... I should put childproof covers over the receptacles though.. Cheap easy and bulletproof

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  9. #29
    Moderator DavidF's Avatar
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    Sprue wax is cheap!
    A calm sea does not make a skilled sailor....

  10. #30
    You've used Ultravest. Basic sanity check here, I am spending 8 hours baking the perforated flask with ultravest in it, up to 1350F and then down to 500F for the pour - according to R&R instructions. Is this correct? I really need to go over a thousand degrees just to pour at 500? Is this what you do every time you cast (i.e. babysit a baking flask the whole day)?

    Thank you!

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