Hello from Florida

Discussion in 'New member introductions' started by Steve Brown, Sep 19, 2021.

  1. Steve Brown

    Steve Brown Copper

    Thank you for approving my membership. I'm a hobby metalcaster in Florida, USA and stumbled across the forum googling for better ideas for flasks. It's apparent that there are a lot of people here more skilled than I am, so I'm looking forward to learning a lot.
    My current project is a set of toddler sized oarlocks for my nephew (he built a little dinghy for his 3 and 6 year old to use.) This project is my first attempt at using a 3D printed pattern (and in fact, the first 3D print I've designed from scratch, as opposed to printing designed downloaded from thingiverse.) I made my first casting attempt this morning and it wasn't entirely successful. The final parts will be bronze (will also be my first bronze casting) but I thought I'd start with aluminum to get a part suitable for a fit check before melting expensive bronze (I was reducing some trashy aluminum extrusions to ingots anyway, it's free and not good for much, but fine for a trial part to check sizing.)
    I struggled with the molding, and by the time I had a mold that wasn't terrible, I was so thrilled that I rushed to pour and forgot the core. The casting on the right is what happened. (On the right is the point my nephew started me with: "can you make these smaller?"; the center is my 3D printed pattern.)
    I had time for a second try, remembered the core, but still had trouble with the sand breaking at the edges (it may be a have been a little bit dry.) The core turned out to be a mistake; I was trying a steel core coated with lamp black, a la Gingery (another personal first). I didn't come out without a fight, and the aluminum was so soft, I had to beat the heck out of the casting (distorting its shape beyond utility) to get it out.
    I'm down to either figure out how to use the core print as a feature to locate a hole to drill (when I was developing the pattern, I spent some time trying to figure out a feature that would locate it before deciding to go with a core) or figuring out how to make 1/4"/6mm diameter sand cores (another new experience for me.)
    HT1 and DavidF like this.
  2. Petee716

    Petee716 Gold Banner Member

    Welcome. Your surface finish looks pretty decent for greensand. Yes, maybe a bit dry. Where the sand pull at the top of the tang(?) in your second picture, you maybe could use a fillet but it looks like it pulled cleanly in your other attempt. Possibly adding some moisture might help.
    You could use a piece of 1/4 brake line for a core. It would be easy to just drill out afterward.

    Tobho Mott likes this.
  3. Tobho Mott

    Tobho Mott Gold Banner Member

    You could probably design and 3d print a corebox for it, but Pete's idea sounds a lot simpler to me, especially just to cast a few of them...

    Welcome to the home foundry!

  4. Peedee

    Peedee Silver

    I would drill it. Seems a lot a lot simpler than coring it. Welcome
  5. Steve Brown

    Steve Brown Copper

    Drilling was plan A when I was designing the pattern, but the catch is there are no flat surfaces to clamp the part or locate the hole, everything's curved or tapered or has draft. I spent some time in the pattern design trying to figure out an easy way to add a locating feature before just deciding to core it. My prior experience with cores is just the kind for an open-sided pattern, i.e. the core is part of the drag, even though it projects above the parting line, so I've not (yet) done many separate core pieces. But how hard can it be?
    Plan B was the steel core.
    I discovered this week that I have some "heat set core oil" (don't remember when I picked that up, must have thought it was going to come in handy some day.) So I made a core box this weekend. Making tiny sand cores turned out to be a frustrating experience, I almost gave up on plan C. No matter what I tried, the cores wouldn't release from the mold. I think the surface area to weight ratio is just too high on the small parts. Before baking, after baking, none of it worked; I just made little messes on the workbench. Closest I came was pushing small section of sand through a bit of soda straw with a pin punch. I could only get about a 2cm length that way, but it would work if my soda straw was the correct ID (or if I redid the pattern to make the core print match the soda straw ID... But I've got a lot of time already invested in finishing the pattern, they come of the printer with a pretty rough finish [sunk cost fallacy, I know]). At the last, Sunday I was about to throw up my hands and try a reckless plan D, just put wooden dowel pieces in the mold and hope that on such a small part, the charring wood wouldn't release so much gas as to ruin the part. But I came up with the idea of lining the core box with a roll of thin paper, and baking the cores in paper like little sand cigarettes. They're in the center of the image:
    Unfortunately, baking them took up the rest of the weekend's time, so unless I get fired from the day job, I won't know how plan C works out until next weekend when I have time to pour.
    Plans E through G (I don't yet know which is which) are:
    • cast them with core prints in place (as I accidentally already did with one) and figure out how to use the core print as a locating and/or chucking fixture to drill out the holes;
    • re-do the pattern and put an extraneous chucking block onto the part;
    • find some SS tubing of appropriate ID and cast permanent bushings in place (I found some 5/16" K&S SS tube that, if the description is to be believed, is about 0.008" oversize on the ID. But it comes shrink-wrapped on a card, I'll have to shell out $8 to try it for size.)

    PS Why is the core box so big? I had 1"x2" stock rescued from scrap a while back, and I thought if I was going to the trouble of match drilling a pair for registration, I'd make it large enough to drill for more core sizes in the future. Or at least that was my thinking before I learned how hard it was to shake a small core out...

Share This Page