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.)
    IMG_20210919_152104.jpg
    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.
    IMG_20210919_152114.jpg
    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.

    Pete
     
    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!

    Jeff
     
  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:
    IMG_20210927_080351.jpg
    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...
     
  6. Rob Hall

    Rob Hall Copper Banner Member

    Welcome aboard! (pun intended)

    Those look like great casts to me!

    As for the holes, they don't have to be super precise, right? I see a lot of purchase for a vise, even for a hand drill.
     
  7. Steve Brown

    Steve Brown Copper

    Thanks.

    Yesterday, my second attempt at pouring bronze parts didn't go too badly (we shall not speak of the first attempt a week earlier):
    IMG_20211023_214808.jpg
    The one in the center didn't fill, not sure why. It was the first poured, should have been hot enough to flow.
    It's clear that bronze behaves differently than aluminum, and doesn't seem to like the same gating arrangements. The dross moves differently, and doesn't clump nicely in the crucible to scoop it out before pouring. I experimented with different gating arrangements (as evident with the part at the top) but I've clearly not mastered it yet.
    The one on the bottom filled properly, but broke at the base of the pin when I shook out the mold. I may have just not waited long enough for it to cool. This one was gated almost same as the aluminum parts, I did not try to put a big runner in to trap dross. I also didn't torch the mold to dry it before putting it together. The part is probably still usable and you can probably see that I had already started to clean up the flashing and finish before I took the picture.
    Surface finish was rough on all, I'm not sure why. Possibly a venting problem, or the metal [*]. Maybe the paper on the cores is out-gassing. I'll make another try soon, try to figure out some ways to isolate potential factors.

    No, the holes don't need to be super precise. They do need to be coaxial (because there's a pin that goes through them), so they have to be lined up with each other. That axis also should be both co-planar and perpendicular to the axis of the central pin that fits in the socket on the gunwale, so that's not subject to excessive wear. Hand drilling an accurate hole on a convex surface is tricky, but I could have figured out a way to line it up and start it on location. And it's a toddler's rowboat, it's not going to be subject to daily wear. Probably would have been fit for purpose that way.
    But I need to figure out cores at some point. And the paper wrapped baked cores have worked very well. I've just had to run a hand reamer through to clean up the rough surface and they're a nice sliding fit for the pins (stainless steel bolts with the threaded end cut off and cross drilled for a tiny cotter pin.) I tested the coring with aluminum pieces, which passed the fit check:
    oarlock.jpg
    (Again, it's a toddler's rowboat. Aluminum would probably hold up for light use. But I want to get this bronze figured out, there are other projects I'd like to be able to tackle.)

    [*] I'm using scrap, discarded "bronze" marine fittings. Pretty corroded, and it became apparent as I dug into it that the definition of bronze for this box of bronze scrap was pretty loose. Taking a file down to clean metal reveals a lot of variation, some whitish and reddish bronzes, some reddish that's clearly straight copper (mostly cut-off pipe ends still stuck in fittings), some yellowish brassy looking stuff. I tried to stick with the stuff that looked bronze-y, but from the exhaust colors when I melted it, I'm pretty sure I burned off some zinc. (Yes, the furnace is in the open, lots of ventilation in the middle of the back yard.) But identifying copper alloy scrap should probably be a different thread.
     
  8. DavidF

    DavidF Administrator Staff Member Banner Member

    Might not be bronze, not all of it anyway..
    I would suggest buying some actual everdur for your next casting session.
     
  9. Steve Brown

    Steve Brown Copper

    I've already got a little bit of new silicon bronze, not enough to make a lot of mistakes with. I felt there was some value in using the stuff that was $1/lb to figure out how some of these things, vice making mistakes at $12-20/lb. I keep the stuff of known provenance strictly segregated (as with my other metals).
    It's definitely all some copper alloy, but I suspect there's some "yellow bronze" (i.e. brass). I tried to sort what I could based on the color of the filings, but I probably let some relatively high zinc stuff through. In the application of interest, the admixtures aren't too critical. The commercial oarlocks are unspecific "manganese bronze", of which most variants are pretty high zinc and low tin anyway.
    Until I can afford X-ray fluorescence, I need to lean on other ways to judge it. (And if I could afford XRF, I wouldn't be so poor as to be fooling around with scrap...)
     

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