Pattern/Rapping fail Sailboat Part

Discussion in 'Sand Casting' started by Tops, Jun 12, 2022.

  1. Tops

    Tops Silver Banner Member

    My youngest brought home a vintage Capri Omega 14. It's in tough shape but would fill the gap between the smallest boat which is barely big enough for one maybe two and my weekender that takes a long time to rig and de-rig after use. The boat had a half wire halyard and a broken masthead casting. The jib was converted to all rope and I want to do the same with the mains. I got it measured, into CAD, printed, pinned, painted, waxed, graphited, powdered, and rammed into a flask with Petrobond. Never mind that I make a little gating block and that I had to 'choke' the flask with pieces of 2x4 so my Petrobond would fill both drag and cope. Things seem to ram up nicely with barely a tennis ball's worth of P-bond left over. I go to rap and extract...stuck. Rap some more, stuck. Try the drag, try the cope...stuck. I get the cope to come out and it is fine. I go to the drag and I tore out a 'muffin top' piece of sand out between the two vanes that will support the rope sheave.

    So, rather that start over...I decide it's an 'outtie' not an 'innie' and I am not redoing this pattern and it's getting warm and the flies are biting and I want to get this done and boy do we have a nice machine shop at work...and let it ride and added a vent/riser that doubles as a 'sand to fit' mechanism and put a couple more oz's of aluminum into to the charge.

    Being that it is me, I go to try my new 4" thermocouple sheathed in graphite and just as I was going from preheat to measure, the graphite slides off into the soup. I rescued the graphite but holed an empty beverage koozie with a piece of hot dross. I go to pour, situation normal but did not get 100% fill in the baby riser but could see it had some metal and my basin was starting to mound up. I poured off a couple ingots and waited for it to stop smoking. Knocked the sand off the work off and besides the 'muffin top outtie' I had some good size shrinks.

    Reworking this piece gets the boat on the water faster but long term I'd like to learn from the mistakes and pattern and cast a version 2.

    It seems:
    1. Not enough draft angle and/or ramming between the vanes. Should I have used a core?
    2. Fillets seem small in retrospect
    3. Would I have needed a riser had I not had the 'muffin incident'?
    4.___________(appreciate and thank you in advance for any input)

    On a positive note, the pan from the 'sand manaagement' thread worked great.

    Some pictures, some with notes. Thanks!
    tops_o14_shakeout.jpg
    tops_o14_shrinks.jpg
    tops_o14_dragside.jpg
    tops_o14_sand.jpg
    tops_o14_rework.jpg
    tops_o14_fits.jpg
     
  2. Monty

    Monty Silver

    The shrinkage is from that big hunk of sand that broke off. The resulting thick section caused it to shrink. You need a big riser to feed a thick casting. That way the shrinkage happens in the riser not in the part. Otherwise the thick section will suck metal from the rest of the casting. When you cut that thick section open, it will probably be full of porosity. I would have used a larger riser, but if you didn't have that big thick section it probably would have worked. I'd try again after polishing the piss out of the pattern in that area. Sometimes you can put a bent wire or two in a section like that to help pull it out by tying it to the rest of the cavity/core.
     
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  3. FishbonzWV

    FishbonzWV Silver Banner Member

    1: Ram that area softly with your fingers and put a couple small screws in it (gagger) to bind it to the rest of the sand.
    2: Increase at least the inside fillets with super glue/baking soda or super glue/accelerator.
    3: No, the part is pretty even in cross section. I would have used a runner and cut gates to feed each flange.
    4: Overall, not a bad job considering the complexity.
    I do see some porosity, tweak your gas down a tad, that's a structural part and needs to be defect free.
     
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  4. Melterskelter

    Melterskelter Gold Banner Member

    To underscore above comments, in my experience, breakage of sand as shown is due to failure of the pattern maker (me) to adequately prep the pattern. Sometimes I look and initially think the pattern is fine, but careful inspection with a tangent light and fingertips will reveal an undercut, paint dribble, pock mark or something. Fixing the pattern fixes the problem. Gaggers (a good idea) might work to hide the problem, but if the pattern is slick and true, they should not be needed. And my bet is that, because there is a problem with the pattern, even with gaggers, the pattern will pull better but still not cleanly. Petro is so strong it should easily be moldable for this pattern.

    And, yes, nice work on a fairly tricky pattern.k

    Denis
     
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  5. Tops

    Tops Silver Banner Member

    Thanks for the replies, I really appreciate the tips and comments on the patterns. I admit that I did not spend much time filling and sanding these and the the FDM layer lines would not help the extraction as printed. Maybe I should clean these off and try one of the smoothing methods recently discussed. The other thought was to split the deeper features in half and draft them more towards the inside in CAD, add bigger fillets, and reprint.
     
  6. Tops

    Tops Silver Banner Member

    Phase 1 of salvor operations complete (bwahahaha!)
    I went to ask a machinist to drill a 11/16" (17.5mm) hole so I could band saw into the 'muffin', instead I got the gate sawn off and a a 11/16 cutter ran between the vanes and the bottom of the vanes around the slot, more or less to the parting line. Drag side down for machining. I think I committed to helping him fix a transom on an aluminum boat I was so excited to see it take more of its intended shape...
    tops_o14_rework1a.jpg
    tops_o14_rework1b.jpg
     
  7. Melterskelter

    Melterskelter Gold Banner Member

    Yes, many a cast part has been "recast" using a milling machine and welder. ;-) I would have done the same for a purely functional part.

    I do not know if you have commented on the apparent cold shut seen in the top photo almost in the center line of the horseshoe-shaped rim. For the intended use this probably does not matter, but it probably indicates your filling rate was slow (that sprue looks a bit on the small side and flow rates in "pipes" increases proportional to the fourth power of the radius. ) and/or your metal temp was low.

    Denis
     
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  8. Tops

    Tops Silver Banner Member

    I thought the sprue seemed small and then I thought I was over thinking it and just went with it. Size as rammed below, maybe a new sprue or two and try the fill thing...?
    image001.png
     
  9. Melterskelter

    Melterskelter Gold Banner Member

    I would think a piece of 1/2 copper pipe, wood dowel, or steel bar would do for forming the sprue. No need for taper. Just tap it a bit left and right, give it a slight twist and out. I know it is popular to use tapered sprues, but in this size sprue probably offers no tangible benefit. Simple is good.

    Denis
     
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  10. Tops

    Tops Silver Banner Member

    Denis, no comments, not exactly sure where you mean. Do you mean the spot just inside the big shrink or where I poked a dowel up through the horseshoe as a vent/indicator so I could see that the mold was full...?
     
  11. Petee716

    Petee716 Gold Banner Member

    I’m assuming it’s where the vent was. If you poked the hole after the pattern was pulled, my guess is that the mold cavity got dinged by the dowel and what we’re seeing is the effect of loose/jaggy sand. If that feature was wanted or needed I would have pushed a piece of brake line down from the top of the cope with the pattern still in the mold. Once the pattern is out I find that modifying the features of the mold near the cavity can be risky business.

    Pete
     
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  12. Melterskelter

    Melterskelter Gold Banner Member

    I guess I thought the "crack" in the casting in the horeshoe area furthest from the sprue was a cold shut. Maybe it was a sand defect of some kind. Hard to tell. But from the picture it looks to me as if there is almost an incompletely integrated rod-shaped maybe 1/4" diameter chunk of aluminum in that area. But, honestly it looks like an incomplete fusion of the metal there. I do agree with Pete that pushing something larger than 1/8" up out of the open mold can be chancey. Again, I know vents are advised as a necessary part of moldmaking. I often include them as 1/16" or 1/32" holes at the far end of a mold made with a pointed wire. But, about equally often it is impractical to make them or I forget and it does not seem to make any difference. I just pour until the pouring basin starts to fill completely and no longer strarts to empty as I back off on pour rate. Once the level of molten metal in the basin just sits there, the mold is full.

    I doubt you will need to pour this pattern again. Puring it again with some changes discussed above miught be interesting, though. If you do, try the larger straight sprue and no vent. Petro is so porous and breathes so well that I think the mold will fill just fine. The same is true for the green sand I use in my foundry.

    Denis
     
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  13. Tops

    Tops Silver Banner Member

    Yes, I poked a flat 3/16" [4.5mm] dowel though the sand after I pulled the horseshoe looking cope pattern. I saw it as a chance to have a warm and fuzzy indicator that the highest part of the flask was full. Then I saw it as a chance to add a little metal outside top center to tune the fit. I did not take pains to make sure sand was cleanly radiused after the poking.

    Kid was surprised I got this far...
     
  14. SRHacksaw

    SRHacksaw Silver

    I'
    I'd probably go with a 3/4" dowel. Half inch seems dinky for that casting. Though nowadays I do use a tapered sprue. I'd probably NOT ram hard between the vanes, just as I avoid ramming hard in greensand cores. Otherwise the core breaks off when you pull. Generally I use hand finger pressure to mold sand in, in locations like that, and use a rammer there only after they are covered.
     
  15. Melterskelter

    Melterskelter Gold Banner Member

    I do not follow your statement concerning a green sand core "breaks off when you pull."

    Denis
     
  16. SRHacksaw

    SRHacksaw Silver

    Tops, you said you were interested in the Gingery lathe, I think? If so 'you'll start out with some challenging greensand core work. If you ram too hard, what happens is the pressure against the sides of the pattern creates more friction when you pull, than the greensand has strength at its base to resist. So it breaks away. Here's the lathe way pattern. If the sand is packed hard into the spaces, it just won't pull.[​IMG]
     
  17. SRHacksaw

    SRHacksaw Silver

    Sorry Melterskelter, cross post, didn't see yours, but the above answers that, I think....?
     
  18. Melterskelter

    Melterskelter Gold Banner Member

    So, you realy were not talking about cores but about sand breaking when you draw a pattern not core.

    I still am puzzled by that statement about soft ramming as that does not square with my experience. Here is a casting I did yesterday that is 65 pounds as cast with gates and is 30x12x4" that I rammed very hard with a pneumatic rammer. Since each side of the mold is 5 inches deep, I actually first ram a layer that compact to about 3.5" and then, after roughening the surface, add the last 1.5 inches. If I try to ram it in one go 5" deep, the sand is too soft and prone to failure. True, I riddled on a layer of sand and then backing sand in the ususal fashion. As you may notice, that the pattern itself is relatively standard except that the built-up lip edge requires the use of 16 loose pieces besides the ususal two-part split pattern. In general I ram all of my patterns very firmly and, at least in my foundry, a soft mold is more prone to bits dislodging
    , collapsing etc. Not saying one way or the other is "right." But soft ramming does not work out well for me.

    Denis
    Side Gate Square1.JPG IMG_6516[1].JPG Square Pattern.jpg Side gate square2.JPG Side gate square4.JPG
     
  19. Tops

    Tops Silver Banner Member

    Here is the part, a ruler, the sprue used, and the proposed sizes of 1/2 and 3/4" [13 and 19mm]. Top of cope is line between masking and dark tape.
    Tops_o14_sprues.jpg
     
  20. Tops

    Tops Silver Banner Member

    Yes, thanks, interested as a process but I am not in a good spot to start one.
     

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