Decided not to treat the previous work as sacred, broke through the analysis paralysis and took a couple whacks at it. Besides, the 'wineglass' shape at the boss seems more appealing than a mis-shaped 'superman' logo... Used the base against the fence on the table saw to cut off the top, then figured out I could use a spacer board on the miter saw to accomplish the same thing for the base and to initiate the relief for the new base. Disk/belt sander was once again the hero for sanding draft angles on the new base. No hurry as I am off to work so plain old wood glue and squared up to the table on the saw.
Looks like a good and simple plan. I don’t know if you have a table saw sled or not. However, I made a simple one (no fancy Kreg brand stop) many years ago and have used it thousands of times. It would make cut off of the top and bottom easier to hold and safer. Mine was made from 3/4” plywood and has hundreds of holes in it from temporary stops, fences, and guides that I have attached one time or another to set up all sorts of cuts. Incidentally, I just clamp a wood block to its fence to act as a stop for multiple cuts of a single length. Here is a one of many links to a decent design. There are many variations. Denis
Thanks Denis. Yes, a sled would be good, never really trusted the miter gauge to deliver odd stuff to the blade. I do not have one but there really is not an excuse. I even have a spare Destaco type toggle clamp to rig on it. I added the brad nails, shot one through the side of the main rib, and tried the baking soda and Superglue repair method as well as the epoxy fillets. In a moment of clarity I added the Bondo going the other direction before the epoxy and tape on the ends to keep the epoxy in place until it gels. With 5g resin and 2.2g hardener mixed and applied, I still had enough to fill one more (half walnut in-the-shell) hole in the garage floor.
All of the recommended patching/filleting materials sanded better than my last round of PE laminating resin+glass spheres+fumed silica. Pattern is painted (a little too much, operator error) and out to dry, regretting not having a shellac or lacquer or something that dries quicker than my old standby Rustoleum. Also got to mull my Petrobond and another batch of green sand which is now airing out in some plastic sleds as it still seems too damp after a couple days and mulling sessions.
Looks like 11oz Alu in the part and 4oz in a sprue-gate-riser (425g total) assuming about .625" (16mm) diameter for each. Flasks are 3" (75mm) deep each cope and drag. - how big diameter for the sprue? Is above ok with a pour cup and taper? -about how long should it take to pour? This will be my largest Alu pour to date. I have done bigger in lead but the molds were more open.
Watched the video, 3D printed a tapered sprue and cup cutter last night. I rammed up the flask, melted, and poured today. For starters I need a longer screed and a cleaner tabletop... I also did not figure on needing 25+ pounds of sand to load the flask. The pour went reasonably well. raining outside and under a large overhang if that matters, making sure not to mix rain and hot metal.. Results are as shown, shrink on the back, missing corners in the front, generally rough finish. I think I messed up most by not having the sprue and gate go to the bottom of the pattern as poured. The sand may be a touch damp as well. Appreciate any other tips to make the next 1 or 2 come out better. I will work on a one size bigger tapered sprue as well.
Hmm, did sand break off your cavity along the base of your flange? That sand ended up at the ends of the flange. The pattern looks like it pulled pretty cleanly. But I have sometimes experienced fractures along edges like that. Next time look really closely there to see if the sand is cracked after you draw the pattern. The shrink itself wouldn't matter from a functional point of view. But to get rid of it you could place a riser right over it maybe 1.5 wide, round and 1.5 high. You could alternatively use simila-sized blind hot riser right at the entry point of the gate. Sprue taper is nice, I guess, but could just as well be a 1/2" straight hole cut with a piece of conduit/pipe. A piece of 1x2 or angle iron makes a good striking tool as does a 1/8 x 1 flat bar or steel ruler, etc. Nothing fancy needed. Let's see what other folks say. What temp was your metal? Overall, not a bad result for the first attempt on this pattern! Denis
You can save sand by taking 1/2" off the drag. My flasks are 3 1/2 cope x 2 1/2" drag. I avoid melting when the humidity is high, it adds H2 to the melt. One of the biggest things I see is you molded in the drag. Ram the drag solid, place the pattern in the cope. Open it up and cut a runner in the drag from the sprue past the entry point of the gate in the cope.
The first thing that struck me was going straight into the mold. That’s a lot of force striking your mold features that can cause erosion among other things. A gating strategy that includes a runner helps to slow the metal as FB illustrated. The metal not reaching the top of the riser is a bit of a mystery. You may or may not have noticed, but is there shrink at the point where the riser meets the casting? The metal in the riser that you were counting on feeding the casting may have frozen long before it was needed. I can’t tell from the pictures. A point that you may or may not have heard discussed is venting. Especially if you are using greensand (vs petrobond), and especially if your sand is on the wet side. Permeability is a feature of the sand and the more moisture, the less permeable it is. The riser on the end lets the air out of the cavity, and that’s all well and good, but gasses including steam have to be able to escape. While the pattern is still in the mold I use a piece of coat hanger and poke holes generously in the cope down to within 1/4” of the pattern without touching it. Not everyone seems to do it, but it’s a recommended practice and worthy of research and discussion. Pete
Thanks Everyone, looking forward to trying again with all of the suggestions: Denis: Check sand for cracks, angle iron striker, blind risers if needed, slightly bigger sprue and/or cut with 1/2" EMT, check temp (do not have pyrometer yet...) Fish: Reverse mold cope for drag, thinner drag rammed solid, runner in drag past gate, lower humidity Pete: Pattern in cope, more runner, venting More 'kindergarten art' to see if I understand the comments:
Part of learning to cast is finding out what the fix is. If you throw too many alterations at it you never learn what actually fixed it. Variation one: suspect sand is a little damp...mull it without adding water Variation two: changing the pattern to the cope with runner and gate Variation three: add the vents Pete recommended If you get a decent cast now, it's fixed. If you have shrinkage then start adding risers to control the shrink.
I rammed it up again with the following changes: -drier sand (proved to be a little too dry, crumbly at the edges and while adding features like the pour basin), first 1/4" ran through 40 mesh screen to make 'facing' sand -bigger sprue (1/2" EMT) , pour basin, and much bigger gate that was lowest spot in pour -inclined flask and mold board 1/4" up on riser end The casting filled in better and smoother than last time, even with the sprue seeming a size too big as I could not keep up with it during the pour. Still a shrink on the back face near the gate. Most of the issues are 'outies' instead of 'inies' so they should clean up easily.
Much better result! That shrink is not a functional problem. If you can tig, just tig it in on the piece and use a riser there next time. I find it much easier to keep up with the pour if I use a large pouring basin with tumblehome sides. I know some folks successfully pour using little keyhole-shaped pouring basins. I suppose that style "wastes" the least metal to fill the basin. But, for me, a big basin with tumblehome sides works far better. That way I can dump a fair bit of metal into it and it has the capacity to then allow the mold to fill and I can see it starting to empty and I can speed up my pour. With a small basin the difference between overfull and empty is an ounce or two. It is hard to regulate a pour that tightly. With a big basin it is maybe 4 or 8 ounces by volume. Using 3.5 x3.5" basin 1.25" deep I can pour 28 pounds of iron in standing seven feet away 7 seconds using a trolley. That does not mean I am particularly coordinated---nope, the basin is very forgiving. The volume really helps and the tumblehome strongly reduces the tendency for metal to slop out as I begin to fill the basin rapidly. Vertical sides are better than outward sloping sides. But when you imagine that first splash of metal hitting the bottom of the basin it shoots out laterally. If it hits an outward sloping side it is guaranteed to slop out. The tumblehome curves that splash back into the basin. It took me a couple years to figure that out. You might not need quite that big a basin. But give it a try. Makes life a lot easier. Then when you become a real expert, go to the keyhole. Me, I'm staying with a big target---more hits that way. Denis
Outies are better than innies any day. You would be a better judge of the overall surface finish than us because you have the piece in-hand, but I like what I’m seeing on the bottom side of the circular feature. As Fishbonz said, too many changes at once can confuse the observations, and you feel like your sand may have been on the dry side, but I think it may have helped. Melt temperature and source of feed metal will make a difference as well from one test to the next. Temperature can be a bit of a wildcard without a pyrometer. Some “light” reading: https://maritime.org/doc/foundry/index.htm ChapterI on metal solidification and chapter VII on gates, risers, and chills. Figure 143 provides a helpful illustration. There’s a lot of information to digest, but it’s a great resource. (I’d stick with the guidance your getting from Bonz and Denis on this job. No need to over complicate things.) I think what Tops and Denis are calling a pouring basin are two different things. Having dug into the mold at the bottom of the sprue created a loose sand situation in that cavity. Then the force of the directly poured metal just dragged it in, visible on the gusset feature. Looks much better Tops. Pete
Thanks Denis. You get extra points for using the word 'tumblehome' Thanks Pete. I did reduce the number of changes after reading that post. Surface finish seems better to me and probably just an extra 30 seconds with a sieve. Thanks Fishbonz. I had intentions to go this way, but a couple things sent me back to 'dancing with the devil I know', mainly not wanting to mess with the riser. I do appreciate the advice, especially the thoughts about not changing so much that the real solution is buried in the other activities. It seems that gating was the biggest deal to improving the second one. The shrink showing up in the same spot was also educational. Does this second picture match better what you would have me read and do in the bold letters? I don't think I understood it 100% before.
In case there is any confusion concerning the idea I was trying to express in words: To get rid of the shrink in the casting, I think making the gate into a "risergate" (not to be confused with Watergate) would move the area of last-freezing metal out of the casting and into the risergate(a word I just now made up that should not be repeated). You can see that the area of greatest mass/surface area ration is right where the shrink occurred. By making the area of greatest mass/surface area adjacent to the casting, the casting will freeze from the far end to the gate and then the riser/gate combo will freeze. Denis
