It is surprising what thin sections will fill. Did you try the scope mount without the extra runner? You can accurately cast holes within several thousandths too.
I was actually surprised to get two that filled right off the hop like that, but then..my entire (although limited) experience with LF has been pretty positive. Have not tried the scope rail again....yet. I was wanting to get a thin backer board to avoid making "apprentice marks" on the mill table, and haven't been to town in a week. Getting a bunch of pieces ready, so will likely cut another out with the hotwire. I don't think I want to cast the holes for the trigger group pivot pins, but have been "pecking" one of the side pieces at the pin locations to make drilling/reaming a simpler task down the road...the little pecks show up quite well and no possible alignment issues. Al
I've done a couple hundred lost foam castings and my experience was it always exceeds my expectations unless I'm really unreasonable. My failures have been from pouring too cool, shallow burial, and occasional gas pockets and shrinkage where the sprue meets the part. It's best to let gas vent back up the sprue. Yeah, it's pretty easy to put a center punch mark in with a pencil point, or a compass point when you're drawing a circle. I have a habit of doing pencil layout on the foam and the layout lines, however light, are preserved for posterity. I have a little concern that a triangle set of holes may show some movement between the foam and the aluminum. I think the foam can crawl inside the plaster as it's melting. I've noticed some evidence of that.
OIF, I think you have been seriously holding back on us. As we say, pictures or it didn't happen! Best, Kelly
What??? 24 pair on this project A shelf for a pharmacy, it's what she wanted I stamped her employees' and kids' names, one per bracket They enjoyed finding their names Lost foam is so incredibly easy. Most of my stuff is just hot wire cut and stuck together and is a bit crude but it works. Stamping lettering on is especially useful. Not posted because it's nothing special. But a little volume does help.
Well there ya-go. The corollary to pictures or it didn't happen is pictures and it did.......back to regularly scheduled programming. Best, Kelly
That's a good looking shelf. Did you coat those brackets before casting? If you did not coat them, what are you using for sand? Surface finish looks pretty good in the picture. A lot can be done with a hotwire and some simple patterns for certain...but the cnc does such a nice job. Did a bit more pattern making today, couple mistakes too. Notice anything wrong with the sprued scope rail lol. Finally making wheels for the furnace too. Al
I brush sheetrock mud on everything. Until I get a vat set up, that is. Then I expect to dip. The only foam I've cut out on my CNC router was for some gear patterns. I'm just too slow at the programming but it does make some super nice cuts. I do use a 3D printer to make reverse stamps for marking foam. But I like to cut out letters from thin foam like the owner's initials on this transmission mount.
Nice to add that personal touch for folks, results in some smiles I'm sure. Have some sanding to do, but will be having a go at dipping as well. Admittedly curious to see how that works out for everyone. Al
If it worked for Kelly it will work for you and me. It will finally Dawn on you that the right amounts of surfactant and water are the keys. I think the type of drywall mud is pretty much irrelevant so long as it stays plastic while wet and does not set like plaster.
Not calling you out. Just wanted to see the raw castings just as they came out of the sand. Want to see color of mud and any carbon residue on the casting and feed system. PM me if you have them. How you planning to sprue your wheels? ....center of the hub or at top of OD with them tilted 45 degrees? Best, Kelly
OIF....It Dawned on me what you did there. lol My drywall mud is much like everyone elses...pre-mix and about 8yrs old. Seems to be working thus far, and I've half a pail or so un-thinned yet. Should last a while. Kelly... Going to sprue straight off the hub for about an inch, then use a foam cup. Tossing around adding 3-4 runners from the rim to the foam cup as well. I know they won't vent anything until it's all full of metal and too late, just extra metal to the rim. Will be a test for the air vibrator too. Essentially what they did with this investment casting; Regards, Al
That's not me, it's a friend. He had made a steel transmission cross member (in his right hand) for a 57 Chevy street rod he's building. I suggested we make an aluminum one, and as I said, put his initials on it. It was a challenge because the brackets he put on the frame were neither level nor parallel, and the transmission tail shaft is angled down 4 degrees and not centered. He had mailed me his steel one and I used it to duplicate the odd angles.
I've got a few pictures. but the second one pretty much shows the feed system. I poured them four per sprue with two buckets of sand so two pours per heat.
I like sprue/gating discussion. You're not asking but I'll try not to let that stop me. Here's four options. Arrows are sprue and red region is potential for unstable mold media....leakers as we say. They're ordered from worst to best (IMO), but 3 would probably be my preference. Here's why. First priority is usually positioning to facilitate best mold packing. Then spruing into the highest point of the part and better yet if it is a massive area and/or the intersection of features that feed the rest of the part. Also preferred is minimizing the number of times the metal front must divide and rejoin, though assessing this can be nebulous and sometimes you just can't feed the part well enough without doing so. If the wheel wasn't open spoked, #1 would be the absolute worst because of the lesser ability to pack under the web/spokes, but the open area between the spokes helps. I like feeding into the hub because it is massive and the spokes are like natural gates to the rim. This is ok but the area under the top of the rim is more prone to mold instability and there isn't as massive of an area to feed the part. If this was attempted, position a spoke directly under the in-gate. Tilting can minimize the depth of undercut areas. I like feeding the hub for the same reason as #1. It also minimizes casting clean up. It needs a longer sprue because the hub is below the highest point in the part. This seems to be the most consistent approach for successful first time runs. It can occasionally pose a problem for feeding massive areas a long way from the sprue. The fact that this part is open spoked and small, it's quite possible any of them would work just fine. I wouldn't bother with them. Some things from other forms of casting don't always translate well to LF. There probably is as much chance it will hurt rather than help. It splits the metal front. In top gated parts, once the metal front stabilizes and starts evaporating and consuming the foam, the fill can be very tranquil and non-turbulent if it is adequately vented through the coating. When this is the case, LF has natural directional solidification and shrinkage in thick sections is rare, unlike it would be in conventional sand casting. Is this the one you built? Build thread please !!! ....and video with picture of the sand dancing. Best, Kelly
Feel free to chime in, advice from people with experience is never a bad thing. I tossed around a bunch of things, trying to picture how the foam would be vaporizing, how the metal would be advancing, where it would be shrinking...at the end of it I looked at my 3" wheel and the foam cup I was going to attach and decided I was likely seriously over thinking things lol. The one I sprued up is just flat into the hub with no risers. The pattern is one that didn't turn out as well as I'd hoped, so no big loss if it ends up as a funny looking ingot. I agree that from an undercut/leaker perspective it's probably about as bad as it could get, but I need some experience with that...I find that I learn more from failure than from success. Finding the limits of "possible" as it were, pretty much still shake my head in wonder that the LF process works at all lol. The air vibrator is the one I built, it runs and vibrates...will be interesting to see how it works with a pail of sand. Al
I did another pour the other day, did a spare wheel, scope rail and the trigger housings. Scope rail came out a tiny bit twisted (my fault) but has a bit of machining allowance on it so might still be salvageable. Trigger housings had a very thin single dipped coat on them and ended up with a varying amount of very small leakers through the coating...some brushed off, the rest came off with a file. Scope rail and wheel were double dipped, and neither had leakers. The spare wheel (fifth...not a third ) was an experiment cutting the whole thing with a ball nose cutter and had some ridges on the flats of the spokes. I expected it to fail being poured flat and once again was pleasantly surprised. Maybe I need to stop expecting the process to fail lol. I think what might be the cause of the leakers was too much Dawn in the mix and resulting entrained air bubbles. Tried to degas the mix with my vacuum pump, but couldn't get a decent seal on the container and the vacuum pump doesn't move a lot of volume so not much effect. The big shop vac was able to pull some vacuum on the container and I left it for a few minutes but this seemed to have barely any effect. A more sturdy container with better sealing is on the list of things I'll be looking for. Heated the melt to 1580F, turned the burner off, skimmed in the furnace and poured straight away. Al
From what I can see from the pictures, the castings look good. I'd have to see the flaw to make sure we're talking about the same thing when we say "leaker". I picked that expression up from FishbonzWV, but it refers to an area where the mold is insufficiently packed, the sand is unstable and moves, and appears to allow the metal to leak into the sand mold causing a flaw that protrudes from casting that looks like a small pile of sand stuck to the surface. They usually occur under overhangs. Without seeing the flaw I can't really say, (post a close up) but bubbles or slight flaws in the coating usually just show up like a pebble stuck to the casting surface or small surface flaw. Here's an example of a small leaker under an overhang on the second Automotive Upright I cast. If the flaw is a leaker, the pattern needs to be positioned differently in the mold, buried deeper in the mold, vibrated more vigorously to better pack the mold, or combinations of the three. BTW, having a success when you thought it failed is a common occurrence for a LF caster......I'm still amazed that the process work's as well as it does. Best, Kelly
