Dan Dubeau
Ultra Member
Here's a project I've been thinking about for a while, and finally got around to "completing". When casting, it's always bothered me wasting the last of a pour on ingots, seems like a waste of energy when I could be making other small frequently used objects. So I came up with a short list of small volume things that should be easily castable in a simple dump mold. I made the mold body a few weeks ago, and finally got around to cutting the cavity last weekend. This morning I turned the threaded inserts. A typical timline of projects I work on.....I made 1/4", 5/16, and 3/8" unc inserts, and once I prove that it works, will make some metric ones as needed. They are 3/4" od O1 drill rod scraps, and ride in a 0.751" dia reamed hole in the mold.
You can vary the shoulder length of of the thumbscrew simple by moving the inserts up and down in the mold and locking it down with the screw from the side.
While I made the inserts I flipped the little foundry on to melt down some scrap.
Once those were done, I leveled the mold in my sand box, and poured the heat to it with a torch for a good while to burn off the condensation and preheat it for pouring. When the crucible came up to temp, I scraped the dross, and gave it a dump.
It filled too quick and I was 100% sure that the "sprue" (all 1/2"x1/2" of it) froze up and sealed off the cavity instantly. I poured off the rest in the sand (charged the crucible with more than I thought....) and tossed the mold into the snowbank out front.
Once cooled down, I took it back inside, and started undoing the mold and was pleasantly surprised by the percent of fill I actually got considering I thought it was a bust, but disappointed at the same time. I have some ideas....
I was happy with the ease at which the halves separated. The threaded insert simply unscrews. There is no draft on the shoulder bore, I'm simply relying on shrinkage to release the part.
The extra on the topside can be easily cold chiseled off flush with the top showing the mighty sprue in all it's glory.
I cut that off with a hacksaw, and chucked it in the lathe for a quick face and while not pretty, it's a "thumb screw". Not a nice one, but useable for a shop made jig or fixture.
Yes it's not perfect, and no matter what I do I'll probably have shrink dimples simply due to the fact I don't have a big riser to feed the cavity as it cools. I'm going to open up the sprue to as big as I can, and I think that should help fill the entire cavity better. The top is "flat" and I have to face off the head anyway, so it doesn't really matter having to face off a larger dia sprue. That might also help feed the casting as it cools too. I'll play around with it a bit more, but I consider it an 80% success at this point, especially for a first pour, and think I can nudge that # closer to mid 90's.
I didn't set out to make saleable thumbscrews to put carrlane out of business. Just looking for a way to use my melts a bit more efficiently and end up with something useful instead of dumping off ingots after pouring a mold. I have a few more ideas for other dump molds too, and now that I know it's viable will chip away at them in my "free time"
.
I'll continue to post my experiments with this mold, and others. I have some thumbscrews to cast for a belt grinder build coming up, so I'll post those too. Might be a few more weeks though....
You can vary the shoulder length of of the thumbscrew simple by moving the inserts up and down in the mold and locking it down with the screw from the side.
While I made the inserts I flipped the little foundry on to melt down some scrap.
Once those were done, I leveled the mold in my sand box, and poured the heat to it with a torch for a good while to burn off the condensation and preheat it for pouring. When the crucible came up to temp, I scraped the dross, and gave it a dump.
It filled too quick and I was 100% sure that the "sprue" (all 1/2"x1/2" of it) froze up and sealed off the cavity instantly. I poured off the rest in the sand (charged the crucible with more than I thought....) and tossed the mold into the snowbank out front.
Once cooled down, I took it back inside, and started undoing the mold and was pleasantly surprised by the percent of fill I actually got considering I thought it was a bust, but disappointed at the same time. I have some ideas....
I was happy with the ease at which the halves separated. The threaded insert simply unscrews. There is no draft on the shoulder bore, I'm simply relying on shrinkage to release the part.
The extra on the topside can be easily cold chiseled off flush with the top showing the mighty sprue in all it's glory.
I cut that off with a hacksaw, and chucked it in the lathe for a quick face and while not pretty, it's a "thumb screw". Not a nice one, but useable for a shop made jig or fixture.
Yes it's not perfect, and no matter what I do I'll probably have shrink dimples simply due to the fact I don't have a big riser to feed the cavity as it cools. I'm going to open up the sprue to as big as I can, and I think that should help fill the entire cavity better. The top is "flat" and I have to face off the head anyway, so it doesn't really matter having to face off a larger dia sprue. That might also help feed the casting as it cools too. I'll play around with it a bit more, but I consider it an 80% success at this point, especially for a first pour, and think I can nudge that # closer to mid 90's.
I didn't set out to make saleable thumbscrews to put carrlane out of business. Just looking for a way to use my melts a bit more efficiently and end up with something useful instead of dumping off ingots after pouring a mold. I have a few more ideas for other dump molds too, and now that I know it's viable will chip away at them in my "free time"
.I'll continue to post my experiments with this mold, and others. I have some thumbscrews to cast for a belt grinder build coming up, so I'll post those too. Might be a few more weeks though....
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