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Cast thumbscrew permanent mold

Picking away at this thing on my desk today, and exposing more of the crater I'm now pretty sure, about 98% that it was simply a bubble that got caught on the bolt head, that wasn't able to get out before the sprue froze up. It's tough to draw big conclusions from such a small sample size, but I'm curious to cast a few more to get a better idea before I draw too many conclusions. I'm going to have a steel rod handy when I cast the next one to poke down into the sprue right after pouring to hopefully pop any bubble that might exist.
How about drilling threaded rod with side pin, so material can flow abound the (obstacle) better?

My second though is to preheat whole thing to 500 in your oven. (the one in your shop)

Dan Dubeau

Ultra Member
I think I'm going to have to that for the 3/8" for sure one as a 3/8" bolt and capscrew head take up the entire cavity almost. Not much room for aluminum to flow around it. A SHCS head will surely catch a bubble and not fill, so there won't be much there to anti rotate it anyway. A roll pin in a cross drilled hole will be perfect. More labour for me, but.....I've come this far lol.

Sticking it my toaster oven would be the best way, but I've only got an already loaded 15amp circuit feeding the entire garage (lights and all). Running that and the foundry will be a no go. I could run another one out there pretty easy, and I've been puting it off for too long I'm running out of good excuses. I've only tripped the breaker once while I had the foundry going, and was turning something on the lathe at the time. I could stick it in the propane forge for a bit too. Weed burner torch is probably the way to go though, I'll set it up on some fire bricks and hit it for about 5 minutes prior to pouring. I'll try and find my infrared themometer to better gauge the preheat temps.

Tom O

Ultra Member
I’m having a brain fart! I’m thinking if you milled off two sides of the bolt head that would reduce the metal flowing around the head and would probably have a better grip being two tangs rather than a bolt head being basically round.

Dan Dubeau

Ultra Member
That might net an improvement for filling. I could try. I'd probably just cut them off with a grinder, as the molten aluminum would hide it anyway. Would probably never torque these up enough to strip the bolt head though. I'm not that strong lol.


Premium Member
Would it work to drill a small hole at an angle from the center of the bolt head thru to the side of the bolt shoulder? That would give the air a path to escape.