Gloomisman Posted July 12, 2010 Report Share Posted July 12, 2010 Guys, I'm seeking your knowledge once again. I have 2 one sided molds that when I pour them I can not get the weight out of them. I have tried cooling the mold and lead to shrink it but it still does not come out. Next I am going to polish the mold inside to make sure there is no spurs holding the weight. What other suggestions do you have? Quote Link to comment Share on other sites More sharing options...
Jig Man Posted July 12, 2010 Report Share Posted July 12, 2010 G have you smoked with candle wax? Quote Link to comment Share on other sites More sharing options...
powerworm Posted July 13, 2010 Report Share Posted July 13, 2010 i agree with jig man...hold the cavity side over a candle flame and get it black with sootthen try pouring your items and see if they dont come out for you!! let us know how it goes...PW Quote Link to comment Share on other sites More sharing options...
Ogajiga Posted July 13, 2010 Report Share Posted July 13, 2010 I once ruined a mold by Dremeling out a bit too much metal - resulted in the deeper part of the mold cavity being wider than the top face. You can figure the result. Quote Link to comment Share on other sites More sharing options...
smalljaw Posted July 13, 2010 Report Share Posted July 13, 2010 Why don't you try the mold release spray, so far just about everyone who has tried it claims it works perfectly so it may be a solution to your problem. Quote Link to comment Share on other sites More sharing options...
Gloomisman Posted July 13, 2010 Author Report Share Posted July 13, 2010 (edited) Jigman. LOL no i havent. Out of the hundred I've resmoked molds some reason I had a moron moment with this one. I just aquired some release from a buddy and I will try that first and then if that doesnt work I will try smoking them. I did polish the mold up yesterday. I used a file and emory cloth. No dremel here for the reason Hawn stated. You can mess one up quick. It took me 3 hrs but hey its worth it. LOL. Thanks guys and I'll keep you updated. hopefully I can pour some of these this week or early next week. Edited July 13, 2010 by Gloomisman Quote Link to comment Share on other sites More sharing options...
Ogajiga Posted July 15, 2010 Report Share Posted July 15, 2010 (edited) Coincidentally, I just ran into a sticking problem when I switched from pouring lead to bismuth/tin alloy in a custom brass mold. Unlike shrinking lead, bismuth expands when cooling, & the sprue would break off leaving the 1/4 oz. jig head so stuck only a hammered awl on the break scar could release the casting. Candle smoking didn't help. Finally spent many hours leveling out high spots with Dremel cutters(manually like GL Man)& finish polishing with rubbing compound & a wooden matchstick, and Voila, problem solved, today in fact. Well actually, it took about four attempts & a lot of 4 letter words... So, I would conclude that sticking castings, especially lead, are the result of mold cavity defects which should be repaired. Think of freezing water in it's plastic bottle, no way the ice can be removed with the ridges and necked down opening. Do-its generally don't have serious design or production defects problems, but I've gotten a few with excessive "orange peel" ruff textured cavities that needed smoothing & polishing to release castings smoothly, mostly bismuth alloy, tho a really ruff one can grip lead pretty good too. Edited July 15, 2010 by hawnjigs Quote Link to comment Share on other sites More sharing options...
Ogajiga Posted July 16, 2010 Report Share Posted July 16, 2010 In case anyone is wondering how a custom machined mold could need repair, it actually wasn't being a melt cast brass mold. The cavity face had irregularities from the cooling metal which didn't significantly affect lead pouring other than cosmetically, but the little bumps & ridges had to be smoothed out to mitigate bismuth alloy sticking. Quote Link to comment Share on other sites More sharing options...
Gloomisman Posted July 19, 2010 Author Report Share Posted July 19, 2010 Well i got it working guys. The polishing helped and fixed the problem. The cast aluminum was so pitted the lead would not shrink that much as it cooled. After I polished it the weights fall right out when cooled. Workin like a champ now. Thanks!!!!!!!!! I also used a release agent but I dont think it made a difference. Quote Link to comment Share on other sites More sharing options...
Ogajiga Posted July 26, 2010 Report Share Posted July 26, 2010 Don't know if this info is useful to anyone, since most don't pour bismuth alloys or use brass molds, but...the "fixed" mold which released a few test castings OK previously locked up jig heads again when hot, just as bad as before. I have no idea why, since lead releases butter smooth and all the Do-its I use to pour bismuth don't stick enuf to be a problem. The small 1/4 oz. jig head design is simple, no features that I can see that would grab enuf to lock in a casting. Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted July 26, 2010 Report Share Posted July 26, 2010 (edited) I think it is all down to the expansion that you talked about in an earlier post (No7). If the cross section is round, then at the split line their is no draft angle and the expansion presses out and grips the mold. I googled bismuth and the expansion is 3.32%, which is considerable. I do not know what the expansion would be with an alloy, but I think that this is the problem. As you mentioned this fact earlier, I think you do too. If this is a big problem, then more doctoring of the mold will be required, to introduce draft angle. Dave Edited July 26, 2010 by Vodkaman Quote Link to comment Share on other sites More sharing options...
Ogajiga Posted July 27, 2010 Report Share Posted July 27, 2010 Yes, the Bi95 Sn5 alloy is probably close to pure bismuth expansion. I thought the physical obstruction features in the mold cavity + adding draft angle were addressed by grinding & smoothing, but apparently not enuf. I'm wondering if brass adheres bismuth more than aluminum at a molecular or atomic level, considering that the hotter the brass mold gets the greater the locking problem? Think I'm done modifying - the formerly flat bottom jig head is starting to look keeled. Quote Link to comment Share on other sites More sharing options...
