Melting Lead & adjusting cast iron weights - Page 1
Forum section: electronics / general

author: mendip_discovery
author_rank: Super Contributor
timestamp: August 25, 2024, 07:54:48 pm
content: At work, we have 500 kg of 20 kg cast iron weights. None of them is 20 kg, for example, the two I have here are 19.8877 kg and 20.3100 kg.It is a holiday weekend and I have the week off work so, I took 100 kg of these weights with me, a set of scales and a good 20 kg weight. The plan is to get them to Class M1 based on OIML specs which is 1000 mg at 20 kg but I will settle for any of the M classes (M2 at 3000 mg or M3 at 10,000 mg).To aid in this I have drilled a 10.8 mm hole ~80 mm deep into the cast iron weight and tapped the hole to M12 and used a M12 x 10 mm grub screw to seal it. This will be my way to make minor adjustments to the weight either by adding some lead shot or ball bearings. I have calculated that I have 27 g of void to play with.There is a cavity for lead under the weight but I wanted the ability to fine tune it in the future as I plan on getting an F1 class weight to do the comparisons with. Remember I just want to get them within a few grams. I melted the lead from the cavity using a MAP gas torch and let it fall into a tray with water.Used the known OK weight to zero the scales then placed the weight I wanted to adjust onto the scale and placed lead on the scale until I got the target weight. I put most of that back in with some extra lead and got it to around -10 g.Now to my problem, I poured the lead into the cavity and tried to heat it and the lead didn't solidify as well as I would have liked. Ended up using a hammer and a drift to mash it together. I am tempted to try heating the lead in an old saucepan and pour it into the cavity, would this be the better option?As I couldn't find any lead shot in the shed tonight I used two M3 bolts in the 10.8 mm x 80 mm hole I had and got it to spot on compared to the known weight, to the resolution of the scales I have which is 0.0001 kg. I checked the known weight after and it had all the zeros so no drift. Will check again tomorrow. Page 12,https://www.oiml.org/en/files/pdf_r/r111-1-e04.pdf 10.8 mm x 70 mm, 45.85 g (Cast Iron) - 72.83 g (Lead) = 26.98 g difference

author: coppercone2
author_rank: Super Contributor
timestamp: August 26, 2024, 07:05:49 am
content: If its dry and you pour it in there it should solidify OK, then you can beat it with a punch to expand it into the threads if its loose

author: BrokenYugo
author_rank: Super Contributor
timestamp: August 26, 2024, 03:20:06 pm
content: Why bother with melting it when you could fully thread the hole and just crank down the screw until the lead bits beneath deform enough to stop rattling?If you want to pour it in and get a nice clean slug at the bottom I think you'll have to preheat the "mold" to around lead melting temps.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 26, 2024, 03:32:50 pm
content: Heck, what does it even matter for it to rattle--? If it's stuck under a screw and the screw is tight, it's not going to loose any-- well, let's put it this way, it would have to shake enough to abrade particles off, and either gain weight by oxidation, or lose weight by shedding those particles through the threads, a most circuitous route I'm sure.And yeah, pouring metal into a chill (room temperature iron) isn't going to settle, it at least needs to be preheated if you expect any settling. I'd wonder if they should be heated much at all, due to weight change -- both desorbing and combusting organics on it, and oxidizing the metal? But I'm not familiar with the exact parts here, just metals generally; there may be standard practice with these, I don't know. It's not like single grams are wildly precise, either.Tim

author: coppercone2
author_rank: Super Contributor
timestamp: August 26, 2024, 08:30:08 pm
content: I think it will work if you just pour it in, maybe it wont be as nice but it should mostly work. Its not like you need to take it out of there. What will mess it up is if its wet. Its a requirement for a complex mold, but why bother for a cylinder fill? I think its a problem, if your mold is narrow in the entrance and expands. if its just a cylinder it should hardly matter

author: mendip_discovery
author_rank: Super Contributor
timestamp: August 27, 2024, 08:05:09 pm
content: So far I have just cut lumps off the ignots I have and using a drift I have mashed them in and they are holding.As it seems to be unclear. There is a cavity under the weight for adding lead and that is where I am doing the majority of adjustment. To around minus 10 grams.I have drilled and tapped a hole at the top so that I could feed lead shot to fine adjust the weight and allow for adjustments later once I get a better weight for comparison. For the moment I have used steel bearings.