Hi Anthony,
“””””””” brian thought that density difference was crazy. to me, it's not that surprising. density accuracy is going to depend on the weight and volume accuracy. so a combined diff of 10% doesn't seem that bad to me.””””””

Thats good perspective also. It was kindof how we had been doing it in the past. Understanding there are variables, but we could get it close.

When .2 ounces became sortof large to explain, i had to dig in deeper to gain more understanding.

So just for your information, here is how “the numbers” come about.

My brother has to make a lead mold. They are “canoe leads” that go on throw nets here in Hawaii. (The guys like to be very particular about the weight being “exact”!


Using the volume of the cad model given to us from our CAM software (and now MoI also) we scale the model to meet desired shape and dims to produce a volume that when plugged into a conversion calculator (the aqua one being mentioned is just one of thousands online) we can generate a model that “should” be x ounces when we cut a closed mold on the cnc.

Previously got him setup by doing some trial and error cuts and going back and forth on volume till he got “x ounces” from a pour. Then i told him, your lead is different by this much, so compensate. But that “compensation grew and grew because it was incorrect for future calcs.

The lead is sourced by diving in fishing spots and picking lost leads, then melting it down, scraping out coral and rubbish, and pouring the mold.

If “7 ounces” was the goal, we could get leads out at 7.02 ounces and just explain “results may vary”

.2 ounces was too much. I have to help him track down what is not right (yesterday)

You have directed me towards the density part, which had me understand better what i am looking at (and also understand how the number could have gotten so far off from what was expected (different density partially, but in combination with bad procedure of “scaling models” too, doubles the error then 2 and a half years later “nothing is right” lol….

I am reworking what will be done from scratch, with less variable from the proper “density”.

Anyway, long winded. But suffice it to say, you helped me a great deal on this. Thanks again.

oh thanks a lot. that was super helpful in understanding what is going on. i was getting lost at various points in the thread. so you have about 10x the variance than you want. .2 oz vs .02 oz. so yeah, that's a big problem. if it's possible to make a very simple cube as a test. that would help with measuring the density more. as a start to the whole process though, it would be a good idea to use whatever the stated density of lead is. that should be pretty reliable. using your measured density, at this point, seems too unreliable right now. i thought the model volume was well known and the weight measurement at least normal. i imagine your weight measurements are fine. it sounds like they have a way of measuring weight that they like. so no reason to change it. it is possible the lead density is varying, based on the unknown nature of your material and the debris that may be in there. hmm, tricky problem. not sure i can be of much help. it sounds fun though. i guess, right now, the only thing density is doing is telling you that there is probably a problem with your volume. of course assuming the weight measurement is decent. it's good that you are talking about low weights. the scales work better in that situation. you can find the scale resolution in the spec sheets. they also sell calibration weights. so that you can make sure the scale is working right. it would be very worthwhile to get those, at this point. they sell them on amazon. i think they are made of brass. sometimes they come in a set. having the set is nice because the scale error isn't always a constant.

hi again,

i had a little time to play with the numbers. i attached a LibreOffice Calc spreadsheet. Not sure if you will be able to open it or not. It should open in Excel though. I'm showing that if you just use the stated density of lead, it wouldn't take much of a volume difference to explain the difference you have (7.2oz vs 7.02oz). It would only take a volume difference of 2.56%. if the object were a cube, the length of each side would only have to be off by 0.85%. given 'you are not going to mars', this seems reasonable to me. the spreadsheet might have errors. i didn't spend a lot of time checking it. the unit conversions were from a quick search of the internet and the density was from an even quicker search.

maybe the calculator will help some in the future though.

anthony

updated the spreadsheet 1; added some more info about typical scales. added some more notes. fixed formatting issues
updated the spreadsheet 2; added more info, comparisons, and calculators
updated the spreadsheet 3; added more comparisons

https://drive.proton.me/urls/TEB0GX5Z4M#vqxN6Xru2rf5

i'll leave the link active for a few months. i don't keep things stored there for too long, due to space constraints.

Thanks Anthony!
I’ll take a look at the spreadsheet later. I’ll also post back to you if i discover the culprit in my workflow.

Hopefully it is legit and not something like a lack of attention

hi burrman,

i've updated the spreadsheet several times. this most recent update, i should mention something. brian's earlier post was comparing 2.2oz vs 2.0oz. that leads to a 10% diff in density or volume. Later, you compared 7.2oz to 7.02oz. that leads to a 2.56% diff in density or volume. the math is the same, it's just what two numbers are being compared. I added this into the spreadsheet. in reality; mass, density, and volume are all unknown to some degree. so you end up going in circles. you have to at least lie to yourself a little and say you know two things, in order to 'measure' the third thing. you can't not know all three things. there is only one equation so you can only have one unknown.

i think someone mentioned this, but you said your measurements are in ounces. so technically you are measuring mass, if the units are right. however, a lot of scales are measuring weight and reporting mass. so it gets confusing. also people say weight when they should say mass and vice versa. i used the word weight in the spreadsheet to match what you were saying. but the units are in mass, which is what you were also saying. i think i know what you mean. it's just weird. i also switched to inputting grams because the scales seem to work better in metric. all labs use metric as well. you can change the spreadsheet as you see fit though.

I've pretty much dropped out of this discussion, but did look up some lead alloy information, links attached:

Fishing lure, and tire lead talk: (alloys less dense than pure lead, usually)
https://www.tidalfish.com/threads/lead-for-pouring-jigs.279917/

Monotype lead, also links to Linotype lead, (whatever those terms mean):
https://www.matweb.com/search/datasheet.aspx?matguid=63031aa385cc4b72b103fa2dc9320ca8&ckck=1

- Brian

Thanks for everything. Working on it now

While researching anodizing, came across the fact that bismuth is also used for fishing sinkers.
http://www.observationsblog.com/sciencetechnologyexperiments/anodizing-and-dying-aluminum-without-battery-acid

There are also Bismuth 58%, Tin 42% alloys, (and other alloys). Melts at 520 degrees Fahrenheit +/_. Density 75% of lead.
Bismuth, 80% of leads density.
Bismuth is brittle.
Bismuth expands 3.3% when solidifying.

Lead melts at 621.5 degrees F.
Tungsten density is 19.25 grams per cubic centimeter, versus Lead at 11.33 g/cc. Melting point, 6,191.6°F, so not relevant.

- Brian