A question for you math wizards.

[JKR]

I have certified 16-1 casting material. I would like to mix a small batch at 20-1. How much pure lead should I add to 10 lbs. of the 16-1 to make 20-1?
Thanks in advance!
JKR

[garandsrus]

2 lbs.

[hoodat]

I can't believe I even opened a thread with that title. jd

[Wilderness]

Your 10 lbs (160 oz) of 16:1 will contain 9.41 oz of tin (160/17).

Converting that tin to 20:1 mix will give you 197.6 oz total (9.41 x 21).

Deduct the original 10 lbs (197.6 - 160 oz), leaves 37.6 oz of additional lead - two and a bit pounds.

[Kosh75287]

Okay, so the THEAD TITLE is a little "counter intuitive" (for me), too, but I got an answer I believe in. Using the
(PbConcentration1)(AlloyWeight1) = (PbConcentration2)(AlloyWeight2), I got that 2.357 pounds of .999 Pb is needed to make 20:1 Pb:Sn alloy:

(PbC1)x(AW1)=AW2. (.5882 x 10)/.476 = AW2 = 12.357.
(PbC2)

Subtracting 10 lbs (W1) from the final weight desired (12.357) for the alloy leaves 2.357 lbs lead required to increase 10 pounds of 16:1 Pb:Sn to 20:1 alloy

2.357 pounds works out to 2 pounds 5.25 ounces. If your specs demand EXACTLY 20:1 alloy, this is the amount to make 20:1 alloy out of 10 pounds of 16:1. I 20:1 is more of a "best recommendation", I think I might add pure Pb in 12 oz. portions, cast, then try.

[poppy42]

Just download the alloy calculator available on the forum and use it!

[M-Tecs]

16 - 1 equals 93.75% lead, 6.25% tin so in ten pounds you have .625 of a pound of tin in your 16-1 alloy. The amount of tin will not change when you add more tin.

20 - 1 equals 95% lead, 5% tin

You have .625 pounds of tin so you will have to add 2 1/2 pounds of lead to your 10 pounds to get the tin down to 5% (20-1).

.625 divided by 12.5 equals 0.05. Convert to % you multiple by 100 which equals 5%

[Wilderness]

Okay, so the THEAD TITLE is a little "counter intuitive" (for me), too, but I got an answer I believe in. Using the
(PbConcentration1)(AlloyWeight1) = (PbConcentration2)(AlloyWeight2), I got that 2.357 pounds of .999 Pb is needed to make 20:1 Pb:Sn alloy:

(PbC1)x(AW1)=AW2. (.5882 x 10)/.476 = AW2 = 12.357.
(PbC2)

Subtracting 10 lbs (W1) from the final weight desired (12.357) for the alloy leaves 2.357 lbs lead required to increase 10 pounds of 16:1 Pb:Sn to 20:1 alloy

2.357 pounds works out to 2 pounds 5.25 ounces. If your specs demand EXACTLY 20:1 alloy, this is the amount to make 20:1 alloy out of 10 pounds of 16:1. I 20:1 is more of a "best recommendation", I think I might add pure Pb in 12 oz. portions, cast, then try.

Kosh - I wondered about the discrepancy between calculations - mine 2 lb 5.6 oz calculated on one decimal place, to your 2 lb 5.25 oz. Found it - .357 lbs x 16 oz is 5.7 oz. Near enough.

We need to be careful about ratio definitions too - 16:1 is 16 parts lead to one of tin, not one part tin in 16 total. I presume the commercial alloy really is 16:1, not one part in 16.

[Noah Zark]

The train arrived in Chicago at 4:50 pm.

Noah

[toallmy]

When I first read this post I got a pencil and piece of paper took off my shoes and socks getting ready to do some serious counting but decided to go take a nap instead , I'm glad I did ....
I would just drop 1 big muffin ingot of plumbing lead in the pot

[dtknowles]

I vote for 2.5 pounds

[indian joe]

16 - 1 equals 93.75% lead, 6.25% tin so in ten pounds you have .625 of a pounds of tin in your 16-1 alloy. The amount of tin will not change.

20 - 1 equals 95% lead, 5% tin

You have .625 pounds of tin so you will have to add 2 1/2 pounds of lead to your 10 pounds to get the tin down to 5% (20-1).

thats what I got - not sure its right - remember our numbers are ratio so 16:1 is 17 parts total - 20:1 is 21 parts total
He has 10 pounds of a 16:1 alloy so divide 10/17 = .588 pounds tin ----.588 x 20 gives 11.76 pounds - (pure lead) now add in the tin? + the .588 pounds tin comes to a total of 12.348 pounds total -- so add 2.348 pounds pure lead

[indian joe]

When I first read this post I got a pencil and piece of paper took off my shoes and socks getting ready to do some serious counting but decided to go take a nap instead , I'm glad I did ....
I would just drop 1 big muffin ingot of plumbing lead in the pot

Yep me too - then scratch a couple boolits with a pencil to see what change we got

[indian joe]

This stuff sounds simple but is quite tricky if we wanna get technical - much depends on what is writ and how that is interpreted
my take - tell me you are using a Ratio of 16:1 says 16 parts lead to one part tin ....total is 17 parts
tell me one part tin in 16 and I get a different message - that is saying 16 pounds in the pot of which one pound is tin - so a 15:1 ratio?

[fc60]

Greetings,

Using the downloadable Alloy Calculator, I get 10 pounds of 16-1 plus 2.25 pounds Pure Lead = 12.25 pounds of 20-1.

Cheers,

Dave

[M-Tecs]

thats what I got - not sure its right - remember our numbers are ratio so 16:1 is 17 parts total - 20:1 is 21 parts total
He has 10 pounds of a 16:1 alloy so divide 10/17 = .588 pounds tin ----.588 x 20 gives 11.76 pounds - (pure lead) now add in the tin? + the .588 pounds tin comes to a total of 12.348 pounds total -- so add 2.348 pounds pure lead

You and Kosh75287 are correct. I overlooked the part total of 17 parts affecting the actual percentage. 94% lead 6% tin.

[Wilderness]

Greetings,

Using the downloadable Alloy Calculator, I get 10 pounds of 16-1 plus 2.25 pounds Pure Lead = 12.25 pounds of 20-1.

Cheers,

Dave

Dave - something wrong there. 10 lbs 16:1 (160 oz) divided by 17 gives 9.41 oz of tin. 12.25 lbs (196 oz) of 20:1 divided by 21 gives 9.33 oz of tin. Looks like we lost some tin in the remix.

[indian joe]

Dave - something wrong there. 10 lbs 16:1 (160 oz) divided by 17 gives 9.41 oz of tin. 12.25 lbs (196 oz) of 20:1 divided by 21 gives 9.33 oz of tin. Looks like we lost some tin in the remix.

tin didnt go missing ----add 2.348 pounds of lead and the numbers will come right.

[Wilderness]

tin didnt go missing ----add 2.348 pounds of lead and the numbers will come right.

Joe

Yes, 2.348 lbs = 2 lbs 5.6 oz, my original calculation.

I was pointing out a possible error in the Alloy Calculator.

I am glad we are not building a bridge.

[indian joe]

Joe

Yes, 2.348 lbs = 2 lbs 5.6 oz, my original calculation.

I was pointing out a possible error in the Alloy Calculator.

I am glad we are not building a bridge.

I am still in favour of the "chuck another muffin pan nugget in an she'll be right mate"