My mixing lead calculations - Right or Wrong????

[358Scout]

I have thirty-six 1 pound bars stamped 70%Pb/30%Sn.
I want to add lead to get a 16:1 ratio
Common Factor for 70/30 = 10
Equals 7:3 ratio or reduced again by a CF of 3 = 2.3:1 ratio.
Does this mean I need to add 13.7 pounds of lead to one bar of solder to get 16:1 mix?

Doesn't that seem like a lot of lead?

 

[smellie]

You HAVE 30%.

You WANT 6.25%.

Cut your Solder (30/6.25=) 4.8 to 1.

 

[Andy]

You need to add 4.1 lbs of pure lead to each 1 lb 70/30 bar to get a 5.1 lbs of a 16/1 mix.

 

[358Scout]

Thanks will try that -

 

[Ol' Flinter]

Andy nailed it:

Each one pound bar of the 70:30 alloy contains, by weight, 4.8 oz of tin and 11.2 oz of lead.
You cannot separate the alloy so you need to add enough lead to get a 16:1 mix. So in the mix for each one pound bar you need to have 16 x 4.8 oz = 76.8 oz of lead.
However, you already have 11.2 oz of lead from your one pound of alloy so you need to add 76.8 - 11.2 = 65.6 oz of lead to each of the one pound bars of 70:30 alloy. 65.6 oz = 4.1 lb.