Alloys

[ACC]

OK, I wish to make 20 pounds of casting alloy. I want to make it at 1:20.

How much Lead to how much tin?

In the alloy spread sheet I got from here it says 3.23% tin and 96.2% lead.

How much is that in ounces?

I was never good with math.

ACC

[bmortell]

20-1 should be 5% tin 95% lead because 100 divided by 20 = 5
but in a whole 20lbs theres no need for math its 1lb tin and 20lb lead

[bmortell]

if you want 20 pounds to be 3.23% tin then add 10.5 ounces tin to 20 lbs pure

[NyFirefighter357]

What are you using for tin, do you have pure tin or are you using a tin alloy like solder, pewter ect.? 18lbs pure & 2lbs of 50/50 gets you 5% tin/95% lead with a BHN of 10 while 19lbs of pure & 1lb of 95/5 solder will get close enough with 4.75% tin/.25% antimony/95% lead with a BHN of 10.2. 1lb of tin & 19lbs pure lead also gives you 5% tin/95% lead.

[kevin c]

My understanding is that it's a ratio: 20 of one thing to 1 of another. So twenty pounds of pure lead to 1 pound of pure tin. The percentages are correct, but IMO it's easier to to make twenty one pounds of alloy by using round, whole numbers than to use the percentages to calculate fractions of pounds or ounces.

You don't have to be dead on, anyway, not unless you are doing some precision experimentation or trying to exactly duplicate an alloy.

[ACC]

Thanks. I always used to let my brother do the math but since he has passed I have to do it. Math makes my head hurt.

ACC

[jdfoxinc]

Try 19 lb lead 1 lb tin.

[white eagle]

Try 19 lb lead 1 lb tin.

that is 19/1 but 20# total

[OS OK]

One little caveat though...if your using a Lee 4-20 pot...18 pounds is about all it'll hold before it's dangerously near overfill. & when you go to flux it'll spill over the edge if you aren't super-careful.

You can only use 90% of each weighted out portion of Pb & Sn if you figure on a 20 pound batch.

[fredj338]

20-1 should be 5% tin 95% lead because 100 divided by 20 = 5
but in a whole 20lbs theres no need for math its 1lb tin and 20lb lead

^^winner^^
As noted you wont get 20# in a 20# pot so 18#-3/4# of tin is close enough.

[OS OK]

^^winner^^
As noted you wont get 20# in a 20# pot so 18#-3/4# of tin is close enough.

I am NO Mathematician ... so I tend to try to reason my way through ratios like this one...

"If there is 18 pounds total of a mixture & that mixture is a '20 to 1' ratio .... hmmmmm ... my little 'pea-brain' is saying that there are 21 parts in that 18 pound mixture?

If I divide the 18 pounds by those 21 parts I'll get ... .85714286 pounds per part.

¿How do I verify that assumption?

If I multiply the .85714286 pounds by 20 parts ( = 17.1428572 pounds ) & add the other 1 part of 21 parts total, ( .85714286 pounds ), I should get 18 pounds.

17.1428572 + .85714286 = 18 pounds ... so that checks.

Now I know we wouldn't go to this extreme to measure our Pb & Sn but it seems reasonable to me that this is the math behind that 20 to 1 blend of 18 pounds of lead & tin.

Am I missing something here about ratios or do I have a missconception of what a ratio actually is? I realize that close enough is actually close enough in this boolit metal but if we were mixing chemicals or something that had to be exact it would matter."

If someone can shed some light on this 'ratio business' I'd be extremely appreciative.

[ole_270]

After 25 years of calculations as a CNC Programmer I quit that stuff when I retired. I downloaded the calculator in the sticky's and don't even think of doing math anymore.

[ulav8r]

I am NO Mathematician ... so I tend to try to reason my way through ratios like this one...

"If there is 18 pounds total of a mixture & that mixture is a '20 to 1' ratio .... hmmmmm ... my little 'pea-brain' is saying that there are 21 parts in that 18 pound mixture?

If I divide the 18 pounds by those 21 parts I'll get ... .85714286 pounds per part.

¿How do I verify that assumption?

If I multiply the .85714286 pounds by 20 parts ( = 17.1428572 pounds ) & add the other 1 part of 21 parts total, ( .85714286 pounds ), I should get 18 pounds.

17.1428572 + .85714286 = 18 pounds ... so that checks.

Now I know we wouldn't go to this extreme to measure our Pb & Sn but it seems reasonable to me that this is the math behind that 20 to 1 blend of 18 pounds of lead & tin.

Am I missing something here about ratios or do I have a missconception of what a ratio actually is? I realize that close enough is actually close enough in this boolit metal but if we were mixing chemicals or something that had to be exact it would matter."

If someone can shed some light on this 'ratio business' I'd be extremely appreciative.

You are exactly right. 20 parts to 1 part will always be be the same whether each part is 1 pound, 1 ton, 1 grain or whatever.

[kevin c]

OS OK, your reasoning is pretty solid, and your technique of adding up all the "parts" is one I use too.

[Land Owner]

A ratio is a relationship between two numbers indicating how many times the larger number contains the smaller.

A ratio of 1:20 is 1 part in 20 parts. The final alloy does not equal 21 parts in total.

bmortell was partially right in that 1 part in 20 parts is 5%. The remaining parts are nineteen (19) twentieths (20ths) equaling 95%.

To make the 1:20 alloy correct in terms of PURE tin and lead, combine 1 pound of tin with 19 pounds of lead (1 part + 19 parts = 20 parts total).



If only 18 pounds can be accommodated in a Lee pot, then multiply 18 pounds by 5% (0.05) for tin (0.9 #'s tin), convert pounds to units of ounces (multiply by 16 oz. per #) for 14.4 ounces of tin.

To maintain the ratio (1:20) the remaining 95% of the 18# alloy has to be lead. Multiply 18 by 0.95 (= 17.1 #'s), convert pounds to units of ounces (multiply by 16 oz. per #) for 273.6 ounces of lead.

Check Sum:

14.4 oz + 273.6 oz = 288 oz

288 oz /16 oz per pound = 18 pounds

Realizing that 273.6 is a large number of oz's, return to the number of pounds of lead (17.1 #'s) and add 17 #'s plus 1.6 oz of lead to the pot (17.1# - 17# = 0.1# * 16 oz per pound = 1.6 oz.)



THIS MATH IS CORRECT and as a Professional Engineer (PE) I approve of this message.

[OS OK]

A ratio is a relationship between two numbers indicating how many times the larger number contains the smaller.

A ratio of 1:20 is 1 part in 20 parts. The final alloy does not equal 21 parts in total.

bmortell was partially right in that 1 part in 20 parts is 5%. The remaining parts are nineteen (19) twentieths (20ths) equaling 95%.

To make the 1:20 alloy correct in terms of PURE tin and lead, combine 1 pound of tin with 19 pounds of lead (1 part + 19 parts = 20 parts total).



If only 18 pounds can be accommodated in a Lee pot, then multiply 18 pounds by 5% (0.05) for tin (0.9 #'s tin), convert pounds to units of ounces (multiply by 16 oz. per #) for 14.4 ounces of tin.

To maintain the ratio (1:20) the remaining 95% of the 18# alloy has to be lead. Multiply 18 by 0.95 (= 17.1 #'s), convert pounds to units of ounces (multiply by 16 oz. per #) for 273.6 ounces of lead.

Check Sum:

14.4 oz + 273.6 oz = 288 oz

288 oz /16 oz per pound = 18 pounds

Realizing that 273.6 is a large number of oz's, return to the number of pounds of lead (17.1 #'s) and add 17 #'s plus 1.6 oz of lead to the pot (17.1# - 17# = 0.1# * 16 oz per pound = 1.6 oz.)



THIS MATH IS CORRECT and as a Professional Engineer (PE) I approve of this message.

Thank you very much Mr. Land Owner, I appreciate your time making this clear and I am grateful.

I am going to keep repeating this until it really sticks! A ratio of 1:20 is 1 part in 20 parts.

charlie

[Rich/WIS]

Don't know if it really matters as long as you do it the same way for each batch to get a uniform alloy. Difference between 19 pounds of lead plus a pound of tin and 20 pounds of lead and a pound of tin is .25%, doubt if it matters much in terms of hardness or castability.

[bumpo628]

The ratio argument mentioned above from both points of view has gone on for many years. I contacted rotometals a while back to settle the matter and they confirmed that that they mix 20 pounds of lead with 1 pound of tin for a total of 21 pounds for their 20:1 alloy. The problem is that they round off the tin percentage (they say 5% in the ad instead of 4.76%) and that makes it more confusing.

The final answer is that a 20:1 mixture has a total of 21 parts. 20 parts lead mixed with 1 part tin. The tin percentage is 4.76% (not 5%).

The argument that there is a total of 20 parts in a 20:1 ratio breaks down when you consider smaller ratios like 1:1 or 2:1. A 1:1 ratio would obviously have a total of 2 parts, not 1.

I hope this clears it up.

For the OP,
I would just mix 10 lbs of pure lead with 1/2 pound of tin since 21 lbs will not fit in a typical melting pot.

[Slugster]

Maybe 15 pounds of lead with 3/4 pound of tin for a 20 pound pot so that you have a little room for chucking in the odd sprue or wrinkled boolit?

[Chill Wills]

Painful

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