round ball mold expansion

[timemeddler]

making ball molds on a cnc, does anyone have any experience with how much effect thermal expansion will affect ball diameter when the mold heats up from room temperature? does it have any significant effect on size from hot to cold? Making a 530 ball mold and was curious if I should undersize or oversize.?

 

[Tumbledown]

Melted lead is only about 750° I can't imagine that being enough to distort a mold to any extent.

 

[timemeddler]

Melted lead is only about 750° I can't imagine that being enough to distort a mold to any extent.

a few hundred degrees is often enough to free a stuck bolt or dowel pin, I can see it changing diameter by a a few thousandths.

 

[ZUG]

You need to consult expansion - shrinkage tables. The Machinist Handbook can give you some good info for shrink fits based on material involved.
You can also take a mold and cast a ball using chamber casting material then cast a pure lead ball and compare them. This will give you some idea on what you are dealing with. I honestly doubt using steel blocks that there would be more than 0.0005" difference in the cast ball compared to the cherry.

 

[Phil Coffins]

The lead will shrink as it cools while the mold will expand as it heats. That machinist hand book will provide the numbers based on the alloys involved. Plenty of mathematicians to keep you entertained.

 

[springfield art]

Melted lead is only about 750° I can't imagine that being enough to distort a mold to any extent.

I think he means the ball itself, does it shrink or expand??

 

[Phil Coffins]

I made this ball mold for my cannon, the bore is 1 3/4” so I made the mold at 1.750” knowing that the lead would shrink. Worked out well with about .005” clearance. As cheap as 54 calibre molds are making one so common would be for the exercise of doing it.
IMG_1087 by Oliver Sudden, on Flickr

 

[springfield art]

A recent old re-run of the Tonight Show, had a guy with melted lead in a pot, and Johnny sticking a hot dog in there; NO GOGGLES or safety gear!

 

[timemeddler]

I made this ball mold for my cannon, the bore is 1 3/4” so I made the mold at 1.750” knowing that the lead would shrink. Worked out well with about .005” clearance. As cheap as 54 calibre molds are making one so common would be for the exercise of doing it.
IMG_1087 by Oliver Sudden, on Flickr

I was mostly curious about how much the temperature of the mold changes things. The basic reason for the project was for work training, I've recently been assigned to operating a cnc machine and I needed something for a project to learn programing on.

 

[kyron4]

Using steel or aluminum ?

 

[timemeddler]

Using steel or aluminum ?

aluminum.

 

[The Crisco Kid]

Borrow an aluminum mold and try casting lead balls at different temperatures. That will give you something you can accurately measure that should answer your question.

 

[ZUG]

I made this ball mold for my cannon, the bore is 1 3/4” so I made the mold at 1.750” knowing that the lead would shrink. Worked out well with about .005” clearance. As cheap as 54 calibre molds are making one so common would be for the exercise of doing it.
IMG_1087 by Oliver Sudden, on Flickr

Nicely done Phil - Your mold looks well made! I would love to see the cherry.

 

[Phil Coffins]

Nicely done Phil - Your mold looks well made! I would love to see the cherry.

No cheery needed, CNC mill work does it all.

 

[Pete G]

I would wonder if temperature made any appreciable difference at all.