What type of brass for molds?

[Chainsaw.]

A friend of mine and I are designing a mold we would like to make out of brass. I'm wondering if any one knows which brass allow is best for mold design.

Thanks.

[john.k]

I would think a good grade of phosphor bronze,say 95/5 to 90/10 Cu/Sn would be best,but high tin bronzes are difficult to machine....another good metal would be beryllium copper,but swarf is poisonous.....An aluminium bronze 90/10 Cu/Al would also be good.......however a mold should not stick to bullet metal,and I suspect any Cu alloy would tend to cause problems if the mold got to bullet metal melt temp......This would rule out the common high lead free machining brasses.

[Grump]

So all youse guys with access to those optical "gun" thingies that analyze our lead samples--please inform us whether that tech can also analyze the brass moulds offered by reputable makers these days?

Now I've seen a 1902 or whatever 6?-cavity round ball mould made out of brass. Used in NG and maybe Big Army bases to make round balls for gallery practice with the .30-40 Krag if I remember my history correctly. Couldn't have been nuthin' too fancy. Works fine and lead don't stick to it. Seen two or three on various auction sites over the years.

[country gent]

I believe a lot are using c360 brass for moulds now. I cant tell you the make up of as to copper tin and other agents. Most makers are also looking for ease of machining in the material. When your in the business of making something tool life becomes important, more so if custom ground tools are used.

[john.k]

C360.000...free cutting leaded brass..61.5%Cu/35.5%Zn/3.0%Pb.

[NoZombies]

Yes, free machining brass is the correct choice.

[longbow]

Absolutely free machining brass! The main point with brass is that it machines so nicely with correct tooling and that is something to remember... cherries should be cut to suit brass if you are cutting brass. Certainly single point tooling is ground with little side rake and 0 back rake for brass. This is something you should check into for sure before ordering or making cherries.

[Mal Paso]

I would think a good grade of phosphor bronze,say 95/5 to 90/10 Cu/Sn would be best,but high tin bronzes are difficult to machine....another good metal would be beryllium copper,but swarf is poisonous.....An aluminium bronze 90/10 Cu/Al would also be good.......however a mold should not stick to bullet metal,and I suspect any Cu alloy would tend to cause problems if the mold got to bullet metal melt temp......This would rule out the common high lead free machining brasses.

Which is why brass molds have tinning issues but try to pry that free machining brass out of machinist's hands. LOL

Absolutely free machining brass! The main point with brass is that it machines so nicely with correct tooling and that is something to remember... cherries should be cut to suit brass if you are cutting brass. Certainly single point tooling is ground with little side rake and 0 back rake for brass. This is something you should check into for sure before ordering or making cherries.

[country gent]

Another is the stress issues with different materials. Free machining brass isn't as affected machining as to stress as some others. Some bronzes and other materials warp from the milling process due to stress build up. I made wear plates from naval bronze for machine rebuilds of lathes mills and surface grinders. these plates were cut from 1/4 sheets and milled to shape thickness of around 3/16". They would come out of the mill with a big bow to them and had to be straightened and then bolted in with a lot of screws before final hand scraping to finish.

The recommended break in of heat cycling brass blocks reduces tinning by getting the desired patinas started before lead is introduced.