CA-ALL *NEED* Copper round bar >3.25" diam by min 6" long

[DPittman]

I know photos & lighting can vary a lot but that almost has the look of bronze. The outside skin can vary but filing or machinining a fresh skiff on the end usually makes it more obvious. I mean if you know its copper then copper it is, just sayin. Many common bronze alloys are +80% copper so they are close cousins. One thing for sure copper machines very gummy soft chips, very different that bronze.

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Yup all true. When I bought it I was thinking it was brass actually. But when I got home and examined it carefully I then noticed it was copper.

 

[RickyD]

You could get some molding sand and try casting it near net shape and then machine it to the desired finish. A very large feeder would be needed to avoid shrinkage defects in the casting. This feeder would have to be thick enough to freeze last to be of any use. Casting copper (well, ie. not full of oxide and air inclusions) is tricky, especially in thick sections. Perhaps not an ideal beginner casting project. But it's possible. I'll leave it to the machinists to say how tricky pure copper is to machine...

If you do want to cast it, I would use a whirl gate to encourage any oxide inclusions to stick to the outer skin of the casting where it can be turned off, instead of remaining in the middle. This is how I've had success casting machining blanks in the past. There is a post or 2 starting showing the use of a whirl gate here, from when a bronze leadscrew nut blank was cast for a local member.

I learned about the whirl gate from Tom Kitchen, formerly AKA sandrammer on youtube. He is a retired US Navy trained molder who actually ran the foundries aboard different ships during his career, so he's probably forgotten more than I'll ever know about making castings. It's a really long video to explain a fairly simple gating system though. Let me know if you want the additional detail, and I will find and post the link.

~1g of 7% phosphor copper brazing rod per pound of copper can be added just before a final (gentle) stir and skim in order to deoxidize the copper and improve its fluidity. The big boys use 15% phos-cu shot at 1.5oz per 100# of melt, feel free to double check my formula which hopefully comes up with a bit less additive not a bit more. Too much degasser makes for brittle castings.

Jeff

Thx, I will look into your whirl gate suggestion.

BTW, I have a pouch of 15% phospor copper shots that I got from Australia, I use them when I melt copper, before pouring.
Quite often, when I pour into my 3"ID graphite mold, approx 3/8" thick wall, my liquid copper kinda looks like boiling, and that creates lots of porosity inside. Should I use a much thicker mold, or using casting sand would be better ?
Thx

 

[RickyD]

My pieces are 3" diameter. They were one but I had chopped it sometime ago for something or another.

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