For reasons explained elsewhere, I am now machining bismuth. Starting with an oversized 1x2x6" and bringing down to size.
Yuch.
I had figured it would be similar to lead or tin. Heavy, soft metals. Well, yes, sort of. It creaks like tin does when squeezed in a vice.
But the differences. My. When using a normal end mill (5/8" carbide), at all feeds and speeds, the bismuth will cut ok (like lead) and then shatter on the edges, breaking off like .2" pieces. Now, the bismuth is indeed a beautiful shinny crystal inside, so the broken spots are very sparkly and all, but it is a very ragged cut.
When using a face cutter (3" with carbide inserts) it starts bad, and gets worse. At slow feeds and speeds (500 rpm say) you get the edge shatter. At medium speed you get the shatter, and also a spray of sand-like sharf. At high speed (2000 rpm) it is worse. It is nice because I had no edge shatter (wonderful) but the sharf is not strings, not curls, not dust, but rather a very fine powder. Smaller than fine sand. Sort of like talcum powder. At creates a cloud of powder, which coats and gets everywhere within five-ish feet. Not like an explosion of talcum which would get all over the shop--the bismuth powder does fall in air.
And this powder is very hard to clean up. A vacuum sort of works. A brush is better. But this powder is adhesive to everything. Plastic, cloth, even all the machine metal. Feels like it might be electrostatic cling somehow. How electrostatic cling clings to metal though is beyond me. I quickly realized not only face protection, but breathing protection was needed. On with the little P95 mask.
My shop vac was able to suck up some of the mess as I ran it and held the nozzle right at the cutter, but mostly the powder got everywhere anyhow.
No doubt there is an expert somewhere who knows exactly how to hand sharpen the tooling to avoid both the edge shatter and the powder. Though who machines bismuth is a mystery, to me at least.
Materials are so interesting. Until you have actually gone done something for real it is amazing how hard it is to imagine the number of ways an idea can not work. So, I dislike machining Titanium (with my little hobby stuff, the self-igniting piles of titanium sharf which burn nearly like magnesium indicates to me this is stuff best left to experts. ) And, I dislike machining copper--it is grabby and breaks bits and so hard to get any sort of acceptable surface finish (again, with my tools). But, most of all right now, I dislike machining bismuth--that fine fine powder is really grungy.
Life is fun.
-Bill
Yuch.
I had figured it would be similar to lead or tin. Heavy, soft metals. Well, yes, sort of. It creaks like tin does when squeezed in a vice.
But the differences. My. When using a normal end mill (5/8" carbide), at all feeds and speeds, the bismuth will cut ok (like lead) and then shatter on the edges, breaking off like .2" pieces. Now, the bismuth is indeed a beautiful shinny crystal inside, so the broken spots are very sparkly and all, but it is a very ragged cut.
When using a face cutter (3" with carbide inserts) it starts bad, and gets worse. At slow feeds and speeds (500 rpm say) you get the edge shatter. At medium speed you get the shatter, and also a spray of sand-like sharf. At high speed (2000 rpm) it is worse. It is nice because I had no edge shatter (wonderful) but the sharf is not strings, not curls, not dust, but rather a very fine powder. Smaller than fine sand. Sort of like talcum powder. At creates a cloud of powder, which coats and gets everywhere within five-ish feet. Not like an explosion of talcum which would get all over the shop--the bismuth powder does fall in air.
And this powder is very hard to clean up. A vacuum sort of works. A brush is better. But this powder is adhesive to everything. Plastic, cloth, even all the machine metal. Feels like it might be electrostatic cling somehow. How electrostatic cling clings to metal though is beyond me. I quickly realized not only face protection, but breathing protection was needed. On with the little P95 mask.
My shop vac was able to suck up some of the mess as I ran it and held the nozzle right at the cutter, but mostly the powder got everywhere anyhow.
No doubt there is an expert somewhere who knows exactly how to hand sharpen the tooling to avoid both the edge shatter and the powder. Though who machines bismuth is a mystery, to me at least.
Materials are so interesting. Until you have actually gone done something for real it is amazing how hard it is to imagine the number of ways an idea can not work. So, I dislike machining Titanium (with my little hobby stuff, the self-igniting piles of titanium sharf which burn nearly like magnesium indicates to me this is stuff best left to experts. ) And, I dislike machining copper--it is grabby and breaks bits and so hard to get any sort of acceptable surface finish (again, with my tools). But, most of all right now, I dislike machining bismuth--that fine fine powder is really grungy.
Life is fun.
-Bill
