- Nov 23, 2018
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Oewww. I thot the things were some kind of cast iron. Well, I'll find out how bad it is when I get tuit. But for now, thanx immensely for the info. I got mine at a scrap yard and they have them all the time. I can get incredible metals here because they have a lot of metal fabrication going on here. They make Genies here, and their scrap costs extra, still it is very high qual and cheap in comparison to having to buy it new. I saw, one time, a complete, un-opened block of 2" thick pieces probably 5feet by 9 or 10 feet. It must have weighed many tons. it was about 5 feet tall --not pile, they were bound together and all in the scrap yard. Can't imagine why they were there. It was worth a fortune in scrap, but what would it have cost new?Richard, I did not find this on the scrap yard, but bought it brand new at a model building shop (costs about 1 Euro/Dollar per cm/half inch). However, the scrap yard is indeed a very good source for these tubes, but you have to be lucky to find them in time before they are cut/bend or thrown into a large pile.
The ID is extremely nice regarding size and surface finish. The composition of the material is unknown to me. Where brass,CI and most aluminium alloys machine like a charm, this material is on the other side of the scale. It is a very tough material that is horrible to machine. Using a carbide insert for steel, gives curly chips/strings of about an inch long. However this leaves a horrible surface finish, almost like 30 grid sand paper. Each time a chip breaks of the surface, it leaves a small sharp burr. Using a carbide insert for aluminium (much charper) results in a completely worn out insert after a single pass.
In my search for a solution I found that the only thing that leaves a decent surface finish and does not eat the tool is using very low RPM i.e. surface feet per minute, a small feed rate and a very sharp HSS tool (below marked in red).
Drawback of this is that the chip does not break at all. You will get a continious long chip of several meters long that will produce a "birds nest" of about a food in diameter per pass. So frequently stopping the lathe and removing the swarf is the only thing you can do. This swarf is so tough that you have to cut it using a wire cutter. You can not tear them by hand without getting cut.
Finally I use a piece of sand paper to smooth out the surface roughness which is still rather high compared to nicely machining material like brass, CI and most aluminium alloys.
Next time I will try to cut them on my CNC lathe with and intermitting feed rate causing the chip to break by stopping the feed every few seconds. Payback for sure will be a more coarse surface finish as each time the chip breaks, it leaves a sharp burr. Just not sure if the tool will survive the intermitting cut as it will engage the material repeatedly.
View attachment 144031
BTW, did you cut it with a band saw?