I was not able to get a good finish. The 1/2 bar was 30"s long so I worked it from each side so 15" bar. It was flexing a lot and I had to dial the middle in probably 1500 more than the ends. The ends did fine but i had to wittle away at center over and over. My skills are not so great.... anyone got more experience at machineing.
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Yeah for long parts like that you need a follow rest, the flexing can cause that finish, as well as the tool.
What sort of tool? And rpm? And problem with a lathe sometimes doing a proper rpm is a dangerous deal. With a follow rest and decent carbide tool and proper feed you would get a better finish.
I'd do that half bar deal as well, that was a smart move. You do have the tool point on center?
Just reread and ....
Do not use a parting tool as the cutter, it is too much pressure on the surface, you need something with maybe a .02 to .03 radius on the tip, with mild steel part, then high speed cutter is fine. The tip radius will help give a better finish, and take very light cuts. Get the feel for it.
Also number 1 rule, always keep the cutting tool as short as possible and as close to the holder as well.
The key thing in machining is the set up and machine need to be as solid as can be.
Make sure the carriage, cross slide etc has no gib play. And spindle as well.
If you don't have a follow rest, only stick maybe 4 inches at a time out of the chuck still using the center, once you get the 15 inches flip and go on the other side. Then could save for a final longer finish cut or just leave it ?
Yes do 4 inches then move it out 4 more inches etc, and is easy to blend the cut that way too. Use a felt pen to mark and lightly touch it to blend with previous cut.