I'm doing an unusual job for me, where we have very long overhang for a couple of boring bars and we're getting a lot of vibration. I'm wondering if anyone has experience with these kinds of jobs and what feed and speed you'd recommend?
Material is 316SS Tube, 1.9" OD and 1.5" ID.
There's no OD work, but I need to bore the inside 1.690" diameter and 4" deep from one end.
So I'm using two 1.25" shank boring bar with CNMG 431 inserts (roughing and finishing), extended 5" from the tool holder so that I can still get some coolant pouring down the lengths...
For roughing passes, I'm trying to go at 400SFM, 0.012ipr, and approx 0.030" depth of cut, so 3 passes... (manufacturer's recommended feed and speed for insert) (I settled on the 0.030" depth (3 passes) because I was getting chip build up and plugging in the tube, so now between passes, I shove a bar down the tube to push all the chips down...)
Finishing pass is 625SFM, 0.007ipr and just cleaning up the last 5-10 thou...(manufacturer's recommended feed and speed for insert)
I seemed to be having some success for the first few pcs, but now just getting ridiculous vibration for both roughing and finishing passes... am I out to lunch trying to run at these speeds given how far the tool is extended?
The vibration is reduced quite a bit when I drop the spindle speed to 50%, so I'd probably be able to get rid of them all together if I dropped to 10-30%... but I've got a lot of parts to run, so I'd rather not do that...
I think I've kind of resolved the issue in a bit of a brute force method: I generated some G-code in an excel spreadsheet, where the machine cuts in 50 thou increments and continuously changes the spindle speed. Code looks something like this:
G96 S400
G1 Z-.05 S450
Z-.1 S350
Z-.15 S450
Z-.2 S350
etc...
This seems to be working and lets me run at these speeds and feeds, though it took some trial and error to get the speed and Z increments correct.
But anyway... all I'm really wondering is whether I'm just running way to fast? Any other recommendations for reducing chatter/vibration in this kind of setup? I've read that up to 4x the bar diameter (so 5" in my case, which is what I'm doing), there shouldn't be much of a problem, but that's not what I'm seeing...
Thanks in advance...