My CNC Cincinnati Hawk 150 started to make a big noise/vibration while Part-off. I make the machine turn counterclockwise with the tool upside down. Somebody told me the problem could be (this is only a possibility) the ways are worn because it's not a normal/good practice to use the CNC that way for Part-off.
What do you think about ? Has somebody had this problem? What do you suggest, changing the ways is a very expensive test to do, I have a small machine shop and I need this machine for my biggest customer.
AFAIK (and I'm more of a hobbyist than anything else), vibration like that is either because of lack of rigidity or because your tool profile is incorrect for the material you're cutting.
The lack of rigidity could be from worn ways, it could be from other things being loose, or it could be because your tool and/or work holding is not providing the rigidity needed to keep the chatter from starting.
I couldn't tell you exactly what tool profile is right: my experience isn't great enough to do anything other than to reduce the rake angle, or to find a real expert and do just what they say.
My experience is with older and cheaper tools, but with all of them you tend to give up some rigidity when you run so that the tool pulls up on the holder -- the ways are designed to resist downward motion, but not upwards to nearly as great a degree.
So: Why are you turning CCW with the tool upside down? Have you tried to run things right side up?
Has the machine done this from day 1 for this job, or did it work OK before and doesn't now? If the latter, then what may have changed?
Have you been using the same tool all along? Could it have gotten dull? Has it been resharpened? Has it been resharpened _properly_?
Is it chipped?
Have you swapped it out for a different tool? Is the different tool as rigid?
Are you using the same tool holder? Is the new tool holder as rigid?
I could go on and on -- but I think your best bets are to look at how everything is held, considering how solidly it is kept in place, and look at your cutting edge to see if it may be causing the problem.
My experience if only with manual machines, but normally the forces push down on the tool post and down on the ways. Most lathes are designed that way. If I understand what you are doing, the forces are pulling up on the tool post and trying to pull the tool post up off the ways. That may be the cause of your problems.
The only time that I've heard of using the lathe in reverse rotation is for threading, so the tool will be moving away from the work piece (so you don't have to stop the lathe just in time to prevent breaking anything). And wherever it was that I read about that, the author was also advising that you use a left-hand tool on the back side of the work, so that the tool would still meet the downward-traveling face of the work.
That is an old machinist's trick when they are using a machine at its upper limit. Most of the machines with Tee slots in the cross slide have, as an accessory, a rear tool holder for parting off. The force is transmitted more directly to the ways without going through the compound so there is less opportunity for " looseness" I don't know anthing about CNC usage but I would expect the same rules to apply
What material are you cutting, how big is it, and how fast are you turning? And what kind of cutoff tool are you using?
I do cutoff with Clausing 5914 late in reverse with upsidedown SGIH blades, and it works just fine. Running in reverse prevents self-feeding of the parting tool into the cut, and keeps the chips from staying in the cut. But it needs a real coolant flood to get fluid to the bottom of the cut.
But before I could part off without bone-jarring chatter, I had to tighten just about everything. It was quite the saga.
I sometimes program the cnc swiss to continue in reverse after tapping, finally going into forward again when the chuck is opened after part-off while fresh stock is being fed out for the next piece...shaves off a bit of cycle time...
First, I hope you mean ccw from the outboard end of the spindle. If otherwise, you are going the wrong way. Do you use a lantern tool post? I gave up on mine many years ago. Not rigid enough. Do you know that the chips are wider than the cut if they heat up at all? That's why one uses a lot of coolant. Is your tool set just on or just below the center line so if it grabs, it pulls away from the cut? Do you tighten all gibs? Have you tried different speeds to see if the vibration rate changes or disappears? How far is the work sticking out of the lathe chuck? I always try to have the cut real close to the chuck. I have a 10 inch manual Atlas lathe, so it is pretty light, but I cut-off successfully on a regular basis, but not usually on a production basis.
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