My Graziano SAG14 is driving me crazy with an issue when doing heavier cuts and mostly when parting off a part. I can't remember it having this in the past but I haven't been able to use it for the past couple of years due to moving, renovating etc. Maybe it got worse over time but I can't remember.
The problem I have is that I get a lot of chatter during heavier cuts, during parting I can't seem to get a straight cut after facing. The face is always concave or convex for 0.5-1mm (around 1/32"). There is no real pattern that I can find that causes it to go either way. During the cut it starts making a lot of noise, but I can't really pinpoint it to the bearings, just overall rattling/knocking. If I continue cutting, usually the tool won't cut and the force will move the part in the chuck, offsetting it with more damage as a result. If I do light cuts, nothing is wrong, surface finish is great. Also, the tool post rotates due to the high forces involved.
The tool used to part off is an Iscar with GTN insert, 3mm wide. 280-400RPM, 0.03mm/rev. Any higher feed and it will crash straight away. Parting diameter is 80mm. Material is C45 (AISI 1045).
I've checked quite a few things but it's looking like I need new spindle bearings which is pretty expensive (yes, they are available and I have a quote). But before calling it, I want to check if there's something I might have missed?
I did the following test: I turned a test piece, Ø50x250 (Ø2"x10") and checked parallelism. I measured 0.08mm which is somewhat higher but can be caused by the relative long stickout and some chatter that I had. It wouldn't explain the concave or convex surfaces that I had. Next I put an indicator on the end of the test piece and tried to lift it up. I can easily, without using much force, lift it 0.1mm (0.004") which seems like a bit too much. The force required to bend the shaft like that would be around 126kg (270lbs). That's not the force I'm exerting with my hand.
When I do the same test but measure between the headstock/bearing and chuck I measure 0,01mm. This is after re-tightening the bearings. I re-tightened them a bit and they do not warm up at 1500RPM.
I already tightened up all gibs. That doesn't seem to have an effect. I tightened the nut on the tool post but it's righthand thread so any force due to cutting or facing will easily loosen this. I'm not sure if there's something wrong there, maybe a conversion that wasn't done properly? There is no locking provision between the washer on the top and the stud. So it untightens by itself rather easily.
My idea is that the following is happening: during parting the spindle is lifted up due to the cutting force. The force is not enough to cut the material and the tool starts to surf across the surface, then when it finally grabs again, the forces are so high it rotates the toolpost. I tried measuring if any lift was happening during cutting by placing a indicator on top of the OD, but I can't really get a good measurement. The needle jumps around too much to make a real reading.
I tried another chuck because I don't like how it's slipping/moving in the chuck, but the results are equal. Strange fact is that when I measure with the mag base on the chuck and the indicator on the part, I get quite a bit of movement as well. I tried to measure between the spindle and the chuck but I can't find any movement. It's not moving on the D1-5 camlock from what I can measure. Maybe it's the chuck?
Any thoughts? Are my chucks worn or how can I check or rule-out the bearings? What about the toolpost connection, anyone had issues with that before? What about the stickout of the test piece? I figure it should be able to turn this without that much chatter but I couldn't. Last cut was 0.25mm DOC (0.01") 0.06mm/rev (0.0024"/rev) and it was still chattering, tried several inserts but that didn't make a difference.
The problem I have is that I get a lot of chatter during heavier cuts, during parting I can't seem to get a straight cut after facing. The face is always concave or convex for 0.5-1mm (around 1/32"). There is no real pattern that I can find that causes it to go either way. During the cut it starts making a lot of noise, but I can't really pinpoint it to the bearings, just overall rattling/knocking. If I continue cutting, usually the tool won't cut and the force will move the part in the chuck, offsetting it with more damage as a result. If I do light cuts, nothing is wrong, surface finish is great. Also, the tool post rotates due to the high forces involved.
The tool used to part off is an Iscar with GTN insert, 3mm wide. 280-400RPM, 0.03mm/rev. Any higher feed and it will crash straight away. Parting diameter is 80mm. Material is C45 (AISI 1045).
I've checked quite a few things but it's looking like I need new spindle bearings which is pretty expensive (yes, they are available and I have a quote). But before calling it, I want to check if there's something I might have missed?
I did the following test: I turned a test piece, Ø50x250 (Ø2"x10") and checked parallelism. I measured 0.08mm which is somewhat higher but can be caused by the relative long stickout and some chatter that I had. It wouldn't explain the concave or convex surfaces that I had. Next I put an indicator on the end of the test piece and tried to lift it up. I can easily, without using much force, lift it 0.1mm (0.004") which seems like a bit too much. The force required to bend the shaft like that would be around 126kg (270lbs). That's not the force I'm exerting with my hand.
When I do the same test but measure between the headstock/bearing and chuck I measure 0,01mm. This is after re-tightening the bearings. I re-tightened them a bit and they do not warm up at 1500RPM.
I already tightened up all gibs. That doesn't seem to have an effect. I tightened the nut on the tool post but it's righthand thread so any force due to cutting or facing will easily loosen this. I'm not sure if there's something wrong there, maybe a conversion that wasn't done properly? There is no locking provision between the washer on the top and the stud. So it untightens by itself rather easily.
My idea is that the following is happening: during parting the spindle is lifted up due to the cutting force. The force is not enough to cut the material and the tool starts to surf across the surface, then when it finally grabs again, the forces are so high it rotates the toolpost. I tried measuring if any lift was happening during cutting by placing a indicator on top of the OD, but I can't really get a good measurement. The needle jumps around too much to make a real reading.
I tried another chuck because I don't like how it's slipping/moving in the chuck, but the results are equal. Strange fact is that when I measure with the mag base on the chuck and the indicator on the part, I get quite a bit of movement as well. I tried to measure between the spindle and the chuck but I can't find any movement. It's not moving on the D1-5 camlock from what I can measure. Maybe it's the chuck?
Any thoughts? Are my chucks worn or how can I check or rule-out the bearings? What about the toolpost connection, anyone had issues with that before? What about the stickout of the test piece? I figure it should be able to turn this without that much chatter but I couldn't. Last cut was 0.25mm DOC (0.01") 0.06mm/rev (0.0024"/rev) and it was still chattering, tried several inserts but that didn't make a difference.