sandiapaul
Titanium
- Joined
- Mar 19, 2004
- Location
- Princeton, NJ USA
So I got my rebuilt lathe set up and in place and mostly leveled. I was in process of making a 2 collar test bar when I noticed an odd finish pattern on the surface. It is like a series of parallel "rings". You can feel them with your fingernail, my guess is they might be a couple or less tenths deep. Frequency of the rings are about .030, regardless of speed and feed.
Lathe is running on a VFD(Teco 7300), 3 HP 1800 rpm motor drives a 2 speed gearbox, output of gearbox drives the spindle. Flat belts throughout, all new, scarfed and glued. Everything runs nice and smooth.
Here was my setup: 1" collet with 1215 steel. Part was sticking out of the collet about 4.5". Cuts were all light, .005-.020. HSS insert cutter, brand new. There was essentially no chatter. Speeds are a guess as I don't know exactly since VFD is not displaying RPM. .0016, .004 and .008 per rev all made the same pattern. Cranking the speed way up and down made no difference in the pattern.
I changed to a piece of 6061 and it was improved, not gone but much less visible.
Before I put the machine in place I ran it a fair amount playing with cutting a piece of 2" D 6061 held in a 8" 3 jaw and I saw none of these patterns.
So I put the 3 jaw on and cut the same piece of 6061 and the finish is outstanding.No rings even under 10x magnification.
I put the steel in the 3 jaw and it too has a great finish.
So I read a post by Forrest taking about this phenomenon with single phase motors, but that is not what I have here. Could the VFD be causing this? Is the large mass of the 3 jaw "evening it out"?
Any thoughts? Kind of a bummer as I spent the last 18 months working on this machine!
Paul
Lathe is running on a VFD(Teco 7300), 3 HP 1800 rpm motor drives a 2 speed gearbox, output of gearbox drives the spindle. Flat belts throughout, all new, scarfed and glued. Everything runs nice and smooth.
Here was my setup: 1" collet with 1215 steel. Part was sticking out of the collet about 4.5". Cuts were all light, .005-.020. HSS insert cutter, brand new. There was essentially no chatter. Speeds are a guess as I don't know exactly since VFD is not displaying RPM. .0016, .004 and .008 per rev all made the same pattern. Cranking the speed way up and down made no difference in the pattern.
I changed to a piece of 6061 and it was improved, not gone but much less visible.
Before I put the machine in place I ran it a fair amount playing with cutting a piece of 2" D 6061 held in a 8" 3 jaw and I saw none of these patterns.
So I put the 3 jaw on and cut the same piece of 6061 and the finish is outstanding.No rings even under 10x magnification.
I put the steel in the 3 jaw and it too has a great finish.
So I read a post by Forrest taking about this phenomenon with single phase motors, but that is not what I have here. Could the VFD be causing this? Is the large mass of the 3 jaw "evening it out"?
Any thoughts? Kind of a bummer as I spent the last 18 months working on this machine!
Paul