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- Jun 12, 2014
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This type of surface finish issue has been discussed in a number of posts, not uncommon with the G4003G and 1236 machines with single phase motors. Sometimes they are solved other times not. If everything else is tight, spindle bearings are set correctly, then the most common source of the problem is belt tension/alignment/matching, and issues surrounding the single phase motor and isolating it from the machine. You have done a very thorough job on the belt concern, checking the usual culprits. Although a lot of people favor the linked belts, there have been some tests on vibration/smoothness of cut and a good cogged belt was found to work the best overall. I like the Gate Tri-Power, but any decent belt should work. The stock belts on most of these machines should get tossed up front. Most of these were pointed out previously: http://www.hobby-machinist.com/threads/lovejoy-coupling-for-lathe.38870/
The insert you are using, tool post, etc. all look good and should work well. You might put you hand on the side of the tool post and see if there is any flex or chatter, also check the gibs, or try to lock the tool post and cross slide and see if there is any difference. Make sure the insert is well seated, and there is no tooling flex. Next step would be to try to do some form of motor isolation, some discussion in the second link below. It could be a balance issue in the motor or just the cogging of the single phase. Three phase gives a much better finish, but I would not want to do the investment and find out it didn't fix the problem, but 3 phase with a VFD have a lot of other upsides. I do recall an issue with the spindle bearing tension causing vibration, and readjusting it helped. But I would go there as a last resort.
Last but not least, if you haven't already dons so, you might look into different feet, improving the rigidity of the bases, and or mass loading the bases with some sand in bags. Check the lathe leveling and the feet are similarly loaded.
If you are seeing the same type of cutting pattern in different metals and with different tooling holders, then very unlikely to be the insert. If you only have one insert holder, you might try another type/design, I like the CCMT/CCGT types as my main insert.
http://www.hobby-machinist.com/threads/grizzly-g4003g-belt-vibration-video.22308/
http://www.hobby-machinist.com/threads/g4003g-motor-vibration-surface-finish-issues-fixed.42604/
The insert you are using, tool post, etc. all look good and should work well. You might put you hand on the side of the tool post and see if there is any flex or chatter, also check the gibs, or try to lock the tool post and cross slide and see if there is any difference. Make sure the insert is well seated, and there is no tooling flex. Next step would be to try to do some form of motor isolation, some discussion in the second link below. It could be a balance issue in the motor or just the cogging of the single phase. Three phase gives a much better finish, but I would not want to do the investment and find out it didn't fix the problem, but 3 phase with a VFD have a lot of other upsides. I do recall an issue with the spindle bearing tension causing vibration, and readjusting it helped. But I would go there as a last resort.
Last but not least, if you haven't already dons so, you might look into different feet, improving the rigidity of the bases, and or mass loading the bases with some sand in bags. Check the lathe leveling and the feet are similarly loaded.
If you are seeing the same type of cutting pattern in different metals and with different tooling holders, then very unlikely to be the insert. If you only have one insert holder, you might try another type/design, I like the CCMT/CCGT types as my main insert.
http://www.hobby-machinist.com/threads/grizzly-g4003g-belt-vibration-video.22308/
http://www.hobby-machinist.com/threads/g4003g-motor-vibration-surface-finish-issues-fixed.42604/