1340gt surface finish problem

I'm disabled and have to sit while working, the crossbar in front was moved back 6" so it wouldn't hit my knees, you can see the bottom of it in the photo.

The lathe is also sitting on a 3' x 6' x3/8" steel plate on top of the REINFORCED wood floor. All the joists have shims between them and the ground to keep them from bowing. They also have been sistered with an additional 2x10 on either side, making each joist 4 1/2" wide. THEN, all the spaces between the joists were filled in with more 2x10's laid flat and screwed down to the sistered joists. (the sistered joists were left 1 1/2" from the top of the original joists)

A glass of water on the floor AND on the headstock show no vibrations at all.

I'm installing a Marathon Black MAX Y-551 inverter motor and a VFD, I'll keep you posted.
 
Late to this post but I had a very similar issue on my Taiwan King 14x40 GH lathe when new. Turns out the power feed shaft was slightly bent. When shaft was removed service guy rolled it on a very flat table & the wow was visible. Suspect it occurred behind the scenes in transport or who knows, even factory. Anyway, with new straight shaft the finish turned into a mirror, resonance gone. The reason why this is fresh on my mind is my clutch is giving me some grief, which is on exact same shaft adjacent to headstock. The ball/spring/detent assembly is starting to click under power feed & I am seeing some surface finish issues. Nowhere near as extreme as before but that kind of slight 'threading overlay' looking issue. It could be picking up some mechanical scuffing or intermittent junk motion from any number of places in power feed drive train - including inside the apron where bar rotates through the gear traversing assembly?

About all I can think of to suggest is replicate your same material & tooling setup. Power up & then traverse the carriage by hand as constant as you can as though you were a robot. Helps to put a bit of friction on the carriage wheel with your left hand. Try some different rpms. If finish consistently looks smoother, at that at least it points you to power feed drivetrain & maybe not motor & bearings & other factors. Keep us informed & good luck.

*edit my apologies I saw you tried this in post#20*
I forgot to mention that I have the same problem with hand feeding as I do with power feeding so I doubt if the problem is with the power feed.
 
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Houston, we no longer have a problem!

Thanks to Mark Jacobs, the VFD guru, I can report that all of my surface finish problems have GONE AWAY! I used the Marathon Black Max inverter motor and WOW, does this thing have power. I can take a .050" doc(.100" on the diameter) and it cuts like butter. I can take more but I'm happy with that, I don't like to push any of my machines.

Here are some pics....
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This last image shows my solution for the motor support. It hit the motor using the original position so I cut it down and flipped it over so it comes up from the bottom, it was a simple fix and it seems to be working well.

Again I want to thank Mark, I screwed up a few things and when I asked him for help he solved the problems IMMEDIATELY.

I also want to thank everyone who posted comments, without this forum I can't even imagine where I would be right now.
 
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Mark, this content is way over my head but when a fella like you is so generous with his knowledge it inspires me tremendously.
 
Once I get some 240v in the new garage in the next couple weeks or so, I may have to contact Mark and ask him how much he'd charge for a complete setup from motor to control panel with the auto-stop feature for my 1340. I will admit that I kinda did a hack job on mine when I was in CO as I was impatient to get started... :rolleyes:

It needs to be done right this time.
 
. I can take a .050" doc(.100" on the diameter) and it cuts like butter. I can take more but I'm happy with that, I don't like to push ANY of my machines..

That's awesome that your problem went bye-bye & we all benefited by seeing your end result. Congrats.

I'll offer another one. My Taiwan 14x40 is generically very similar to yours. Its actually had a pretty easy life until I started doing more machining lately. Recently I have been fighting what I thought was a clutch issue kicking out, strange noises & related surface finish problems. The carriage assembly was finally dismantled yesterday with some help from a good buddy who volunteered his time. We discovered the worm wheel in the apron on the power drive rod was slowly eating its way into the cast iron U bracket that contains it, so it developed lateral end play slop. I was only taking 0.015" DOC passes in 1144 SP steel when the racket started. Now, this was probably coincidental timing that loaded the power drive a bit more than usual, like the straw that broke the camels back. I will take some pics & fully document this so others can see. And I think this assembly can be improved. In fact in a Keith Fenner video series, this is exactly what he dealt with on his lathe & he silver soldered a bronze thrust washer which is probably the most straightforward option. I'm considering tossing the cast iron POS altogether & making an entire new block with some better features.

So my amateur machinist precautionary words of wisdom are: maybe your motor is capable of plowing big time metal but there may be a weaker link in the system, at least in stock lathe form. I'm pretty sure my clutch was set conservative up until now, so somehow the wear still slowly occurred on the driveline. My read (hope!) is its reacting to the bad friction in the worm gear issue. Not to dilute your great post, but just curious if you consider 50-thou type DOC is something a lathe like this should be able to handle no problem over extended life?
 
Rick, it is interesting that you had this surface issue problem, but glad it was resolved going to 3 phase. I have heard of similar issues with single phase lathes (of this size), but seems to be sporadic and have not seen it reported with 3 phase lathes. One consideration, is that when we start changing the mounting structure of the machine, it changes the harmonics/vibration nodes which can be exacerbated with rigidity. I saw this on my 1340GT, where changing to solid feet and stiffening the base exacerbated the vibration peak at 650RPM and 1250RPM. This only occurred with heavier chucks, so this size machine is more sensitive to any imbalance in the system. Also, VFD's variable speed allows RPMs where you will always find a resonant peak for the structure. In larger machines with VFDs, this can often lead to catastrophic failure if the system is completely rigid, and often they program the VFD to have skip frequencies to avoid the resonant peak RPMs. It may be that the stiffer support frame you made may have transmitted the single phase motor pulsations, which showed up on the surface finish. In many cases, individuals have isolated the motor from the machine with rubber feet, and this issue has been resolved. I like your idea of using a drill motor to power the machine and evaluate the surface finish, I think that tells the tale that this was a single phase motor issue. I still think it is important to check the other mechanical issues that others have mentioned, especially with an older machine. Regarding DOC, I see no issues with taking a 0.100" diameter cut with this size machine, but the motor/VFD combination you used is surprisingly powerful and I wouldn't want to test which will break first on deeper cuts.

I still feel 3 phase is the way to go with these machines, either using an RPC or a VFD. The BlackMax motors are killer on these lathes, but the stock 3 phase motors performs quite well also. Glad I could help you out with your lathe. Very nice install on your VFD enclosure, your lathe is now on steroids.
Mark
 
Best guess is that the nut for the crossfeed is loose. You should be able to tighten with no more than removal of the compound.
 
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