1340gt surface finish problem

In that picture above, it just looks like a machined finish with a sharp tool to me. Try the setting on E and 8, also whats the radius on the insert? The tool also looks high to me, but that might just be the camera angle.
In both the coarse and fine "threads", the lead looks like it is many times larger than the feed, like multi start threads. It is interesting that it is not parallel to the feed, but does change lead angle with the feed.
 
I have seen this problem a couple times on otherwise good working machines, both times it was a chip under toolpost or toolpost (nut) block sitting a thou proud in the slot. Pretty easy to check and rule out.
 
Your feed rate is very high, in the video the gear selection suggests 0.006 IPR where you should be around 0.002. The usual feed rate is 0.001-0.003 IPR. Try slowing down the feed, like E-7, move the left gear lever to the next position "E". Most of the time I use E-8 and E-7 for a better finish, E-6 or E-5 to remove more material. This equates to around 0.002-0.0035 IPR.

Jet - Recommend Cutting Speed of Lathe.jpg
 
Don't know if this would have any effect on it but shouldn't the turning speed be way higher, like 3000 rpm since he is turning aluminum?
 
Yes, that looks to be about 1" diameter aluminum, so 2,400 rpm would be reasonable. Figure on 600-1,200 sfpm for aluminum and carbide.

A traveling rest might help, too. IIRC once you get over 8:1 length/dia, you start getting a surprising amount of deflection from the work bending.

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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
Missed this comment, I still would slow down the feed rate as noted by Matt. I routinely turn aluminum 1" stock at 700-900 RPM with carbide inserts and can easily shave a few thousandth off at a couple of inches out. I normally run about 1/2 the published SFM, as this is often based on industrial machines with more rigidity. A 1" D at 1000 RPM is ~260 SFM.
 
Post #3 notes that he is turning 5/8" rod, so even at 1/2 published speed it would be 1500 rpm for HSS. He is running at 475 and 770. Maybe a higher rpm combined with a slower feed would help but I'm no expert. I only started turning a year ago and only do it for a hobby. I have a lot to learn. So I am just throwing this out to see if it makes sense. I'm sure one of the more experienced members will know.
 
Missed this comment, I still would slow down the feed rate as noted by Matt. I routinely turn aluminum 1" stock at 700-900 RPM with carbide inserts and can easily shave a few thousandth off at a couple of inches out. I normally run about 1/2 the published SFM, as this is often based on industrial machines with more rigidity. A 1" D at 1000 RPM is ~260 SFM.
Several of the previous photos show two speeds side by side, .0055" and .0027", the .0027" is the slowest feed this machine has. All it does is make the ridges closer together and it also seems to change the angle of them as well. That seems odd to me, why would the angle of the ridges change direction when you change the feed rate???

I just tried the slowest feed with the highest rpm(1800)and there is no improvement.

I also tried lowering the tool bit and it didn't help.
 
I believe you're dealing with something loose. Machines all have inherent resonant frequencies at which they vibrate. If you change the speed or mass, the frequency changes. I think the change your seeing is because you're changing speed of the feed. Finding what's loose should cure this issue.
 
That makes perfect sense, the problem is WHAT is loose!:) I've checked the motor and the external gears, the only thing left is to tear it apart. I shouldn't have to do that on a machine that's only 3 months old!
 
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