How would I deal with this finishing issue on my Atlas Craftsman lathe?

[ARC-170]

I'm not getting a very smooth finish when I use the carriage power feed on my 12" Atlas Craftsman lathe. I suspect it has something to do with the vibrations caused by the gears meshing, because it doesn't happen when I hand feed the carriage. Have a look:

On top is a cut made with a carbide bit using the power feed, in the middle is a cut made with a HSS bit using the power feed and the bottom is a cut made with a HSS bit that was hand-fed. All cuts were 0.015" in steel. The machine didn't struggle at all. No lube.

It's hard to see in the photo, but the top one feels rough and the middle one is wavy.

What could be causing this and is there a solution? I've gone thru and tightened up all the bolts on the gears, the gibs are tight, and the tool is secure.

 

[jwmay]

Is that hot rolled steel?

 

[ARC-170]

Is that hot rolled steel?

I'm not sure. I've machined it with the lathes at the school I teach at and the finish is fine. My lathe does this with ALL materials using the power feed.

 

[jwmay]

Well I guess you could check your half nuts. What’s your compound orientation look like? You need to ensure that once you’re in the cut, that the compound isn’t under any weird loads. I’ve had where the compound lead screw would unwind under resonance.

It’s a weird problem that’s hard to diagnose without hands on.

But I’m sure somebody more clever than I will be along shortly.

 

[ShagDog]

What is the feed speed you are using on the power feed. Oil might help

 

[ARC-170]

What is the feed speed you are using on the power feed. Oil might help

0.0048"

 

[woodchucker]

so given that you say you can hand feed and it doesn't happen, is that with the same cutting tool?
How about feed rate, are you feeding by hand about the same rate as the when engaged?
If the gear train is that noisy, have you tried a heavy grease on the gears to quiet it down and see if that helps?
Are your gears tightly meshed? Have you tried loosening the fit so it has some freedom to relax while turning? it makes a big difference.

 

[ARC-170]

Well I guess you could check your half nuts. What’s your compound orientation look like? You need to ensure that once you’re in the cut, that the compound isn’t under any weird loads. I’ve had where the compound lead screw would unwind under resonance.

It’s a weird problem that’s hard to diagnose without hands on.

But I’m sure somebody more clever than I will be along shortly.

Well, it IS a Craftsman lathe, which is notorious for not being the most rigid machine! lol. BUT, it works fine when I manually feed it. I don't feel anything when I'm handfeeding it in the way of wondering or anything like that.

I am wondering if this issue is unique to my machine or if others with the same machine have or have had the same issue.

 

[ShagDog]

0.0048"

You may want to try a slower feed rate and some cutting oil and see what happens.

 

[ARC-170]

so given that you say you can hand feed and it doesn't happen, is that with the same cutting tool?
How about feed rate, are you feeding by hand about the same rate as the when engaged?
If the gear train is that noisy, have you tried a heavy grease on the gears to quiet it down and see if that helps?
Are your gears tightly meshed? Have you tried loosening the fit so it has some freedom to relax while turning? it makes a big difference.

Same tool, about the same rate, plenty of grease, gears all have decent backlash (not too tight or too loose). My first thought was that the gears were too loose and vibrating, sending that thru the gear train and into the parts.

You may want to try a slower feed rate and some cutting oil and see what happens.

I tried that, not much better.