Atlas 3995 Chattering

[Backyardmachineshop]

I almost never feed mine by hand more than a couple thou to sneak up on a shoulder, I power feed everything. The rack on this lathe and the gear reduction for the handwheel make is super difficult to feed cleanly because the gear meshes aren't super tight.

 

[gedkins]

So that cut between centers on the aluminum was by hand? That cut wasn't bad if not just inconsistent. It's an engine lathe use that power feed. See if that makes a difference with that particular cutter, feeding by hand didn't even enter the realm of thought for me.

I tried the power feed early on ( misspoke before) at the slowest speed. The results were the same, that is the reason I did use it going forward. I had a benchmark.

 

[gedkins]

I think I have an unassociated issue now. After reassembling the head and putting new plain v belts on the spindle drive my 3/4 hp single phase motor (110 volt) will not drive the lathe to full speed on the last two highest speeds. The original motor was a 3/4 hp 3 phase. Are any of you Atlas 3995 owners running a single phase 110 volt 3/4 without issue?

 

[Backyardmachineshop]

I think I have an unassociated issue now. After reassembling the head and putting new plain v belts on the spindle drive my 3/4 single phase motor (110 volt) will not drive the lathe to full speed on the last two highest speeds. The original motor was a 3/4 hp 3 phase. Are any of you Atlas 3995 owners running a single phase 110 volt 3/4 without issue?

Your belts are too tight. Pulling too much load on the motor. I did that to myself the first time I set my lathe up. I figured tighter was better but the opposite is actually true.

 

[Backyardmachineshop]

You have much less mechanical advantage in the higher speed ranges than you do in the lower speed ranges

 

[matthewsx]

Three phase motors are generally considered better for finishes.

I think the first dozen or so parts I made on my Star were finished with a file and emery paper.

Keep at it, it will come into focus as you learn more about the machine, materials and cutters.

John

 

[gedkins]

Your belts are too tight. Pulling too much load on the motor. I did that to myself the first time I set my lathe up. I figured tighter was better but the opposite is actually true.

Loosened and it helped, cannot get to highest speed now. Thinking motor is just marginal and I can fix that with a new one.

 

[gedkins]

All, some progress made. Tried a HSS cutter not used to date, very little relief on the sides and flat topped, which is not good for steel, but result was far better for all materials. I live close to a true expert machinist and I am going to borrow one of his known good turning bits and try some more experiments. The results you see here could not be repeated anywhere beyond 2 inches from the chuck, vibration and deflection caused lots of surface smearing. These cuts were all less than an inch away. All the while cutting these I could feel a vibration through the cross feed wheel. For the life of me I cannot figure where it is coming from. All gibs are snug. There is no slop in any of them. Tool post is tight and is an Aloris. Cutter was set set dead center of workpiece. Every cut I made the lathe groaned and rattled in places I could not ascertain. Never take more than .010 in a pass. Not the head cover, no loose bolts, etc. Still the finish is better across the board. I am already gray, I will be bald by the end of the month...

 

[pontiac428]

I guess I should point out that when you set up the gear train on the Atlas, that you need to leave some amount of gap (and endure the resulting backlash in the feed screw that comes with) between the gear teeth. It's tough to measure worn Zamak, so it's kind of a feel you have to learn when the gears are set up "right". Too tight and the inherent imprecision in the gears' concentricity will cause the train to trip over it's own feet by making a ruckus of vibration and periodic tension as the works turn. Set the banjo and the gear position while turning the chuck by hand to see what I mean. It's another "Atlas thing".

 

[gedkins]

I guess I should point out that when you set up the gear train on the Atlas, that you need to leave some amount of gap (and endure the resulting backlash in the feed screw that comes with) between the gear teeth. It's tough to measure worn Zamak, so it's kind of a feel you have to learn when the gears are set up "right". Too tight and the inherent imprecision in the gears' concentricity will cause the train to trip over it's own feet by making a ruckus of vibration and periodic tension as the works turn. Set the banjo and the gear position while turning the chuck by hand to see what I mean. It's another "Atlas thing".

I have been very careful to set the gearing with the proper spacing. There is slop in the drive train. But again, for these tests I am not using the power feed so that it does add another variable.