Interupted cuts can be aches with correct inserts but requires a robust rigid setup or you'll kill your insert. A sharp HHS tool bit with a correct relief would work for what you're after. Run the largest HHS tool bit you can fit in your holder although it looks to be under 3/8". BTW, you'll need a tail stock center to support the commutator or any longish item.
On your spindle bushing. I use oilite bushing on machines that won't spin faster than 120 RPM spinning that fast. Example, I rebuilt a 72" Box and Dab break and used these oil impregnated busing for all pivot points and added ball oilers to keep it flushed prior to use. The Oilite bushing sweat oil at the fist sign of friction, then reabsorbs the oil once the friction stops (cools). Using this type of bushing on a spindle more than likely will pull all the oil from said bushing. You lathe should have oilers of some sort over the original bushings. If you di decide to use Oilite bushings that require machining, a very sharp HHS is recommended to keep from smearing the oil pours closed. This material is pours and relies on these pours to sweat the oil.
My recommendation is use bronze bushings and keep them oiled.
Lastly,
Your chuck is too big for that size lathe. That much rotating mass on that anemic sized spindle could spell disaster resulting in injury.
Large chuck will tempt you to turn something too large and if it doesn't fail it will surly stall your machine. My 1640 lathe uses an 8" 3-jaw chuck and a 10" independent chuck so
I'll share a couple of shots on machining Oilite and show the how its sweats when friction is applied.
The Oilite bushing I sourced from a local bearing house along with other sizes (no machining required).
This particular bushing has a 4" ID and came in 5" length. I needed two for the Dries& Krump break. The break manufacture is still in business but they quoted me $80 each plus shipping, these are not Oilite material . I ordere the larger single Oilite from the bearing house and made the two I needed for $48 and some left over.
Here, I'm cutting a slight bevel prior to parting.
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The two new Oilite replacements. In the backrounf you can see the original still in the large link. Its made from bronze and had a oil groove machined into the middle. The link has a small hole for lubrication that lined up the the groove.
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After removing the old sloppy bushing (from lack of oil) the new Oilite bushings were pressed in after the link was blasted and painted.
The photo you see shows were I drilled a small hole. Look closely and you'll see the oil that sweated out during the drilling process. Drilling took less than a minute as you can imagine but the amount of oil speaks for the Oilite. Once the bushing temp was normalized the oil was reabsorbed. You see why I wouldn't recommend this for a higher RPM application.
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The original oil hole on the links were opened up to accommodate a ball oiler. The white thing inside the hole resembles a cigarette filter. The idea is to soak the inset via ball oiler to keep a slight drip on the new Oilite bushings to flush out ware particles during use.
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The ball oiler installed.
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For your lathe, I bet you have a spring loaded flip up style oiler. Some upgrade these to larger vial type that show the oil reservoir and they also have a small needle valve for metering the oil delivery.
Something like this;
Not trying to rain on your parade over the chuck size but I would regret not saying something and you get hurt. Remember, You're standing in harms way if the chuck separates at RPM.
If I may ask, what parts are you hoping to turn with this lathe? Lastly, post up a photo of the front of the machine so we can peek at gearbox.
I hope this helps.
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